,transcriber's ,notes3 ,underscores 80 before and after a word or phrase indicate italics in the original text4 ,equal signs 80 before and after a word or phrase indicate bold in the original text4 ,small capitals have been converted to ,,solid capitals4 ,illustrations have been moved so they do not break up paragraphs4 ,old or antiquated spellings have been preserved4 ,typographical and punctuation errors have been silently corrected4 ,,the ,,manufacture ,,of ,,mineral ,,and ,,lake ,,pigments ,,the ,,manufacture ,,of ,,mineral ,,and ,,lake ,,pigments ,,containing ,,directions ,,for ,,the ,,manufacture ,,of ,,all ,,artificial ,,artists' ,,and ,,painters' ,,colours1 ,,enamel ,,colours1 ,,soot ,,and ,,metallic ,,pigments ,a ,text-,book ,for ,manufacturers1 ,merchants1 ,artists and ,painters ,,by ,,dr4 ,,josef ,,bersch ,,translated ,,from ,,the ,,second1 ,,revised ,,edition ,,by ,,arthur ,c4 ,,wright1 ,m4,a4 7,,oxon471 ,b4 ,,sc4 7,,lond47 ,,formerly ,,assistant ,,lecturer ,,and ,,demonstrator ,,in ,,chemistry ,,at ,,the ,,yorkshire ,,college1 ,,leeds ,,with ,,forty-,,three ,,illustrations ,,in ,,the ,,text ,,london ,,scott1 ,,greenwood ,,co4 ,publishers of the 8,oil and ,colourman's ,journal0 #ai ,,ludgate ,,hill1 ,e4,c4 #aija ,the sole right of publishing this work in ,english rests with the above firm4 ,,preface4 ,we know hardly another branch of chemical technology which has made such remarkable advances of late as the manufacture of colours2 a large number of pigments have been recently discovered1 distinguished by beauty of shade and permanence4 ,chemists are continually endeavouring to replace handsome and poisonous colours by others equally handsome but non-poisonous4 ,in writing this work ,i have endeavoured to give it such a character that it may be a text-book for the practical man1 only those methods have been given which certainly lead to a good result2 in the case of new pigments ,i have only described methods of preparation which ,i have myself found to give good results4 ,since it cannot be imagined that any one quite ignorant of chemistry could successfully manufacture colours 7colours being always made by chemical processes which occasionally are rather complicated71 ,i have1 therefore1 presupposed a knowledge of the principles of chemistry4 ,in the short sketch of the chemical properties of the raw materials used in making ordinary pigments1 the principal properties of the materials used by the colour maker are given4 ,in order to make this treatise useful to dealers in and consumers of colours1 the chapters dealing with the examination of pigments have been so arranged that the nature or adulteration of a pigment can be determined quickly and with certainty by any one4 ,recipes1 which originated at a time when empiricism ruled in chemistry1 have been omitted1 since they would only detract from the clearness of the matter4 ,as far as it is possible ,i have avoided the 8recipe fetish10 and have endeavoured to make clear to the reader the chemical processes to which regard must be had in the manufacture of the different pigments4 ,since the appearance of the first edition there have been many valuable innovations in the mineral colour industry1 to which regard has been given in preparing this second edition in so far as they possess a really practical value4 ,a critical examination of proposals and formul1 which are found in large numbers in the journals1 has been avoided1 since ,i wished to keep for my book that character of a reliable text-book and book of reference which was ascribed to it in the form of its first edition4 ,,dr4 ,,josef ,,bersch4 ,,translator',s ,,preface4 ,if excuse be needed for presenting a translation of ,dr4 ,bersch's book at so long an interval after the publication of the original 7#ahic71 it must be sought in the paucity of the ,english literature on the subject4 ,it is hoped that the practical nature of the work will make it acceptable to the ,english reader4 ,the subject-matter of the original has been preserved in the translation without alteration or addition1 with the exception of an unimportant change in the order of arrangement4 ,the metric system of weights and measures has been used throughout2 for the convenience of those who are not familiar with this system1 directions are given in an appendix for converting into ,english weights and measures4 ,the section on paint grinding 7,chapter ,,lxix47 is perhaps somewhat incomplete2 for a more detailed and modern account of this branch of the subject the reader is referred to ,practical ,paint ,grinding1 by ,mr4 ,j4 ,cruickshank ,smith1 ,b4 ,sc41 shortly to be issued by the same publishers4 ,a4 ,c4 ,,wright4 ,,hull1 ,january1 #aija4 ,,table ,,of ,,contents4 ,,page ,,chapter ,i4 ,,introduction #a ,,chapter ,,ii4 ,,the ,,physico-,,chemical ,,behaviour ,,of ,,pigments #h ,,chapter ,,iii4 ,,raw ,,materials ,,employed ,,in ,,the ,,manufacture ,,of ,,pigments #ad ,,chapter ,,iv4 ,,assistant ,,materials #af ,water--,chlorine--,ammonia--,the ,hydrometer--,sal ,ammoniac or ,ammonium ,chloride--,ammonium ,sulphide4 ,acids4--,hydrochloric ,acid--,sulphuretted ,hydrogen --,sulphuric ,acid3 ,oil of ,vitriol1 ,nordhausen ,sulphuric ,acid--,nitric ,acid--,aqua ,regia --,carbon--,carbonic ,acid ,gas4 ,organic ,acids4--,acetic ,acid--,oxalic ,acid--,tartaric ,acid4 ,,chapter ,v4 ,,metallic ,,compounds #cb ,alkalis4--,potassium ,compounds--,potassium ,carbonate --,potassium ,hydroxide--,potassium ,nitrate--,potassium ,bitartrate--,potassium ,bichromate--,potassium ,sodium ,chromate--,chrome ,alum--,potassium ,ferrocyanide --,potassium ,ferricyanide--,sodium ,salts--,sodium ,carbonate--,sodium ,hydroxide--,sodium ,thiosulphate --,sodium ,chloride--,salts of the ,alkaline ,earth ,metals4 ,calcium ,compounds4--,calcium ,oxide--,calcium ,hydroxide --,calcium ,carbonate--,calcium ,sulphate--,calcium ,phosphate --,magnesium ,carbonate--,barium ,compounds--,barium ,chloride4 ,aluminium ,compounds--,aluminium ,sulphate4 ,the ,alums4--,potassium ,aluminium ,alum--,roman ,alum--,soda ,alum--,ammonia ,alum--,alumina and ,hydrate of ,alumina4 ,compounds of the ,heavy ,metals4--,zinc ,compounds--,cadmium ,compounds--,iron ,compounds--,ferrous ,sulphate--,ferrous ,chloride--,manganese ,compounds--,nickel ,compounds--,cobalt ,compounds--,chromium ,compounds--,molybdenum1 ,tungsten and ,vanadium ,compounds--,antimony ,compounds--,bismuth ,compounds --,tin ,compounds--,arsenic ,compounds--,lead ,compounds --,lead ,sulphate--,lead ,nitrate--,lead ,acetate--,basic ,lead ,acetate--,lead ,chloride--,copper ,compounds--,copper ,sulphate --,copper ,nitrate--,copper ,acetate--,mercury ,compounds --,mercurous ,nitrate--,mercuric ,nitrate--,mercurous ,chloride --,mercuric ,chloride--,silver ,compounds--,gold ,compounds4 ,,chapter ,,vi4 ,,the ,,manufacture ,,of ,,mineral ,,pigments #ga ,white ,mineral ,pigments--,white ,lead4 ,,chapter ,,vii4 ,,the ,,manufacture ,,of ,,white ,,lead #gg ,manufacture of ,white ,lead from ,metallic ,lead4--,dutch ,process3 ,casting the ,lead into ,sheets--,building up the ,stacks--,removal and ,grinding of the ,white ,lead--,white ,lead ,mills--,hard ,white ,lead--,soft ,white ,lead4--,german ,process4--,french ,process3 ,preparation of the ,solution of ,basic ,lead ,acetate--,preparation of the ,carbonic ,acid and ,precipitation of the ,white ,lead--,manufacture of ,white ,lead by ,means of ,natural ,carbonic ,acid4--,english ,process4--,other ,methods4 --,oxychloride ,white ,lead3 ,lead ,sulphite--,lewis ,bartlett's ,white ,lead ,pigment4--,white ,lead -,antimony ,pigments3 ,lead ,antimonite--,lead ,antimonate4 ,,chapter ,,viii4 ,,enamel ,,white #aaf ,lithopone4 ,,chapter ,,ix4 ,,washing ,,apparatus #abj ,filter ,presses4 ,,chapter ,x4 ,,zinc ,,white #abf ,griffith's ,zinc ,white--,tungsten ,white--,white ,antimony ,pigments3 ,antimony ,trioxide--,antimony ,oxychloride --,bismuth ,white--,tin ,white--,manganese ,white --,magnesia ,white or ,mineral ,white--,annaline4 ,,chapter ,,xi4 ,,yellow ,,mineral ,,pigments #acc ,,chapter ,,xii4 ,,chrome ,,yellows #acd ,lead ,chrome ,yellow--,preparation of the ,lead ,solution --,precipitation of the ,chrome ,yellow --,the ,pale ,chrome ,yellows4 ,,chapter ,,xiii4 ,,lead ,,oxide ,,pigments #adc ,red ,lead1 ,minium4 ,,chapter ,,xiv4 ,,other ,,yellow ,,pigments #adh ,cassel ,yellow--,montpellier ,yellow--,turner's ,yellow or ,english ,yellow--,naples ,yellow--,antimony ,yellow --,calcium ,chrome ,yellow--,barium ,yellow1 ,yellow ,ultramarine or ,permanent ,yellow--,zinc ,chrome ,yellow --,cadmium ,chrome ,yellow--,cadmium ,yellow--,lead ,iodide --,mars ,yellow--,siderin ,yellow--,aureolin--,tungsten ,yellow--,nickel ,yellow--,mercury ,yellow or ,turpeth ,mineral--,yellow ,arsenic ,pigments--,lead ,arsenite --,thallium ,pigments4 ,,chapter ,,xv4 ,,mosaic ,,gold #afj ,chrysean4 ,,chapter ,,xvi4 ,,red ,,mineral ,,pigments #afc ,vermilion--,black ,mercuric ,sulphide--,red ,mercuric ,sulphide4 ,,chapter ,,xvii4 ,,the ,,manufacture ,,of ,,vermilion #aff ,dry ,method3 ,chinese ,vermilion4--,wet ,method3 ,firmenich's ,method--,liebig's ,process--,infusible ,white ,precipitate--,electrolytic ,process --,mercuric ,iodide4 ,,chapter ,,xviii4 ,,antimony ,,vermilion #agh ,appendix--,antimony ,blue4 ,,chapter ,,xix4 ,,ferric ,,oxide ,,pigments #ahj ,vogel's ,iron ,red--,macay's ,english ,red--,indian ,red4 ,,chapter ,,xx4 ,,other ,,red ,,mineral ,,pigments #ahf ,chrome ,red or ,chrome ,vermilion--,cobalt ,red--,cobalt ,magnesia ,red--,cobalt ,arsenate--,chromium ,stannate --,silver ,chromate4 ,,chapter ,,xxi4 ,,purple ,,of ,,cassius #aij ,magnesia ,gold ,purple--,alumina ,gold ,purple4 ,,chapter ,,xxii4 ,,blue ,,mineral ,,pigments--,,iron-,,cyanogen ,,pigments #aid ,chinese ,blue--,prussian ,blue--,mineral ,blue--,soluble ,prussian ,blue--,special ,processes for the ,manufacture of ,chinese ,blue--,turnbull's ,blue --,antwerp ,blue4 ,,chapter ,,xxiii4 ,,ultramarine #bjd ,,chapter ,,xxiv4 ,,the ,,manufacture ,,of ,,ultramarine #baa ,preparation of ,mixtures for ,ultramarine--,ultramarine ,violet--,chlorine and ,steam ,process--,hydrochloric ,acid and ,air ,process--,ammonium ,chloride ,process --,pale ,blue ,ultramarine--,ultramarine ,red4 ,,chapter ,,xxv4 ,,blue ,,copper ,,pigments #bbf ,bremen ,blue and ,green--,neuberg ,blue--,lime ,blue --,payen's ,mountain ,blue--,oil ,blue--,copper ,hydroxide4 ,,chapter ,,xxvi4 ,,blue ,,cobalt ,,pigments #bcj ,cobalt ,blue1 ,thnard's ,blue1 ,cobalt ,ultramarine1 ,king's ,blue1 ,leyden ,blue--,cruleum--,cobalt ,zinc ,phosphate4 ,,chapter ,,xxvii4 ,,smalts #bcc ,preparation of the ,charge--,fusion of the ,charge --,grinding the ,fused ,mass--,tungsten ,blue --,tessi du ,motay's ,blue--,molybdenum ,blue4 ,,chapter ,,xxviii4 ,,green ,,mineral ,,pigments--,,green ,,copper ,,pigments #bdj ,green ,copper ,pigments3 ,copper ,carbonate--,copper ,arsenite --,scheele's ,green--,swedish ,green--,brunswick ,green --,green ,verditer--,neuwied ,green--,copper ,oxychloride4 ,,chapter ,,xxix4 ,,emerald ,,green #bdd ,manufacture of ,emerald ,green from ,verdigris--,manufacture of ,emerald ,green from ,copper ,sulphate--,mitis ,green or ,vienna ,green--,copper ,stannate--,kuhlmann's ,green--,elsner's ,green--,casselmann's ,green--,lime ,green--,patent ,green--,copper ,borate--,copper ,silicate 7,egyptian ,blue74 ,,chapter ,,xxx4 ,,verdigris #beb ,blue ,verdigris--,distilled or ,crystallised ,verdigris --,german ,verdigris4 ,,chapter ,,xxxi4 ,,chromium ,,oxide #bfj ,chrome ,green4 ,,chapter ,,xxxii4 ,,other ,,green ,,chromium ,,pigments #bfd ,guignet's ,green--,emerald ,green--,chrome ,green ,lake --,turkish ,green--,leaf ,green4--,chromium ,phosphate ,pigments3 ,arnaudan's ,green--,plessy's ,green --,schnitzer's ,green--,chromaventurine--,chrome ,blue 7,garnier74 ,,chapter ,,xxxiii4 ,,green ,,cobalt ,,pigments #bfh ,cobalt ,green4 ,,chapter ,,xxxiv4 ,,green ,,manganese ,,pigments #bgj ,manganese ,green--,rosenstiehl's ,green--,bttger's ,barium ,green--,manganous ,oxide--,manganese ,blue4 ,,chapter ,,xxxv4 ,,compounded ,,green ,,pigments #bgc ,chrome ,green--,elsner's ,chrome ,green--,silk ,green --,natural ,green--,non-arsenical ,green4 ,,chapter ,,xxxvi4 ,,violet ,,mineral ,,pigments #bgf ,chromic ,chloride--,manganese ,violet--,tin ,violet1 ,mineral ,lake--,copper ,violet1 ,guyard's ,violet4 ,,chapter ,,xxxvii4 ,,brown ,,mineral ,,pigments #bgi ,lead ,brown--,manganese ,brown--,pyrolusite ,brown --,prussian ,brown--,iron ,brown--,copper ,brown --,chrome ,brown--,cobalt ,brown4 ,,chapter ,,xxxviii4 ,,brown ,,decomposition ,,products #bhc ,humins--,bistre4 ,,chapter ,,xxxix4 ,,black ,,pigments #bhe ,charcoal ,blacks3 ,true ,charcoal ,black--,vine ,black --,vine ,black from ,wine ,lees--,vine ,black from ,pressed ,grapes--,bone ,black or ,ivory ,black4 ,,chapter ,,xl4 ,,manufacture ,,of ,,soot ,,pigments #bid ,the ,manufacture of ,soot ,blacks on the ,large ,scale4 ,,chapter ,,xli4 ,,manufacture ,,of ,,lamp ,,black #cjg ,calcination of the ,soot--,pine ,black4 ,,chapter ,,xlii4 ,,the ,,manufacture ,,of ,,soot ,,black ,,without ,,chambers #cac ,,chapter ,,xliii4 ,,indian ,,ink #caf ,neutral ,tint ,black--,appendix3 ,black ,mineral ,pigments --,chrome ,copper ,black--,chrome ,black4 ,,chapter ,,xliv4 ,,enamel ,,colours #cai ,white ,enamels--,coloured ,enamels3 ,yellow ,enamels--,red ,enamel--,blue ,enamels--,green ,enamel--,violet ,enamel --,black ,enamel4 ,,chapter ,,xlv4 ,,metallic ,,pigments #cbf ,shell-,gold--,shell-,silver--,imitation ,silver4 ,,chapter ,,xlvi4 ,,bronze ,,pigments #cbi ,electrolytic ,copper ,bronze--,tungsten ,bronze ,pigments4 ,,chapter ,,xlvii4 ,,vegetable ,,bronze ,,pigments #cci ,appendix3 ,the ,brocade ,pigments4 ,,pigments ,,of ,,organic ,,origin4 ,,chapter ,,xlviii4 ,,lakes #cdc ,,chapter ,,xlix4 ,,yellow ,,lakes #cdh ,dutch ,pink--,weld ,lake--,gamboge ,lake--,prepared ,gamboge--,fustic ,lake--,quercitron ,lake--,purree or ,indian ,yellow--,the ,colouring ,matter of ,saffron--,colouring ,matter of ,gardinia ,grandiflora4 ,,chapter ,l4 ,,red ,,lakes #ced ,cochineal and ,carmine ,,chapter ,,li4 ,,the ,,manufacture ,,of ,,carmine #ceg ,cenette's ,method--,munich1 ,vienna1 ,paris or ,florentine ,lake--,ammonia-,cochineal4 ,,chapter ,,lii4 ,,the ,,colouring ,,matter ,,of ,,lac #cfc ,lac ,dye4 ,,chapter ,,liii4 ,,safflower ,,or ,,carthamine ,,red #cff ,safflower ,carmine--,alkanet4 ,,chapter ,,liv4 ,,madder ,,and ,,its ,,colouring ,,matters #cgj ,garancin--,garanceux--,madder ,extract--,the ,constituents of ,madder4 ,,chapter ,,lv4 ,,madder ,,lakes #cge ,madder ,carmine4 ,,chapter ,,lvi4 ,,manjit 7,,indian ,,madder7 #cgh ,chica ,red1 ,curucuru1 ,carajuru--,bigonia ,chica4 ,,chapter ,,lvii4 ,,lichen ,,colouring ,,matters #chj ,archil--,french ,purple--,cudbear--,litmus4 ,,chapter ,,lviii4 ,,red ,,wood ,,lakes #chd ,,chapter ,,lix4 ,,the ,,colouring ,,matters ,,of ,,sandalwood ,,and ,,other ,,dye-,,woods #chh ,,chapter ,,lx4 ,,blue ,,lakes #cij ,indigo--,the ,constituents of ,indigo4 ,,chapter ,,lxi4 ,,indigo ,,carmine #cid ,indigo ,mills--,blue ,lake4 ,,chapter ,,lxii4 ,,the ,,colouring ,,matter ,,of ,,logwood #cih ,logwood ,extract--,kohlrausch's ,process for ,obtaining ,concentrated ,extracts of ,colouring ,matters and ,tannins4 ,,chapter ,,lxiii4 ,,green ,,lakes #dji ,chlorophyll--,sap ,green--,chinese ,green1 ,lokao --,charvin's ,green4 ,,chapter ,,lxiv4 ,,brown ,,organic ,,pigments #dad ,asphaltum--,sepia4 ,,chapter ,,lxv4 ,,sap ,,colours #daf ,,chapter ,,lxvi4 ,,water ,,colours #dai ,moist ,water ,colours4 ,,chapter ,,lxvii4 ,,crayons #dbc ,crayons for ,earthenware4 ,,chapter ,,lxviii4 ,,confectionery ,,colours #dbg ,,chapter ,,lxix4 ,,the ,,preparation ,,of ,,pigments ,,for ,,painting #dbi ,paint ,mills4 ,,chapter ,,lxx4 ,,the ,,examination ,,op ,,pigments #dcd ,mineral ,pigments--,examination with the ,blowpipe --,reactions of the ,white ,pigments--,reactions of the ,yellow ,pigments--,reactions of the ,red ,pigments--,reactions of the ,blue ,pigments --,reactions of the ,green ,pigments--,reactions of the ,brown ,pigments--,reactions of the ,black ,pigments4 ,,chapter ,,lxxi4 ,,examination ,,of ,,lakes #dde ,reactions of the ,organic ,colouring ,matters4 ,,chapter ,,lxxii4 ,,the ,,testing ,,of ,,dye-,,woods #ddi ,the ,colorimeter4 ,,chapter ,,lxxiii4 ,,the ,,design ,,of ,a ,,colour ,,works #deg ,,chapter ,,lxxiv4 ,,commercial ,,names ,,of ,,pigments #dfj ,,appendix4 ,,the ,,conversion ,,of ,,metric ,,into ,,english ,,weights ,,and ,,measures --,,centigrade ,,and ,,fahrenheit ,,thermometer ,,scales #dfi ,,index4 ,,chapter ,i4 ,,introduction4 ,it is doubtful whether another branch of applied chemistry is recorded of so great an age as the colour industry2 at the present time there is hardly a race on the face of the earth which does not make use of colours in some form1 either for the decoration of their persons or surroundings4 ,the art of preparing colours is as ancient as their use4 ,it is true that we find from the most remote historical records that the so-called earth colours were almost solely employed1 and principally those which exist ready formed in nature4 ,but these natural colours also require their particular process of preparation before they fulfil their object1 even though this be merely a mechanical operation1 such as powdering or levigating4 ,that the oldest nations of whom we possess lasting records1 either written or otherwise1 really understood the preparation of colours by chemical processes is shown by the common occurrence in the ,egyptian mural pictures of figures clad in brightly coloured garments1 a proof that the ,egyptians not only understood the science of colour manufacturing1 but also the more advanced art of fastening colours upon fabrics--dyeing4 ,the writings of the ancient ,greeks1 and in part also the scanty remains of their buildings1 prove to us completely that they understood the use of colours to such an advanced degree that they already employed them for pictures as works of art4 ,that the ,greeks were also acquainted with the preparation of colours and dyeing follows from various passages from the classical writers1 in which magnificently decorated rooms and beautifully coloured garments are often described4 ,among the ,romans1 who were the pupils of the ,greeks in the arts and manufactures1 the prodigal luxury which existed in ,rome1 especially under the emperors1 caused a great demand for colours1 which were used in the most profuse manner for the decoration of house and attire4 ,the ,roman colour makers had advanced so far in their art that they could colour the human hair rose-red4 ,a glance at ,east ,indian fabrics and pictures1 or at the ancient ,chinese buildings1 whose colouring is a matter of marvel to-day1 shows that the ,oriental were not behind the ,western nations in the discovery of colours and the art of manufacturing them4 ,in so old an industry it is not remarkable that great changes have taken place in the course of time4 ,the thousands and thousands of experiments made by the alchemists in the attempt to prepare gold failed in their main object1 but the tremendous expenditure of time and trouble in this work was not fruitless2 upon the great mass of chemical facts discovered by the alchemists were laid the foundations of scientific chemistry4 ,we find on reading the writings of the alchemists that the colour industry is indebted to them for an immense number of its products2 the reason being that the alchemists worked by preference on metals1 earths and mineral compounds1 and from these substances a large number of colours are obtainable1 of which many are still in use to-day1 and1 on account of their cheapness1 will continue in use4 ,the period in which the painters were also the colour makers lies not far behind us4 ,the preparation of many a colour of particular beauty was treated by the fortunate owner of the recipe as a great secret4 ,it was sold by him at a great price4 ,what a difference between that time and the present6 ,there is now no painter among civilised races to whom it would occur to prepare his own colours2 the chemical works provide them for him at a low price and in such a condition that they can be immediately used for painting4 ,the ,italian painters prepared the highly prized blue pigment1 ultramarine1 by laborious toil from the costly lapis lazuli2 to-day1 this same colour1 more beautiful and deeper in hue1 is made by several works1 and sold at a price which bears no comparison with that of the colour obtained from the mineral4 ,the latter was worth many times its weight in gold3 a pound of the finest ultramarine can now be bought for a shilling or two4 ,we find a similar comparison in the case of the fine scarlet pigment known as vermilion3 formerly the natural vermilion1 cinnabar1 was sold at a very high price2 at the present time the finest vermilion1 prepared artificially1 can be bought at a low rate4 ,it is no longer necessary for any one to use natural ,chinese vermilion as an artists' colour4 ,whilst formerly mineral colours were used in great preponderance1 we now know a great number of vegetable and animal colouring matters4 ,the discovery of the sea route to ,india and the discovery of ,america had an important influence in this development4 ,from these countries1 as from other tropical lands1 come the majority of the plants which contain colouring matters4 ,the attempt to change these colouring matters into insoluble compounds led to the discovery of the lake pigments4 ,with the advance of chemical knowledge the number of colours grew apace2 e4g41 the discovery of chromium was of great importance to the colour industry3 it presented us with a large number of new colours4 ,to a more limited extent1 the discovery and study of uranium1 molybdenum and other metals were the occasions for the invention of new colours4 ,in more recent times1 efforts in the colour industry have been especially directed to making colours more permanent and1 at the same time1 harmless4 ,in the first respect1 the position at present leaves much to be desired2 but1 as regards the second property1 great advances have been made4 ,the colours in use in former days were almost all very poisonous compounds2 the greater number were derived from lead1 copper1 mercury or arsenic4 ,more recently these poisonous substances have been in many cases replaced by innocuous materials1 so that among the colours now in use1 though the list is much more comprehensive than of old1 there are but few poisonous to a high degree4 ,in all civilised states the use of poisonous colours has been much restricted by law1 and in those cases in which an article is to be manufactured for use as food the employment of such colouring matters has been absolutely forbidden4 ,for example1 in ,germany by the law of #eth ,july1 #ahhg1 concerning the use of dangerous colours in the preparation of foods and condiments1 the application of the permissible colours has been exactly defined4 ,during the last decades the colour industry and1 still more1 dyeing have undergone a complete change4 ,the momentous discoveries which have been made in these departments leave far behind the advances which have been made in other branches of chemical technology1 the manufacture of explosives1 perhaps1 excepted4 ,we allude here to the beautiful colours which have been made from coal-tar1 colours which far surpass in beauty all hitherto known1 and which we can already prepare in every shade and hue4 ,unfortunately1 we can only employ the coal-tar colours1 as such1 in a restricted measure among the pigments2 they are of more importance in dyeing4 ,we use the term pigments here in the narrow sense of such substances which1 when spread out on certain materials1 provoke a certain sensation of colour4 ,dyeing is1 on the contrary1 that branch of colour chemistry which generally has for its object the simultaneous production of the colour and its fixation upon a fabric4 ,this definition was at least applicable to the majority of the colours which were in use before the discovery of the coal-tar colours and their introduction into the industry4 ,since1 however1 the latter have acquired so great a preponderance in dyeing1 it is no longer applicable1 for the dyers use at present a large number of substances which are included in the narrow definition of pigments4 ,the greater part of the coal-tar colours are substances which1 in solution1 when brought in contact with a fabric1 adhere to it and colour it permanently4 ,according to their use and preparation1 pigments are divided into a number of classes1 and one speaks of painters'1 artists'1 enamel1 porcelain and glass colours1 also of oil1 honey1 water and cake colours4 ,although this division is important for trade purposes1 it is of little moment for the colour maker1 for he can prepare the same colour for both purposes1 either for oil or water colour4 ,what is of the greatest interest for the colour maker is the preparation of the pigment itself4 ,the conversion of the prepared pigment into 7oil or water7 paint is unaccompanied by difficulties4 ,when we look for a practical classification for pigments1 we find that there are colours which exist ready formed in nature1 and others which can only be obtained by certain chemical processes1 at times very complicated4 ,as regards the first group of pigments--those which exist ready formed in nature--the processes which they undergo at the hands of the colour maker are almost entirely mechanical treatments--grinding1 sieving1 levigating and similar operations--in order to convert them into such a condition that they can be used for painting4 ,since a large number of these pigments belong to that class of minerals which mineralogists call earths1 these pigments have also been designated earth pigments1 a term which we shall retain on account of its general use1 although it is incorrect1 since many of the so-called earth pigments are not obtained from 8earths0 in the mineralogical sense4 ,among the pigments which are prepared by human skill many divisions can be drawn4 ,a large number of pigments are prepared from mineral sources2 an equally important number are derived from the animal and vegetable kingdom1 the latter consisting of combinations of organic materials with certain inorganic substances4 ,some few pigments 7putting aside the coal-tar colours7 are simply organic products1 as1 for example1 the majority of the black pigments1 which consist of carbon4 ,the following classification is drawn up on the lines indicated above3-- #a4 ,natural ,colours or ,earth ,pigments4--,found ready formed in nature and requiring only mechanical preparation to be usable4 ,a large number of handsome and also cheap colours belong to this class4 #b4 ,artificially ,prepared ,mineral ,pigments4--,obtained by certain chemical processes1 and1 according to their composition1 either compounds of metals with sulphur1 oxygen1 iodine1 cyanogen1 etc41 or of oxides with acids1 i4e41 salts4 #c4 ,lakes4--,compounds of colouring matters from the animal or vegetable kingdom with a mineral substance1 such as lead oxide or alumina4 ,as a fourth group we might take those colours which do not fall into the previous classes1 as1 for example1 the black pigments composed of carbon2 but since this division is not made in practice we shall not regard this species of pigment as a particular group1 but shall discuss them in the proper place4 ,as an entirely new group of colours are to be classed those which are generally called coal-tar colours4 ,these colours1 which1 at present1 are the most important in dyeing and calico printing1 are prepared from so-called organic compounds 7more properly1 carbon compounds74 ,the manufacture of these colours is a separate branch of chemical industry4 ,,chapter ,,ii4 ,,the ,,physico-,,chemical ,,behaviour ,,of ,,pigments4 ,in a work which1 as its title indicates1 is devoted to a description of the manufacture of pigments1 the properties of those substances which are necessary for the preparation of colours cannot be exhaustively considered2 we must1 therefore1 presuppose a knowledge of the elements of chemistry4 ,we have to consider in this book the chemistry of colours2 the reader will1 therefore1 not expect an exposition of general chemical laws2 we shall only state certain facts which are of value to the manufacturer4 ,with the description of the manufacture of each pigment and of the materials required for that manufacture1 we shall still discuss the chemical processes which must be conducted in the preparation of the colours1 so far as it is necessary in order to understand them4 ,in this chapter we shall say a few words about the physical and chemical behaviour of pigments in general4 ,the great majority of pigments are prepared by the process of precipitation1 generally by mixing the solutions of two substances1 upon which an interchange of the constituents occurs and the less soluble compound separates in pulverulent form from the solution as a precipitate4 ,most of these colours are obtained by the admixture of the solutions of two salts2 the preparation of the so-called chrome yellow may be taken as an example4 ,in the preparation of this pigment1 a solution of a lead salt1 sugar of lead 7lead acetate71 is mixed with a solution of bichromate of potash1 whereupon a precipitate of lead chromate 7chrome yellow7 is formed1 whilst potassium acetate remains dissolved4 ,the lead chromate is formed because the acetic acid has a greater affinity for potash than for lead oxide1 wherefore an interchange of acid and base takes place1 but the lead chromate being insoluble in water consequently separates in the form of a precipitate4 ,many mineral pigments are produced in the form of precipitates by passing sulphuretted hydrogen or carbonic acid gas into certain metal solutions4 ,in these cases a similar exchange takes place between the reacting substances to that given in the case of chrome yellow2 the metals have a greater affinity for the sulphur or for the carbonic acid than for the substances with which they are already united1 they unite with the former1 and the new compound separates as an insoluble substance4 ,we have examples of such compounds in cadmium sulphide1 which is obtained by passing sulphuretted hydrogen into the solution of cadmium in an acid1 and in white lead1 which is formed by the saturation of a solution of lead acetate by carbonic acid4 ,many organic colouring matters1 soluble in water1 have the property of forming compounds with metallic oxides1 soluble with great difficulty1 when their solutions are mixed with a salt of lead1 tin or aluminium1 and the oxide is separated from the solution by an alkali4 ,the precipitates obtained in this way are insoluble compounds of the colouring matter and the oxide of the metal2 they are called lake pigments1 or1 briefly1 lakes4 ,a large number of pigments1 often of great beauty1 is obtained in this manner4 ,the lakes are widely used in all branches of painting and dyeing4 ,of great importance for the quality of the pigment is the physical condition of the precipitate2 this is either crystalline or amorphous1 that is1 non-crystalline4 ,when a crystalline precipitate is examined under the microscope1 it is seen to consist of very small1 coloured1 transparent crystals4 ,the amorphous precipitates are1 however1 in such a fine state of division that even with the highest magnification they transmit little or no light1 and consequently appear opaque4 ,these different characters of precipitates have the greatest influence on that property of pigments which we call covering power4 ,in consequence of its transparency1 a crystalline precipitate will allow the colour of the surface upon which it is spread to appear through1 hence it must be laid on much more thickly than is necessary with an opaque pigment1 of which a thin coating is sufficient to make the colour of the surface beneath invisible4 ,how extremely important is the crystalline or non-crystalline nature of a precipitate in practice is seen by a consideration of white lead4 ,this pigment1 lead carbonate1 can be made by mixing solutions of a lead salt and a soluble carbonate 7soda72 but in this case a lead carbonate of crystalline nature is formed1 which1 being transparent1 is of so small covering power that this process has no application in the manufacture of white lead2 but a far more troublesome method is used by which a non-crystalline product1 amorphous lead carbonate1 is obtained4 ,many pigments are formed by burning 7oxidising7 metals1 as1 for example1 zinc white2 others are prepared by melting salts together1 as ,naples yellow2 others again are formed by very complicated processes still partially unexplained1 as is the case with ultramarine4 ,in the manufacture of colours we find all chemical processes in use4 ,it may be here remarked that it is quite possible to manufacture some colours1 indeed a large number1 according to fixed directions1 without any particular chemical knowledge being necessary to carry on the processes4 ,indeed1 in works we find most processes being carried out by ordinary labourers who are quite destitute of any knowledge of chemistry4 ,we must1 however1 add that we are convinced that any colour maker who works simply in a purely empirical manner1 according to a stereotyped recipe1 will never be in the position to raise himself above the position of a workman2 he will not be able1 when a slight mishap occasions a change in the ordinary course of the process1 to devise a means of overcoming the defect1 but will be compelled to dispose of the faulty product in the condition in which it exists4 ,such a manufacturer is in a condition of blind dependence on the chemical works and dealers from whom he receives the raw materials requisite for the preparation of his colours4 ,if he should receive materials which contain impurities not to be detected by empirical methods1 the inevitable result will be that the colours produced from them will not be equal to the standard4 ,if1 in making a colour which is the outcome of several processes1 a workman once makes a mistake1 the product will not be of the required quality4 ,on the contrary1 if the manufacturer possesses a certain amount of chemical knowledge1 it will not be difficult for him to ascertain the causes of a failure in a process1 and1 at the same time1 to devise means by which the defects may be removed4 ,the manufacturer is more and more in the habit of buying the chemicals which he requires for his manufactures rather than of making them himself4 ,he should1 therefore1 be in a position to form an opinion as to the usability and purity of these substances1 which will only be possible when he has the knowledge requisite for subjecting them to a chemical examination4 ,although we shall presuppose1 as we have said1 that those who intend to concern themselves with colour manufacturing possess an acquaintance with the principles of chemistry1 yet this book has been so planned that it may be of use 7we hope7 to the practical man who is innocent of chemical knowledge4 ,on this account1 we have devoted care to the description of those raw materials which are bought in large quantity1 and to the simple investigation of their purity4 ,when the manufacturer has the advantage of a chemical education1 apart from his endeavours to produce colours lacking nothing in beauty or depth of shade1 he will direct his endeavours in two directions1 in respect of which great advances are yet to be made--the permanence and harmlessness of his colours4 ,many pigments possess the undesirable property of losing their brightness under atmospheric influences2 many1 indeed1 fade away completely in the course of time4 ,we have only to examine a picture some centuries old2 in spite of the care bestowed on its preservation1 we can say with certainty that1 in the course of time1 it will be so completely altered that nothing will remain of the original colours4 ,it is the endeavour of the sensible manufacturer of colours to make only such as remain unaltered by atmospheric action1 and also undergo no change when they are mixed with other pigments4 ,although it may be highly desirable that the painter should possess a knowledge of the chemical properties of the colours he uses1 still it should be the first object of the maker to take care that he places on the market only colours which will remain as much as possible unaltered when used alone1 and will remain undecomposed when mixed4 ,this is1 unfortunately1 not the case with many colours now in use4 ,we shall return later to this point1 of such extraordinary importance to the artist4 ,the second point to be observed1 is to produce only harmless colours4 ,the advances of chemistry have made known to us a series of colours which have the advantage over others known for a longer period that they are non-poisonous4 ,unluckily1 these harmless colours frequently fall behind the poisonous colours in brilliance1 and generally they are more expensive4 ,here1 too1 is opened to the manufacturer a wide field of activity4 ,the more completely poisonous substances disappear from the colours in use1 the more widespread will be the use of colours4 ,we should remark that the expression 8poisonous colours0 is to be used with a certain reserve4 ,many pigments which contain lead1 copper1 antimony1 mercury1 etc41 are poisonous1 because they contain poisonous metals2 but poisoning with them will not readily take place on account of their insolubility4 ,it is different with the very poisonous arsenic compounds1 which should be removed from the list of colours in common use2 many a misfortune caused by them would then be avoided4 ,endeavours to produce innocuous colours have been more successful than the efforts after permanence4 ,there are now very few commonly used colours which can be accounted very poisonous compounds1 and which cannot be replaced by other colours of equal beauty4 ,on the whole1 we are now in the position to prepare harmless colours suited to most purposes4 ,special endeavours should be made to sell these1 so that such cases of poisoning should not occur as1 for example1 caused by gingerbread which had been wrapped in paper coloured by emerald green4 ,,chapter ,,iii4 ,,raw ,,materials ,,employed ,,in ,,the ,,manufacture ,,of ,,pigments4 ,as we have mentioned before1 the manufacturer of colours now generally uses materials supplied to him by chemical works4 ,the purer these are1 the easier it will be to work with them1 and the finer will the colours turn out4 ,we have indicated that it is important for the manufacturer to know accurately the properties of his materials in order to be able to estimate their value4 ,many substances required in certain cases must be made by the colour manufacturer1 since1 on account of their condition1 they cannot form articles of commerce--chlorine and sulphuretted hydrogen1 for example4 ,in addition to the substances which are not to be bought1 there are others which do occur in commerce1 but are sold at so high a price that the manufacturer is compelled to make them himself4 ,this is the case with the cobalt compounds1 from which many beautiful colours are made4 ,the producers of these demand such prices that it is to the interest of the colour maker to prepare them for his own use4 ,in the following chapters1 we shall deal with the more important raw materials which are employed in colour manufacturing1 and shall restrict our remarks to what is of particular importance thereto4 ,for more detailed accounts of these raw materials the reader is referred to the text books of chemistry1 in which he will find them minutely described1 in so far as they are chemical products4 ,the materials employed may be divided into assistants in the processes and components of the manufactured pigment4 ,the assisting substances are those which are used in the manufacture of a colour without entering into its composition2 from the component materials the colours are directly derived4 ,for example1 in the manufacture of ,prussian blue1 yellow prussiate of potash1 an iron salt1 water 7in which the salts are dissolved7 and nitric acid are used4 ,in the blue obtained are contained portions of the iron salt and of the yellow prussiate1 these are1 therefore1 component materials1 whilst water and nitric acid are simply assistants1 since they do not enter into the composition of the pigment4 ,in colour making a large number of assisting materials are employed1 which comprise a considerable number of elements and compounds4 ,since these are of great importance for our purpose1 we shall describe their properties1 and1 when necessary1 briefly the method of preparation4 ,among the component materials are to be reckoned a large number of salts of the alkaline earth and earth metals and of all the heavy metals4 ,in addition1 there are also the substances of animal or vegetable origin used in lake making4 ,in the description of the raw materials1 if we were to overstep the line drawn here1 we could include a great variety of compounds1 those1 for example1 used in the manufacture of the so-called aniline dyes4 ,these substances form1 however1 as we have stated1 the object of a particular branch of manufacture1 which forms a separate division of colour chemistry1 but with which is not to be confounded what has been hitherto designated the manufacture of colours4 ,,chapter ,,iv4 ,,assistant ,,materials4 ,water1 ,h,o #ah4a--,this substance plays a tremendous part in colour making2 almost all the substances which are used in solution are dissolved in water2 the removal from precipitates of admixed foreign bodies1 the so-called washing1 is always accomplished with water4 ,the chemist does not understand by water quite that liquid which in general speech is so designated4 ,we must consider the water which is at the disposal of the colour maker4 #a ,we append the chemical formula and the molecular weight to the description of each compound4 ,water1 in the chemical meaning of the word1 is a liquid composed only of hydrogen and oxygen1 and leaving no residue when evaporated4 ,such water is not found in nature2 it can only be obtained by distillation of well or river water4 ,the water which falls in long continued rain1 or is obtained by melting snow1 is most nearly like distilled water2 it contains only small quantities of dissolved substances1 and generally such as would be without influence in colour making4 ,water of this description is available for but a limited use2 the large quantities of water required in a colour works must be taken from springs or streams4 ,these waters contain1 however1 more or less large amounts of dissolved salts1 which act in a marked manner upon the substances dissolved in them4 ,in almost all spring and well waters is found carbonate of lime2 such waters are called 8hard04 ,river water contains generally little carbonate of lime2 it is then called 8soft water04 ,the influence of the carbonate of lime is especially evident when salts of lead1 copper1 iron and other heavy metals are dissolved in water2 the carbonate of the particular metal gradually separates from solution1 and the liquid becomes very turbid4 ,when only hard waters containing much lime are at the service of the manufacturer1 turbid solutions are often obtained1 which must be filtered before use4 ,in many cases this can be avoided by adding milk of lime to the water in a large vessel2 the free carbonic acid unites with the lime1 and thus the carbonate of lime1 which is only soluble in water containing free carbonic acid1 separates as a fine precipitate4 ,water which has been treated in this way becomes clear after some time1 through the deposition of the carbonate of lime2 it is then soft water4 ,in order to separate the carbonate of lime in this way1 no more than the requisite quantity of milk of lime should be added1 so that no lime remains in excess1 since this would cause precipitates when salts of lead1 copper1 iron1 etc41 were dissolved4 ,in many cases--for example1 when lead or barium salts are dissolved--the lime contained in the water can be made harmless by slightly acidifying with acetic or nitric acid4 ,water which contains sulphate of lime 7gypsum7 is equally useless for many purposes1 as1 for example1 the solution of lead and barium salts4 ,these metals form insoluble compounds with the sulphuric acid1 which render the solution turbid1 and can be removed only with difficulty by filtering1 on account of their great fineness4 ,they are more easily removed by allowing to settle4 ,water containing gypsum often contains in addition small quantities of sulphuretted hydrogen4 ,however small the quantities of this gas may be1 they still make the water absolutely useless for certain purposes in the manufacture of colours2 for example1 for the preparation of all pigments containing lead which are obtained by precipitation4 ,the sulphuretted hydrogen forms black compounds with lead1 copper1 bismuth1 mercury and other metals1 which impair the brilliance of the colour4 ,a colour made under these conditions is never clean1 its hue is injured by the admixture of the black substance4 ,water which contains much common salt 7sodium chloride7 is unsuitable for the solution of lead1 mercury and silver salts4 ,in consequence of the great affinity of these metals for chlorine1 turbid solutions are obtained when their salts are dissolved in water containing common salt4 ,some waters contain a considerable quantity of iron4 ,such waters deposit on evaporation1 and often on standing exposed to the air1 a brown powder of ferric hydrate1 which would have considerable influence on the shade of a pigment4 ,white pigments1 in the preparation of which such a water is used1 have always a brownish tinge2 yellow and red pigments are also unfavourably affected4 ,carbonate of lime and common salt occur in small quantities in every well water4 ,the colour maker must do the best he can with such a water2 its use will not particularly harm the shade of the colours prepared with it if the amount of the impurities is not very large4 ,water containing much iron is practically useless2 the oxide of iron would injure the colours so much that it would not be possible to obtain brilliant shades4 ,water from wells in the neighbourhood of deposits of turf or cemeteries often contains considerable quantities of organic substances which act injuriously on the shade of pigments2 such water should not be used in colour making4 ,the impurities in a water are more or less harmful according to the purpose for which it is to be used4 ,sulphate of lime is generally more injurious than carbonate of lime1 since the precipitates which the latter causes in solutions of the salts of certain metals can be prevented by the addition of acids4 ,this is not the case with sulphate of lime2 when lead or barium salts are dissolved in water containing this substance1 a precipitate of lead or barium sulphate is obtained1 which is insoluble4 ,in dealing with the salts of costly metals1 such as mercury or silver1 it is better to dissolve them in distilled water1 or1 at least1 very pure rain water4 ,the rain water which runs from zinc or well tiled roofs is generally very pure2 for practical purposes it may be regarded as free from carbonate and sulphate of lime1 sulphuretted hydrogen and common salt4 ,the colour maker should take care to obtain as much of this pure water as possible by erecting large rain-water tanks4 ,the less impurity a water contains the more useful it is for our purpose4 ,after rain water soft river water is the best1 and after this the softer well waters4 ,all mineral waters distinguished by a high content of salts or gases are quite useless for colour making2 for this reason sea water is disqualified4 ,an accurate analysis of a water is much too complicated for the manufacturer2 it is sufficient for him to convince himself of the absence of certain substances4 ,water which1 some time after the addition of a little tannic acid solution1 acquires a clear green or a bluish to black shade contains much iron1 and is useless4 ,water which coagulates a large quantity of a solution of soap in alcohol is very rich in carbonate or sulphate of lime4 ,in order to decide approximately in what relative proportion these salts are present1 a solution of barium chloride is added to the water so long as a precipitate forms4 ,if this disappears completely on the addition of nitric acid1 the water contains only carbonate of lime2 if it only partly dissolves1 sulphate of lime is also present4 ,the presence of chlorine is shown by a considerable turbidity on acidifying the water with nitric acid1 boiling and adding silver nitrate4 ,if the precipitate obtained on the addition of a lead salt is not pure white1 but discoloured1 the water contains sulphuretted hydrogen1 which has formed black lead sulphide4 ,in order to test the water for organic substances1 about a litre is evaporated to dryness in a porcelain dish1 and the residue heated to redness2 if it turns brown and black1 and possibly gives off a smell of burnt feathers1 the water contains much organic matter4 ,pure water is coloured permanently red by a solution of potassium permanganate2 but if it contains organic matter1 the solution is decolourised after some time and a brown precipitate is deposited at the bottom4 ,from the amount of this precipitate an idea of the quantity of organic matter present may be obtained4 ,it is only necessary to be very scrupulous concerning the quality of the water when it is to be used for the solution of salts or the extraction of dye-woods4 ,for washing precipitates1 which requires a large volume of water1 there can generally be used1 without detriment1 water containing much lime1 but it must be free from iron and sulphuretted hydrogen4 ,the latter is particularly harmful to most of the lead colours1 which would lose in beauty by washing with water containing this substance4 ,it is hardly necessary to say that the water used in colour making must be quite clear4 ,muddy river water must in every case be completely freed from the solid particles contained in it1 either by settling or by filtering4 ,filters filled with well washed sand give good results for this purpose4 ,chlorine1 ,cl #cee4--;,for some operations in colour making it is necessary to employ chlorine4 ,this is a greenish yellow gas at ordinary temperatures1 which is characterised by a suffocating smell and the energy with which it unites with most elements4 ,on account of its injurious effects on man certain precautions have to be observed in preparing chlorine1 and it is advisable to erect the apparatus necessary for its production in a separate room1 so that the workmen are not injured by the gas4 ,illustration3 ,,fig4 #a4 ,formerly chlorine was exclusively made in lead apparatus1 because this metal is one of the least readily attacked4 ,when such an apparatus is used for the first time a layer of lead chloride is formed1 which1 like a varnish1 protects the metal beneath from further attack4 ,fig4 #a represents an apparatus formerly employed for the preparation of chlorine in chemical works4 ,in the upper part of the pear-shaped vessel1 ,k1 there are four openings1 two of which1 ,d and ,c1 are provided with water lutes4 ,this means that the opening is surrounded by a moat containing water1 into which the rim of the cover dips1 thus making a joint4 ,through the middle opening goes the axle of the stirring apparatus1 ,r2 in the fourth is a lead safety funnel1 ,j4 ,solid materials are introduced through ,d1 liquid through ,j2 the tube ,c carries away the chlorine formed2 the tube ,a1 furnished with a stop cock1 can draw off the fluid contents of the apparatus4 ,since lead melts at low temperature1 the apparatus cannot be heated over the fire without danger1 therefore it is surrounded by an iron jacket1 ,w1 which is filled with water1 or else the apparatus is heated by steam introduced into ,w4 ,larger quantities of chlorine are more conveniently prepared in an apparatus1 of similar structure1 made of stone or earthenware1 which have the advantage over lead that they are not at all attacked by chlorine4 ,illustration3 ,,fig4 #b4 ,fig4 #b exhibits the construction of such an apparatus of medium size4 ,it is constructed of sandstone or earthenware2 the lid and some of the smaller parts can be made of either earthenware or lead4 ,the pyrolusite is introduced at ,g in large pieces2 ,h is the funnel for pouring in the acid2 ,e ,k ,d1 the steam pipe2 ,c1 the perforated false bottom upon which the pyrolusite lies2 ,f1 the delivery tube for the chlorine2 ,j1 the opening for running off the manganese chloride2 a1 the leaden cover4 ,to prepare chlorine1 #a part 7by weight7 of common salt1 #a part of powdered pyrolusite1 #b parts of vitriol and #a part of water are used4 ,the salt and the pyrolusite are introduced through ,d into the apparatus 7,fig4 #a72 the acid1 diluted with the water1 is poured in through the funnel1 the materials are mixed by the stirrer and gently warmed until chlorine appears1 when the application of heat must be considerably diminished or the chlorine will be violently evolved4 ,pyrolusite and hydrochloric acid are now generally used for the preparation of chlorine1 because the solution of manganese chloride1 left at the end of the operation1 is valuable4 ,if all the chlorine made in one operation is not at once required for the manufacture of a colour1 it can be utilised by sending it into a box filled with slaked lime1 which is converted into chloride of lime or bleaching powder4 ,the liquid run away from the apparatus at the conclusion of the operation contains manganese and sodium sulphates1 or manganese chloride as the case may be1 and can be used for the preparation of manganese pigments4 ,ammonia1 ,,nh #ag4--;,ammonia is obtained from chemical works in the form of a strong solution of ammonia gas in water1 which is generally very pure4 ,the density of an aqueous solution of ammonia is the smaller the more ammonia it contains1 and thus the strength of a solution of ammonia can easily be formed by means of the hydrometer4 ,the following table shows the percentage of ammonia1 ,,nh1 in a liquid of known specific gravity at the temperature of #ad ,c43-- ---------------------------------------- --------- ,specific ,ammonia ,specific ,ammonia ,gravity4 per cent4 ,gravity4 per cent4 ---------------------------------------- --------- #jhhe #cfjj #jiec #aaej #jhhf #cejj #jiee #aajj #jhhi #cdjj #jieg #ajej #jhia #ccjj #jiei #ajjj #jhic #cbej #jifa #iej #jhie #cbjj #jifc #ijj #jhig #cacj #jife #hej #jijj #bfjj #jifh #hjj #jije #beci #jigj #gej #jibe #aied #jigb #gjj #jicb #ageb #jigd #fej #jidg #acdf #jigf #fjj #jiea #abjj #jigh #eej ---------------------------------------- --------- ,the ,hydrometer4--,in the above table the percentage content of the ammonia solution is given according to its specific gravity1 that is1 according to the ratio between the weight of any volume of the liquid and the weight of an equal volume of water4 ,according to scientific principles1 only those hydrometers should be used which are graduated in specific gravities4 ,in spite of all exertions in this direction1 manufacturers have not yet been induced to use such instruments in every case4 ,hydrometers1 with quite arbitrary scales1 such as those of ,baum and ,twaddell1 are frequently found in works4 ,these hydrometers generally only show that a liquid is of so many degrees on the particular scale1 and the manufacturer in using them is restricted to the following out of a certain recipe which requires the use of a liquid of a certain strength which is expressed in degrees ,baum1 etc4 ,he does not learn by this how many per cent4 of the particular substance are dissolved in the water when the liquid has a certain hydrometric strength4 ,for the sake of uniformity1 it is urgently to be desired that all manufacturers who use the hydrometer to estimate the content of a liquid in ammonia1 potash1 soda1 hydrochloric1 sulphuric1 nitric acids1 etc41 should employ simple specific gravities4 ,this is desirable1 because the percentage strength of a solution1 corresponding to the specific gravity1 can be at once accurately found from tables4 ,on these grounds1 in the present work1 we have restricted ourselves to tables showing simply the specific gravities of solutions and the corresponding composition4 ,sal ,ammoniac or ,ammonium ,chloride1 ,,nh,cl #ece4--,this substance comes into commerce in the form of a white crystalline meal1 more rarely in the form of sugar loaves 7crystallised sal ammoniac7 or of flat cakes 7sublimed sal ammoniac74 ,it is usually very pure1 since impure forms1 generally containing much iron1 are difficult of sale4 ,at a particular temperature sal ammoniac is volatile2 it is used in certain mixtures in order to prevent the temperature1 on heating1 from rising beyond a certain point4 ,like ammonia1 it is more used in dyeing4 ,ammonium ,sulphide1 ,,nh,,hs4--,this compound is obtained by leading sulphuretted hydrogen into ammonia solution so long as it is dissolved1 and a test portion of the liquid still gives a white precipitate with a solution of magnesium sulphate4 ,ammonium sulphide decomposes by long standing in the air1 sulphur being separated4 ,it gives precipitates with the salts of certain metals1 for example1 iron1 cobalt1 manganese1 zinc1 nickel4 ,these precipitates1 which consist of the sulphides of the metals1 are not formed by sulphuretted hydrogen in acid solutions4 ,,acids4 ,in colour making many acids are used for the solution of metals1 the production of precipitates1 for oxidations and so forth4 ,commercial acids1 especially inorganic acids1 generally contain not inconsiderable quantities of impurities which are injurious in the manufacture of many colours4 ,hydrochloric ,acid1 ,h,cl #cfe4--,the commercial acid 7muriatic acid1 spirits of salt7 generally contains large quantities of iron1 which colour it yellow--fortunately1 in many cases1 this is not a disadvantage1 and also at times the iron can be removed from solutions made in the acid4 ,another impurity is sulphuric acid4 ,this can be detected by diluting and adding barium chloride2 if sulphuric acid be present1 a white precipitate1 or1 at least1 a cloudiness1 appears4 ,ordinary hydrochloric acid is a solution of hydrochloric acid gas in water4 ,the strongest acid contains #dbhe per cent4 of the gas1 and has the specific gravity #aba4 ,the following table gives the strengths of acids of various specific gravities3-- ---------------------------------------- ------------- ,specific ,hydrochloric ,specific ,hydrochloric ,gravity4 ,acid ,gravity4 ,acid per cent4 per cent4 ---------------------------------------- ------------- #aba #dbhe #aaj #bjbj #abj #djhj #aji #ahge #aai #chhh #ajh #afga #aah #cfcf #ajg #aedi #aag #cdcd #ajf #achf #aaf #cbcb #aje #aadi #aae #cjcj #ajd #hig #aad #bhbh #ajc #fic #aac #bfbf #ajb #dhi #aab #bdbd #aja #bjc #aaa #bbbb ---------------------------------------- ------------- ,sulphuretted ,hydrogen1 ,h,s #cd4--,this is a gas of acid properties smelling like rotten eggs2 it precipitates the sulphur compounds of many metals when led into the acid solution of the corresponding salt4 ,this substance is seldom required in colour works1 so that it is convenient to have an apparatus which permits of the preparation of any required quantity4 ,fig4 #c represents an apparatus devised by the author1 which is well adapted for the preparation of sulphuretted hydrogen4 ,it consists of a small1 wooden tub1 on whose upper edge lies a thick paper ring1 so that the lid may be pressed down air-tight by the screws ,b4 ,through the lid pass a tap-funnel1 ,t1 a movable screw1 ,s1 and a tube1 ,r1 to carry away the gas4 ,on the screw ,s hangs a basket1 ,k1 by a handle2 this is filled with pieces of iron sulphide as large as nuts4 ,the tub is filled to about one-third of its height with a mixture of #i parts of water and #a part of sulphuric acid4 ,illustration3 ,,fig4 #c4 ,when sulphuretted hydrogen is required the basket is lowered by the screw1 ,s1 until it dips in the liquid2 according as the basket dips more or less into the liquid a fast or slow current of the gas is obtained4 ,when the gas is no longer required the basket is raised out of the liquid1 and the evolution of gas at once ceases4 ,the funnel1 ,t1 serves for the introduction of the liquid1 the tap1 ,h1 for drawing off the iron sulphate solution1 which can be used with advantage for the preparation of fine iron colours4 ,the apparatus should not be opened so long as sulphide of iron remains in the basket4 ,sulphuric ,acid comes into the market in two different forms3 oil acid2 both are used in colour making4 ,oil of ,vitriol1 ,h,,so #ih1 is a colourless1 oily liquid of high specific gravity2 it is generally tolerably pure1 and contains1 as a rule1 only a small quantity of lead1 the presence of which is indicated by a turbidity on largely diluting the acid4 ,the amount of pure sulphuric acid in the liquid is practically determined by taking the specific gravity4 ,the table indicates the relation between the specific gravity and the content of sulphuric acid4 ---------------------------------------- ---------------------- ,specific ,gravity4,sulphuric ,acid,specific ,gravity4,sulphuric ,acid per cent4 per cent4 ---------------------------------------- ---------------------- #ahdhe #ajj #ahjdc #hi #ahdge #ii #agifb #hh #ahdfj #ih #aghgj #hg #ahdci #ig #agggd #hf #ahdaj #if #agfgc #he #ahcgf #ie #agegj #hd #ahccf #id #agdfe #hc #ahbij #ic #agcfj #hb #ahbcc #ib #agbde #ha #ahagi #ia #agabj #hj #ahaae #ij ---------------------------------------- ---------------------- ,nordhausen ,sulphuric ,acid1 ,h,s,o ,h,,so ,,so1 is generally a yellowish brown liquid1 which gives off white fumes in the air4 ,it contains varying quantities of sulphur trioxide dissolved in sulphuric acid4 ,it often contains selenium1 which separates as a red powder when the acid is diluted4 ,the presence of this impurity does not interfere with the use of the acid for dissolving indigo1 the only purpose for which it is required in the colour factory4 ,nitric ,acid1 ,,hno #fc4--,this acid1 which is used in the preparation of many colours1 is distinguished by the readiness with which it gives up part of its oxygen1 and thus converts metals like antimony and bismuth into oxides1 and transforms other compounds into a higher state of oxidation4 ,there are two kinds of nitric acid3 ordinary nitric acid1 a colourless liquid which is more or less pure2 and fuming nitric acid1 a yellow or orange-coloured liquid1 fuming strongly in the air1 which consists of a solution of nitrogen peroxide1 ,,no1 and nitric oxide1 ,,no1 in nitric acid4 ---------------------------------------- -------------------- ,specific ,gravity ,nitric ,acid ,specific ,gravity ,nitric ,acid at #ae ,c4 per cent4 at #ae ,c4 per cent4 ---------------------------------------- -------------------- #aecj #ajjjj #acbc #eejj #aebj #igjj #abhd #ejdi #aeji #idjj #abea #dejj #aejc #ibjj #abaa #djjj #adii #iajj #aahe #cchf #adie #ijjj #aaeg #cjjj #adgh #hejj #aach #bega #adfj #hjjj #aabj #bcjj #addb #gejj #ajhi #bjjj #adbc #fiif #ajfg #aejj #adjj #fejg #ajbb #aada #acdf #fjjj #ajaj #djj ---------------------------------------- -------------------- ,since the action of nitric acid chiefly depends on its oxidising properties1 which are possessed by both kinds1 it generally does not matter which is used4 ,the usual impurities are chlorine and sulphuric acid2 the presence of the first is shown by silver nitrate solution1 of the latter by barium chloride1 in each case added after diluting4 ,when the acid is used for oxidations these impurities do not interfere1 but nitric acid containing chlorine cannot be used to dissolve silver1 because the chlorine would form insoluble silver chloride4 ,the strength of nitric acid is gauged by its specific gravity as given in the table4 ,aqua ,regia4--,a mixture of #b parts of hydrochloric acid and #a part of nitric acid gradually turns orange or yellow and evolves chlorine4 ,this liquid1 which can dissolve gold in consequence of the free chlorine it contains 7hence its alchemistic name1 from gold1 the 8king of metals071 is used as a very powerful oxidising agent in colour making4 ,carbon1 ,c #ab1 is the only one of the non-metallic elements to be mentioned here2 by itself it forms a group of very important pigments1 which we shall describe in detail at a later stage4 ,carbonic ,acid ,gas1 ,,co #dd1 is used in the manufacture of white lead1 which it precipitates from lead acetate4 ,this is1 however1 a particular branch of colour making carried on in special works4 ,in describing this manufacture we shall return to the preparation of carbonic acid on a large scale4 ,,organic ,,acids4 ,the organic acids which are important in colour making are acetic1 oxalic and tartaric acids4 ,acetic ,acid1 ,c,h,o #eh4--,the very dilute form of this substance is known commonly as vinegar1 the stronger as pyroligneous acid1 and the purest as glacial acetic acid2 the latter is1 however1 scarcely used4 ,formerly in colour making ordinary vinegar was used1 but now pyroligneous acid is almost exclusively employed4 ,this is distinguished by its strong empyreumatic smell1 which1 however1 is without importance in colour making4 ,the strength of a solution of acetic acid cannot be found by a simple estimation of specific gravity1 since the density does not increase with the percentage of acetic acid4 ,if an accurate estimation of the strength of acetic acid is required1 it must be obtained by neutralising the acid with an alkali by a process of volumetric analysis4 ,for practical purposes1 where it is generally known whether a very strong or a more dilute acetic acid is under consideration1 the following table1 showing the connection between specific gravity and percentage strength1 is sufficient4 ---------------------------------- ,specific ,acetic ,specific ,acetic ,gravity4 ,acid ,gravity4 ,acid per cent4 per cent4 ---------------------------------- #ajfce #ajj #ajeh #dh #ajfgj #ih #ajee #df #ajfij #if #ajed #dd #ajgjf #id #ajeb #db #ajgaf #ib #ajea #dj #ajgcj #ij #ajdi #ch #ajgcj #hh #ajdg #cf #ajgcj #hf #ajde #cd #ajgcj #hd #ajdb #cb #ajgcj #hb #ajdj #cj #ajgce #hj #ajch #bh #ajgcb #gh #ajce #bf #ajgcj #gf #ajcc #bd #ajgbj #gd #ajca #bb #ajgaj #gb #ajbg #bj #ajgjj #gj #ajbe #ah #ajgjj #fh #ajbc #af #ajfij #ff #ajbj #ad #ajfhj #fd #ajag #ab #ajfgj #fb #ajae #aj #ajfgj #fj #ajab #h #ajffj #eh #ajjh #f #ajfdj #ef #ajje #d #ajfcj #ed #ajjb #b #ajfbj #eb #ajja #a #ajfjj #ej ---- ---- ---------------------------------- ,oxalic ,acid1 ,c,h,o4#b;,h,o #abf1 has but a limited use in colour making4 ,it comes into commerce in the form of more or less pure white crystals which readily dissolve in water1 and are almost pure oxalic acid1 containing only small quantities of oxalate of lime1 the presence of which is without importance for the purposes to which the acid is put in colour making4 ,frequently1 instead of oxalic acid1 the acid potassium oxalate 7salt of sorrel7 is used4 ,tartaric ,acid1 ,c,h,o #aej1 occurs as white or yellowish crystals1 with a slightly burnt smell1 which dissolve readily in water1 and have a strong acid taste4 ,the pure acid1 which is white and without smell1 is considerably dearer than the yellow variety4 ,the impurities of the latter1 which are small in quantity1 are without influence on the colours prepared by its help1 so that this form is generally used4 ,,chapter ,v4 ,,metallic ,,compounds4 ,,alkalis4 ,the compounds of the alkali metals1 potassium and sodium1 play a considerable part in colour making4 ,formerly the potassium compounds were in general use1 but the sodium compounds are at present obtainable at a much lower price1 and in most cases they can be used equally well4 ,thus1 in colour making1 sodium compounds are chiefly employed4 ,the cyanogen compounds are an exception2 their potassium compounds are used exclusively4 ,potassium ,compounds4--,the potassium compounds which are chiefly used in colour making are potassium carbonate 7potashes1 pearl-ash71 potassium hydroxide 7caustic potash71 potassium nitrate 7saltpetre71 potassium tartrate 7tartar71 and potassium ferrocyanide and ferricyanide 7yellow and red prussiate of potash74 ,the cyanogen compounds have peculiar properties4 ,we shall describe them separately after the potassium and sodium compounds4 ,potassium ,carbonate 7carbonate of potash71 ,k,,co #ach1 is known commercially as potashes1 a name derived from its former method of preparation by heating the ashes of plants in pots4 ,at present potashes are prepared in large quantities from other sources4 ,pure potash forms crumbling lumps with a slight yellow or bluish grey tinge1 rapidly absorbing moisture from the air1 and in time completely liquefying4 ,the yellowish tinge is caused by oxide of iron1 the bluish by manganese compounds4 ,the so-called calcined potash has been strongly heated1 and thus all organic substances contained in it have been destroyed4 ,potashes are in no way pure potassium carbonate2 they contain a mixture of all those salts which are found in plants--potassium sulphate and chloride1 small quantities of silicic acid1 etc4 ,these impurities are rarely harmful1 still it is generally necessary to know the percentage of pure potassium carbonate contained in potashes4 ,although at present in commerce the strength of potashes is frequently guaranteed1 it is still desirable to estimate the strength4 ,it is sufficient for practice to allow a small quantity1 say #ajj grammes1 to stand with an equal quantity of very cold water for some hours1 then to filter and pour a similar quantity of water over the residue on the filter4 ,the weight of undissolved substance subtracted from #ajj gives with sufficient accuracy the weight of pure potassium carbonate contained in #ajj parts of potashes4 ,this method is founded on the fact that potassium carbonate dissolves readily even in cold water1 but the other salts with difficulty4 ,this procedure can also be used to obtain pure potassium carbonate from crude potashes2 it is only necessary to filter and evaporate to dryness the solution obtained by pouring very cold water on crude potashes4 ,potassium ,hydroxide 7,potassium ,hydrate1 ,caustic ,potash71 ,,koh #ef4--,the commercial variety consists of very deliquescent white lumps1 generally containing a large quantity of impurities4 ,on this account caustic potash1 or rather a solution of it1 is prepared in the colour works4 ,with this object #aa parts of potash1 contained in a tub with an opening at the bottom1 are mixed with #ajj parts of cold water4 ,two hours later1 the clear solution is run off into a clean iron pan1 in which it is heated to boiling4 ,to the boiling solution is added milk of lime prepared from water and #ce parts of quicklime4 ,after the liquid has boiled a few minutes1 a small portion is filtered and hydrochloric acid added to the clear filtrate2 if no effervescence occurs1 then all the potassium carbonate is converted into caustic potash4 ,should effervescence occur1 milk of lime is added until a new portion no longer effervesces on the addition of hydrochloric acid4 ,then the pan is covered with a well-fitting lid1 and the cooled liquid1 if not required for immediate use1 preserved in well-corked glass bottles4 ,the strength of a caustic potash solution can be found by means of a hydrometer4 ,the following table shows the relation between the specific gravity of a solution and the percentage of caustic potash it contains3-- -------------------------- ,specific ,caustic ,potash ,gravity4 per cent4 -------------------------- #ajf #dg #aaa #ie #aae #acj #aai #afb #abc #aie #abh #bcd #aci #cbd #aeb #dbi #afj #dfg #afh #eab -------------------------- ,potassium ,nitrate 7,saltpetre71 ,,kno #aja1 consists of large crystals1 which quickly dissolve in water4 ,on heating it readily gives up oxygen1 and thus finds use as an oxidising agent4 ,in former times1 when the colour manufacturer was compelled to make his own materials1 saltpetre was of great importance in colour making2 at present1 when such materials are to be bought at low prices and no colour maker prepares his own1 saltpetre is little used4 ,potassium ,bitartrate1 ,c,h,,ko #ahh4--,this salt1 known as tartar in large crystals1 and as cream of tartar in the form of meal1 is occasionally used in colour making4 ,it is little soluble in cold water1 but more easily in hot4 ,the hot solution is generally used4 ,potassium ,bichromate 7,bichromate of ,potash71 ,k,cr,o #bie4--,this salt is made in special works1 by melting chrome iron ore with saltpetre and extracting the mass with water1 when a yellow solution of potassium chromate is obtained2 to this sulphuric acid is added1 which unites with half the potassium1 thus leaving potassium bichromate1 which is obtained by evaporation of the solution in fine red crystals4 ,these are purified by recrystallisation4 ,at present1 in place of the above method1 calcium chromate is formed by roasting chrome iron ore with lime2 the calcium chromate is then decomposed by a soluble potassium salt1 thus forming potassium chromate4 ,potassium bichromate is unaltered in air2 it dissolves easily in water1 and is of great importance in the preparation of many colours1 in particular chromium oxide and the lead pigments4 ,the commercial salt generally contains potassium sulphate1 with which at times it is intentionally adulterated4 ,the adulteration is detected by dissolving in water1 adding half the volume of pure hydrochloric acid1 and cautiously and carefully dropping in spirits of wine4 ,a rapid action takes place1 which is only assisted by warming when necessary4 ,the red liquid changes to emerald green4 ,if barium chloride be now added1 a white precipitate is obtained in the presence of potassium sulphate4 ,potassium ,sodium ,chromate1 ,k,na,cr,o #bgi1 is also used in colour making4 ,its solution is made by adding soda to a solution of potassium bichromate so long as an effervescence of carbonic acid occurs1 and until the liquid turns red litmus paper blue2 the solution of the double salt is yellow4 ,chrome ,alum1 ,k,cr7,,so74#ab;,h,o #dii4--,this salt occurs in commerce as beautiful violet crystals4 ,it is obtained as a by-product in the manufacture of aniline and anthracene dyes1 and may often be bought at lower prices than other chromium salts2 #ajj parts of water dissolve approximately #bj parts of chrome alum4 ,potassium ,ferrocyanide1 ,k,fe7,,cn74#c;,h,o #dbb4--,the potassium iron cyanogen compounds are made in special works1 particularly in the neighbourhood of large towns1 by melting potashes with nitrogenous organic substances and iron1 washing out the mass and purifying the salt so obtained by recrystallisation4 ,potassium ferrocyanide 7yellow prussiate of potash7 forms large transparent crystals of a peculiar soft nature1 which dissolve readily in water4 ,it often contains considerable quantities of potassium sulphate1 up to #e per cent41 and it is to be noted that the impurity is much the cheaper of the two salts4 ,when barium chloride is added to a solution of the salt1 a white precipitate forms if sulphate be present4 ,the behaviour of yellow prussiate towards iron salts is noteworthy4 ,with ferrous salts1 for example green vitriol 7copperas71 it gives a white precipitate which gradually turns blue in the air2 with ferric salts1 for example ferric chloride 78nitrate of iron071 it at once gives a blue precipitate4 ,potassium ,ferricyanide 7,red ,prussiate of ,potash71 ,k,fe7,,cn7 #cbi1 is obtained by passing chlorine through a solution of yellow prussiate until the liquid smells strongly of chlorine and no longer gives a precipitate with a solution of a ferric salt4 ,the solution then contains potassium ferricyanide and chloride4 ,the former is obtained by evaporating and allowing to crystallise4 ,pure potassium ferricyanide forms beautiful dark red crystals1 which readily dissolve in water4 ,the solution gives a blue precipitate with ferrous salts1 but only a brown colouration and no precipitate with ferric salts4 ,both yellow and red prussiate are used in the preparation of several much used colours1 for ,prussian and ,chinese blues1 and several others4 ,all cyanogen compounds1 with the exception of yellow prussiate1 are extremely poisonous4 ,the following table gives the solubility of potassium ferricyanide at different temperatures3-- ---------------------------------------- ----------- #ajj ,parts of ,water ,temperature4,specific ,gravity dissolve ,parts of ,salt4------------ of ,solution4 ,c4 ---------------------------------------- ----------- #cc #d4dd #a4aea #cf #aj4jj #a4afd #dj4h #ae4ej #a4agh #eh4h #cg4hj #a4bbe #gg4e #ajj4jj #a4bej #hb4f #ajd4dj #a4bfe ---------------------------------------- ----------- ,sodium ,salts4--,in chemical properties the sodium salts are very similar to the potassium salts1 and1 being cheaper1 they are generally used in place of the latter4 ,sodium ,carbonate 7,soda ,crystals71 ,na,,co4#aj;,h,o #bhf1 is made in enormous quantities in great works and in a very pure state4 ,it forms large transparent crystals1 which effloresce in the air1 losing a large quantity of water1 and so falling to a white powder4 ,although this property does not interfere with the use of soda1 since it is generally used in solution1 yet efflorescence should be as far as possible avoided by keeping the salt in well-closed packages1 because effloresced soda dissolves more slowly than crystallised1 since it has to combine with water before it can enter into solution4 ,in the retail trade a form of soda is found which is adulterated with very large quantities of ,glauber's salt4 ,this is recognised by the different form of the crystals4 ,manufacturers sell soda stating its strength4 ,the colour maker should only buy with this guarantee4 ,sodium ,hydroxide 7,sodium ,hydrate1 ,caustic ,soda71 ,na,o,h #dj1 comes into commerce in the form of hard masses1 the use of which would be very convenient for the colour maker if it were not often very impure4 ,thus it is better to prepare a solution oneself1 which is accomplished in the manner given above for caustic potash4 ,caustic soda and caustic potash have similar properties2 they have a corrosive action on the skin1 readily unite with carbonic acid from the air1 and separate the heavy metals from their solutions in the form of hydrated oxides4 ,the strength of caustic soda solutions is given in the following table3-- ---------------------------------------- ,specific ,caustic ,specific ,caustic ,gravity4 ,soda ,gravity4 ,soda per cent4 per cent4 ---------------------------------------- #bjj #ggh #adj #bij #ahe #fcf #acf #bfj #agb #ech #acb #bcj #afc #dff #abi #aij #aef #dab #abc #afj #aej #cfh #aah #acj #adg #cdj #aab #ij #add #caj #ajf #dg ---------------------------------------- ,besides soda and caustic soda1 few soda salts are used in colour making4 ,however1 sodium nitrate 7,chili saltpetre71 ,na,n,o1 is frequently used instead of ordinary saltpetre1 from which it differs in being deliquescent4 ,sodium ,thiosulphate 7,hyposulphite71 ,na,s,o4#e;,h,o #bdh1 is a common article of commerce1 being much used by photographers2 it is used in a few cases in colour making4 ,it forms large crystals with a somewhat bitter taste1 permanent in air and readily soluble in water4 ,sodium ,chloride 7,common ,salt71 ,na,cl #ehe1 which has a little application in colour making1 is sufficiently pure in the form in which it is generally used for household purposes4 ,,salts ,,of ,,the ,,alkaline ,,earth ,,metals4 ,the metals which are known as the alkali earth metals have much similarity with the alkali metals in their compounds1 with the difference that their alkalinity is much less1 and that their salts are much less soluble in water4 ,for colour making the compounds of three of these metals--calcium1 barium and magnesium--are used4 ,,calcium ,,compounds4 ,the most important calcium compounds are lime and carbonate and phosphate of lime4 ,carbonate of lime is used as a pigment1 and will be dealt with in detail among the mineral colours2 it will be but briefly described here4 ,calcium ,oxide 7,quicklime71 ,ca,o #ef4--,when chalk and limestone1 which consist of calcium carbonate1 are heated1 carbonic acid is evolved1 and calcium oxide1 commonly called quicklime1 is left4 ,for our purposes only very pure quicklime is to be used4 ,its ordinary impurities are iron oxide and magnesia3 the former is found in lime made from red or brown limestone2 the latter in lime made from dolomitic limestone4 ,the presence of oxide of iron is recognised by the reddish tinge of the quicklime2 if magnesia be present1 a small quantity of the quicklime1 when mixed with a very large quantity of water1 leaves an insoluble residue which consists of magnesia4 ,when quicklime and water are brought together they unite very energetically and form calcium hydroxide or slaked lime4 ,according to the quantity of water used for slaking1 either dry slaked lime1 lime paste1 or milk of lime is produced1 all of which find a use in colour making4 ,calcium ,hydroxide 7,slaked ,lime71 ,ca7,,oh7 #gd4--;,in order to prepare slaked lime1 which contains lime united with just the necessary quantity of water1 the pieces of quicklime are sprinkled with water from a watering can4 ,the water is rapidly taken up and the sprinkling is repeated until the lumps begin to fall to a fine powder2 in the process the lime becomes very hot4 ,the slaked lime is then passed through a sieve in order to separate the larger pieces of quicklime which have not been slaked2 the powder must be kept in well closed packages1 since it energetically absorbs carbonic acid out of the air4 ,if so much water is added to the lime that a homogeneous wet mass is formed which can be readily moved with a shovel1 one has then lime paste1 which can be conveniently kept in pits as the masons do2 it may be stored in this way for many months without appreciable alteration1 still it is better to keep it covered4 ,to prepare milk of lime1 so much water is used in slaking that a milky liquid is formed1 or the lime paste is mixed up in the proper quantity of water4 ,slaked lime dissolves in #gjj to #hjj parts of water2 on standing1 the undissolved slaked lime settles to the bottom of the milk of lime3 thus it is better to prepare milk of lime immediately before use1 and to stir it well to prevent the settling of the solid particles4 ,slaked lime in one of its forms is often used instead of the more costly caustic soda in order to precipitate metallic oxides from their salts4 ,at times one finds a too strongly burnt lime1 so-called 8dead-burnt0 lime1 which is very slowly slaked by water4 ,such quicklime is slaked by allowing it to lie in water for days1 or by means of hot water1 which accomplishes the slaking more quickly4 ,calcium ,carbonate1 ,ca,c,o #ajj1 is found naturally in large quantities as chalk1 which consists of the skeletons of extremely small animals4 ,by powdering and levigating1 it is converted into a soft powder1 which is used to lighten the shade of lakes and other colours4 ,calcium ,sulphate 7,gypsum71 ,ca,s,o4#b;,h,o #agb4--,this mineral1 when finely powdered1 is added to some colours4 ,calcium ,phosphate 7,bone ,ash71 ,ca7,,po7 #caj1 is sometimes used to lighten the shade of certain colours which might be injured by calcium carbonate4 ,it comes in large quantities as a fine1 white powder from ,south ,america4 ,naturally1 only quite white bone ash can be used2 if not completely burnt it is grey1 and will then impair the shade of colours with which it is mixed4 ,magnesium ,carbonate 7,magnesia71 ,mg,c,o #hd1 is also used as an addition to colours in order to obtain pale shades4 ,it is most cheaply obtained by dissolving magnesium sulphate 7,epsom salts7 in water and adding soda solution so long as a precipitate forms1 which is then washed and dried4 ,the magnesium carbonate prepared in this way is a very fine1 light powder1 insoluble in water1 which can be mixed with the most delicate colours without harming them4 ,white magnesia is an extremely light powder1 which may be used when it can be bought at as low a price as the above preparation4 ,barium ,compounds4--,the raw material used for the preparation of barium pigments is either barium sulphate 7barytes1 heavy spar7 or barium carbonate 7witherite74 ,the latter is much more rare than barytes1 which is almost exclusively employed in the preparation of barium compounds4 ,the barium compounds of particular importance for our purpose are barium chloride and nitrate4 ,barium ,chloride1 ,ba,cl4#b;,h,o #bdd4--,this salt is now a common article of trade1 and can be bought at a low price4 ,when pure it forms colourless crystals readily soluble in water4 ,if the colour maker is able to get cheap barytes and fuel1 it may be advantageous for him to prepare barium chloride himself4 ,to prepare barium chloride from barytes1 the latter is very finely ground and levigated1 intimately mixed with coal1 and the mixture subjected to a very high temperature1 when barium sulphide is formed1 which is dissolved by washing out the mass with water and converted into barium chloride by adding hydrochloric acid1 sulphuretted hydrogen being evolved4 ,the best method is to mix #d parts of barytes with #a part of bituminous coal and so much coal-tar that a plastic mass is formed1 which is well kneaded and made into small cylinders #c centimetres in diameter and #aj centimetres long4 ,these cylinders are placed in layers in a cylindrical furnace with a good draught1 which contains at the bottom a layer of coal #ae to #bj centimetres thick1 then a layer of the cylinders1 then again coal1 and so on until the furnace is full4 ,the lowest layer of coal is lighted1 and the whole burnt at a bright red heat1 when the barium sulphate is changed into sulphide4 ,hydrochloric acid is poured over the residue and the insoluble part1 consisting chiefly of unaltered barytes1 is used for the next operation4 ,witherite 7barium carbonate7 can be converted into barium chloride in a very simple manner4 ,hydrochloric acid is added1 in which it dissolves with the evolution of carbonic acid4 ,the solution is allowed to stand twenty-four hours with excess of witherite2 the whole of the dissolved iron is thus precipitated4 ,the solution is then filtered1 evaporated down and left1 when pure barium chloride crystallises out4 ,barium chloride and all soluble barium salts should only be dissolved in pure water 7rain or distilled74 ,water which contains carbonates or sulphates always gives a turbid solution by precipitating barium carbonate or sulphate4 ,,aluminium ,,compounds4 ,the compounds of the earth metal aluminium play a very important part in colour making1 since they form beautifully coloured compounds with many organic colouring matters4 ,formerly alum was the only material used in colour factories for the preparation of the alumina compounds2 at present aluminium sulphate is used1 and when it is sufficiently pure it is the most valuable material1 because it contains the greatest quantity of alumina4 ,under the designation of alum only one compound1 the so-called potash alum1 was at one time found in commerce1 but now there are other alums1 which contain soda or ammonia in place of potash4 ,these salts are of equal use in colour making to potash alum4 ,the preference is to be given to the compound which contains the largest proportion of alumina4 ,the chief point to be observed in connection with alumina compounds for use in colour making is that they shall be free from iron1 because iron oxide1 which would be precipitated out of the solution along with the colours1 in consequence of its red colour would spoil the shade of the pigment4 ,aluminium ,sulphate 7,sulphate of ,alumina71 ,al7,,so74#ah;,h,o #ffd4--;,any manufacturer who can obtain cheap china clay 7kaolin7 and sulphuric acid can himself prepare this compound with advantage4 ,the apparatus used for this purpose is an iron pan containing sand1 in which is placed a large earthenware dish4 ,in this dish are put very finely ground kaolin and strong sulphuric acid1 and the mixture is heated so strongly that the acid boils1 evolving heavy1 white vapours4 ,it is absolutely necessary to heat in this manner in order to avoid dangerous accidents4 ,sulphuric acid bumps so violently on boiling that it may even break a thick earthenware dish4 ,the use of a sand bath makes the bumping harmless4 ,china clay1 which consists of silicate of alumina1 is decomposed by heating with sulphuric acid into silicic acid and sulphate of alumina4 ,the original milky liquid becomes more transparent during boiling1 and has at last the appearance of starch paste4 ,kaolin contains varying quantities of silica4 ,the quantity of sulphuric acid necessary for its decomposition can only be found by trial4 ,the quantities are chosen so that a small amount of kaolin remains undecomposed in order that the aluminium sulphate shall contain no free sulphuric acid4 ,when the decomposition is finished the pan is allowed to cool and the solid mass is brought into a vat filled with water1 in which it is stirred until dissolved2 then the liquid is left until the jelly-like mass of silicic acid has sunk to the bottom1 when the clear solution of aluminium sulphate is drawn off and can at once be used4 ,if solid aluminium sulphate is required--and this is to be recommended when large quantities are to be prepared--the solution is evaporated in earthenware dishes until a portion solidifies when dropped on a cold plate4 ,the molten aluminium sulphate is then cast in prismatic blocks1 which are preserved in boxes4 ,these blocks are of a pure white colour and very crystalline2 they dissolve with difficulty in cold1 but readily in hot water without residue4 ,the solution has an acid taste1 even when it contains no excess of sulphuric acid4 ,when the blocks have a yellowish tinge1 this denotes the presence of iron1 and the solution must be freed from this impurity4 ,nowadays sulphate of alumina can be obtained so cheaply that it is hardly of advantage to make it4 ,,the ,,alums4 ,these are double salts of aluminium sulphate and potassium1 sodium or ammonium sulphate4 ,there are also other double sulphates known as alums which1 in place of aluminium1 contain chromium1 iron1 etc41 but they are not of interest here4 ,it may still be observed that all alums1 whatever their composition1 possess the property of crystallising together from mixed solutions1 so that crystals can be obtained in which every existing alum is contained4 ,the potassium1 sodium and ammonium aluminium alums are used in colour making4 ,potassium ,aluminium ,alum1 ,k,al7,,so74#ab;,h,o #dgd4--,this is the substance commonly called alum4 ,like all alums it crystallises in fine octahedral crystals1 which at first are quite transparent1 but slowly effloresce in the air and become covered by a white powder4 ,it dissolves with difficulty in cold1 but readily in hot water4 ,the solution has at first a sweet taste1 with an astringent after-taste4 ,alum comes into the market in different forms1 of which the following are the most important3 as crystallised alum1 in the form of large crystals united together2 as alum meal1 a coarse crystalline powder obtained by rapidly cooling and stirring a hot alum solution4 ,on account of the larger surface this form dissolves more quickly than the large crystals4 ,roman alum is the name of a variety chiefly imported from ,italy2 it owes its reputation to its great purity--it contains a very small quantity of iron4 ,in order to prepare alum quite free from iron from the ordinary alum containing iron1 it is recrystallised1 that is1 as much as possible is dissolved in boiling water and the solution quickly cooled with continual stirring2 the small crystals so obtained are then washed with cold water4 ,the residual saturated solution of alum1 which contains the greater part of the iron1 can be used for the preparation of those colours which are not injured by the presence of iron4 ,the solubility of alum in water varies greatly at different temperatures4 ,the table gives the weight of alum dissolved by #ajj parts of water at different temperatures4 ---------------------------------------- ----- ,temperature4,crystallised ,alum4,anhydrous ,alum4 ---------------------------------------- ----- #j ,c4 #cij #baj #aj 0 #ieb #dii #bj 0 #aeac #ggd #cj 0 #bbja #ajid #dj 0 #cjib #adhh #ej 0 #ddaa #bjji #fj 0 #fffe #bfgf #gj 0 #ijfg #ceaa #hj 0 #acddg #deff #ij 0 #bjica #ehfd #ajj 0 #cegdh #gdec ---------------------------------------- ----- ,when potash alum is heated it loses water1 #ge per cent4 of the total at #fa ,c42 at #ib ,c4 it melts completely1 and all the water is lost by continued heating at #ajj ,c4 ,the residue is known as burnt alum4 ,in alum the whole acidity of the sulphuric acid is not neutralised2 the solution has always an acid reaction2 if soda solution is added1 the escaping carbonic acid causes the liquid to effervesce4 ,if soda solution is added until a further addition would cause a precipitate1 a solution of so-called neutral alum is formed which has no longer an acid reaction4 ,neutral alum is occasionally required in colour making4 ,in preparing it the soda solution must be added with great care when the liquid is near its point of neutralisation4 ,any addition of soda solution after this point is reached will cause a separation of alumina4 ,this is not desirable1 since it is generally only wished to precipitate the alumina in combination with colouring matters4 ,roman ,alum4--,under this name1 or that of 8cubic alum10 a variety of alum is sold1 generally at a rather higher price than ordinary alum1 from which it is distinguished by its crystalline form4 ,ordinary alum forms octahedral crystals often the size of a child's head1 but cubic alum well formed cubes4 ,the property of crystallising in cubes may be imparted to any alum solution by the addition of a little potash4 ,much so-called ,roman alum is made in ,german works in this way4 ,when this alum contains very little iron it is quite equal in quality to the best ,roman alum1 for the higher value of the latter is entirely due to its small content of iron4 ,the alum prepared in the province of ,naples is still better than ,roman alum2 it contains less iron4 ,when alum is required for the preparation of lakes of bright and delicate shades1 it is indispensable to use a preparation free from iron1 because the brownish yellow oxide of iron would appreciably injure the shade4 ,alum1 free from iron1 is most simply prepared by dissolving alum in boiling water1 running the boiling solution quickly through a cloth1 and quickly cooling with constant stirring4 ,the alum meal prepared in this way contains much less iron than the original alum1 the iron salts remaining dissolved in the mother liquor4 ,when this alum meal is collected and cold water poured over it to free it from mother liquor1 it is generally sufficiently pure to be used for any purpose1 but if not1 it is again recrystallised4 ,the alum liquors containing the iron are used for the preparation of colours which are not injured by the presence of iron4 ,to test alum for iron yellow prussiate of potash is used1 which gives a blue precipitate with ferric salts4 ,the test is carried out by dissolving #aj grammes of alum in #a litre of water1 placing the solution in a tall1 narrow cylinder standing on white paper1 adding #aj to #bj drops of a saturated solution of yellow prussiate1 and well stirring4 ,on looking down through the liquid1 if a distinct colouration is at once evident1 the alum contains much iron1 and must be recrystallised2 indeed1 the crystals would generally be coloured yellow4 ,on the contrary1 if the solution does not show a blue tint until after standing several days1 the alum contains but a small quantity of iron1 and can be used for most purposes without further purification4 ,alum quite free from iron is a rare commercial article2 the test will generally show a feeble blue colouration4 ,if this is not intense and no blue precipitate is deposited at the bottom1 the alum is tolerably pure1 and can be used in colour works4 ,the longer the time before the blue colouration appears the poorer is the alum in iron4 ,soda ,alum1 ,na,al7,,so74#ab;,h,o #deh1 is made in some alum works4 ,it has the greatest similarity in properties with the potash salt1 but is distinguished by a much greater solubility in water and more rapid efflorescence in air4 ,soda alum can be bought at varying prices2 that containing iron is much cheaper than that free from iron4 ,when the latter is to be bought at a fair price it is to be preferred to potash alum1 since1 as we shall show later1 it contains a larger proportion of alumina4 ,ammonia ,alum1 7,,nh7,al7,,so74#ab;,h,o #dec4--,this compound of aluminium sulphate and ammonium sulphate is now often met with2 the more expensive potassium sulphate in ordinary alum is replaced by ammonium sulphate1 which is cheaply obtained from the ammoniacal liquor of the gas works4 ,ammonia alum is better for our purpose than potash alum since it contains more alumina1 is generally cheaper and dissolves more easily in water4 ,unfortunately most commercial ammonia alum contains so much iron that it has to be recrystallised before it can be used in colour works4 ,one hundred parts of water dissolve at different temperatures the quantities of ammonia alum given in the table3-- ---------------------------------------- --------------------- ,temperature4,crystallised ,ammonia ,alum4,anhydrous ,ammonia ,alum4 ---------------------------------------- --------------------- #j ,c4 #ebb #bfb #aj 0 #iaf #dej #bj 0 #acff #feg #cj 0 #aibi #ije #dj 0 #bgbg #abce #ej 0 #cfea #aeij #fj 0 #eabi #baie #gj 0 #gaig #bfji #hj 0 #ajcjh #ceai #ij 0 #ahghb #ejcj #ajj 0 #dbaij #gjhc ---------------------------------------- --------------------- ,of the different alums1 ammonia alum contains the largest and potash alum the smallest proportion of alumina4 ,the composition of the three commonly occurring alums is given in the following table3-- ---------------------------------------- --------------- ,potash ,alum4,soda ,alum4,ammonia ,alum4 ---------------------------------------- --------------- ,potash1 ,k,o #iie ,soda1 ,na,o #fhj ,ammonia1 ,,nh #chi ,alumina1 ,al,o #ajhc #aabj #aaij ,sulphuric acid1 ,,so #ccga #cdij #cfaj ,water1 ,h,o #deea #dgaj #dhaa ---------------------------------------- --------------- ,thus ammonia alum is to be preferred to soda alum and soda to potash alum1 whilst the latter is used on account of its greater purity4 ,in a colour works1 in which large quantities of alum are used1 it is advantageous to work with ammonia alum which is recrystallised on the works4 ,the alums and aluminium sulphate are the alumina compounds in ordinary use in colour works2 aluminium acetate could also be used if it were to be had at a reasonable price4 ,alumina1 ,al,o #ajb1 and ,hydrate of ,alumina4--,pure alumina1 or rather hydrate of alumina1 is required in the preparation of many colours4 ,when the solution of an aluminium salt is precipitated by soda1 the carbonic acid escapes with effervescence1 and a gelatinous precipitate is formed which it is extremely difficult to wash clean4 ,the precipitate1 which consists of hydrate of alumina1 shrinks very greatly in drying1 and turns to a horny mass2 when strongly heated it loses water1 and becomes a white1 insoluble powder of anhydrous alumina4 ,a variety of hydrate of alumina1 heavy1 and therefore easily washed1 is obtained by boiling a solution of alum with a plate of zinc lying on a copper plate until all the alumina has separated4 ,by collecting this on a filter and pouring hot water over it a number of times it is obtained quite pure4 ,alumina plays a particularly important part in the manufacture of cobalt colours4 ,when treated with a cobalt salt and heated it takes a fine blue shade4 ,in the foregoing those metals and their compounds have been treated which are extensively used in preparing colours without themselves forming coloured compounds4 ,the chromates and prussiates are an exception to this4 ,the ammonia compounds1 the alkalis and alkaline earths1 also the acids1 are used in making many colours1 although they do not contain colouring principles4 ,the alumina compounds are in similar case4 ,themselves colourless1 they form at the same time a carrier for the coloured compound and bring it into a suitable form for use as a pigment4 ,an example will explain what we mean by 8carrier0 of the colouring matter4 ,logwood contains a very handsome colouring matter which can be extracted by water4 ,in order to be able to employ this colouring matter as a pigment it is combined with alumina1 a compound insoluble in water being formed1 which is called a lake4 ,in this compound the alumina is to be regarded as the carrier of the colouring matter1 which it has fixed in an insoluble form4 ,in dyeing1 which in many respects is closely allied to colour making1 the property of certain metallic compounds1 themselves colourless1 of fixing dyes is commonly utilised1 the metallic compound being called the mordant4 ,the fabric is first prepared with the metallic compound or mordant1 and the colour then formed by bringing the mordanted material in contact with the colouring matter4 ,the 8heavy metals0 form1 among their numerous compounds1 a great number of coloured substances1 and several of them are distinguished by a great wealth of coloured derivatives2 for example1 copper1 chromium and cobalt form coloured compounds only4 ,although the use of pigments derived from the heavy metals has been considerably restricted in recent years by the discovery of a series of colouring matters which replace them1 yet they are now1 and always will be1 of very great importance in the manufacture of colours4 ,it is1 therefore1 necessary briefly to describe the various metals which are used in colour making1 so that the manufacturer may know what metals produce harmless colours1 permanent and unaltered by the atmosphere1 and what do not4 ,the metals are divided into two great groups1 designated1 according to their specific gravities1 the group of the light and of the heavy metals4 ,the light metals comprise the alkali1 alkaline earth and earth metals1 whose important compounds we have just described4 ,the specific gravity of each of these metals is less than five times that of water4 ,the heavy metals have a specific gravity exceeding #e2 they are generally divided into groups1 which are known by the name of the commonest metal in the group4 ,these are as follows3-- ,zinc group ,zinc1 ,zn #fe4 ,iron group ,iron1 ,fe #ef4 ,tungsten group ,tungsten1 ,w #ahd4 ,antimony group ,antimony1 ,sb #abj4 ,tin group ,tin1 ,sn #aai4 ,lead group ,lead1 ,pb #bjg4 ,silver group ,silver1 ,ag #ajh4 ,gold group ,gold1 ,au #aig4 ,platinum group ,platinum1 ,pt #aid4 ,to the zinc group belong the metals zinc1 cadmium and indium1 of which only the two first are of importance here4 ,the iron group comprises iron1 manganese1 cobalt1 nickel1 chromium and uranium1 all of which are used in the manufacture of colours4 ,the antimony group contains antimony and bismuth1 the latter of which is of little importance4 ,to the tin group belong tin and the rare metals titanium1 zirconium1 thorium1 niobium and tantalum2 of these tin alone is important in colour making4 ,in the lead group are lead and thallium2 lead produces many important pigments4 ,the silver group contains silver1 copper and mercury1 the two latter of which are important4 ,of the gold group gold alone is of interest1 and its importance has been diminished by the discovery of far cheaper substances which replace it4 ,in the platinum group1 which contains platinum1 iridium1 rhodium1 ruthenium1 palladium and osmium1 only platinum itself is used as a colour2 it is employed in porcelain painting to produce the peculiar metallic shimmer known technically as 8lustre40 ,the behaviour of the compounds1 of the metals mentioned above towards sulphuretted hydrogen is of the greatest importance to the colour maker1 since on it depends the alterability of the pigments when exposed to the atmosphere4 ,many metallic compounds are unaltered by the sulphuretted hydrogen present in the air1 whilst others are in a high degree affected by it and become gradually darker1 so that their colour may in the end approximate to black4 ,the pigments containing lead1 copper1 mercury and bismuth are extremely susceptible to the action of sulphuretted hydrogen1 by the action of which they form black compounds4 ,since colours which contain these metals are not permanent1 but darken considerably1 endeavours have been made for a long time to replace them by others not susceptible to the action of sulphuretted hydrogen4 ,thus it is desirable to manufacture only colours free from metals forming black compounds with sulphuretted hydrogen4 ,for the same reason pigments which contain sulphur should not be mixed with those containing metals which form black sulphur compounds4 ,the rules laid down in the preceding paragraphs are of the greatest importance for the artist1 for by following them he will succeed in composing a 8permanent palette10 that is1 containing only such colours as will not1 by their composition1 bring about the speedy ruin of the painting4 ,although the majority of the compounds of the heavy metals are poisonous1 some possess this property in an eminent degree4 ,these are chiefly colours which contain arsenic1 antimony1 copper and lead4 ,so far as it is possible1 these colours should be dispensed with and harmless pigments sold in their place1 though this is not always possible1 since several poisonous colours cannot be replaced by innocuous ones4 ,,compounds ,,of ,,the ,,heavy ,,metals4 ,zinc ,compounds4--,zinc oxide1 ,zn,o1 and zinc sulphate1 ,zn,s,o4#g;,h,o1 are the compounds of this metal used in the colour industry4 ,zinc oxide1 which is used as a white pigment1 is a powder which turns yellow when heated1 and is not acted upon by sulphuretted hydrogen4 ,zinc sulphate 7white vitriol7 occurs as colourless crystals1 or more frequently as greyish white crystalline masses4 ,the freedom of zinc sulphate from iron is of particular importance2 the commercial article is seldom satisfactory in this respect4 ,in order to free commercial zinc sulphate from iron1 the property of zinc hydroxide of precipitating iron oxide from neutral solutions may be employed4 ,the zinc sulphate is dissolved in water1 and ammonia added in small quantities until the precipitate of zinc hydroxide remains on stirring4 ,when the liquid is left in contact with the precipitate and stirred up once or twice a day1 if iron is present the precipitate will turn yellowish brown1 owing to the separation of ferric hydroxide1 and in the course of a few days all the iron will be removed from solution4 ,the liquid should then give no blue colouration with yellow prussiate of potash4 ,zinc oxide is used as a white pigment1 zinc chromate as a yellow1 and zinc cobalt compounds as green colours4 ,cadmium ,compounds4--,cadmium is a metal which possesses great similarity to zinc1 with which it occurs in nature4 ,in the preparation of cadmium compounds the metal is generally used4 ,this is dissolved in dilute sulphuric acid1 hydrogen is evolved1 and a solution of cadmium sulphate obtained4 ,cadmium is used in colour making only for the preparation of the beautiful cadmium yellows4 ,iron ,compounds4--,these are of the greatest importance to the colour maker4 ,several1 in which iron alone is the colour principle1 are very valuable3 ochre1 rouge1 ,venetian red1 sienna and umber1 for example4 ,iron compounds are also used in the preparation of many colours4 ,the most important is3-- ,ferrous ,sulphate 7,green ,vitriol1 ,copperas71 ,fe,s,o4#g;,h#j4--,this substance1 which occurs commercially in a form of great purity at a very low price1 is generally the starting point in the preparation of iron pigments4 ,when pure1 it forms fine sea-green crystals1 with an astringent metallic taste1 which are not poisonous and are easily soluble in water4 ,after long exposure to the air1 ferrous sulphate becomes covered with an ochre-coloured crust1 consisting of basic ferric sulphate4 ,the ferrous oxide contained in the green vitriol has united with oxygen and been converted into ferric oxide4 ,the latter requires a larger quantity of acid than ferrous oxide for the formation of soluble salts1 so that an insoluble basic salt is separated4 ,the same thing occurs when a solution of ferrous sulphate is exposed to the air4 ,when green vitriol1 or any other ferrous salt1 is exposed to the action of oxidising agents1 such as chlorine or nitric acid1 the iron is rapidly changed into the ferric state4 ,this transformation is of particular importance in the manufacture of certain blue pigments4 ,we give in a table the relation between the percentage of crystallised ferrous sulphate 7,fe,s,o4#g;,h,o7 contained in a solution at #ae ,c4 and its specific gravity3-- ---------------------------------------- ---------- ,specific ,percentage of ,specific ,percentage of ,gravity4,ferrous ,sulphate4,gravity4,ferrous ,sulphate4 ---------------------------------------- ---------- #ajjj #j #aaah #ba #ajje #a #aabe #bb #ajaa #b #aaca #bc #ajaf #c #aacg #bd #ajba #d #aadc #be #ajbg #e #aadi #bf #ajcb #f #aaee #bg #ajcg #g #aafa #bh #ajdc #h #aafh #bi #ajdh #i #aagd #cj #ajed #aj #aahj #ca #ajei #aa #aahg #cb #ajfe #ab #aaic #cc #ajga #ac #abjj #cd #ajgg #ad #abjf #ce #ajhb #ae #abac #cf #ajhh #af #abai #cg #ajid #ag #abbf #ch #aajj #ah #abcb #ci #aajf #ai #abci #dj #aaab #bj ---- ---- ---------------------------------------- ---------- ,yellow and red prussiate1 which have been already mentioned1 also belong to the iron compounds4 ,they have been separately mentioned because the iron is contained in them in a peculiar form as a portion of an organic radical4 ,ferrous ,chloride1 ,fe,cl1 may sometimes be used instead of green vitriol4 ,when iron is dissolved in hydrochloric acid hydrogen is given off and a solution of ferrous chloride is obtained2 but when rouge is dissolved in the same acid1 ferric chloride is formed4 ,when iron is dissolved in nitric acid1 in consequence of the oxidising properties of this acid a ferric salt is obtained4 ,iron forms two series of salts3 in the ferrous compounds the iron is in the same form as in green vitriol and the corresponding salts2 in the ferric compounds the iron is contained in a higher state of oxidation4 ,by powerful oxidising agents1 as nitric acid or chlorine1 ferrous compounds are converted into ferric4 ,manganese ,compounds4--,manganese 7,mn7 is a metal whose compounds show great similarity with those of iron1 like which it forms two oxides 7also others71 manganous oxide 7,mn,o7 and manganic oxide 7,mn,o74 ,the salts of manganous oxide are not oxidised in the air like those of ferrous oxide4 ,the raw material used in the preparation of manganese compounds is the mineral pyrolusite1 which is manganese dioxide 7,mn,o74 ,manganese sulphate 7,mn,s,o7 forms rose-red crystals containing varying quantities of water4 ,the residues from the preparation of chlorine can be used as the material for the preparation of colours4 ,according as pyrolusite and hydrochloric acid or pyrolusite1 salt and sulphuric acid are used for this purpose a solution of manganous chloride or sulphate is obtained4 ,manganese compounds have but a restricted use in colour making4 ,nickel ,compounds are generally coloured green1 but they are not used as pigments4 ,cobalt ,compounds4--,among these are found many important pigments4 ,all cobalt compounds are coloured2 in beauty and variety of shade they can only be compared with those of chromium4 ,in properties cobalt is very similar to iron and nickel4 ,the form in which cobalt is used in preparing colours is either cobalt nitrate1 ,co7,,no74#f;,h,o1 or cobalt chloride1 ,co,cl4#f;,h,o4 ,both salts are articles of commerce1 but generally they are so dear that it is more profitable for the colour maker to prepare them direct from the cobalt minerals4 ,a simple method for preparing cobalt compounds from the ores is therefore given4 ,the most important cobalt ores are speiss cobalt1 a compound of cobalt and arsenic1 and cobalt glance1 a compound of cobalt1 arsenic and sulphur4 ,the former mineral often contains only small quantities of cobalt1 and it is advisable for our purposes to use cobalt glance1 which contains from thirty to forty per cent4 of cobalt4 ,this mineral is first roasted1 that is1 is heated with a plentiful air supply1 by which means the arsenic is driven off4 ,on account of the poisonous nature of the arsenic vapours the roasting must be conducted in a furnace with a very good draught4 ,under the name of zaffre1 roasted cobalt ores come into commerce4 ,these may be used in the preparation of cobalt compounds1 by which means the operation of roasting is avoided4 ,according to the quality of the ore which has been used to obtain zaffre1 it contains a very varying proportion of cobalt4 ,the varieties richer in cobalt must be used2 they are technically known by the mark ,,fs1 or ,,ffs 7the best74 ,the roasted cobalt ores or zaffre are treated with fused acid potassium sulphate1 when the salts of iron and manganese are decomposed1 whilst cobalt and nickel sulphates remain unchanged4 ,in a ,hessian crucible are melted #cjj parts of acid potassium sulphate1 and #ajj parts of the powdered zaffre are gradually added1 mixed with one part of green vitriol and one part of saltpetre2 the mixture is heated so long as sulphuric acid escapes4 ,the mass is then boiled with water and the red solution treated with sulphuretted hydrogen so long as a precipitate is formed2 this may contain copper1 manganese1 and bismuth4 ,after filtering1 soda is added to the boiling liquid2 cobalt carbonate is precipitated1 which can be converted into nitrate or chloride by solution in the corresponding acid4 ,if cobalt sulphate is required1 the solution1 after treatment with sulphuretted hydrogen1 need only be evaporated to crystallisation1 when the sulphate separates in fine red crystals4 ,cobalt nitrate and chloride are very soluble in water2 to obtain them their solutions must be strongly evaporated and quickly cooled whilst stirring4 ,the crystals of cobalt nitrate and chloride absorb moisture from the air and deliquesce2 they must be kept in glass vessels with well-ground stoppers4 ,the cobalt compounds which are to be used in colour making must be free from iron1 nickel and arsenic1 which would detract from the cleanness of the colours4 ,if the precipitate produced by soda contains iron it is mixed with excess of solution of oxalic acid1 and after a few hours the cobalt oxalate is filtered from the liquid1 in which all the iron is dissolved4 ,the cobalt oxalate can then be converted into nitrate or chloride by treatment with nitric or hydrochloric acids4 ,these salts form the material for the preparation of the cobalt compounds1 a large number of which are used as extremely durable red1 blue and green pigments2 several of them1 such as cobalt blue1 cannot be exactly replaced by other pigments4 ,on account of the industrial importance of the cobalt colours1 these directions for the preparation of the soluble cobalt salts from the ores have been given with some detail4 ,the preparation of the cobalt colours will be given in extenso later on4 ,chromium ,compounds4--,as the name indicates1 this metal yields numerous coloured compounds 71 colour72 in fact1 only coloured chromium compounds are known1 and the colours are most varied--yellow1 green1 red and violet4 ,on this account the chromium compounds are among the most important used in colour making2 a great number of colours are prepared by their aid4 ,chrome ironstone1 as we have already stated1 is the raw material for the preparation of chromium compounds4 ,from it potassium bichromate is made on a large scale in special works1 so that no colour maker is compelled to prepare chromium salts himself4 ,when the chromium pigments contain no metal blackened by sulphuretted hydrogen1 they have the desirable property of being unaltered by the atmosphere4 ,like the cobalt compounds1 they are distinguished by their great stability when heated2 on this account1 they have a large use in porcelain painting4 ,molybdenum1 ,tungsten and ,vanadium ,compounds on account of their cost have a very limited use as pigments4 ,molybdenum compounds are obtained from molybdic acid2 compounds of tungsten from the metal2 and those of vanadium from ammonium vanadate4 ,antimony ,compounds can be used in the preparation of several pigments1 but1 on account of their behaviour towards sulphuretted hydrogen1 the pigments cannot be regarded as really permanent1 and their use is generally diminishing4 ,the so-called antimony vermilion is the only antimony compound at all extensively employed4 ,bismuth ,compounds possess properties very similar to those of antimony4 ,only one bismuth preparation is used as a pigment1 and this is very sensitive to the action of sulphuretted hydrogen1 being changed into black bismuth sulphide4 ,tin ,compounds are employed in two ways3 some are themselves colours1 such as stannic sulphide 7mosaic gold72 others1 themselves colourless1 are used in making pigments1 as stannous and stannic chlorides4 ,stannous ,chloride1 ,sn,cl4#b ,h,o1 is obtained when tin is dissolved in hydrochloric acid1 hydrogen being evolved4 ,stannic ,chloride1 ,sn,cl1 is formed when tin is dissolved in a mixture of hydrochloric and nitric acids 7aqua regia74 ,tin compounds have1 similarly to aluminium salts1 the property of forming coloured insoluble compounds 7lakes7 with many organic colouring matters4 ,their use for this purpose is extensive4 ,arsenic ,compounds formerly played an important part in colour making4 ,they were used in the manufacture of a large number of pigments1 very beautiful but extremely poisonous4 ,at the present time1 we can1 fortunately1 entirely dispense with arsenic in colour making2 the arsenic colours can be replaced by others equally handsome and less1 or not at all poisonous4 ,the most important of the arsenic compounds is the trioxide ,as,o1 or ,arsenious ,acid1 commercially known as white arsenic4 ,this substance is obtained in large quantities as a by-product in the extraction of several metals4 ,it forms masses which are either glassy or have the appearance of porcelain4 ,freshly sublimed arsenic trioxide is glassy2 this form gradually changes into the porcellaneous variety1 it dissolves with difficulty in water4 ,a strong solution can only be obtained by boiling for many hours4 ,the compounds of arsenic with sulphur1 formerly extensively used as pigments1 have now almost fallen into disuse4 ,lead ,compounds belong to the substances most largely used in making colours4 ,unfortunately all lead colours have two very important drawbacks4 ,they are all very poisonous and at the same time extremely sensitive to sulphuretted hydrogen1 so that they are very considerably altered by the action of the small quantities of that gas contained in the atmosphere of an ordinary dwelling4 ,a striking example of this is seen in the lead paints used on the doors of water-closets4 ,the paint1 at first pure white1 becomes gradually darker1 and at last almost black1 the lead compound having been changed into black lead sulphide4 ,on account of this great sensitiveness of lead compounds1 it would be better if they could be excluded from the list of colours4 ,great care must be taken not to mix lead compounds with others which contain sulphur2 a discolouration of the mixture would be the inevitable result in a very short time4 ,the oxides of lead and a number of its salts are themselves pigments1 for example1 litharge1 ,pb,o1 red lead1 ,pb,o1 and white lead 7basic lead carbonate74 ,these pigments are prepared on a large scale in particular works4 ,at this point only those lead compounds will be mentioned which are generally used for the preparation of other lead pigments2 they are3 lead sulphate1 nitrate1 acetate and chloride4 ,lead ,sulphate1 ,pb,s,o1 is formed when sulphuric acid or the solution of a sulphate is added to the solution of a lead salt2 so obtained it is a white crystalline powder insoluble in water4 ,this substance is generally not made in colour works1 but is purchased from chemical works or dye houses1 of which it is a by-product4 ,in this form 7lead bottoms7 it is generally not sufficiently pure1 but contains admixtures of sulphuric acid or aluminium salts1 from which it is freed by washing4 ,the lead sulphate is stirred up in water1 the heavy precipitate allowed to settle1 the wash water drawn off1 and after repeating this process until the wash water no longer shows an acid reaction1 the purified precipitate is dried4 ,in this condition it is a heavy1 white powder1 and can alone be ground into paint4 ,but on account of its crystalline nature1 which reduces the covering power1 such use is inadvisable4 ,lead ,nitrate1 ,pb7,,no74--,this very important compound may be bought1 but it is advisable to prepare it in the works4 ,water is placed in a wooden tub1 then half the volume of nitric acid is added1 and finely powdered litharge gradually stirred in1 the liquid being kept in constant movement4 ,when it is seen that the litharge is only slowly dissolved1 the liquid is well stirred after each addition of litharge and then tested by litmus paper4 ,when this is no longer reddened1 the nitric acid is completely saturated1 and the liquid contains only lead nitrate in solution4 ,it is allowed to stand until the insoluble portions have settled1 and then drawn off into another vessel where crystals of lead nitrate separate in a few days4 ,if the salt be required in solid form1 the solution may be evaporated in earthenware dishes2 generally the solution is used as it is obtained4 ,pure lead nitrate forms white crystals which are not particularly soluble in water1 #a part requiring #b parts of water at the ordinary temperature4 ,lead nitrate is decomposed on heating1 like all nitrates1 and litharge remains4 ,the solution of this salt is used in the preparation of those lead pigments which are obtained by precipitation1 for example1 chrome yellow4 ,lead ,acetate1 ,pb7,c,h,o74#c;,h,o4--,the compounds of lead with acetic acid are of great importance4 ,two of these are to be considered3 neutral lead acetate1 commonly known as sugar of lead1 and basic lead acetate4 ,it may be advisable to manufacture both these compounds1 the latter always4 ,neutral lead acetate comes into commerce in the form of colourless heavy crystals1 which are often covered by a white powder of the basic acetate2 they dissolve readily in water1 and the solution has a sweetish taste1 hence the name 8sugar of lead04 ,frequently the solution is very turbid2 this is caused by the carbonates contained in the water4 ,the turbidity may be removed by the addition of a little acetic acid4 ,it is only economical for the colour maker to prepare sugar of lead when he can obtain cheap raw materials1 lead or litharge and vinegar4 ,pyroligneous acid may also be used if it is colourless1 its odour being without importance for this purpose4 ,the best method for preparing lead acetate from litharge is to place the vinegar in a tub and hang in it a strong linen bag filled with finely ground litharge4 ,the tub is kept covered for a few days and its contents then tested with red litmus paper4 ,when this is turned blue1 the liquid is drawn off and vinegar gradually added whilst stirring1 until blue litmus paper is just turned red4 ,in this process1 after neutral lead acetate has been formed1 more lead oxide is dissolved1 and the liquid thus acquires an alkaline reaction4 ,the further addition of acetic acid reconverts the basic salt into neutral lead acetate4 ,lead acetate solution may1 with advantage1 be prepared directly from metallic lead4 ,for this purpose1 lead is granulated by melting and pouring in a thin stream into cold water1 where it solidifies in irregular pieces4 ,this is done in order to give the lead as large a surface as possible4 ,three high narrow tubs placed one above the other so that liquid may flow from the highest to the middle1 and from this into the lowest1 are filled with granulated lead4 ,vinegar is placed in the uppermost vessel to cover the lead2 after twenty-four hours it is allowed to flow into the middle1 and after a further twenty-four hours into the lowest tub4 ,in this way1 a solution of basic lead acetate is formed1 to which the necessary quantity of acetic acid is added to bring it into the neutral condition4 ,if crystalline lead acetate is required1 the liquid is evaporated down and quickly cooled with stirring1 so that small crystals are formed4 ,generally1 however1 evaporation is unnecessary1 since lead acetate is always used in solution in preparing colours4 ,if the lead acetate solution be not colourless1 which is generally the case when coloured acetic acid is used1 the defect may be removed by stirring a little bone black into the liquid and filtering after twenty-four hours1 when a completely colourless solution is obtained4 ,it is always necessary to know exactly how much lead acetate is contained in the solutions prepared by these processes4 ,the lead or the litharge is therefore weighed and the volume of the lead acetate solution measured4 ,one hundred parts by weight of crystallised lead acetate are obtained from #fbed parts of lead4 ,lead acetate solutions must be kept in well-covered vessels4 ,the carbonic acid of the air will turn the liquid turbid4 ,the turbidity may be removed by the addition of acetic acid4 ,in the following table is given the percentage of crystallised lead acetate contained in solutions of different specific gravities3-- ---------------------------------------- ,specific,crystallised,specific,crystall ised ,gravity4,lead ,acetate,gravity4,lead ,acetate per cent4 per cent4 ---------------------------------------- #ajjjj #j #aahfi #bf #ajjfd #a #aaiee #bg #ajabg #b #abjdj #bh #ajaia #c #ababf #bi #ajbee #d #abbaa #cj #ajcai #e #abcjc #ca #ajchf #f #abcie #cb #ajdec #g #abdhf #cc #ajebj #h #abegh #cd #ajehg #i #abffi #ce #ajfed #aj #abgfh #cf #ajgbe #aa #abhfg #cg #ajgif #ab #abiff #ch #ajhfg #ac #acjfd #ci #ajici #ad #acafc #dj #aajaj #ae #acbfi #da #aajhd #af #accgf #db #aaaei #ag #acdhb #dc #aabcd #ah #acehh #dd #aacji #ai #acfie #de #aachd #bj #achaj #df #aadfd #ba #acibe #dg #aaedd #bb #adjda #dh #aafbd #bc #adaef #di #aagjd #bd #adbga #ej #aaghd #be ---- ---- ---------------------------------------- ,basic ,lead ,acetate1 ,pb7,c,h,o74#b,pb,o4--,this salt may be regarded as a compound of neutral lead acetate with lead oxide4 ,it is obtained by digesting vinegar with excess of litharge or with metallic lead1 and also by treating lead acetate solution with litharge so long as the latter is dissolved4 ,in the method last given1 #ajj parts of sugar of lead require about #aah parts of litharge to produce a saturated solution of basic acetate4 ,the solution of this compound is alkaline2 it turns red litmus paper blue4 ,when exposed to the air1 a turbidity is quickly produced owing to the separation of lead carbonate4 ,in one white lead process basic lead acetate is the starting point of the manufacture4 ,lead ,chloride1 ,pb,cl1 is seldom used in making colours4 ,it may be prepared by stirring powdered litharge in common salt solution until the powder appears white4 ,this1 when washed1 constitutes basic lead chloride4 ,on adding hydrochloric acid to the washed mass until the liquid remains acid1 lead chloride is obtained in the form of crystalline needles1 which are very little soluble in cold1 but more easily in hot1 water4 ,like any other soluble lead salt1 lead chloride may be used in the precipitation of colours1 but is seldom employed on account of its small solubility4 ,basic lead chloride was1 at one time1 used as a white pigment1 and after melting1 by which it is turned yellow1 as a yellow pigment2 it is no longer in use for these purposes4 ,copper ,compounds4--,these are generally green or blue1 and have an extended use in the production of colours4 ,the metallic copper which is used in the preparation of colours is of the ordinary commercial quality4 ,the impurities which it contains are generally so small in quantity that they are without importance for our purpose4 ,copper ,sulphate 7,bluestone1 ,blue ,vitriol71 ,cu,s,o4#e;,h,o4--,this is the commonest of the commercial copper salts1 and on that account deserves our especial attention4 ,it forms large sky-blue crystals1 which effloresce slightly in the air1 possess an unpleasant metallic taste1 and are poisonous1 like all soluble copper compounds4 ,copper sulphate comes into commerce in a very pure form1 but some qualities contain zinc sulphate or ferrous sulphate4 ,the presence of zinc may be detected most easily by boiling the solution with excess of caustic soda1 when copper oxide separates as a black powder1 whilst zinc oxide remains dissolved4 ,when sulphuretted hydrogen is passed through the liquid1 a white precipitate of zinc sulphide is formed4 ,iron is detected by passing sulphuretted hydrogen through the solution so long as a precipitate is formed1 allowing the liquid to stand in a covered vessel1 pouring it off from the precipitate1 adding nitric acid1 boiling and adding a solution of potassium ferrocyanide2 a blue precipitate denotes the presence of iron4 ,copper sulphate is rarely found which is quite free from iron and zinc4 ,if these impurities are present in but small quantity1 the zinc not exceeding #a per cent4 and the iron at most #je per cent41 the copper sulphate may be regarded as sufficiently pure for our purposes4 ,it may be here remarked that copper sulphate obtained from mints is generally of great purity1 and hence particularly adapted for colour making4 ,when copper sulphate and other copper salts are dissolved in water1 pale blue flocks of copper carbonate generally separate4 ,this is due to the carbonate of lime contained in the water4 ,an addition of a few drops of sulphuric1 nitric or hydrochloric acid suffices to prevent this separation4 ,copper ,nitrate1 ,cu7,,no74#f;,h,o4--,this salt may occasionally be obtained in colour works as a by-product4 ,when nitric acid is poured over copper1 there follows a copious evolution of nitric oxide1 which produces brown fumes of nitrogen peroxide in air4 ,nitric oxide may be used to convert ferrous into ferric salts1 a transformation required in making ,prussian blue4 ,in working in this way1 nitric acid is poured over copper contained in a vessel provided with a delivery tube for the gas4 ,the blue solution is at once used4 ,pure copper nitrate forms fine blue crystals1 which very readily deliquesce in the air4 ,the solution is therefore generally used as it is prepared4 ,copper ,acetate1 ,cu7,c,h,o74,h,o4--,copper is readily attacked by acetic acid4 ,a number of salts are formed1 of which some are used as pigments4 ,for our purpose it will be sufficient to describe the manufacture of verdigris2 few colour makers prepare any other copper acetate4 ,a solution of this salt is most simply prepared in the following manner3 ,slaked lime is stirred with strong vinegar1 and the solution left in contact with the excess of lime so long as it has a weak acid reaction4 ,the solution1 which contains acetate of lime1 is poured into a solution of copper sulphate so long as a precipitate of sulphate of lime is formed4 ,when this has been separated from the liquid1 the latter is ready for further treatment4 ,it contains only a very small quantity of dissolved sulphate of lime1 which is not harmful in the preparation of colours4 ,in addition to the copper compounds mentioned here1 several others were formerly used as pigments1 or in the preparation of pigments which are no longer employed1 because copper compounds of good colour can be obtained in a cheaper manner4 ,the same precautions should be taken in the use of copper colours which were mentioned for lead pigments2 copper compounds are equally sensitive towards sulphuretted hydrogen1 by which they are gradually discoloured4 ,mercury ,compounds4--,mercury forms compounds which1 vermilion in particular1 are used as pigments1 and others which are used in the preparation of pigments4 ,in many cases metallic mercury is the starting point in the preparation of the mercury compounds4 ,the compounds commonly known as calomel and corrosive sublimate are also used4 ,mercurous ,nitrate1 ,hg,n,o4--,nitric acid acts upon mercury in a manner differing according to its strength1 and according to whether the mercury or the nitric acid is used in excess4 ,in order to prepare mercurous nitrate1 acid free from chlorine must be diluted at least with four times its volume of water1 and the mercury must be in excess4 ,on warming1 the mercury is gradually dissolved1 and1 on cooling1 the solution deposits colourless crystalline needles of the salt4 ,a further crop of crystals is obtained after evaporating the solution4 ,when the action of nitric acid is over1 the solution must be at once separated from the excess of mercury to prevent the formation of basic salts4 ,if the salt has been properly made1 it is completely soluble in water1 but if a lemon yellow precipitate is formed on dissolving1 the nitrate contains a basic salt1 which can only be dissolved by warming and adding more nitric acid4 ,mercuric ,nitrate1 ,hg7,,no71 is most simply obtained by warming mercury with very strong nitric acid4 ,the heating must be continued until a test portion of the solution no longer gives a precipitate with hydrochloric acid4 ,when this solution is evaporated1 nitric acid is given off1 and a salt crystallising in white needles is obtained1 which dissolves in water with the separation of a yellow basic salt4 ,it is therefore better to use the hot solution1 which contains a little free acid1 without evaporating4 ,instead of mercurous and mercuric nitrates1 the corresponding sulphates may be used1 but the chlorides are more frequently employed since they can be readily obtained from the makers4 ,mercurous ,chloride 7,calomel71 ,hg,cl1 is obtained pure by adding common salt solution to a solution of mercurous nitrate and washing the precipitate1 which is insoluble in water4 ,mercuric ,chloride 7,corrosive ,sublimate71 ,hg,cl a common article of commerce1 is prepared by heating a carefully made mixture of mercuric sulphate and common salt1 when mercuric chloride sublimes4 ,it is a white crystalline mass1 soluble in #ace parts of water at #bj ,c41 and soluble in #c parts of alcohol4 ,although all mercury compounds are very poisonous1 corrosive sublimate requires particular care in handling1 since its easy solubility makes it surpass all other mercury compounds in poisonousness4 ,the mercuric sulphate required in the above preparation is obtained by heating mercury with sulphuric acid4 ,corrosive sublimate can also be prepared by adding hydrochloric acid to mercurous nitrate1 and heating1 with gradual addition of hydrochloric acid until a clear solution is formed1 from which mercuric chloride crystallises on cooling4 ,silver ,compounds4--,silver nitrate1 ,ag,n,o1 is the only one of importance here4 ,it is obtained by dissolving silver in nitric acid1 when a blue solution is obtained because commercial silver contains copper1 evaporating the solution to dryness1 melting the residue1 and keeping it molten until all the copper nitrate is decomposed4 ,this point is recognised when a small portion of the melt dissolved in water does not give a blue colouration with excess of ammonia4 ,fused silver nitrate forms a white crystalline mass readily soluble in water and turning black when exposed to light1 like many other silver compounds4 ,gold ,compounds4--,gold is now very little used in preparing colours4 ,the compound used for this purpose is gold chloride1 ,au,cl1 which is obtained by heating gold with hydrochloric acid1 and adding nitric acid in small quantities until all the metal is dissolved4 ,by careful evaporation of the yellow solution gold chloride is obtained in brownish yellow crystals1 which easily dissolve in water4 ,the compounds of molybdenum1 vanadium and uranium are less used than those of gold1 yet these metals find a special use in the preparation of colours for porcelain painting and for colouring glass1 for which they are of great importance4 ,the preparation of their compounds from the raw materials is complicated and not remunerative to the colour maker2 they should be obtained from chemical works4 99 99 99 99 99 ,in the foregoing1 the most important compounds of inorganic origin used in making colours have been briefly described1 less in order to teach the methods for their preparation than to give the manufacturer the means of learning their properties4 ,since the great development of chemical industries during the last decades it is more advantageous for the colour maker in most cases to draw his supply of these substances from works of good reputation than to make them himself2 only in the case of a few substances1 which are sold at unreasonably high prices1 will it be profitable for him to prepare them himself4 ,,chapter ,,vi4 ,,the ,,manufacture ,,of ,,mineral ,,pigments4 ,by mineral pigments we understand those which consist of compounds of metals with elements such as sulphur1 chlorine and iodine1 or with compound radicals1 such as cyanogen1 or of metallic salts4 ,looking at the classification of mineral pigments from the chemical standpoint1 a grouping according to the constituents would appear preferable1 and we should have groups of colours consisting of metallic oxides1 sulphides1 salts1 etc4 ,in such a division of pigments1 according to their constituents1 no regard would be taken of the colour of the pigment4 ,the white zinc oxide would be placed in the same group with yellow lead oxide and red lead oxide2 and red mercury sulphide and yellow cadmium sulphide would fall into the same group of the sulphur compounds4 ,the chemical composition of a pigment is of less importance to the colour manufacturer than its shade1 and it therefore appears to us more reasonable to prefer to classify mineral pigments according to similarity of colour4 ,we shall therefore place all those mineral pigments together which possess the same colour4 ,common usage differs from the scientific in the description of colours4 ,in the physical sense1 yellow1 red and blue are the so-called 8simple colours10 between which lie orange1 green and violet as 8mixed colours04 ,physics knows no white colour and no black colour1 but describes white as a mixture of all the simple colours and black as the absence of colour4 ,a grey or brown shade1 produced by different mixtures of simple colours1 is just as little known in the scale of colours as white or black4 ,the colour maker follows1 as we have said above1 the common manner of speaking2 to him white and black are equally as much colours as red and green4 ,besides the pure principal colours 7yellow1 red and blue71 and the mixed colours obtained from them 7orange1 green and violet71 colour makers distinguish many shades of each colour--lemon yellow1 sulphur yellow1 cherry red1 blood red1 violet blue1 etc4 ,for the present purpose it is of great importance to accurately distinguish the several shades1 for the value of many colours is in proportion to their beauty of shade4 ,the colour maker is often required to produce a colour of some particular shade1 which he accomplishes in many cases by a suitable alteration in the process by which the colour is made1 in other cases by mixing different colours1 in which event chemistry is of no help to him2 he must depend on the sensitiveness of his eyes to colour4 ,white ,mineral ,pigments4--,we are acquainted with a great number of white or1 more properly1 colourless mineral compounds2 they possess the property of reflecting1 undecomposed1 all the rays of light which fall upon them1 in consequence of which they produce that impression upon the eye which we call white4 ,according as a white substance reflects every ray of light or absorbs a portion1 we see it as a brilliant pure white or1 in the latter case1 as a white with a grey tinge4 ,if a white body reflects the majority of the rays of light falling on it1 but decomposes a small number1 we perceive a white which has a yellow1 blue or red tinge4 ,the most valuable white for the colour maker is evidently that which reflects1 unaltered1 all the rays of light2 it is the most brilliant1 and free from every tinge of colour4 ,the physical condition of the substance is most important4 ,solid substances are either crystalline1 that is1 possess definite shapes formed according to a regular law1 or they are amorphous1 that is1 are composed of irregularly formed particles4 ,snow and white lead may serve as representatives of these two classes4 ,snow is composed of small colourless crystals of ice1 the flat surfaces of which reflect1 undecomposed1 the light falling on them4 ,the smaller are the crystals1 the more pure appears to us the whiteness of the snow1 and the thinner is the layer of snow required to produce the sensation of whiteness4 ,but if the snow crystals are larger1 the white appears to have a bluish tinge1 and only a thick layer of snow is opaque4 ,white lead1 being an amorphous substance in a condition of very fine division1 reflects the light very regularly1 so that a thin layer of white lead appears quite opaque4 ,among the artificial pigments1 crystalline or amorphous1 exactly the same conditions hold good as between snow and white lead4 ,of amorphous pigments a very thin layer is in most cases sufficient to make the surface upon which they are spread invisible1 or1 as the technical expression runs1 8to cover10 whilst crystalline substances possess a smaller covering power4 ,a striking example of this is seen by a comparison of two white pigments1 white lead and 8patent white0 7lead oxychloride74 ,the former is amorphous1 the latter crystalline4 ,both are completely colourless and reflect white light1 but in consequence of its amorphous condition and finer particles1 white lead possesses far greater covering power than 8patent white04 ,among all other colours the same rule holds4 ,amorphous pigments have always a greater covering power than crystalline4 ,the smaller the crystals of the latter the greater is their covering power1 so that in preparing pigments of a crystalline character care must be taken to make the crystals as small as possible4 ,from the above definition of white pigments it follows that an immense number must exist1 since every colourless substance in a state of fine division appears white4 ,generally only those bodies are used which are insoluble in water1 or almost insoluble1 and which possess great covering power4 ,the following may be mentioned as white pigments1 only a few of which are in use3 white lead1 white zinc1 permanent white1 lead oxychloride1 lead sulphate and sulphite1 zinc oxychloride1 lead antimoniate1 antimony white1 tin white1 tungsten white1 and in addition certain earths1 pipe clay1 china clay1 etc4 ,several of these pigments are far too expensive for ordinary use1 and have no advantage over much cheaper pigments except for very special purposes1 such1 for example1 as bismuth white for cosmetics4 ,in general use we find very few artificial white pigments2 these are lead1 zinc and barium compounds4 ,circumstances may arise which make it expedient for the colour maker to manufacture other white pigments1 for example1 a demand for them1 or favourable opportunities for obtaining the requisite raw materials4 ,the white lead pigments1 of which there is a large number1 as we have indicated1 all have the great disadvantage that they are not permanent1 that is1 are changed by atmospheric influences4 ,it is well known that lead is a very delicate reagent for sulphuretted hydrogen1 with the sulphur of which it forms a black compound4 ,now the air1 especially in towns1 contains sulphur in the form of sulphuretted hydrogen or ammonium sulphide2 though the quantity is very small1 the fate of every white or coloured lead pigment is decided by it2 after a longer or shorter time it will be discoloured1 will gradually darken1 and finally be turned black4 ,in spite of this great changeableness of lead pigments they are used by artists and painters1 although the majority could be replaced by more permanent pigments entirely unaltered by the atmosphere4 ,,white ,,lead4 ,this pigment1 which in addition to other good properties has remarkable covering power1 was amongst the earliest known artificial pigments4 ,already in the fourth century before ,christ1 ,dioscorides described the preparation of white lead1 which was obtained by exposing lead to the action of the vapours of vinegar1 removing the white layer and treating it with water4 ,the ,roman writers describe a similar method2 they use the name cerussa1 under which white lead is known to-day in commerce4 ,although white lead has been so long known1 it was left to ,bergmann1 in #aggd1 to show that it contained carbonic acid2 before that it was believed to be lead acetate4 ,the development of analytical chemistry was followed by a knowledge of its constitution and the use of more rational methods of manufacture4 ,whilst in the middle ages the manufacture of white lead was almost exclusively in the hands of the ,dutch and ,venetians1 in later years it gradually spread1 and now many works are concerned in the manufacture of this pigment4 ,that adulterations of white lead were not rare in former times appears from the writings of ,basil ,valentine1 an alchemist of the fifteenth century4 ,commercially white lead is known under most varied titles1 of which the following are the principal3 ,white lead1 ,venetian white1 ,dutch white1 ,krems white1 ,kremnitz white1 flake white1 etc4 ,according to its chemical composition1 white lead is a compound of lead carbonate and lead hydroxide1 that is1 a basic lead carbonate4 ,commercial white lead1 apart from intentional admixtures of other white substances1 contains lead carbonate and lead hydroxide in varying proportions1 as is shown by the following analyses by ,mulder1 who found that all the samples examined by him were composed according to one or other of the following formul3-- #b ,pb,c,o4,pb7,,oh71 containing #hfbg per cent4 of ,pb,o4 #e ,pb,c,o4#b,pb7,,oh7 0 #hehf 0 0 #c ,pb,c,o4,pb7,,oh7 0 #hede 0 0 #d ,pb,c,o4,pb7,,oh7 0 #hejj 0 0 ,according to ,hochstetter1 the manufacture of white lead must be directed to obtaining the compound #b ,pb,c,o47,,oh71 which possesses the following percentage composition3-- ,pb,o #hfcb ,,co #aacf ,h,o #bcb ,the compound of this composition is distinguished by being completely amorphous1 and so possesses the greatest covering power4 ,commercial white leads1 as is seen from the formul of ,mulder1 may differ appreciably from this composition1 when they will have a smaller covering power1 since they will contain some quantity of neutral lead carbonate1 ,pb,c,o 7containing #hcdf per cent4 of ,pb,o71 which is crystalline4 ,white lead is prepared according to very different methods1 the principle of which consists in subjecting a solution of tribasic lead acetate to the action of carbonic acid1 by which the basic carbonate is produced and the neutral acetate formed1 the latter being then reconverted into the basic acetate1 which again serves to produce white lead and so on4 ,,chapter ,,vii4 ,,the ,,manufacture ,,of ,,white ,,lead4 ,the processes by which white lead is or was manufactured may be divided1 according to the principal operations1 in the following manner3-- #a4 ,processes in which metallic lead is subjected to the action of acetic acid vapour1 whilst the vessel in which this operation is conducted is exposed to a higher temperature4 ,in the oldest so-called ,dutch method this increase of temperature is effected by the decomposition of manure1 by which the vessels containing the lead and acetic acid are surrounded4 ,in consequence of the heat produced by this fermentation1 acetic acid and water are volatilised1 and oxygen also being present1 lead acetate is formed4 ,also1 as a consequence of the oxidation of the lead1 heat is produced1 which accelerates the process1 and lead oxide is formed in large quantity1 which unites with the neutral acetate already formed to produce a basic compound4 ,the vessels in which this process is taking place are in an atmosphere containing much carbonic acid produced by the fermentation of the surrounding organic matter2 this carbonic acid converts the basic lead acetate into white lead4 ,the ,german or ,austrian method is to be regarded as an improvement on this rough process4 ,the heat necessary for the normal course of the chemical reactions is produced from fuel2 the carbonic acid formed by the combustion of the fuel is used to convert the basic lead acetate into white lead4 #b4 ,in the above methods the manufacture of white lead commences with the production of white lead from metallic lead and acetic acid4 ,in the so-called ,french method a solution of basic lead acetate is decomposed by carbonic acid into white lead and neutral lead acetate1 which latter is again converted into basic acetate4 #c4 ,the ,english method4 ,the principle of this process consists in moistening litharge with a solution of lead acetate and exposing it to the action of carbonic acid1 whereby white lead is formed4 ,methods for manufacturing white lead1 which are often advanced as entirely new processes1 may be always traced to one of the above1 from which they deviate but little in principle1 and the deviations cannot always be regarded as improvements4 ,in the following detailed account of the manufacture of white lead we shall adhere to the classification just given1 according to which there are three principal methods3 7#a7 ,manufacture of white lead from metallic lead1 acetic acid and carbonic acid 7,dutch and ,german processes72 7#b7 manufacture of white lead from basic lead acetate 7,french process72 and 7#c7 from litharge moistened with lead acetate solution 7,english process74 ,we should remark that every year 8new0 processes for the manufacture of white lead are patented4 ,the majority of these will not be mentioned2 to those acquainted with the principles of chemistry they at once appear impracticable4 ,,manufacture ,,of ,,white ,,lead ,,from ,,metallic ,,lead4 7a7 ,,dutch ,,process4 ,this essentially primitive process1 when properly conducted1 produces white lead of good colour and covering power1 which are the properties for which this pigment is valued4 ,it is now seldom used1#b because other methods give a product of equal colour in a shorter time4 ,it is1 however1 of economic interest1 as showing how a branch of industry may rise from crude beginnings to a high state of perfection4 ,the operations comprised in the ,dutch process are as follows3-- #b ,in ,england the ,dutch process is in general use4--,,translator4 7#a7 ,casting the lead into sheets2 7#b7 placing these sheets in pots and arranging the pots in the stacks 7placing the pots containing lead and acetic acid in the bed of manure72 7#c7 removing the pots from the stack2 7#d7 separating the white lead formed in the pots2 7#e7 further purification of the impure white lead by grinding1 washing and drying4 #a4 ,casting the ,lead into ,sheets4--,at first sight it would appear unsuitable to cast lead in sheets1 since this metal can be readily rolled into sheets of any thickness4 ,experience has1 however1 shown that rolled lead is only slowly attacked by acetic acid vapours1 whilst cast sheets are rapidly attacked4 ,an iron pan about one metre in diameter1 with an iron cover furnished with a pipe opening into a flue1 is used for melting the lead4 ,this arrangement is designed to protect the workman from the dangerous vapours evolved from the molten metal4 ,at the workman's side of this cover is a counterpoised slide1 which only remains open when the counterpoise is held in check by a lever4 ,in front of the kettle there is an iron plate movable about a horizontal axis4 ,the lead being heated to just above its melting point1 the workman takes #g to #h kilogrammes of metal in a ladle1 and pours it on the plate1 which is horizontal4 ,the lead solidifies in a very short time1 but before it is completely solid the plate is inclined towards the pan so that the still liquid lead runs back into it1 leaving a very thin sheet on the plate4 ,the hard sheet is removed from the plate1 and the latter cooled by cold water to be ready for a new casting4 ,the sheets made in this way are not more than #a to #b millimetres thick4 ,they are then cut into strips of a width to suit the size of the pots in which they are converted into white lead2 the width of the sheets is generally #e to #f centimetres4 ,since the rate at which the white lead is formed depends on the surface of the metallic lead1 instead of continuous sheets the lead is generally cast into gratings4 ,for this purpose an iron plate1 upon which are intersecting strips1 is used instead of the flat plate4 ,plates for the casting are also used containing grooves intersecting at right angles4 ,in the first case1 plates are obtained in which are openings meeting at right angles1 and in the second case1 according to the distance of the grooves apart1 a more or less wide-meshed lattice work4 ,illustration3 ,,fig4 #d4 #b4 ,building up the ,stacks4--,the rolled-up lead plates are placed in the pots4 ,these 7,fig4 #d7 are somewhat conical in shape2 they have at some distance from the bottom a projecting ring1 or sometimes three projections only1 upon which the lead spiral rests4 ,before the spirals are put in position1 a quantity of ordinary vinegar1 about a quarter of a litre1 is poured in4 ,there must be sufficient room below the spiral so that it shall not be in contact with the vinegar4 ,the insides of the pots are glazed at least half-way up1 so that the liquid does not penetrate the porous earthenware4 ,the pots have a capacity of about #a litre1 and a diameter at the top of #aj centimetres4 ,if lead plates are used1 the pots are about #bj centimetres high2 if gratings are used the pots may be lower1 by which there is economy in room and a larger number can be placed in one stack4 ,the stacks1 built up of pots and manure1 are of different sizes2 it is not advisable to make them too small1 or the loss of heat would be considerable4 ,a stack #d to #e metres long1 #c metres wide and #f to #g metres high will contain #f1jjj to #h1jjj pots and #i1jjj to #aa1jjj kilogrammes of lead4 ,the stack consists of a rectangular pit walled on three sides2 the fourth side is open1 with the earth dug out in the form of an inclined plane1 in order to permit the introduction of the pots and the manure4 ,the construction of the stack is commenced by placing the pots at the bottom in rows1 avoiding interspaces as much as possible4 ,in a stack of the size mentioned a layer contains #a1jjj to #a1bjj pots4 ,between the pots containing lead and acetic acid are arranged a number of larger ones containing acid only2 the object of these is to furnish acetic acid vapour4 ,when the pots are in place1 #c or #d lead plates are placed on each spiral1 the top plate forming the cover2 immediately over the pots strong wooden planks are laid1 and upon them a layer of boards1 which must fit so tightly that nothing can fall through4 ,on the boards is spread out a layer of fresh stable manure1 with which the space between the outside row of pots and the wall is also filled4 ,the layer of manure is #cj to #dj centimetres thick4 ,upon the lowest layer of pots1 a second1 third and so on are built up exactly in the same manner1 so that the whole stack is filled with alternating layers of pots and manure4 ,in order to prevent the cooling of the uppermost layer of pots1 it is covered with a thicker layer of manure #fj to #gj centimetres thick4 ,when lead plates and the taller pots are used1 a stack will generally contain #ae layers2 but when gratings and the smaller pots are employed1 #ah layers can be packed into the same space4 ,in arranging the layers of pots1 care should be taken to leave spaces at tolerably equal distances1 so that the air necessary for the oxidation of the lead may enter4 ,to prevent the cooling of the stack at the front1 where it is not protected by masonry1 when full it is walled up with boards2 a board roof also protects the erection from rain4 ,in place of manure1 spent tanners' bark can be used1 which in the same manner ferments1 producing heat and carbonic acid4 ,in places in the neighbourhood of large tanneries this spent bark is generally obtainable at lower prices than stable manure1 which is more valuable for agricultural purposes2 the former has also a very considerable advantage1 white lead made by means of spent tanners' bark being generally of a purer white than that made with manure4 ,the reason for this is that in the decomposition of animal excrement small quantities of sulphuretted hydrogen are produced1 a gas which produces black lead sulphide when it comes into contact with lead compounds4 ,according to the results of practical experience1 pigs' dung cannot be used in the manufacture of white lead2 so much sulphuretted hydrogen is evolved from it that the white lead is not white1 but has a greyish tinge4 ,when bark is used in place of manure1 a discolouration of white lead by sulphuretted hydrogen is not to be feared1 but there is the drawback that a longer time is necessary for the corrosion of the lead1 because the bark decomposes more slowly than the manure1 and accordingly gives out less heat and carbonic acid4 ,according to the climate of the country1 the stacks may be differently erected4 ,in colder countries it is necessary to sink them in the earth and surround them with masonry1 as directed above2 but in warmer climates such effectual protection against cooling is unnecessary1 yet in all cases it is better to sink the stack in the earth on account of the regularity of temperature so obtained4 ,instead of sinking the stacks in the earth1 they may be built in the open when there is a plentiful supply of manure or bark2 but they must then be surrounded by a very thick layer of manure to prevent cooling4 ,it is a desirable alteration in the construction of the stacks to provide the pots with lids1 and so avoid the use of the layer of boards separating each two layers of pots4 ,the object of the cover is simply to prevent dirt from falling into the pot4 ,it should not fit tightly on the edge1 or the entry of carbonic acid into the interior of the pot would be made difficult4 ,the lids are therefore rounded and fit loosely on the pot4 ,when pots with lids are used1 the lowest layer is covered with manure in the ordinary way2 upon this again comes a layer of pots1 and so on4 ,the transformation of the lead may be regarded as complete in four to six weeks when manure is used1 but with bark the time extends to ten weeks4 ,the quantity of white lead obtained varies in different cases2 for example1 from a stack #e metres long1 #d metres wide1 and #f metres high1 into which #ab1jjj kilogrammes of lead were put1 #aj1jjj kilogrammes of white lead were obtained1 and #d1jjj kilogrammes of lead remained unaltered4 ,in another case1 for a stack of #h layers #bhj kilogrammes of vinegar and #i1fjj to #ab1jjj kilogrammes of lead were used1 and there was a residue of #aj to #ae per cent4 of lead4 #c4 ,removal and ,grinding of the ,white ,lead4--,the stack is pulled down after the lapse of the necessary time2 the lead plates and rolls are collected in wooden boxes and brought into the room where the white lead is separated from the metallic lead4 ,formerly the white lead was removed from the sheets exclusively by manual labour1 an operation extremely dangerous to the workman4 ,it is quite impossible to prevent the formation of white lead dust1 so that the men were continuously in an atmosphere charged with the poisonous material1 and1 as a consequence1 suffered from the various forms of lead poisoning4 ,in order to diminish as much as possible the injurious effects of white lead on the health of the workmen1 manual labour has been1 as far as possible1 replaced by machinery1 yet the greatest care is necessary in the different manipulations of so poisonous a substance as white lead4 ,when the white lead is removed by manual labour1 an operation which ought to be forbidden1 the lead sheets are unrolled and struck together1 whereupon the greater part of the white lead falls off4 ,to remove the remainder of the white lead the plates are laid one upon the other and struck with a hammer until the white lead is loosened2 or the plates are cleaned with metal brushes4 ,the masses of white lead obtained in this way are contaminated by larger or smaller quantities of metallic lead1 from which they must be freed by a further mechanical operation1 namely grinding4 ,the larger pieces of the white lead1 which have a thickness of several millimetres1 were picked out and sold separately under the name of flake white4 ,this was formerly a highly prized quality of white lead1 its appearance being a guarantee of its purity4 ,the flake white generally found in the market nowadays is not obtained in this manner1 but by mixing white lead with a solution of dextrin1 forming plates from the paste and drying them slowly in the air4 ,in order to separate the white lead mechanically from the remains of the lead sheets1 grooved rollers are used1 between which the sheets are passed4 ,in order to guard against dust1 the rollers are surrounded by a closed casing1 in which there is also a sieve which serves to separate the larger pieces of white lead 7flake white7 from the fine dust4 ,the arrangement is represented in ,fig4 #e4 ,the unrolled plates pass through the opening1 ,b1 on to an endless leather band1 by means of which they are carried between the grooved rollers1 ,d and ,e2 after they have passed through these they go between a second pair of rollers1 ,f and ,g1 which are placed nearer together2 they then fall into the drum-shaped sieve1 ,h1 out of which they leave the apparatus in the direction of ,k4 ,the white lead falls through the sieve1 is caught in trucks placed at ,j1 and carried away to the mills4 ,illustration3 ,,fig4 #e4 ,a mechanical arrangement for the separation of white lead from the unaltered metallic lead1 due to ,horn1 is represented in ,figs4 #f and #g4 ,it consists of a drum1 in which is the spindle1 b1 provided with the arms1 c4 ,the teeth1 e1 on the arms reach nearly to the lower curve of the drum1 but pass at a somewhat greater distance from the upper portion so that the pieces of lead can fall down again after they are carried up4 ,the material is fed in through the hopper1 t1 the rotation of the arms loosens the white lead from the pieces of metallic lead1 and it is carried on by the water which passes through the sieve1 #c1 and the stop cock1 h1 into the settling tank4 ,the lead pieces which are carried forward have their progress checked by the bridge1 o1 they are collected by the perforated scoop1 n1 are raised above the hopper1 m1 and fall out of the apparatus at r4 ,if it is required to continue the treatment of the material in the drum for a longer period it is only necessary to close the hopper1 m1 by the slide1 n4 ,illustration3 ,,fig4 #f4 ,illustration3 ,,fig4 #g4 ,white ,lead ,mills4--,before the white lead is subjected to the real process of grinding1 it is generally first ground dry1 or1 more properly1 pressed or crushed4 ,this crushing is accomplished by means of vertical or edge-runner mills1 which consist of mill-stones running round upon a stone bed about a vertical axis4 ,the mill is surrounded by a wooden casing to prevent the escape of dust4 ,wet grinding1 which is done between mill-stones1 may be carried out in two ways1 with the production of hard or soft white lead4 ,the former is obtained when the lead acetate is not removed1 the latter when all the lead acetate is washed out4 ,illustration3 ,,fig4 #h4 ,hard ,white ,lead presents a shining mass1 broken with difficulty4 ,this appearance is a guarantee against adulteration with barytes2 white lead1 which contains this adulterant1 does not give a smooth1 but an uneven earthy fracture4 ,hard white lead is rather difficult to grind1 and requires very careful treatment to be brought into that state of fine division in which it is usable4 ,the dry white lead1 after powdering under the edge-runners1 must pass through a sieve1 which retains the particles of metallic lead1 before it is subjected to wet grinding4 ,the mills used for wet grinding differ little1 or not at all1 from the ordinary pattern4 ,illustration3 ,,fig4 #i4 ,a mill designed by ,richter of ,knigsee1 in ,thuringia1 for wet grinding1 is constructed as follows 7,figs4 #h and #i74 ,the shaft1 ,f ,e1 is driven by a water-wheel and the necessary gearing at #fj revolutions per minute2 the bevelled cog-wheel ,g1 by means of the cog-wheels ,h and ,j1 drives the shafts ,k and ,l1 which1 by means of the bevelled cog-wheels a and b1 communicate to the runner stones of the mills1 ,m1 ,n and ,o1 a speed of #adj revolutions per minute4 ,c ,d is the framework for the support of the storied arrangement of mills1 f and g are bearings with cast-iron cups to receive the escaping oil1 i is a clamp fastening the axle d to k4 ,a steel cup in k rests upon the hardened top of the spindle1 l2 the bed stone rests upon the beam n 7#hj millimetres thick7 and is prevented from lateral movement by the surrounding oo2 p is a wooden support in the opening in the bed stone1 carrying the stuffing box1 q1 which prevents the white lead from running out1 and connects the spindle1 l1 with the bed stone4 ,the runner stone1 r1 is surrounded by the box1 s1 cemented with white clay inside and out and fastened to the bed stone4 ,the lever1 t1 turning about w1 moved by the screw1 u1 and handle1 v1 regulates the position of the runner4 ,the diameter of the stones is #ie centimetres4 ,thirty kilogrammes of white lead1 mixed with water1 are fed into the top mill of the series shown on the right2 the mixture flows by the spouts1 e1 into the lower mills1 and is received in vessels1 from which it is emptied into the holder1 ,p4 ,from ,p it goes through the #c mills on the left4 ,after passing through #f mills1 white lead without barytes is ready for use4 ,if the white lead contains an admixture of barytes1 it is put through the #c mills on the left a second time4 ,in #bd hours #ijj to #a1bjj kilogrammes 7#ah to #bd cwt47 of white lead are ground4 ,in dry grinding1 mills are used arranged so that the formation of dust is avoided1 a matter which is of particular importance4 ,the usual size of these mills has a diameter of #ij to #ie centimetres for both runner and bed stone4 ,the grinding surfaces of both stones have radial grooves4 ,illustration3 ,,fig4 #aj4 ,fig4 #aj represents the construction of ,lefbre's white lead mill1 which is designed to give the greatest protection possible to the workmen4 ,at ,a1 the white lead masses are enclosed in a hopper lined with bronze1 with internal angular projections2 by means of ,m1 which is grooved in a similar manner1 the larger lumps are broken up and enter the mill itself by means of the hopper under ,a4 ,the mill consists of bed stone1 ,h1 and runner1 ,k4 ,the grinding surfaces are grooved to facilitate the delivery of the ground white lead4 ,as the illustration shows1 the stones are completely covered by ,m1 so that the escape of dust is almost completely prevented4 ,the ground white lead is conducted by the tubes1 ,o ,o1 to the drums1 ,o ,o1 from which it is packed4 ,in order to obtain hard white lead1 the material which has been ground dry under the edge-runners is mixed with water to a soft paste1 or if water has been added whilst the lead was under the edge stones1 more is now added to make the paste thin enough to be ready for the mills1 where it is ground1 being fed in regularly by means of a copper spoon4 ,the paste issuing from the mill is collected in earthenware pans or plaster of ,paris moulds1 in which it is dried4 ,these pans have usually the shape of a truncated cone1 which was the form in which white lead was formerly brought into trade from ,holland4 ,in drying1 water is lost1 and the mass of white lead shrinks1 so that the lump can be removed from the mould after a few days on turning it upside down4 ,the drying is accomplished either in the air or in artificially heated stoves4 ,the heating must at first be gradual1 or the mass of white lead would shrink so rapidly that the cone would be full of cracks1 and then easily fall to pieces4 ,when once the drying has reached a certain stage1 the temperature of the stove may be raised to #ej ,c4 7#abb ,f47 without danger of breaking the lumps4 ,when quite dry1 the surface of the white lead1 which is now rough1 must be smoothed by scraping1 when it is ready for the market4 ,soft ,white ,lead4--,the hard white lead prepared as just described consists of very heavy and very hard lumps of the purest white4 ,when soft white lead is required1 the admixed lead acetate must be removed by washing4 ,this is accomplished by adding a larger quantity of water1 either when grinding under the edge-runners or in the mills1 so that a thin pulp is formed2 this is run into a receiver1 in which is a stirrer4 ,the white lead is not completely prevented from sinking by the stirrer2 a soft mud is deposited at the bottom of the vessel1 which can only be stirred up with difficulty on account of its high density4 ,when this vessel is full1 the stirrer is stopped and the milky liquid allowed to settle1 which happens in a short time on account of the high specific gravity of white lead4 ,the clear liquid above the white lead is drawn off into a tank lined with cement4 ,it is advisable to arrange the stirrer so that it may be placed at any height in the vessel2 if this is the case1 by gradually lowering the stirrer whilst in motion1 the white lead lying at the bottom can be mixed up with fresh water4 ,these operations are repeated until all the lead acetate is removed4 ,soda solution is added to the wash waters in order to recover the lead dissolved in them as lead acetate2 lead carbonate is precipitated and settles at the bottom of the tank4 ,this precipitation may also be effected by putting lumps of limestone in the tank4 ,the paste remaining in the washing tubs1 which now contains only pure white lead and water1 is filled into bags of closely woven material and the water pressed out by a gradually increasing pressure1 until a stiff pulp remains behind4 ,this is then completely dried1 either in the air or in drying stoves4 ,soft white lead forms either irregular lumps or a soft1 heavy powder4 ,the lower qualities of white lead contain a smaller or larger quantity of finely ground barytes2 the higher the proportion of barytes the smaller is the covering power of the mixture4 ,a very simple method for detecting barytes in white lead will be given later4 7b7 ,,german ,,process4 ,the ,german or ,austrian method of making white lead is also known as the chamber process1 since the formation takes place in closed chambers1 constructed of wood or masonry4 ,in the older processes1 cast lead sheets were bent double and hung on cross bars in a wooden box with a water-tight bottom1 with the precaution that the plates did not touch4 ,a number of these boxes1 generally #ij1 were arranged in a hot room1 each box being about #af metre long1 #jd metre wide and #jc metre high4 ,on the bottom of each box was poured a mixture of vinegar or dilute acetic acid and wine refuse1 and the box was covered with a well-fitting lid4 ,the temperature of the room was gradually raised week by week2 during the first week remaining at #be ,c41 during the second at #ch ,c41 the third at #de ,c4 ,at the commencement of the fourth week the temperature was raised to #ej ,c41 at which it was kept for a fortnight4 ,at this high temperature a considerable quantity of acetic acid is evaporated1 causing the formation of lead acetate1 which is converted1 by the carbonic acid evolved from the wine refuse1 into basic lead carbonate4 ,when the proper temperatures have been maintained1 on opening the boxes almost all the lead is found changed into white lead1 which is knocked off1 and the residual lead used in casting new plates4 ,it is easy to conceive that the boxes may be well replaced by brick chambers1 in which a large number of lead plates are brought and into which acetic acid vapours and carbonic acid are introduced after the room has been closed4 ,chambers are used which can contain #ab1jjj to #ab1ejj kilogrammes of lead4 ,these chambers1 in which the lead plates are hung upon wooden supports1 have an opening immediately above the bottom1 which is connected with a retort in which vinegar1 containing #d to #e per cent4 of acetic acid1 is boiled4 ,after about #ab hours1 by the simultaneous action of the vapours of acetic acid and the oxygen of the air1 lead acetate is formed4 ,carbonic acid is now led into the chambers4 ,the carbonic acid is obtained by burning charcoal in a cylindrical furnace2 it is cooled by being passed through a long iron tube before it enters the chamber4 ,for #ab1ejj kilogrammes of lead there are required every day about #dhb litres of dilute acetic acid1 obtained by mixing strong acetic acid with water until the mixture contains #de per cent4 of the acid1 and #ah kilogrammes of charcoal1 from which the carbonic acid is obtained4 ,the time required is #e or #f weeks1 and the residue of unaltered lead varies from #aj to #ce per cent4 ,the white lead obtained by this process is quite usable1 but the process has the considerable disadvantage that there is no control over the quantities of materials used4 ,in order to produce a certain quantity of white lead of a certain composition1 definite quantities of lead1 oxygen1 acetic acid and carbonic acid are necessary4 ,if1 then1 the apparatus can be so arranged that the quantities of material employed can be accurately measured1 a great advance will have been made1 for the operation will be no longer conducted at random1 but under definite unchangeable conditions4 ,the quantities of carbonic acid and acetic acid can be calculated beforehand4 ,the volumes of the gases required may be measured without difficulty by meters of the type used for measuring coal gas4 ,upon this principle are based a number of more modern methods4 ,illustration3 ,,fig4 #aa4 ,according to the process of ,major1 the vapours of water and acetic acid are introduced at the same time into the chambers filled with lead plates1 in order to produce basic lead acetate4 ,this part of the process requires about #ab hours4 ,then carbonic acid is introduced2 it is produced by burning charcoal in an iron cylinder1 through which air is forced4 ,by means of this carbonic acid1 which is at a comparatively high temperature1 about #fj ,c41 the lead acetate is quickly changed into white lead4 ,a portion of the lead acetate remains undecomposed2 in order to remove this1 at the close of the operation ammonia is injected1 which decomposes the lead salt4 ,the ammonia salts now present are finally driven out by means of superheated steam4 ,major's apparatus is depicted in ,fig4 #aa4 ,a and ,b are chambers with horizontal gratings upon which the lead lies2 ,c is the furnace for burning the charcoal1 provided with a fan4 ,the products of combustion from ,c pass under the boiler ,d1 their passage being regulated by the valve1 a2 they then heat the boiler ,e1 containing acetic acid1 and enter the chambers1 ,a and ,b1 through the flue1 b1 or are directed by the valve in b into the chimney1 d4 ,the gases1 after passing through the chamber1 find an exit at e4 ,the steam pipe1 f1 conducts steam into the boiler ,e1 through g1 and also into the chambers1 ,a and ,b1 thus heating them and providing the necessary moisture2 h is the funnel for filling ,e2 the pipe1 k1 carries the acetic acid vapours into the chambers4 ,after the thin lead plates have been brought into the chambers they are closed and the temperature raised to #di to #fj ,c41 steam and acetic acid vapours are led in for #aj to #bj hours in order to form the basic acetate1 then the furnace gases are introduced at a temperature of #fj ,c4 ,the white lead obtained in this manner can be finished in the ordinary way by washing and grinding1 but it is better to remove the lead acetate by introducing ammonia1 and then hot air or superheated steam1 as previously stated4 ,illustration3 ,,fig4 #ab4 ,illustration3 ,,fig4 #ac4 ,the process is complete in #b to #d weeks4 ,gartner1 working according to this process with #aej kilogrammes of lead in a chamber #abf metre long1 #jgh metre high and #jgh metre wide1 obtained good white lead in #bh days4 ,the apparatus designed by ,h4 ,kirberg for the manufacture of white lead is illustrated in ,figs4 #ab1 #ac and #ad4 ,the lead plates are hung upon the laths1 a1 in the chambers2 the supports of the laths1 b1 go through the slits1 c1 in the supports1 d1 and project through the walls at e4 ,the carriers1 b1 hang from bolts by brass wire4 ,by striking the end of the laths1 e1 they are made to swing so that the white lead loosely adhering to the lead plates is shaken off and fresh surfaces of metal are exposed4 ,the openings in the walls through which the ends of the laths project are closed by indiarubber4 ,in order to prevent the production of dust when the chambers are emptied1 water is introduced in a fine spray upon the lead plates from the copper tubes1 v1 placed under the roof of the chamber4 ,the water washes off the remains of the white lead from the plates4 ,illustration3 ,,fig4 #ad4 ,in a similar manner1 the white lead process may be carried out in a shorter time when the gases enter the chamber under increased pressure2 but this is attended with difficulties1 since continuous supervision of the apparatus and of the tightness of the chamber is necessary4 ,illustration3 ,,fig4 #ae4 ,the apparatus of ,w4 ,thompson 7,fig4 #ae7 consists of a chamber1 ,a1 constructed with a false roof1 ,b1 to carry off the condensed vapours1 and provided at both sides with doors1 through which the waggons1 carrying the lead1 are introduced and removed4 ,the pipes1 n1 which convey air and carbonic acid1 are provided with branches1 e1 which reach to the sides of the chamber1 and are joined to the perforated tubes1 ,d4 ,the pipes1 n1 are provided with reservoirs1 b1 which prevent the too rapid entry of the air or carbonic acid1 and at the same time give a sufficient heating surface4 ,upon the waggon1 ,e1 are the frames1 v1 which support the lead plates4 ,the plates may be solid or gratings2 they are #c to #ab millimetres thick1 and are arranged at intervals of about #be millimetres in the frames4 ,the troughs1 ,f1 for the reception of the acetic acid are filled from the reservoir1 ,z4 ,the steam pipe1 ,c1 effects the evaporation of the acid2 the steam pipe1 d1 heats the chamber at the commencement of the process1 and also when ,c is out of use4 ,when the chamber is filled with lead1 the troughs1 ,f1 are filled with acetic acid of #e per cent4 strength4 ,the chambers are closed1 and steam is led through ,c and d until the temperature in the chamber reaches #be to #ej ,c41 and the evaporation of the acid begins4 ,then air is forced in under a small pressure through n1 e1 ,d during #c to #d days1 after which follows a mixture of equal parts of carbonic acid and air1 continued until the formation of white lead is complete4 ,when plates #c millimetres thick are used1 and the temperature is gradually raised from #be to #ej ,c41 about #ab days are required2 but if the plates are #ab millimetres thick1 #bh days are necessary4 ,for the proper carrying out of this process it is important that the temperature of the chamber should be very gradually raised from #be to #ej ,c4 ,in the process of ,p4 ,rey molten lead is poured in a thin stream into water1 and the 8granulated0 metal then placed in vessels1 in a layer #cj centimetres thick1 upon a grating #e centimetres above the bottom4 ,in the bottom are narrow tubes which1 reaching above the lead1 serve to admit air4 ,acetic acid is allowed to flow over the lead from vessel to vessel4 ,in order to obtain the proper solution1 a layer of lead1 #b metres thick1 is necessary1 so that #f to #g vessels are arranged1 one above the other4 ,if lead acetate solution be used1 the layer of lead need only be #ab metre thick4 ,the solution of basic lead acetate is then treated with carbonic acid according to the ordinary process4 ,in addition to the modifications of the ,german white lead process which have been described1 many others have been proposed4 ,the principle of many of these methods is1 that finely divided lead is much more rapidly converted into white lead than lead in the form of plates2 finely divided lead exposes an enormously greater surface to the action of the acetic acid and other materials than do lead plates4 ,in ,rostaing's method the lead is changed into very small pellets1 by allowing the melted metal to flow on to a rapidly rotating iron disc2 the molten lead1 in consequence of the centrifugal force due to the rapid rotation1 assumes the form of very small drops1 which are thrown off the disc and cooled in a vessel of cold water4 ,torassa recommends that lead1 obtained in pellets by pouring into cold water1 should be brought into a rapidly rotating vessel1 whereby the greater part will be converted into fine dust 7874 ,this lead dust is said to be then converted into white lead by simple exposure to air1 lead oxide being first formed1 and from it basic lead carbonate4 ,this process is not workable on a large scale4 ,the rapid oxidation of finely divided lead by air has been applied by several inventors to the manufacture of white lead4 ,the processes of ,woods1 ,m',cannel and ,grneberg are founded upon this transformation4 ,in essentials they are as follows3 lead is finely divided in iron or earthenware cylinders1 and either carbonic acid and air1 or a mixture of these with acetic acid vapour1 are introduced by means of the axle of the cylinders4 ,if a special apparatus is not provided1 as it should be1 on the large scale1 to separate the unaltered lead from the white lead1 the lumps coming from the chambers must be subjected to a process of levigation1 in which the lead1 being the heaviest body1 will be first deposited2 the last portions deposited consist of the purest white lead1 the lower layers of which will be tinged more or less grey by an admixture of finely divided lead and lead peroxide4 ,white lead manufactured by the ,german process occasionally exhibits perceptible reddish or greyish tinges1 the cause of which lies in the defective execution of the process4 ,the red tinge denotes the presence of free lead oxide1 caused by the use of an insufficient quantity of acetic acid4 ,a grey tint is due to the presence of metallic lead or an excess of lead carbonate4 7c7 ,,french ,,process4 ,the ,french process for making white lead is based upon the reaction which occurs when carbonic acid is passed into a solution of basic lead acetate2 basic lead carbonate is precipitated and neutral lead acetate remains dissolved2 the latter is again converted into basic acetate1 from which carbonic acid again separates white lead and so on4 ,this process1 at present used on an enormous scale1 is due to the ,french chemist ,thnard1 who first put it into operation on the large scale at ,clichy1 near ,paris4 ,the method is also known as the ,clichy process4 ,the operations of this process are divided into the production of the basic acetate and the treatment of its solution with pure carbonic acid1 whereby the basic carbonate is precipitated4 #a4 ,preparation of the ,solution of ,basic ,lead ,acetate4--,the preparation of this compound has been already described2 the following is supplementary to what was previously given4 ,if litharge be used1 it is dissolved in wooden tubs heated by steam4 ,the acetic acid is brought nearly to boiling by open steam1 and the finely ground litharge gradually added4 ,in consequence of its high specific gravity1 the litharge would quickly sink to the bottom1 so that it is advisable to keep the liquid in motion by means of a stirrer1 and to allow the litharge to fall in in a thin stream4 ,the introduction of the latter is continued until the specific gravity of the solution indicates that the liquid contains three equivalents of lead oxide to one equivalent of acetic acid4 ,in working with metallic lead1 this must be used in a finely divided form2 it is cast1 as in the ,dutch process1 into thin sheets or gratings1 or into flat wires or ribbons4 ,these ribbons are easily made by melting the lead in a pan provided with a delivery pipe with stop cock2 beneath the latter is brought a vessel1 which can be moved backwards and forwards upon a tram line1 filled with water4 ,when the melted lead is allowed to flow into this vessel1 which is being moved backwards and forwards1 the metal forms long1 thin ribbons1 which possess a large surface4 ,a wooden tub is almost completely filled with these lead ribbons1 which are then covered with acetic acid4 ,after a short time the acid is run off1 when1 by the action of the air1 so energetic an oxidation of the lead takes place that the contents of the tub become heated1 and steam and acetic acid vapours begin to rise4 ,when this is seen1 the original acetic acid is pumped back into the tub1 and left there for some hours in contact with the lead in order that it may dissolve the lead oxide4 ,when the solution has reached a specific gravity of #aacbf to #aadae1 it is drawn off from the undissolved lead1 which again1 in a short time1 in consequence of the rapid oxidation1 becomes warm1 and is treated with fresh acetic acid4 ,the lead ribbons become finally so thin that they fall together by their own weight1 and form tight masses1 upon which air and acetic acid can no longer act4 ,these residues are then removed from the solution vessel and new ribbons introduced4 ,the residues have a velvety appearance2 when they are mixed up with water they make it dark1 and from the turbid liquid a fine1 velvet-black powder soon separates1 which consists of finely divided silver4 ,the liquid still remains turbid owing to the suspension of fine particles of carbon4 ,the lead ores1 especially galena1 often contain notable quantities of silver2 silver lead is generally desilverised before use2 usually1 however1 small quantities of silver remain in the lead4 ,when the lead is dissolved in acetic acid1 this silver settles as a soft powder at the bottom of the vessels in which the lead residues from the solution tubs are washed4 #b4 ,preparation of the ,carbonic ,acid and ,precipitation of the ,white ,lead4--,the carbonic acid required for precipitating the basic carbonate is obtained either by heating limestone in a small furnace1 from which the gas is drawn by a pump1 or directly by burning charcoal4 ,in the former case very pure carbonic acid is obtained1 and1 as a by-product1 valuable quicklime2 in the latter case precautions must be taken to produce pure carbonic acid4 ,illustration3 ,,fig4 #af4 ,the furnace designed by ,kindler for preparing carbonic acid 7,fig4 #af7 consists of a conical furnace1 burning coal or coke upon the hearth1 a4 ,the passage1 c1 is divided by a vertical wall1 in order to avoid obstruction from the piling up of fuel4 ,the space1 ,k1 is filled with limestone1 through which the carbonic acid passes2 the tanks1 e1 filled with water1 cool the limestone1 and the gas1 which then passes through the water in the washing vessel1 ,d1 is drawn off by a pump4 ,in the old process at ,clichy the apparatus depicted in ,fig4 #ag was used4 ,the basic lead acetate was made in the wooden tub1 ,a1 provided with the stirrer1 ,b ,c4 ,the solution was run off from this vessel by means of the cock1 b1 into the settling tank1 ,e1 in which the mechanical impurities separated from the solution4 ,the clear liquid ran into the decomposing vessel1 a large shallow covered tank1 holding #i1jjj to #aj1jjj litres4 ,in this tank opened #hjj copper tubes1 given off from the large pipe1 ,s4 ,the small furnace1 ,d1 in which limestone was burnt with coke1 produced the carbonic acid2 from the pipe at the top of the furnace the carbonic acid was brought into the ,archimedean screw1 h ,k1 was washed with water1 and pumped into the solution of lead acetate4 ,the introduction of the carbonic acid was continued from #aj to #ab hours1 after which the apparatus was left at rest until the liquid in the decomposing tank had become quite clear1 through deposition of the white lead4 ,the clear solution1 now containing neutral lead acetate1 was run off into the receiver1 m1 from which the pump1 ,p1 carried it back into the dissolving tub1 ,a1 where it was treated with fresh quantities of litharge4 ,the solution of neutral lead acetate drawn off from the white lead had approximately a specific gravity of #ajija4 ,the white lead at the bottom of the decomposing tank was a tolerably thick paste4 ,it was transferred to the tank1 ,o1 and washed several times with water4 ,the first wash waters1 which contained small quantities of lead acetate1 were returned to the dissolving tub4 ,the resulting white lead formed a very soft powder2 it was at once placed in the drying pans4 ,the white lead prepared by this process is a precipitate containing no coarse lumps1 so that grinding is unnecessary4 ,illustration3 ,,fig4 #ag4 ,theoretically1 the quantity of acetic acid with which the process is commenced is sufficient to form an unlimited quantity of white lead1 since all the acetic acid brought into the decomposing tank in the form of basic acetate is returned to the dissolving tub as neutral acetate4 ,in practice1 however1 matters are somewhat different4 ,small quantities of acetic acid are lost in the wash waters2 each time the solution of lead acetate is pumped back into the dissolving tub1 a small quantity of acetic acid must be added to make up the loss4 ,illustration3 ,,fig4 #ah4 ,the method pursued by ,ozouf1 in ,france1 is a considerable improvement on ,thnard's process4 ,pure carbonic acid is used for the precipitation1 and white lead of similar composition to that produced by the ,dutch process is obtained1 since the introduction of the carbonic acid can be regulated according to the volume and strength of the lead solution1 and thus white lead of any desired composition can be produced4 ,the most elaborate precautions for the health of the work-people are taken4 ,the preparation of pure carbonic acid gas is based upon the absorption of this gas from a mixture of gases by a solution of sodium carbonate1 and its evolution on heating the solution4 ,the apparatus is shown in ,figs4 #ah and #ai4 ,the products of combustion obtained from the stove1 ,a1 are drawn by the air pump1 ,e1 through the pipe1 ,c1 into the cooler1 ,b1 which is regularly fed with cold water by ,d4 ,the gases compressed in the receiver1 ,e1 deposit moisture there1 and then proceed through #c horizontal cylinders1 ,f1 of sheet-iron1 provided with agitators1 in which the carbonic acid is absorbed by a cold solution of sodium carbonate of #i ,b4 ,the unabsorbed gases escape into the atmosphere through ,g 7,fig4 #ai74 ,the sodium bicarbonate solution is received in the wooden tank1 ,h1 after passing through the #c cylinders1 ,f4 ,the pump1 ,i1 of the alternating pump1 ,i ,i1 lifts the sodium bicarbonate solution out of ,h and sends it through the pipe1 ,k1 into the tubular cylinder1 ,j1 which stands upon a cylinder of larger diameter1 ,j1 communicating with it only by the vertical tubes4 ,the bicarbonate solution rises between the tubes in ,j1 passes through the pipe1 ,l1 drops in a fine spray through the rose forming its mouth1 and by means of the vertical tubes passes into ,j and thence into ,m1 where it is heated by means of a steam coil to #ajj ,c4 ,carbonic acid is then evolved1 and the residual solution of neutral sodium carbonate1 after cooling in the vessel1 ,r1 by means of the cold coil1 is drawn off by the pump1 ,i1 again to enter the cylinders1 ,f1 by means of the pipe1 ,k4 ,the carbonic acid evolved in ,m1 together with steam1 enters ,j through ,n1 and in rising in the tubes of the cylinder1 ,j1 is cooled by the falling spray of bicarbonate solution4 ,the cooling is completed in the coil1 ,o1 surrounded by water2 the vessel1 ,p1 separates the condensed water and passes the gas on into the holder1 ,q4 ,the pipe1 ,s1 connecting ,p with the suction pipe of the pump1 ,j1 serves to restore to the solution of sodium carbonate the water it has lost1 thus maintaining the proper concentration4 ,the cost of #a cubic metre of carbonic acid is #aj centimes1 of #a kilogramme #e centimes4 ,illustration3 ,,fig4 #ai4 ,for the production of white lead1 the carbonic acid1 by means of the pipe1 ,u 7,figs4 #ai and #bj71 enters the cylinder1 ,t1 provided with an agitator and containing a solution of basic lead acetate4 ,by means of the pump1 ,v1 the lead solution is fed into the cylinder1 ,t1 through ,w4 ,the absorption of the gas proceeds rapidly2 the progress of the operation is followed by the observation of a pointer moving over a scale2 as the gas holder sinks the pointer moves upwards4 ,after the precipitation of white lead1 the contents of ,t are emptied into the tub1 b1 in which rotate rakes attached to a vertical axis of iron plated with copper4 ,when the white lead has settled1 the supernatant solution of neutral lead acetate is drawn off through the pipe1 c1 by means of the pump1 d1 and conducted into the water-tight vessel1 ,x1 containing a stirrer on the vertical axis1 ,w1 made of coppered steel4 ,here litharge is added1 and the resulting solution of basic lead acetate is conveyed to the cylinders1 ,t1 by means of the pump1 ,v1 as already described4 ,the white lead in the tub1 b1 by putting the stirrer in motion1 is washed once with water which has been previously purified by a little lead acetate4 ,it then goes into another tub provided with stirrers1 where it is several times washed1 sodium carbonate being added to the last wash water until a sample of the white lead is not coloured by a drop of potassium iodide solution4 ,in this way the wash water is obtained free from lead1 and the product is said to be of better quality4 ,this1 however1 is not in accordance with the fact that good ,dutch white lead generally contains some lead acetate4 ,the two-cylinder pump1 h1 which is in connection with the gas holder1 forces gas over the surface of the liquid in ,t in order to drive it into tubs which are not in the position shown for b in the illustration1 and into which there is no direct flow4 ,the washed white lead is brought into bags which are pressed in a hydraulic press1 dried1 ground1 sieved and packed in casks4 ,these troublesome and often dangerous operations have been modified by ,ozouf in the following manner4 ,the pulp white lead runs from the tub1 b1 into the hopper1 g1 where it is kept mixed by a small stirrer1 and from which it passes on to the cylinder1 f1 heated by gas from the inside4 ,in its rotation the cylinder carries along the white lead and dries it1 it is then removed by a knife below the hopper1 and falls on to an inclined plane4 ,the hopper and cylinder are in a room provided with a good draught4 ,illustration3 ,,fig4 #bj4 ,the lumps coming from the drying room are placed by workmen wearing respirators in buckets on an endless chain1 are carried to the mills1 ground and sieved2 then1 by means of an ,archimedean screw1 the white lead is conveyed to a cask in which it is evenly pressed by means of a special mechanism4 ,a bell announces when a cask is full4 ,manufacture of ,white ,lead by means of ,natural ,carbonic ,acid4--,in districts where currents of carbonic acid gas issue from the ground1 they can be used in the manufacture of white lead1 and are actually utilised for this purpose4 ,natural carbonic acid may1 of course1 be used for any of the white lead processes4 7d7 ,,english ,,process4 ,in this process1 now no longer in use1 white lead was obtained by mixing litharge to a stiff paste with a weak solution of lead acetate and exposing the paste to the action of carbonic acid4 ,by continually kneading the mass by means of grooved rollers or of rotating cylinders1 through the hollow axis of which carbonic acid was led1 the paste was thoroughly brought into contact with the carbonic acid4 ,by this process a good product is only obtained when pure litharge1 entirely free from the oxides of iron and copper1 is used4 ,the copper oxide may be removed from the litharge by means of ammonia if this can be obtained at a low price2 but oxide of iron cannot be removed1 and very small quantities of it are sufficient to impart a yellow tinge to the white lead4 7e7 ,,other ,,methods4 ,in ,payen's process the lead sulphate obtained in considerable quantities as a by-product in calico printing is the raw material employed4 ,by treating this lead sulphate with a solution of ammonium or sodium carbonate1 white lead and ammonium or sodium sulphate are produced4 ,the white lead is then freed from the soluble salts by washing1 mixed with a small quantity of lead acetate1 and pressed into the drying moulds4 ,by boiling lead sulphate with caustic soda and passing in carbonic acid 7,puissant's process71 a white lead is obtained which differs considerably in composition from ordinary white lead4 ,many methods have been proposed with the object of converting insoluble lead salts1 obtained as by-products or by an inexpensive process1 by treatment with alkaline or alkaline earth carbonates1 into white lead4 ,the fact that none of these methods has obtained a permanent footing in the industry shows that each must be accompanied by serious defects1 or can only be practicable under peculiar conditions4 ,magnesium carbonate is used in ,pattison's process to decompose lead chloride4 ,dolomite 7magnesian limestone7 is the raw material for the magnesium carbonate4 ,coarsely powdered1 it is heated at a low red heat1 when magnesia is formed1 the calcium carbonate remaining almost entirely unaltered1 since it requires nearly a white heat for its decomposition4 ,the powder ground in water was1 when treated with carbonic acid under a high pressure1 soluble1 magnesium bicarbonate being formed1 the saturated solution of which contains #bc per cent4 of magnesia1 and has a specific gravity of #ajbh4 ,the solution of lead chloride contains #a part of the salt in #abf parts of water2 it is mixed with a slight excess of the magnesium carbonate solution as quickly as possible4 ,the liquid is drawn off from the mixing vessel into a large receiver in which a precipitate deposits1 consisting of white lead and a little oxychloride4 ,after drying1 the precipitate is ground with a small quantity of caustic soda to decompose the oxychloride4 ,a few days afterwards the mass is washed to remove sodium chloride and the product dried4 ,the process of ,dale and ,milner is similar to the above magnesia process4 ,litharge1 lead hydroxide or insoluble lead salts are mixed with sodium bicarbonate solution1 and1 with repeated additions of water1 ground until the formation of white lead is completed4 ,the lead compound and sodium bicarbonate are used in equivalent proportions4 ,according to the process of ,p4 ,bronner 7,german patent #eb1bfb71 #c molecules of freshly precipitated lead sulphate are heated with a solution of #b molecules of caustic soda1 when the basic sulphate #b ,pb,s,o4,pb7,,oh7 is formed according to the equation-- #c ,pb,s,o #b ,na,o,h #b ,pb,s,o4,pb7,,oh7 ,na,,so4 ,or #d molecules of lead sulphate are decomposed by #b molecules of caustic soda1 according to the equation-- #d ,pb,s,o #b ,na,o,h #c ,pb,s,o4,pb7,,oh7 ,na,,so4 ,this transformation takes place at a temperature of #gj ,c4 ,the resulting basic sulphate1 although pure white1 cannot be used as a pigment on account of its lack of covering power2 but by heating with a solution of sodium carbonate it is converted into white lead4 #b ,pb,s,o4,pb7,,oh7 #b ,na,,co #b ,pb,c,o4,pb7,,oh7 #b ,na,,so4 #c ,pb,s,o4,pb7,,oh7 #c ,na,,co #c ,pb,c,o4,pb7,,oh7 #c ,na,,so4 ,by this process1 which is harmless to the workmen1 the lead sulphate obtained as a by-product in the preparation of mordants for calico printing1 can be converted into good saleable white lead4 ,the lead sulphate may also be obtained from litharge1 lead acetate or nitrate4 ,it occasionally happens that white lead has a rose tint1 which is clearly perceptible by comparison with a pure white sample4 ,this colouration occurs in white lead made from argentiferous lead4 ,a very small quantity of silver is sufficient to produce the tinge of colour4 ,occasionally white lead which has been ground in oil and used for painting turns perceptibly yellow1 the colouration being similar to that observed on a surface painted with white lead from which light is almost excluded4 ,the yellow colouration is due to lead oxide4 ,this has been proved by suspending such a white lead in water and treating it with carbonic acid1 after which a surface painted with it remains permanently white4 7f7 ,,oxychloride ,,white ,,lead4 ,under the name of white lead1 but differing from it in composition1 various products are found which consist of lead oxychloride4 ,this compound is also known as ,pattison's white lead4 ,pattison's white lead can be much more cheaply manufactured than real white lead1 the raw material employed being the cheap galena4 ,the finely-powdered mineral is boiled with strong hydrochloric acid in closed lead vessels4 ,sulphuretted hydrogen is evolved1 which may be burnt to sulphur dioxide and so used to make sulphuric acid4 ,a hot saturated solution of lead chloride remains1 from which the salt separates in small crystals on cooling4 ,the crystals are drained in a basket and washed with cold water to remove the acid4 ,the pure lead chloride is then dissolved in hot water and mixed with lime water4 ,pattison obtained lime water from dolomite by burning it1 treating with a little water to remove the easily soluble salts1 and1 after the removal of this wash water1 treating the residue repeatedly with water in order to obtain a clear solution of pure hydrate of lime4 ,when pure limestone is used1 it may be treated with water immediately after burning without any preliminary preparation4 ,two equivalents of lead chloride are used to one equivalent of calcium hydroxide4 ,practical experience showed that the best product was obtained when the precipitation was very rapidly brought about4 ,with this object1 both solutions entered the precipitation tanks through pipes with narrow slits at the side1 so that the liquids met in a thin layer1 in which the precipitation of the pigment was instantaneous4 ,it is also necessary that lead chloride should be in excess throughout4 ,the liquid is allowed to stand for the precipitate to settle1 which it does in a brief time on account of its high specific gravity4 ,the solution now contains the small excess of lead chloride in addition to calcium chloride2 lime water is added until the liquid turns red litmus paper blue4 ,from the alkaline solution all the lead soon separates as lead hydroxide1 which is dissolved in hydrochloric acid1 and thus again comes into the process4 ,in order to utilise the large quantities of hydrochloric acid obtained in the manufacture of soda1 ,percy described a process in which galena is ground with hydrochloric acid1 whereby in #cj to #dj hours all the lead is converted into lead chloride1 whilst the stony admixtures are unattacked4 ,the lead chloride is then separated by levigation from the undissolved minerals and washed until free from iron1 when it is dissolved in hot water and converted into oxychloride by means of lime water4 ,lead ,sulphite1 ,pb,s,o1 can be obtained by passing sulphur dioxide into a solution of basic lead acetate2 lead sulphite is precipitated and a solution of neutral lead acetate remains4 ,the process is similar to the ,french white lead process1 with the difference that sulphur dioxide is used instead of carbon dioxide4 ,lead sulphite has no advantages over white lead1 and is more expensive2 it has thus never found practical application4 ,lewis and ,bartlett's ,white ,lead ,pigment4--,in the lead works at ,zoplin1 in ,missouri1 galena is smelted with limestone and coal1 lead fume being obtained in addition to metallic lead4 ,the lead fume deposits are ignited1 and again worked for lead and lead fume4 ,this last lead fume can at once be used as a white pigment2 it consists principally of lead sulphate1 lead oxide and zinc oxide4 ,,white ,,lead-,,antimony ,,pigments4 ,lead antimonite and antimonate are both heavy1 white powders which can be used as pigments4 ,they are dearer than white lead1 to which they are inferior in covering power1 and which they do not exceed in permanence4 ,lead ,antimonite is obtained by heating #e parts of finely powdered antimony with #bj parts of sulphuric acid until a dry1 white mass of antimony sulphate is left4 ,this is fused with soda ash1 the melt is extracted with water1 and lead antimonite obtained by precipitating with lead acetate4 ,lead ,antimonate is formed by introducing in small quantities at a time a mixture of #a part of finely powdered stibnite 7antimony trisulphide7 with #e parts of sodium nitrate into a red-hot crucible1 boiling the mass with water and precipitating the solution with lead acetate4 ,,chapter ,,viii4 ,,enamel ,,white4 ,barium sulphate1 known as permanent white1 enamel white1 blanc fixe1 barytes white1 is the only white pigment which is absolutely unaltered by exposure to the atmosphere4 ,lead pigments are discoloured in the course of time1 and in the end turn black2 bismuth white behaves in the same manner2 zinc white is much more lasting1 but not quite permanent4 ,enamel white is really permanent2 it deserves the greatest attention from the colour manufacturer1 especially as it can be made by a very simple and cheap method4 ,when sulphuric acid or a soluble sulphate is added to the solution of a barium salt1 all the barium is at once precipitated in the form of barium sulphate4 ,when quite pure1 barium sulphate forms an extremely soft1 brilliantly white powder1 which offers complete resistance to the action of the atmosphere1 and also of strong acids and alkalis4 ,it is extremely insoluble1 and can be precipitated from the most dilute solutions1 and is then obtained in so fine a state of division that it cannot be filtered from the liquid2 it passes through the closest filter together with the liquid4 ,when the barium solution is heated to boiling before precipitation1 the precipitate is somewhat coarser1 and can be filtered off without difficulty4 ,barium sulphate occurs ready formed in nature as the mineral barytes or heavy spar4 ,finely ground barytes may be used alone as a pigment1 but more commonly is used for reducing white lead1 for which purpose it is particularly applicable on account of its high specific gravity4 ,this admixture must be regarded as diminishing the quality of the pigment1 because ground barytes has far less covering power than white lead4 ,artificial barium sulphate is in a state of division which cannot be reached by grinding barytes1 consequently it considerably surpasses the latter in covering power4 ,the raw material for the manufacture of enamel white is either barytes or witherite 7barium carbonate72 the latter1 however1 occurs so rarely1 in comparison with barytes1 that the greater quantity of all barium compounds is obtained from barytes4 ,if witherite is obtainable in large quantity1 enamel white can be prepared from it by dissolving in hydrochloric acid and precipitating the solution of barium chloride so obtained by sulphuric acid4 ,if the witherite is very pure1 the process may be simplified by treating the mineral directly with sulphuric acid1 and separating the enamel white by a process of levigation from the impurities4 ,in this case it is1 however1 necessary to add a small quantity of hydrochloric acid to the sulphuric acid1 for the latter forms on the surface of the witherite1 at the commencement of the reaction1 a thin layer of barium sulphate1 which is quite sufficient to prevent the further action of the acid on the witherite lying below4 ,the hydrochloric acid forms barium chloride1 which is at once decomposed by the sulphuric acid into barium sulphate and free hydrochloric acid2 this again dissolves a fresh quantity of witherite1 and this process is repeated until the mineral is completely and quickly dissolved4 ,enamel white is1 however1 generally prepared from barytes1 which is ground into a very fine powder and converted into barium sulphide by heating with coal 7see pages #da and #db74 ,hydrochloric acid acting on the sulphide produces barium chloride and sulphuretted hydrogen4 ,the covering power of a pigment is greater the finer its state of division1 so that it would appear advisable to precipitate a weak solution of barium chloride by sulphuric acid at the ordinary temperature4 ,when the barium sulphate has been completely precipitated1 a solution of pure hydrochloric acid remains1 which ought to be utilised2 but when very dilute barium chloride solution is used1 the hydrochloric acid is so dilute as to be useless4 ,the barium chloride is1 therefore1 given in practice such a strength that it has a specific gravity of about #aaih2 when the barium sulphate has been precipitated from this solution the residual hydrochloric acid has a specific gravity of #ajdc4 ,water of considerable purity must be used to dissolve the barium chloride4 ,experience has shown that water which contains appreciable quantities of organic matter does not give a pure white product4 ,the presence of sulphate of lime in the water1 which precipitates barium sulphate1 need not be regarded1 because the barium sulphate is so finely divided that it remains suspended in the liquid1 and is carried down on precipitation of the enamel white by sulphuric acid4 ,carbonate of lime in the water causes the separation of barium carbonate2 this may be avoided by slightly acidifying the barium chloride solution1 thus converting the calcium carbonate into chloride4 ,according to ,c4 ,a4 ,f4 ,meissner1 artificial barytes1 suitable for use in oil paints1 is obtained by precipitating barium salts by soluble sulphates in place of sulphuric acid1 then quickly heating the washed and dried precipitate in a muffle to a red heat and throwing into cold water4 ,as has been already stated1 enamel white is the most permanent pigment that exists2 it appears destined in course of time to replace white lead and all other white pigments1 especially as its cost is generally lower than that of the other white pigments4 ,it costs1 for example1 only half as much as white lead4 ,at present1 the principal uses of enamel white are found in paper staining2 it is not used to any extent in oil paints4 ,on account of its permanence1 it should be used in the place of white lead and white zinc4 ,it also appears particularly suitable for obtaining pale shades2 it can be mixed with any other pigment in any quantity without altering it in the least4 ,this is1 of course1 only true when the enamel white is completely pure1 and when it has been freed from every trace of hydrochloric acid by careful washing4 ,,lithopone4 ,a white pigment is obtained1 according to ,orr's process1 by lixiviating crude barium sulphide1 obtained by igniting barytes with coal1 with water and dividing the solution into two parts4 ,zinc chloride is added to the first portion1 then zinc sulphate1 and finally the second portion of barium sulphide solution4 ,the white precipitate obtained by this process contains one equivalent of barium sulphate to two equivalents of zinc sulphide4 ,it is collected1 quickly dried1 heated in retorts to redness1 and1 whilst still hot1 thrown into cold water1 by which its density and therefore covering power are increased4 ,the pigment is finally washed and ground4 ,it is a good white1 but when mixed with lead pigments discolours them by reason of the sulphide it contains4 ,,chapter ,,ix4 ,,washing ,,apparatus4 ,in all colour works operating on a large scale1 special apparatus is used1 in which are carried out the washing1 pressing and drying of the pigments obtained as precipitates4 ,only pigments prepared in small quantities are filtered through filter paper4 ,the treatment of enamel white and white lead requires the use of apparatus for this purpose in a special degree4 ,we insert a short description here4 ,the preparation of enamel white takes place most conveniently in tubs provided with a stirring apparatus4 ,when the precipitate of barium sulphate has once settled to the bottom1 it is very difficult to again mix it up with water by means of a hand stirrer1 an operation which must be often performed in washing4 ,if vessels be used provided with a suitable mechanical stirrer1 the precipitates are rapidly and thoroughly washed4 ,we have already stated that vessels with a stirrer capable of being raised out of the liquid were specially suitable for washing white lead4 ,such an arrangement can with advantage be used in washing all precipitates4 ,many of the mineral pigments have to be freed from admixed salts by washing4 ,a description follows of an effective washing apparatus with movable stirrer4 ,in the cylindrical vessel 7,fig4 #ba71 which may be of any size1 is a vertical iron shaft rotating upon a pin in the bottom of the vessel4 ,on this axis is a horizontal wooden crosspiece1 the under surface of which is studded with brushes2 the disc1 which this crosspiece carries1 is united by means of two bars with a second1 in which is cut a screw moving on the screwed shaft4 ,the shaft is rotated by means of the cog-wheels shown in the illustration4 ,the handle fastened to the upper disc enables the crosspiece carrying the brushes to be raised or lowered4 ,when the handle is held fast1 this crosspiece rises or falls according to the direction of rotation of the axis4 ,the pipe shown at the side supplies the water for washing the precipitates4 ,illustration3 ,,fig4 #ba4 ,in the preparation of colours liquids have often to be brought into the precipitating vessel which would attack the iron of the stirring apparatus1 so that it is advisable to make the connecting rods between the two discs of such a length that the screws may be above the vessel4 ,all iron parts of the apparatus dipping into the liquid should be protected by asphaltum varnish4 ,when a specially heavy precipitate is to be washed1 such as enamel white1 chrome yellow or white lead1 the stirrer is raised as high as possible before the commencement of the operation4 ,when the precipitate has formed and settled1 the liquid is run off1 the water tap opened1 and the stirrer slowly brought down to the precipitate2 the brushes fastened to the crosspiece stir up first the top of the precipitate1 then the next portions1 and so on until the whole of the precipitate has been stirred up into the liquid4 ,when this has been accomplished1 the stirrer is kept going for some time1 so that the water may take up as much of the soluble materials as possible2 it is then raised out of the vessel1 in which the precipitate again settles4 ,as a rule1 two or three washings of permanent white1 in an apparatus of the construction described1 are sufficient to render it quite free from acid4 ,washing must be continued until the wash water leaves blue litmus paper quite unchanged4 ,when dry1 precipitated barium sulphate is a very soft powder of great whiteness1 which1 on account of the fineness of its particles1 can be readily ground with binding materials4 ,enamel white loses1 in a remarkable manner when completely dry1 a great portion of its covering power and of its valuable property of being easily ground with oil or size to a homogeneous paste4 ,it is not known whether this alteration is caused by a molecular change of the barium sulphate1 as is not altogether improbable4 ,in order to preserve the valuable properties of enamel white it is not1 as a rule1 completely dried1 but is brought into the market in the form of pulp1 which is obtained by bringing the washed precipitate into strong linen bags and allowing the water to drop through4 ,this object is more quickly accomplished when the last wash water is drawn off only to such a point that1 when the precipitate is again mixed up by means of the stirrer1 a thin paste is formed4 ,this paste is run into a centrifugal machine1 of which ,fig4 #bb is an illustration4 ,in the drum1 ,b1 provided with an outflow1 ,r1 the smaller removable drum1 ,c1 with perforated walls1 is caused to rotate by gearing1 ,g1 to which it is attached by the screw1 ,v4 ,the drum1 ,c1 is lined by a tight linen bag4 ,illustration3 ,,fig4 #bb4 ,when the drum is in rapid motion1 the thick liquid in the washing vessel is run in4 ,in consequence of the centrifugal force due to the rapid rotation1 the whole mass is at once thrown on the sides of the drum1 the liquid penetrates the fine openings1 is caught in the outer vessel1 and runs away to a receiver1 in which it is kept until the finest particles of the precipitate1 which will penetrate even the closest fabric1 have settled4 ,the operation is continued until the excess of water has been separated1 when the bag containing the precipitate is lifted out of the drum4 ,centrifugalised enamel white is a fairly stiff1 white paste1 which should be packed in sacks lined with oiled paper to prevent drying4 ,illustration3 ,,fig4 #bc4 ,,filter ,,presses4 ,in recent years the use of filter presses for separating liquids from precipitates and for washing the latter has become general4 ,a filter press consists1 as shown in ,fig4 #bc1 of a number of frames1 between which are perforated plates and sheets of filter cloth1 and which can be pressed tight together by a screw4 ,a powerful pump forces the liquid containing the precipitate into the hollow spaces of the frames 7known as chambers71 in which the solid body remains1 whilst the liquid goes through the filter cloth4 ,by afterwards pumping fresh water through1 the solid remaining in the chambers is soon completely washed4 ,,chapter ,x4 ,,zinc ,,white4 ,zinc oxide1 known as a pigment under the name of zinc white1 is one of the most important white pigments4 ,although not absolutely permanent1 yet it has1 in common with enamel white1 the valuable property of preserving its whiteness in air containing sulphuretted hydrogen4 ,its low price has brought it into general use4 ,although zinc white is a most important pigment1 it is very seldom made in colour works1 because on account of its origin it is a product of metallurgical processes4 ,zinc white in chemical composition is pure zinc oxide2 it is formed when zinc vapour burns in air4 ,in zinc-smelting works zinc white is obtained by putting zinc in tubes which are heated to whiteness2 the zinc vapours burn when they come in contact with the air1 and the zinc oxide is caught by special arrangements4 ,the retorts used for this purpose are similar to those employed in the manufacture of coal gas4 ,from #h to #ah of these retorts are arranged in a furnace1 in two rows1 one above the other4 ,in the lid of the retorts is an opening1 which serves for charging and for carrying off the zinc vapours4 ,when the operation is commenced1 the retorts being heated to a white heat1 two zinc plates are brought into each1 the metal is soon volatilised1 and the vapours pass through the above-mentioned openings4 ,a current of air1 heated to #cjj ,c41 is blown in to meet the zinc vapours1 which take fire and burn with a blinding white flame1 producing a very fine white powder1 which is carried by the current of air through a series of chambers in which it deposits4 ,illustration3 ,,fig4 #bd4 ,c4 ,freitag recommends for the production of zinc white the use of retorts of oval section1 ,a1 ,fig4 #bd4 ,these retorts1 containing crude zinc1 are heated to a white heat1 and then a mixture of generator gas from coke and air is introduced by ,b and the pipe running through ,b4 ,the zinc burns completely in the flame of the generator gas1 which contains excess of oxygen4 ,a product of faultless nature is said to be obtained in this way4 ,in zinc works zinc white is always made in the manner which has been described4 ,it may also be obtained as a by-product in another metallurgical operation1 the desilverisation of lead by ,parkes' process4 ,in this process an alloy of silver and zinc is obtained4 ,by sending a current of superheated steam over the molten alloy the zinc decomposes the steam1 hydrogen and zinc oxide being formed4 ,the zinc white is carried by the current of gas into chambers1 in which it deposits4 ,the zinc white obtained by burning zinc is1 as has been said1 a very fine pure white powder1 which can at once be used for paint without further preparation4 ,the price of zinc white is rather higher than that of white lead1 but the difference is counterbalanced by the greater covering power of the zinc white4 ,ten parts by weight of zinc white completely cover a surface for which #ac parts of white lead are required4 ,whilst white lead cannot be mixed with many pigments1 such as those which contain sulphur1 zinc white may be mixed with all without fear of alteration4 ,zinc white is even better than enamel white for producing pale pigments from lakes2 it has a lower specific gravity than enamel white1 so that the mixture with the light lake can be more easily made4 ,zinc grey1 which is produced by some works1 is zinc oxide discoloured by metallic zinc4 ,pure zinc white always has a pure white colour2 if it is tinged with grey it is contaminated by metallic zinc1 whilst a brownish hue denotes the presence of cadmium oxide4 ,the latter impurity will be rarely met with in commercial samples1 since cadmium is worth much more than zinc4 ,zinc oxide is used by the colour maker in the preparation of ,rinmann's green2 it is also used1 as stated above1 as an addition to other pigments4 ,griffith's ,zinc ,white4--,this pigment1 which is equal in covering power to white lead1 consists of zinc oxysulphide4 ,it is obtained by precipitating a zinc solution with a solution of barium sulphide1 washing1 drying1 igniting and grinding the precipitate4 ,as it contains sulphur1 it should not be mixed with copper or lead pigments4 ,tungsten ,white 7,lead ,tungstate71 ,pb,w,o1 is obtained as a heavy powder by precipitating a solution of sodium tungstate with lead acetate and treating the precipitate1 which consists of basic lead tungstate1 with dilute acetic acid1 by which lead oxide is dissolved and a salt of the above composition left4 ,this white pigment is dearer than other lead pigments1 and has no special advantages over them2 it is1 therefore1 seldom used4 ,,white ,,antimony ,,pigments4 ,antimony forms a number of white compounds which can be made by a simple and inexpensive process1 and might1 therefore1 be used as pigments4 ,two antimony compounds in particular are so used--antimony trioxide and oxychloride 7powder of algaroth74 ,antimony ,trioxide occurs ready formed in nature as white antimony or antimony bloom4 ,it is very simply prepared by burning the metal in air1 when it forms soft needles with a silvery lustre4 ,it is only necessary to heat melted antimony to a little above its melting point in a crucible placed in a slanting position1 when the metal takes fire and burns with a blue flame4 ,nitric acid converts metallic antimony very quickly into antimony oxide with a copious evolution of brown fumes4 ,antimony trioxide may be more cheaply prepared from antimony sulphide1 artificial or natural 7stibnite71 by finely powdering1 moistening with water1 and gently warming on plates4 ,oxidation takes place1 the sulphur is converted into sulphur dioxide and the antimony to trioxide4 ,the heating should not be carried too far1 or the antimony takes up further oxygen and forms the tetroxide4 ,antimony ,oxychloride1 or ,powder of ,algaroth1 is obtained by dissolving stibnite in strong hydrochloric acid1 the operation being performed under a chimney to carry off the sulphuretted hydrogen4 ,the solution of antimony trichloride1 when the impurities have settled1 is poured into a large vessel of water4 ,at once a pure white precipitate is formed1 which quickly sinks2 it is washed with water until the washings have no acid reaction4 ,washing should not be continued too long or the oxychloride will be further decomposed2 by washing with hot water it is almost entirely changed to antimony trioxide4 ,the precipitate1 after washing with cold water1 has generally the composition expressed by the formula ,sb,o,cl4 ,antimony oxide and oxychloride are both very crystalline powders1 and have in consequence small covering power4 ,bismuth ,white is not used as a painters' pigment2 it has no advantage over the white pigments previously described1 and is much more expensive4 ,its only use as a pigment is for the preparation of white cosmetics1 and even for this purpose zinc white is now frequently used2 it is cheaper and quite as satisfactory4 ,bismuth white is prepared by treating metallic bismuth with fuming nitric acid4 ,the white precipitate at first formed completely dissolves in an excess of acid1 and when the solution is poured into a large quantity of water1 basic bismuth nitrate--bismuth white--separates4 ,pure bismuth white is a soft1 heavy powder1 brilliantly white2 it must be preserved in air-tight vessels as soon as it is dry1 otherwise it acquires a yellowish tinge4 ,bismuth compounds are1 if possible1 more susceptible to the action of sulphuretted hydrogen than lead compounds4 ,the yellow colouration1 turning to black in the course of time1 is due to black bismuth sulphide4 ,tin ,white is used for earthenware enamels4 ,it is obtained by treating granulated metallic tin with very strong fuming nitric acid4 ,the heavy1 white powder which is formed is separated from the undissolved tin by floating4 ,tin white has no application as a pigment2 when mixed with glazes it gives them a handsome1 milky appearance4 ,manganese ,white4--,when large quantities of a solution of impure manganese chloride are at hand1 such as are produced in the preparation of chlorine1 manganese carbonate may be obtained4 ,a small quantity of soda solution is first added and the liquid left for several days so that the oxide of iron may separate4 ,when this is the case an addition of soda gives a pure white precipitate4 ,magnesia ,white or ,mineral ,white is obtained1 according to ,t4 ,h4 ,cobley1 by mixing a solution of magnesium sulphate with calcium chloride1 adding #aj per cent4 of aluminium chloride to the mixture and stirring in slaked lime so long as a precipitate is formed4 ,a cheaper process is to precipitate mixed solutions of magnesium and aluminium sulphates by slaked lime4 ,annaline4--,a white pigment is recommended for use under this name2 it consists of dead-burnt gypsum1 which has been converted into a fine powder by grinding and levigating4 7,dead-burnt gypsum has been so strongly heated that it is not able to again unite with water47 ,to obtain paler shades of certain colours1 additions are made of natural pigments1 such as chalk1 which has been converted into a very fine powder by levigation4 ,an addition of chalk to a heavy mineral pigment1 such as chrome yellow1 is not advisable2 it would1 besides1 seriously diminish its covering power4 99 99 99 99 99 ,in the preceding pages1 a large number of white pigments has been enumerated4 ,it would be easily possible to increase the list1 but the result would be of no practical interest1 for other pigments1 neither in respect of quality nor price1 can compete with the cheaper white pigments4 ,although white lead has at the present time an enormous use1 it is to be hoped that this pigment1 of good colour but little permanence1 may be replaced entirely in the course of time by zinc white1 and for some purposes by enamel white4 ,white pigments1 in addition to their use alone1 are employed to produce tints1 which are obtained by mixing deeper colours with the white pigment4 ,by adding the proper quantity of white to a colour it is possible to produce all paler shades of that colour4 ,for example1 the different varieties of the red lakes which are found in commerce are obtained by mixing white pigments with the deep red lakes4 ,the particular white pigment to be employed in these mixtures depends on the nature of the colour and on its specific gravity4 ,it should always be remembered that white lead will not increase the permanence of a colour1 since it will be discoloured in a short time by the action of the atmosphere4 ,in the manufacture of fine colours for artists lead pigments should be absolutely excluded4 ,to produce paler shades of colours which contain lead and therefore have a high specific gravity1 e4g41 chrome yellow1 white lead may be used2 for other colours1 barytes or zinc white should be employed4 ,in the case of lakes enamel white is too heavy2 zinc white or magnesia is suitable4 ,,chapter ,,xi4 ,,yellow ,,mineral ,,pigments4 ,as was the case with white pigments1 so with yellow3 of the large number known very few are in extensive use4 ,in former times the number of yellow pigments employed in painting was far greater than at present2 several1 formerly in general use1 have dropped out1 partially or entirely1 owing either to their poisonous character or to their replacement by others1 deeper and more handsome4 ,especially since the discovery of cadmium yellow and the development of the manufacture of chrome yellows1 many colours once in general use have properly fallen into disuse4 ,again1 unfortunately1 the most important of the yellow mineral pigments contain lead1 and have little stability2 but a series of yellow colours free from lead is known1 and though some of them are inferior in shade to the lead pigments they surpass the latter in permanence4 ,in addition to lead compounds1 pigments derived from barium1 zinc1 antimony and cadmium are in general use4 ,the yellow lead pigments were formerly preferred1 and at present1 so far as concerns beauty1 they must be regarded as superior to other mineral yellows4 ,the endeavour to provide the artist with permanent colours has resulted in the use of others1 perhaps less brilliant1 but very lasting4 ,under the name of chrome yellow a single pigment consisting of lead chromate was formerly understood2 to-day1 under this title is comprised a series of pigments containing zinc or barium in place of lead1 but all commercially known as chrome yellow4 ,,chapter ,,xii4 ,,chrome ,,yellows4 ,the chrome yellows are the lead1 zinc or barium salts of chromic acid4 ,in describing the different methods used in making these colours1 lead chrome yellow will be taken first1 since this is the one most largely used4 ,,lead ,,chrome ,,yellow4 ,both neutral and basic lead salts of chromic acid are known4 ,neutral lead chromate is found in nature as the somewhat rare mineral crocoisite1 which is found in very small but perfectly shaped crystals in many lead mines4 ,neutral ,lead ,chromate1 ,pb,cr,o1 is formed as a very heavy precipitate of a fine deep yellow colour when a solution of potassium chromate or bichromate is added to a solution of a lead salt in water4 ,when exactly equivalent quantities of potassium chromate and lead solution are used1 and the strength of the solutions is the same1 the product has the same shade each time the operation is performed4 ,it is not immaterial whether the one or the other salt is in excess1 or whether strong or weak solutions are used2 all these conditions modify the shade of the chrome yellow produced4 ,many colour makers are apparently of the opinion that some particular skill of the workman is necessary to produce chrome yellow of a particular shade4 ,this is1 however1 not the case2 manufacturers who know the simple conditions which are important in making chrome yellows may produce any desired shade without difficulty4 ,neutral lead chromate readily parts with half the chromic acid it contains4 ,when treated with alkalis1 such as lime or caustic soda1 or even when digested with finely ground litharge1 the neutral salt gives up half of its chromic acid1 and is converted into the basic chromate or chrome red1 ,pb,cr,o4 ,basic lead chromate has1 as the name chrome red indicates1 a fine red colour4 ,if the quantity of lime or caustic soda used is sufficient to decompose only a portion of the neutral lead chromate1 a mixture of the yellow neutral and the red basic chromate is formed1 the shade of which will incline to yellow or red according as it contains a preponderance of one or the other compound4 ,the pigment known as orange chrome is a mixture of approximately equal parts of the neutral and basic lead chromates4 ,in order to brighten the deep yellow shade which distinguishes neutral lead chromate1 it is either mixed with a white pigment1 or a white substance 7lead sulphate7 is precipitated from the solution simultaneously with the lead chromate4 ,in this manner all the imaginable pale yellow shades1 lemon yellow1 sulphur yellow1 etc41 can be obtained4 ,just as the quantities of the solutions used and their strength influence the shade of the chrome yellow they produce1 so it also appears to be not immaterial which lead salt is employed4 ,colour makers are generally agreed that the finest product is obtained from neutral lead acetate4 ,any lead salt1 even insoluble in water1 may be used for the preparation of chrome yellow4 ,the affinity of chromic acid for lead is so great that an interchange of constituents occurs between the insoluble salt and the potassium chromate4 ,chrome yellow may be made from lead acetate1 chloride or sulphate2 the resulting substances are the same1 but there is a considerable difference in regard to the beauty of the product4 ,the finest chrome yellow1 which leaves nothing to be desired in beauty of shade1 is obtained by proceeding in the following manner3 ,lead acetate is dissolved in water1 the solution diluted with an equal volume of water1 and then mixed1 under constant stirring1 with a similarly diluted solution of potassium chromate or bichromate4 ,the precipitate is immediately formed1 and quickly sinks to the bottom in consequence of its high specific gravity4 ,it is washed with clean water so long as this removes soluble salts4 ,the precipitate is then drained on cloths and dried in the air4 ,the finest product is obtained by working with the following proportions3-- ,sugar of lead #ajj ,potassium bichromate1 or #ej ,potassium chromate #dj ,if lead sulphate is used the following quantities are to be employed3-- ,lead sulphate #ajj ,potassium bichromate #be ,in the case of lead chloride the following is the proportion3-- ,lead chloride #ajj ,potassium bichromate #bg ,the chrome yellows prepared from insoluble lead salts have no particular beauty1 but they may be used for mixed colours such as the spurious chrome green4 ,preparation of the ,lead ,solution4--,many makers of chrome yellow do not use commercial lead acetate1 but prepare its solution themselves4 ,the preparation of this solution requires neither much space nor labour1 so that considering the high price of lead acetate this procedure may be regarded as advisable1 but only when acetic acid is obtainable at a low rate4 ,the following is the method by which lead acetate solution is made4 ,lead is granulated by pouring the molten metal from a height of several yards into cold water1 which is kept in rapid motion4 ,the smaller the particles of lead1 the larger surface they will possess1 and the more quickly they will dissolve4 ,for the solution of the lead small tubs are used1 #ej centimetres in diameter and #ij to #ajj centimetres in height1 provided with a tap immediately above the bottom to run off the liquid4 ,four of these vessels are so placed1 one above the other1 that the contents of each may be run into the one next below it4 ,the lead in the top vessel is covered with acetic acid2 in a few minutes this is allowed to flow into the second vessel1 and similarly after a few minutes from the second to the third1 from the third to the fourth1 from which it runs away into a receiver below4 ,after this treatment it contains but a small quantity of lead acetate2 the object of the operation is to start the oxidation of the lead1 which quickly follows when air has sufficient access1 the lead particles lose their metallic appearance and become covered with a white layer4 ,when this is the case1 the acetic acid is pumped from the receiver back into the top vessel1 where it is left one to two hours in contact with the lead4 ,it is then run off into the second1 and thence into the third and fourth1 remaining in each vessel for about the same time2 the resulting liquid is an almost completely neutral solution of lead acetate4 ,the treatment with acetic acid is continued so long as lead remains undissolved4 ,the solution of potassium chromate is prepared in a tub4 ,the salt is easily soluble1 and warming is unnecessary if the chromate is placed in a basket1 lined with close linen cloth1 hung in the liquid so that it is immersed to half its depth4 ,the salt rapidly dissolves1 its solution has a greater density than water1 in consequence of which it sinks and fresh quantities of water continually come in contact with the salt4 ,precipitation of the ,chrome ,yellow4--,before the chrome yellow can be precipitated it is necessary to estimate the quantity of lead acetate contained in the solution1 since upon this depends the quantity of potassium chromate solution to be used4 ,if the lead solution contained only acetate and water1 its strength could be simply found by means of the hydrometer4 ,it contains1 however1 varying quantities of acetic acid1 on which account the hydrometer would give very inaccurate results4 ,the test by which the relation between lead solution and potassium chromate solution is found is performed in the following manner3 ,the lead solution is measured off in a cylinder divided into #ajj divisions2 the same volume of potassium chromate solution is measured and placed in a high narrow vessel2 the lead solution is gradually added to the chromate solution so long as a precipitate is formed4 ,the precipitate settles rapidly1 and there is no particular difficulty with a little practice in finding with sufficient accuracy the quantities required for the precipitation4 ,in order to precipitate #ajj litres of potassium chromate solution1 there are required as many litres of lead solution as were used divisions of the cylinder4 ,the preparation of the chrome yellow is now a very simple matter4 ,whilst steadily stirring1 the measured quantity of lead solution is run into the solution of potassium chromate2 the precipitate is allowed to settle1 is well washed and dried4 ,it does not make any difference to the colour whether potassium chromate or bichromate is used2 the same product is obtained in each case4 ,it is stated by ,dullo that chrome yellow prepared by the preceding process alters in colour on long keeping4 ,this is ascribed to the formation of a basic compound4 ,according to the same author1 a chrome yellow free from this objectionable property is obtained by using lead nitrate in place of acetate and an excess of potassium chromate solution4 ,the writer has kept chrome yellow1 made from lead acetate1 for years without observing the slightest alteration in the colour4 ,on chemical grounds1 it is incomprehensible that a chrome yellow prepared from lead nitrate should have different properties to the same substance prepared from another soluble lead salt1 and freed from foreign substances by sufficient washing4 ,the product of this process is that which par excellence is known as chrome yellow1 the chemist's neutral lead chromate2 it exhibits a characteristic deep yellow colour1 a shade which is known as chrome yellow4 ,under the microscope chrome yellow is seen to be a crystalline mass2 it will possess greater covering power the smaller the crystals4 ,now1 the motion of a liquid in which crystals are forming prevents the production of large crystals1 thus the reason is clear for the rapid stirring of the solutions in the preparation of this pigment4 ,according to ,c4 ,o4 ,weber1 who has published an exhaustive account of chrome pigments 7,dingler's ,journal1 #bhb71 the cost of the lead chrome pigments varies greatly according to the raw materials employed4 ,assuming that #ajj kilogrammes of litharge cost #ce marks1 #ajj kilogrammes of #cj per cent4 acetic acid #be marks1 and #ajj kilogrammes of #fj per cent4 nitric acid #bf marks1 ,weber calculates that #ajj kilogrammes of litharge1 in a form suitable for making chrome yellow1 will cost as follows3-- ,from lead acetate at #ef marks per #ajj kilogrammes #if marks 0 0 solution made in the works #hj 0 0 lead nitrate at #ej marks per #ajj kilogrammes #ge 0 0 0 solution made in the works #fd 0 ,by the basic lead acetate method #ea 0 0 0 chloride 0 #dj 0 ,white lead method #ee 0 ,the ,pale ,chrome ,yellows4--,when the solution of the chromate used for the precipitation of the lead solution is mixed with sulphuric acid1 then a mixture of lead sulphate and lead chromate is formed on precipitation4 ,lead sulphate is white1 so that the colour of the precipitate would be paler according to the quantity of sulphuric acid added to the potassium chromate solution4 ,there are1 however1 compounds of lead chromate and lead sulphate1 of which we know two4 ,their composition is expressed by the formul3-- ,pb,cr,o4,pb,s,o and ,pb,cr,o4#b,pb,s,o4 ,the former is a beautiful lemon yellow shade1 the latter nearly approaches sulphur yellow4 ,by corresponding alterations in the quantity of sulphuric acid added1 all intermediate shades can be obtained4 ,on the works these shades are made in the following manner3 buckets are used for taking the potassium chromate solution out of the vessel in which it was made2 these buckets hold #abe litres4 ,now1 if the solution of potassium chromate has been made from #be kilogrammes of the salt and #gej kilogrammes of water1 one of these buckets holds exactly #jdc kilogramme of chromic acid4 ,in order to obtain the lemon yellow compound1 #jci kilogramme of sulphuric acid must be added to a bucketful of solution2 #jgh kilogramme must be added to obtain the sulphur yellow chrome4 ,these liquids are prepared by pouring the sulphuric acid in a thin stream into the potassium chromate solution made as above1 the liquid must be stirred whilst the sulphuric acid is being added4 ,the lemon chrome has the peculiar property of increasing considerably in volume soon after formation1 a property to which regard must be had in the manufacture4 ,a description of the rational preparation of the lemon and sulphur yellow shades of chrome yellow on the manufacturing scale follows4 ,in making lemon chrome1 the tub in which the precipitation is to take place is two-thirds filled with water1 the lead solution is stirred in1 and then the chromate solution1 mixed with the proper quantity of sulphuric acid1 is run in2 the liquid is well stirred so that the precipitate may form as quickly as possible throughout the whole liquid4 ,the precipitate is allowed to settle1 the liquid drawn off1 and the colour washed twice with water as quickly as possible4 ,the paste is then removed from the tub and poured on a strong linen strainer4 ,at first1 the fine precipitate goes through the strainer1 the liquid is poured back on the strainer until the size of its pores is so far diminished by the precipitate itself that only clear liquid runs through4 ,the precipitate is left on the strainer until it forms a stiff mass1 which can be easily spread out upon boards by spatulas4 ,to obtain a good1 that is1 a loose product1 it is necessary to carry out the processes so quickly that the swelling mentioned above does not take place while the colour is being strained1 but when it has been spread out on the boards4 ,this swelling only takes place completely when the layer of precipitate is fairly thin4 ,large boards should be used1 upon which the precipitate is spread out in a very thin layer4 ,to prevent the mass--which is still fairly fluid--from running off the boards1 they are provided with raised edges1 and the paste is spread out smoothly in these flat trays4 ,if the operations have been properly performed1 the precipitate at once begins to swell and becomes of a loose nature4 ,when it has acquired a buttery consistency it is cut up1 by means of a thin sheet of brass1 into prisms1 which are placed near one another standing on the narrow side1 and dried first in the shade and then in the sun4 ,it is necessary that the drying should take place slowly at first1 or the cakes will crack or even fall to pieces4 ,the precipitate cannot be washed completely in the tub1 because it often begins to swell on the strainers1 consequently a crystalline crust covers the surface of the cakes during drying4 ,this layer must be removed by scraping the cakes of colour1 in which operation small quantities of chrome yellow dust become suspended in the air4 ,to protect the workman against poisoning by this lead compound1 precautions must be taken against breathing in the dust4 ,the simplest and most efficacious is to tie a wet sponge over mouth and nose2 this retains the particles of dust in the inspired air4 ,the dust1 scraped off the cakes1 is put into water1 in which the salts dissolve1 whilst the chrome yellow sinks to the bottom4 ,in this process for preparing chrome yellow the solution of potassium acetate left after the precipitation contains a considerable quantity of free acetic acid1 which may be utilised to dissolve lead4 ,when sulphur yellow chrome is to be made1 the process is substantially the same as for the preparation of the lemon shade1 but with the difference that everything is done to prevent the swelling of the precipitate4 ,the precipitation and washing of the precipitate are done as quickly as possible3 the washed precipitate is filled into press bags and strongly pressed4 ,care must be taken in the pressing that the pressure is only gradually increased2 if powerful pressure is applied at once1 even the strongest cloths will be burst4 ,the more thoroughly the precipitate is pressed1 the closer will be the fracture of the chrome1 a property which is regarded as a sign of good quality in this species of chrome yellow4 ,the manufacture of chrome yellow is intimately connected with that of a number of colours1 varying from orange to dark red1 which are known under the names of chrome orange or chrome red4 ,in accordance with the division adopted of pigments according to their colour1 chrome orange and chrome red will be considered among the red mineral pigments4 ,,chapter ,,xiii4 ,,lead ,,oxide ,,pigments4 ,lead monoxide1 ,pb,o1 exists in two different modifications2 in the crystalline form1 as litharge1 which is generally pale yellow with a reddish tinge1 and amorphous1 as massicot1 which is yellowish red4 ,lead monoxide is a product of metallurgical works rather than of colour works2 still the preparation of the crude oxide falls in the domain of the colour maker1 since from litharge several pigments may be prepared by a simple treatment4 ,massicot is obtained by heating white lead1 lead nitrate or red lead1 and also by heating melted lead in the air1 with the precaution that the oxide formed does not itself melt4 ,litharge is obtained as a by-product in several metallurgical processes1 such as the cupellation of lead containing silver1 in which the lead is melted in a furnace with a shallow hearth and a powerful current of air blown over the melted metal4 ,the lead is oxidised1 the oxide melts at the high temperature approaching #ajjj ,c41 and flows through an orifice in the wall of the furnace1 whilst the silver remains on the cupel4 ,the litharge is ground and levigated and1 according as it is pale yellow or reddish1 sold under the name of silver or gold litharge4 ,both massicot and litharge have no particularly striking colour2 they are seldom used as pigments4 ,litharge has an extensive use in oil boiling and for the manufacture of lead peroxide1 which is used for matches4 ,red ,lead1 ,minium4--,lead forms a number of other oxygen compounds1 one of which1 red lead1 has the composition1 ,pb,o4 ,it is a bright red powder1 used as a pigment and as a constituent of certain cements 7for gas and water pipes74 ,red lead is1 like litharge and massicot1 a metallurgical product1 but1 by working on a small scale1 products can be obtained of a much brighter colour than the produce of the large scale4 ,illustration3 ,,fig4 #be4 ,red lead is made in two ways--directly from metallic lead or by heating easily decomposed lead salts4 ,when it is made from the metal1 the following is the process3 the lead1 which must be very pure1 is melted in a reverberatory or calcining furnace1 oxidised to massicot by the air passing over it1 and the massicot then1 by careful heating1 changed into red lead1 a process in which particular care must be taken that the mass is not melted4 ,by continued heating the massicot absorbs about #b per cent4 of oxygen1 and changes in colour to a bright red4 ,the art in making red lead by this process lies in maintaining the proper temperature2 the furnaces are constructed so that the temperature may be regulated during the heating4 ,a reverberatory furnace is used1 in which is a stirring apparatus1 so that the heated mass may be continually turned over to accelerate the oxidation4 ,muffle furnaces are also used1 in which the massicot is placed in crucibles on an iron plate1 which can be pulled out of the furnace for observation of the change of colour4 ,whatever method is used1 the temperature must be so regulated that over-heating of the material is avoided1 otherwise litharge is formed1 which is only very slowly converted into red lead4 ,illustration3 ,,fig4 #bf4 ,mercier states that the muffle furnaces are arranged as shown in ,fig4 #be4 ,the muffle1 a1 is #be metres long and #b metres wide2 its bottom rests on an iron plate4 ,the passage1 d1 running under the muffle is #bj centimetres high2 it is divided by a partition1 and at each end are two hearths1 c1 #gj centimetres long and wide4 ,the products of combustion pass from the long passages into side channels1 f1 provided with dampers1 go round the muffle and unite in the space1 g4 ,the flue1 k1 at the back of the muffle is provided with dampers1 m1 which exactly regulate the current of air through the muffle2 n is the chamber in which are collected the particles of oxide carried over by the draught4 ,the furnaces used for manual labour consist1 according to ,percy 7,figs4 #bf and #bg7 of a rectangular or circular hearth1 a1 of about #c metres diameter1 which is deeper in the middle and has two fireplaces1 b4 ,the low arch surmounting the hearth is covered with sand in order to prevent cooling4 ,illustration3 ,,fig4 #bg4 ,when finished1 the red lead is drawn out of the furnace and finely ground under edge-runners1 or occasionally levigated4 ,the temperature necessary in making red lead is that at which the angles of the muffles1 when these are used1 begin to show a dark red glow4 ,orange lead1 which is a brighter variety of red lead1 is prepared from lead salts2 white lead or lead nitrite is used for this purpose4 ,the latter salt is made by the process of ,pischon1 by heating #a equivalent of lead nitrate with #d equivalents of granulated lead and water at a temperature between #ej and #fj ,c4 ,after about #b hours1 the lead nitrite separates in the form of a granular yellow mass4 ,according to ,burton's process1 lead carbonate is oxidised by heating with #bj per cent4 of sodium nitrate and extracting the mass with water4 ,there are also other methods by which red lead is obtained from litharge by the use of potassium chlorate or saltpetre2 but these methods1 without producing a finer product than those previously given1 are more expensive1 and consequently have found no application on the large scale4 ,,chapter ,,xiv4 ,,other ,,yellow ,,pigments4 ,cassel ,yellow1 also known as mineral or ,veronese yellow1 has now a very restricted use2 it has been replaced by the deeper and cheaper chrome yellow4 ,much of the ,cassel yellow of commerce is nothing but chrome yellow shaded with barytes4 ,as regards chemical composition1 ,cassel yellow has the following formula3 ,pb,cl4#g,pb,o4 ,it is obtained by heating litharge1 red lead or white lead with ammonium chloride4 ,to #aj parts of the lead compound #a part of ammonium chloride is used2 on melting1 ammonia is set free1 by which part of the lead oxide is decomposed1 metallic lead separating4 ,the melted mass is poured off from the lead into iron moulds1 in which it solidifies to a very crystalline substance of a fine yellow colour4 ,by grinding and levigating1 the ,cassel yellow is prepared for use4 ,pale yellow shades1 obtained by admixtures of barytes1 are occasionally encountered4 ,montpellier ,yellow consists1 like the preceding pigment1 of basic lead chloride4 ,it is obtained by gradually mixing #djj parts of powdered litharge with a solution of #ajj parts of common salt in #djj parts of water4 ,after each addition of salt solution the pasty mass must be thoroughly stirred1 or it will harden4 ,when all the salt solution has been mixed with the litharge to a homogeneous white mass1 the latter is treated with water to remove excess of salt1 and the washed material dried and melted in earthenware crucibles4 ,the melt1 which has a bright yellow colour1 is ground and levigated1 when it forms a handsome pigment4 ,there are several other yellow pigments of similar composition1 of which one only need be mentioned1 obtained by treating a solution of zinc chloride with lead hydroxide4 ,turner's ,yellow or ,english ,yellow is prepared by two methods3 either by melting #g parts of finely ground litharge with #a part of common salt2 or by treating litharge with a solution of common salt and converting the white oxychloride into a yellow pigment by melting4 ,naples ,yellow4--,this handsome pigment1 which is1 unfortunately1 susceptible to the action of sulphuretted hydrogen1 is known commercially under different names4 ,naples yellow takes its names from the fact that it was formerly exclusively made in ,italy1 where the method was kept secret1 a secret which disappeared with the advance of analytical chemistry4 ,naples yellow is now known to be lead antimoniate4 ,naples yellow is a handsome pigment4 ,its preparation is more tedious than that of chrome yellow1 hence it is now rarely employed4 ,the author has had practical experience that much of the so-called ,naples yellow of commerce is nothing but a suitably shaded chrome yellow4 ,naples yellow can be prepared by different methods4 ,according to the oldest1 given by ,brunner1 #a part of pure tartar emetic is carefully and thoroughly ground with #b parts of lead nitrate and #d parts of common salt4 ,the mixture is melted at a low heat in a ,hessian crucible1 and the fluid mass poured on a cold iron plate4 ,after cooling1 it is boiled out with water1 when lead antimoniate remains as a powder of a more or less deep yellow colour4 ,it is not easy to obtain this favourable result with certainty in every case4 ,if a certain temperature is exceeded only by a little1 a hard mass results1 which by long boiling does not become a fine powder1 but a sandy substance of little brilliance4 ,even when the operation succeeds1 the product often varies considerably in shade1 sometimes a sulphur yellow1 at other times an orange pigment being formed4 ,as a rule1 the paler product is obtained at a lower temperature2 by stronger heating1 darker products of a red shade are obtained4 ,according to another recipe1 #b parts of tartar emetic are melted with #d parts of lead nitrate and #h parts of common salt4 ,the mass is treated with very dilute hydrochloric acid for a long time1 which extracts some quantity of lead oxide1 a deeper product being thus obtained4 ,care is1 however1 necessary in this treatment2 acid of too great strength would spoil the whole product4 ,the ,paris method for ,naples yellow is as follows3 metallic antimony is oxidised by melting in air2 to #ab parts of antimony1 #h parts of red lead and #d parts of zinc oxide are used1 and the mixture is melted at a low red heat4 ,a cheap1 but not particularly bright product1 can be obtained from old printer's type4 ,the metal1 which is an alloy of antimony and lead1 is powdered1 mixed with #c parts of saltpetre and #d parts of common salt1 melted1 and the mass washed out with water4 ,other formul which are said to yield a good result are as follows3 #ab parts of white lead1 #c parts of antimony oxide1 #a part of ammonium chloride1 #a part of alum4 ,or3 #af parts of stibnite1 #bd parts of lead1 #a part of common salt and #a part of ammonium chloride4 ,the intimate mixture of these materials is first gently heated with access of air1 then more strongly1 and the mass extracted with water4 ,there are many other recipes for the preparation of ,naples yellow1 the majority of which are distinguished by an apparently arbitrary arrangement of the materials2 for there is no scientific reason4 ,if it were possible to accurately obtain any desired high temperature in a furnace1 the manufacture of ,naples yellow would no longer be a matter of skill1 but the same product could be obtained at every attempt4 ,since this is not yet the case1 the exact procedure for the preparation of this colour can only be found by careful experiments4 ,naples yellow is1 as has been said1 a handsome colour1 and offers a great resistance to varied reagents4 ,it is only changed by one of them1 sulphuretted hydrogen1 by the prolonged action of which it is turned completely black4 ,antimony ,yellow is very similar in composition to ,naples yellow4 ,it consists of a mixture of lead antimoniate with the oxides of lead and bismuth4 ,it is prepared by the process recommended by ,merom by intimately mixing #c parts of finely powdered bismuth with #bd parts of powdered stibnite and #fd parts of saltpetre1 melting the mixture and shaking it whilst molten into water4 ,the brittle mass is finely powdered1 washed and dried1 then melted with #abh parts of litharge and #h parts of sal ammoniac4 ,the mass obtained has a fine pale yellow colour2 when powdered it is antimony yellow4 ,this pigment has almost fallen into disuse because of its instability and the high price of bismuth4 ,calcium ,chrome ,yellow4--,calcium forms a yellow pigment with chromic acid1 which1 although far surpassed by the lead chromes in fineness of shade1 has the advantage over them of greater stability and cheapness4 ,for purposes for which cheap and at the same time permanent colours are required calcium chrome yellow can be recommended4 ,it is most simply prepared from potassium chromate and calcium chloride1 which1 as a by-product of many chemical operations1 is obtainable at very low prices4 ,the deepest pigment is obtained when the precipitation is done with a boiling solution of the chromate4 ,calcium chromate1 in addition to its use alone1 may be employed instead of white pigments to produce pale shades from deep lead chromes4 ,this addition should not be carried to a great extent or the chrome will be made too light1 since calcium chromate has a much lower specific gravity than lead chromate4 ,barium ,yellow1 ,yellow ,ultramarine or ,permanent ,yellow4--,this pigment consists of barium chromate4 ,the finest product is obtained when a solution of a barium salt1 generally barium chloride1 is precipitated boiling by a solution of potassium chromate4 ,the very finely divided precipitate has a pale yellow colour very similar to that of pale lead chromes4 ,this handsome pigment is distinguished by the valuable property of being practically unaltered by the atmosphere2 it is only attacked by strong acids and alkalis4 ,by long heating1 the colour of this compound is gradually changed to a handsome green1 which consists of a compound of barium and chromic oxides1 and has occasional use as an artists' colour4 ,in order to obtain this pigment1 the heating must be intense and long continued4 ,according to the author's experiments1 it is not sufficient to heat for a short time to a very high temperature2 in that way a mass is obtained of very unequal colour4 ,the best result was obtained by spreading barium yellow in a thin1 even layer in a flat porcelain dish and heating to whiteness for #aj hours4 ,zinc ,chrome ,yellow4--,zinc chromate is inferior to lead chromate in beauty1 but has the advantage of permanence4 ,it does not blacken in an atmosphere of pure sulphuretted hydrogen1 and resists very well the action of other agents4 ,zinc yellow may be prepared by the immediate precipitation of a solution of zinc sulphate by a solution of potassium chromate1 both being boiling1 but the very bright precipitate obtained in this way is not stable2 on washing1 it gives up chromic acid continually to the wash water1 and only a pale yellow residue remains4 ,a very fine colour is obtained in the following manner3 zinc sulphate is dissolved in water and boiled for half an hour with #a per cent4 of white zinc whilst stirring4 ,this operation effects the separation of iron oxide and the neutralisation of the free acid generally present in commercial zinc sulphate4 ,when the solution has cleared by standing1 it is precipitated by a solution of potassium chromate1 the precipitate collected on a filter and allowed to drain completely2 it is then washed with very small quantities of water and finally dried4 ,a pure yellow precipitate is only obtained when all the iron oxide has been removed by boiling the zinc sulphate solution with white zinc2 if the liquid contains only a very small quantity of iron1 it has yet a very considerable influence on the colour1 the yellow is not pure1 but has a brownish tinge4 ,zinc yellow is used alone1 and mixed with other pigments4 ,chrome yellows of all possible shades may be obtained in this way4 ,chrome yellows are often found in commerce which consist essentially of zinc chromate4 ,cadmium ,chrome ,yellow4--,when a solution of cadmium sulphate1 or any other cadmium salt1 is mixed with a solution of potassium chromate1 a precipitate of cadmium chromate1 ,cd,cr,o1 is formed4 ,this pigment has a beautiful1 deep yellow colour1 in no way inferior in shade to the finest lead chromes1 and having the great advantage over the latter of being entirely unaltered by the atmosphere2 it is thus to be highly recommended for artistic purposes4 ,the high price at which it is sold prevents its general use1 though now that cadmium compounds are to be obtained at so much lower prices than formerly1 the price of cadmium chromate appears to be excessively high4 ,cadmium ,yellow is cadmium sulphide1 ,cd,s2 in nature it occurs as the somewhat rare mineral greenockite4 ,cadmium yellow is obtained by dissolving metallic cadmium in sulphuric acid1 and precipitating the solution with sulphuretted hydrogen4 ,the solution of cadmium sulphate must be digested for some time with excess of cadmium1 in order to separate the foreign metals present as impurities2 the colour is not so fine when a quite pure cadmium solution is not used4 ,cadmium yellow is a very bright yellow4 ,several shades are obtained according as the solution of cadmium sulphate used in its precipitation is neutral or acid4 ,the reason of this difference in shade lies apparently in the different size of the crystals of which the precipitate is composed4 ,the deep1 pure yellow colour becomes still deeper by fusion1 which takes place at a white heat4 ,weak alkalis1 acids and sulphuretted hydrogen do not alter cadmium yellow2 it is thus to be regarded as a durable artists' colour4 ,it can be mixed with ultramarine without decomposition1 when a fine green is formed2 but mixed colours cannot be made from cadmium yellow and blue copper pigments1 since these would blacken in the light4 ,lead ,iodide4--,on precipitating a solution of lead nitrate with potassium iodide1 lead iodide is formed4 ,this is but slightly soluble in water1 and1 when dry1 has a handsome1 deep yellow colour4 ,unfortunately it is not permanent1 but is decomposed on exposure to light4 ,it can be used for bronzing1 but other and cheaper pigments are available for this purpose4 ,on account of the great solubility of lead iodide in a solution of potassium iodide1 it is prepared in another way1 and accurately weighed quantities are used4 ,calcium iodide may be used instead of the potassium salt2 #ajj parts of iodine1 #ae parts of fine iron filings and #be parts of lime are mixed with sufficient water to form a thin paste1 which is warmed until all the iodine is dissolved1 when water is added1 the liquid filtered1 and the residue washed in order to extract all the calcium iodide4 ,the solution and wash waters are united1 then a solution of #aeb parts of lead acetate is added1 when all the iodine is precipitated as lead iodide4 ,a simpler method is to dissolve equal parts of lead nitrate and potassium iodide separately1 each in #bj parts of hot water1 to mix the solutions and cool quickly1 when lead iodide separates in very small crystals4 ,when pure lead iodide is melted in the absence of air1 and the fused mass powdered1 a product of yet finer colour is formed4 ,it is necessary to completely imbed the crucible in which the fusion is performed in the fire4 ,the action of air on the melted mass would produce a basic iodide4 ,the fine golden yellow colour of lead iodide adapts it especially for the production of gold bronzes on wall papers and fabrics4 ,mars ,yellow1 which is generally reckoned among the best artists' colours1 is usually a mixture of ferric oxide and calcium sulphate or alumina4 ,the pigment is prepared by mixing a solution of ferrous sulphate with milk of lime1 when ferrous oxide is precipitated1 which becomes yellowish brown on exposure to air1 in consequence of the oxidation of the ferrous oxide4 ,by heating the precipitate1 according to the temperature different shades are obtained1 varying between yellow and red4 ,in addition to ,mars yellow1 ,mars orange and ,mars red are found in commerce4 ,the manufacture of this pigment is very simple3 #a part of ferrous sulphate is dissolved in #aj parts of water1 and the solution mixed with milk of lime made from #a part of quicklime and #dj parts of water4 ,if it is desired to produce a darker shade1 and especially a product to be afterwards converted into ,mars orange1 the amount of ferrous sulphate is increased to #b parts4 ,when the mixture has been made1 it must be stirred for a long time1 in order that the reacting substances may come thoroughly into contact4 ,the precipitate1 which at first is greenish grey1 soon acquires by the action of the air the colour of ferric hydroxide1 which becomes deeper on drying4 ,when dried and finely ground ,mars yellow is heated in thin layers1 it changes to dark yellow1 and finally to orange red1 a similar alteration taking place to that occurring when ferric hydroxide itself is heated4 ,a ,mars yellow of a deeper shade1 consisting of a mixture of ferric hydroxide and alumina1 is obtained by precipitating with caustic soda a solution of ferrous sulphate and alum4 ,the sodium sulphate which is formed at the same time must be removed as completely as possible by washing with boiling water4 ,by calcining ,mars yellow for a long time at a high temperature1 ,mars brown is produced1 a fine brown pigment4 ,the value of ,mars yellow and the pigments obtained from it lies not only in their fine shade1 but in their permanence1 which distinguishes the majority of the iron colours4 ,siderin ,yellow4--,this not very handsome yellow consists of ferric chromate2 it is obtained by adding a neutral solution of ferric chloride to a strong boiling solution of potassium bichromate so long as a precipitate is formed4 ,siderin yellow is said to be used both in oil and water1 and to be particularly adapted for use in sodium silicate paints1 since in the course of time it forms a stony mass with that substance4 ,the low price of iron salts would make it desirable to employ chromates of iron1 but it appears to be difficult to obtain a compound of constant composition4 ,in experiments with this object the author did not succeed in obtaining products of the same shade4 ,others have probably been equally unsuccessful1 for siderin yellow has never been used in quantity1 as it would have been were there no difficulties in the way of its preparation4 ,aureolin is a double nitrite of cobalt and potassium1 ,co7,,no74#c ,,kno4 ,this pigment is prepared by adding excess of potassium nitrite to a solution of cobalt nitrate acidified with acetic acid4 ,as the liquid cools1 a deep lemon yellow crystalline powder separates1 which1 when dry1 is known as ,indian yellow or aureolin4 ,it is distinguished from other yellow pigments by being unaffected by sulphuretted hydrogen4 ,the potassium nitrite required in the preparation of this pigment is most easily made by melting saltpetre in a thick iron vessel and stirring in fine iron filings in small quantities as soon as the saltpetre begins to decompose4 ,the iron glows brightly and burns to oxide1 the saltpetre changes to potassium nitrite4 ,the mass is dissolved in a little hot water1 the solution filtered and cooled1 when most of the undecomposed saltpetre crystallises out1 whilst the nitrite remains in solution4 ,after further evaporation and separation of another crop of potassium nitrate crystals1 the solution can be used to precipitate the aureolin4 ,it is advisable to use strong solutions in the precipitation of aureolin2 the finest precipitate is obtained in this way4 ,if dilute solutions are used1 the precipitate forms gradually2 it is then coarse and has little covering power4 ,according to the method of ,hayes1 aureolin is prepared by passing into a solution of cobalt nitrate the vapours produced by pouring nitric acid over copper and allowing air to enter4 ,caustic potash is added to the liquid from time to time4 ,in this way all the cobalt can be obtained in the form of a yellow precipitate4 ,tungsten ,yellow4--,finely powdered tungsten is introduced in small quantities into fused potassium carbonate so long as effervescence occurs4 ,after boiling with water and filtering1 calcium tungstate is precipitated from the filtrate by means of calcium chloride4 ,the moist precipitate is added to hot dilute nitric acid until the liquid is only slightly acid1 when it is boiled for half an hour and allowed to cool4 ,the precipitate1 after washing with a little water and drying1 is a deep lemon yellow powder4 ,nickel ,yellow consists of nickel phosphate4 ,it is obtained by adding sodium phosphate to a solution of nickel sulphate or nitrate1 and heating the pale green precipitate to redness4 ,nickel yellow has a pleasing shade1 and is distinguished by great permanence4 ,up to the present it has found little use as an artists' colour1 but on account of its permanence1 which does not distinguish many yellow pigments1 its use is to be recommended4 ,mercury ,yellow or ,turpeth ,mineral is a basic mercuric sulphate of the formula ,hg,,so4 ,it is obtained by heating #aj parts of mercury with #ae parts of sulphuric acid in a porcelain dish in a good draught1 until a white crystalline mass of neutral mercury sulphate remains4 ,this salt1 ,hg,s,o1 is decomposed in contact with water into free sulphuric acid and a basic salt of the above composition4 ,the decomposition is effected by treating the finely powdered neutral sulphate with hot water so long as the washings are acid1 when a handsome lemon yellow substance remains4 ,the wash waters contain acid mercuric sulphate4 ,they are allowed to stand with mercuric oxide so long as this is dissolved1 and the solution then used to prepare new quantities of mercury yellow4 ,turpeth mineral has a very bright shade and great covering power1 but it has little permanence4 ,sunlight soon turns it grey1 and air containing sulphuretted hydrogen in a short time turns it quite black1 mercury sulphide being formed4 ,yellow ,arsenic ,pigments4--,the extremely poisonous character of arsenic pigments has practically banished these handsome and cheap colours from use4 ,in many countries their use is justly illegal4 ,the majority of arsenic pigments have1 therefore1 merely historic interest4 ,the two yellow arsenic pigments are found in nature as realgar and orpiment2 though these are not rare minerals1 the artificial products were generally used as pigments1 and when they were in common use they were generally made in metallurgical works1 in which minerals containing arsenic were treated4 ,realgar1 ,as,s1 has an orange red colour1 whilst orpiment1 ,as,s1 is a pure yellow4 ,when these substances were used as pigments they had the same drawbacks in regard to mixing with other pigments as other sulphur compounds4 ,king's yellow is finely powdered natural or artificial orpiment4 ,lead ,arsenite is a permanent deep yellow1 but extremely poisonous4 ,it can be made by fusing an intimate mixture of #ajj parts of white arsenic with #ge parts of gold litharge1 grinding and levigating the mass4 ,cadmium yellow1 which has still more permanence and is less poisonous1 replaces this pigment4 ,thallium ,pigments4--,thallium is a metal which exhibits certain similarities to lead4 ,by precipitating a solution of a thallium salt with potassium chromate or bichromate1 according to the proportion between the quantities of the two salts1 precipitates are obtained of yellow1 orange or deep red colour1 or1 after fusion1 brown4 ,by the addition of a mixture of potassium chromate and ferricyanide to a mixture of a thallium salt and ferrous sulphate an olive green pigment is obtained4 ,on account of the rarity of thallium compounds1 technical employment is out of the question1 and the sensitiveness of thallium pigments towards sulphuretted hydrogen prevents their use for artistic purposes4 ,,chapter ,,xv4 ,,mosaic ,,gold4 ,mosaic gold consists of tin disulphide1 ,sn,s1 fine scales of a golden yellow colour1 which sublime undecomposed at a fairly high temperature and withstand the action of chemical reagents4 ,it has a peculiar greasy nature1 and can be easily ground4 ,it is1 therefore1 much used for bronzing picture frames1 as a pigment for painters and for wall papers4 ,tin disulphide can be prepared either in the wet or the dry way2 in the wet way1 by the action of sulphuretted hydrogen on a solution of tin tetrachloride4 ,the yellow precipitate so obtained has no handsome colour4 ,a far finer product is obtained in the dry way4 ,the process is often regarded as accompanied by particular difficulties1 but in reality it is quite simple4 ,it is only necessary in preparing this pigment to take care not to raise the temperature above a certain point1 otherwise a great portion of the tin disulphide will be decomposed into sulphur and tin monosulphide4 ,to prevent the temperature from rising too high1 an addition of ammonium chloride is made4 ,this salt is volatile at a certain temperature2 heat which would otherwise raise the temperature above this point is used in volatilising the ammonium chloride4 ,with a little care it is easy to interrupt the operation before all the ammonium chloride has been driven off4 ,the mosaic gold then obtained has a real golden glitter4 ,if the temperature rises too high1 grey tin monosulphide is formed1 which naturally considerably diminishes the brilliancy of the product4 ,ammonium chloride may be replaced by mercury or mercury compounds1 which are volatile at a temperature below that at which mosaic gold is decomposed4 ,when mercury compounds are used1 both on account of their cost and poisonous nature the heating must be conducted in glass retorts in order to recover the mercury4 ,this operation requires great care if loss due to the breakage of the glass vessels at the high temperature is to be avoided4 ,the process in which metallic mercury is used gives the finest product of all1 and is to be recommended when a pigment is to be prepared which shall as nearly as possible approximate to the appearance of gold4 ,in order to obviate the danger and loss associated with the use of glass vessels1 manufacturers who make mosaic gold in large quantity should use an iron vessel4 ,this will last a very long time4 ,such an apparatus consists of an iron pan with a broad rim1 upon which is fastened a head which has the form of a retort neck2 to this are connected short1 wide tubes leading to a chamber in which substances not condensed in the retort neck may deposit1 so that the use of this inexpensive apparatus will not only be without danger1 but will be accompanied by the recovery of almost the whole of the volatilised substances4 ,the pan is filled with the materials1 the head placed on1 the joint tightly luted1 and the retort neck connected with the chamber by the wide iron tubes4 ,there are many formul for the preparation of mosaic gold4 ,some of the most important are given1 which in every case will yield a good result3-- ,tin filings #dj parts ,sulphur #ce 0 ,ammonium chloride #be 0 ,the tin filings1 which must be very fine1 are well mixed in a mortar with the sulphur and ammonium chloride4 ,the heating is gradual at first2 when the evolution of vapours has ceased the temperature is very slowly increased to a dark red heat4 ,the mosaic gold is found as a yellow mass at the bottom of the vessel1 but partly in crystalline scales on the walls and head of the retort4 ,other recipes are as follows3-- ,tin dioxide #hj parts ,sulphur #fj 0 ,ammonium chloride #cj 0 ,tin filings #de 0 ,sulphur #ce 0 ,ammonium chloride #be 0 ,in all these cases the chief endeavour should be not to raise the temperature too high2 a dark red heat is sufficient to give a perfectly satisfactory result4 ,when metallic mercury is used1 it is employed in the form of an amalgam with tin1 which is then in such a finely divided condition that it readily enters into chemical combination with the sulphur4 ,the amalgam is most simply obtained by heating #a part of mercury almost to boiling1 and stirring #b parts of tin filings into the hot metal2 #ah parts of this amalgam mixed with #g parts of sulphur and #f of ammonium chloride are heated together4 ,the mosaic gold made after any of these methods may be used for gilding gold frames or as a painter's pigment4 ,much so-called gold paint consists of mosaic gold ground with a thick gum solution4 ,chrysean4--,wallach found that when a current of sulphuretted hydrogen was passed through a saturated solution of potassium cyanide a precipitate was formed1 which had the formula ,c,h,n,s4 ,this substance1 chrysean1 is similar in appearance to mosaic gold2 its technical employment is prevented by its extremely poisonous nature and its high cost as compared with mosaic gold4 ,,chapter ,,xvi4 ,,red ,,mineral ,,pigments4 ,,vermilion4 ,this beautiful scarlet red pigment1 which has been used for so long a time1 consists of mercuric sulphide1 ,hg,s4 ,the same compound occurs ready formed in nature as cinnabar2 picked pieces of this mineral come into the market under the name of mountain vermilion 7,bergzinnober74 ,a far larger quantity of vermilion is made artificially4 ,mercuric sulphide exists in two forms--as a black non-crystalline powder and in the crystalline form1 which is used as a pigment4 ,each modification may be transformed into the other by suitable treatment1 and each may pass into the other spontaneously under certain conditions4 ,in the manufacture of vermilion1 the black form of mercuric sulphide plays an important part2 it is1 therefore1 necessary to give an account of the chemical behaviour of the two modifications before proceeding to an account of the method by which vermilion is made4 ,black ,mercuric ,sulphide may be obtained either by the direct union of metallic mercury with sulphur1 or by precipitating the solution of a mercuric salt with sulphuretted hydrogen4 ,it is most simply formed by rubbing together equal parts of sulphur and mercury moistened with water1 until the mixture is uniformly black4 ,it is1 however1 difficult in this way to convert all the mercury into sulphide4 ,a better result is obtained when the mixture is moistened by ammonium sulphide instead of water4 ,in this case the time required for the operation is shortened by warming the vessel4 ,if the mortar is placed in hot water it is generally sufficient to grind for about two hours to bring about the combination of the mercury and sulphur4 ,this compound can also be easily obtained by heating mercury with sulphur4 ,in a vessel1 placed under a chimney with a good draught1 which is necessary to carry away the poisonous mercury vapours1 #f parts of the metal are heated nearly to boiling and #a part of sulphur added4 ,combination takes place at this temperature with a slight explosion1 and pure mercuric sulphide results when the heating is continued until the excess of sulphur is driven off4 ,for the purpose of the manufacture of vermilion1 black mercuric sulphide is most simply made by filling a thick-walled vessel with equal weights of mercury and sulphur1 moistening the mixture with water and shaking or rotating the vessel for several hours4 ,this can be done either in a rotating cylinder containing iron balls1 or the vessel can be fastened to any rotating object--to a water-wheel or to the fly-wheel of a steam-engine4 ,the vessel in which the combination is effected should of course not be quite full4 ,it has been found that a more jerky motion than that of rotation effects the combination of the mercury and sulphur in a shorter time4 ,for example1 an opportunity of fastening the vessel to a saw-mill would be of great advantage4 ,the mercuric sulphide made by the above methods is a velvety black mass1 which1 even when exactly equivalent weights of sulphur and mercury have been used1 is never quite pure4 ,carbon bisulphide will always extract a certain quantity of uncombined sulphur4 ,the most important property of the black sulphide for the present purpose is that it is changed into the crystalline modification by heating to the temperature at which it volatilises4 ,the sublimed mercuric sulphide has the well-known fiery scarlet colour characteristic of vermilion4 ,red ,mercuric ,sulphide1 or vermilion1 exhibits1 for a sulphur compound1 considerable resistance to the action of chemical reagents2 dilute mineral acids do not decompose it4 ,unfortunately1 vermilion has another property which makes it quite unsuitable for the artist's use3 in the course of time it gradually turns dull and at last is completely discoloured4 ,this alteration of colour can only be ascribed to a return of the red crystalline modification into the black non-crystalline4 ,when a white pigment is tinted by vermilion it should not be a lead pigment1 or in a brief time it will turn black4 ,a white pigment such as zinc white1 which is not acted upon by sulphur compounds1 should be used4 ,,chapter ,,xvii4 ,,the ,,manufacture ,,of ,,vermilion4 ,the red modification of mercuric sulphide can be prepared in the wet or the dry way4 ,the latter was formerly in general use1 but at present the wet method is more generally employed1 as it more easily and certainly produces a handsome pigment4 ,each method has its advantages1 and both will be described4 7a7 ,,dry ,,method4 ,the numerous prescriptions which have been given for the manufacture of vermilion by the dry method are all founded on endeavours to convert black mercuric sulphide into the red form4 ,many of these prescriptions contain directions for the soundness of which no reason can be discovered1 and it is not going too far to say that none exists1 and that operations described as essential for the success of the process have been inserted merely to give the recipe the appearance of novelty4 ,it cannot be denied that certain manipulations impart a greater brilliancy to the product1 although it is impossible to assign a physical or chemical reason2 but the manufacturer will quickly be able to differentiate the valuable from the worthless in these processes4 ,two conditions have the greatest influence on the beauty of the pigment--the temperature at which the black sulphide is sublimed1 and the complete freedom of the vermilion from excess of sulphur4 ,of less importance is the repeated grinding of the vermilion2 the oftener it is ground1 the smaller the crystals become and the paler the shade4 ,the operation of grinding the pigment in ordinary mills is known practically as 8preparing10 the extraction of excess of sulphur by boiling with alkaline liquids as 8refining10 the product4 ,the usual process in ,holland1 especially in the ,amsterdam works1 is as follows3 ,the black sulphide is made by heating #bgj parts of mercury with #cge parts of sulphur in copper pans--the fire is so regulated that the temperature is not high enough to ignite the sulphur4 ,if properly prepared the product has now a pure black colour4 ,it is immediately finely ground and preserved in earthenware bottles containing only #jg kilogramme each4 ,it is sublimed from hemispherical vessels1 provided with iron covers carefully joined to the rim of the sublimation vessel by a suitable fire-resisting cement4 ,generally #c such vessels are contained in one furnace4 ,the operation is commenced by heating them until the bottom shows a dark red heat4 ,the temperature should now be increased to such an extent that1 when the contents of one of the above-mentioned small bottles are poured into the vessel1 a small flame only appears2 if on the contrary the contents burn explosively1 the temperature is too high1 and further quantities of the black sulphide must not be added until the vessels have cooled down to a certain extent4 ,if1 on introducing the first quantity of mercuric sulphide1 a flame appears unaccompanied by an explosion1 the contents of several of the bottles may be introduced2 the openings through which this addition is made are immediately closed by a well-fitting iron plate4 ,from time to time this cover is raised and fresh quantities of mercuric sulphide added4 ,the operation lasts about #cf hours1 when double the quantity of mercuric sulphide1 made from the above mixture of mercury and sulphur1 will have been introduced into the #c vessels4 ,for the complete success of the process1 the accurate regulation of the temperature to which the vessels are exposed is particularly important2 in practice1 the temperature is judged by the height of the flame which issues on removing the iron plates3 if this reaches to #a metre the fire is too fierce1 but if the flame is very small the fire must be increased4 ,towards the end of the sublimation the mass in the vessels is stirred about every #ae minutes4 ,as soon as the sublimation is finished the fire is extinguished4 ,the vessels are broken when completely cold2 the vermilion is then found in the upper portion as a sublimate of fibrous character4 ,the vermilion made by this process requires simply wet grinding under ordinary mills and drying to be ready for market4 ,in the great mercury works at ,idria1 in ,austria1 vermilion is also made from the black sulphide4 ,the latter is made by mixing #hd parts of mercury with #af parts of finely powdered sulphur in rotating vessels driven by water power1 the operation lasting about #c hours4 ,this quantity of sulphur is larger than is required to form mercuric sulphide2 experience has shown that the combination takes place more rapidly when more than the equivalent quantity of sulphur is used4 ,heat is developed by the reaction and the temperature of the mixture rises to over #cj ,c4 ,the black sulphide is then sublimed in cast-iron vessels1 which are pear-shaped and built #f together in a furnace2 each holds a charge of #cae kilogrammes of black4 ,several periods are distinguished during the heating of the mass in the sublimation vessels4 ,the operation is commenced by heating #b of the vessels first4 ,as soon as the vapours of sulphur1 issuing from the neck of the vessels1 take fire with explosion1 the fire is made to heat the adjacent vessels4 ,when the contents of all the vessels have exploded1 the first part of the process known as the 8evaporation0 is at an end4 ,earthenware heads are then placed on the vessels and the fire is increased until the excess of sulphur present begins to distil2 its vapours take fire in the air with a slight explosion4 ,when this takes place1 earthenware receivers are attached which have only a small opening for the escape of uncondensed vapours4 ,the sulphur condenses in these4 ,when sulphur vapours are no longer given off in quantity1 the intermediate period 7stckperiode7 is finished and the real sublimation of the vermilion commences4 ,the fire is now considerably increased and the sublimed vermilion collects in the cooler parts of the apparatus4 ,when the sublimation is completely finished1 small blue flames1 which quickly vanish1 appear at the joints of the apparatus4 ,the furnace is allowed to get quite cold1 when the various parts of the apparatus are taken apart1 the vermilion deposited in the tubes is carefully removed1 so that they may be again used1 whilst the receivers and head are broken1 so that the vermilion they contain can be collected4 ,the larger pieces form lump vermilion2 the fragments of the receivers are cleaned with a wet brush to collect what adheres4 ,the whole process of sublimation from the introduction of the black to the end lasts about #g hours4 ,the sublimed vermilion is ground in mills which differ little from ordinary grinding mills4 ,to prevent the formation of dust1 water is added and the stones are surrounded by wooden casings4 ,the red paste from the mills1 which is now known as vermilion1 is then refined4 ,the refining consists in extracting the excess of sulphur by means of boiling potash solution2 #cjj kilogrammes of the ground vermilion are stirred up with water in a tub1 the water is drawn off and the wet mass brought into an iron pan1 in which it is heated with #bbe kilogrammes of potash lye for about #aj minutes4 ,according to the composition of the crude vermilion the lye has a strength of from #aj to #ac ,b4 ,the smaller the quantity of sulphur1 the weaker is the potash solution2 it is1 or was1 made in ,idria in a very primitive manner1 by extracting wood ashes4 ,for vermilion of a bright red shade potash solution of #aj1 for the dark red of #aa1 and for 8,chinese vermilion0 of #ac is used4 ,the excess of sulphur1 together with a trace of mercuric sulphide1 dissolves in the potash solution2 the sulphur chiefly forms potassium pentasulphide4 ,when the boiling is finished1 the vermilion is carefully washed and dried in dishes placed in a heated furnace4 ,during drying1 the vermilion agglomerates2 finally the lumps are broken and sieved4 ,chinese ,vermilion is in similar case to ,indian ink4 ,both substances are in common use in ,europe1 they far surpass in quality our own manufacture1 and in neither case do we know the exact method by which they are made4 ,genuine ,chinese vermilion so far surpasses ,european in brightness that it is bought at five or six times the price4 ,it is said on unauthenticated authority to be made by subliming a mixture of #d parts of quicksilver with #a part of sulphur in earthenware pots closed by an iron plate1 which is kept constantly wet and serves as a receiver1 on which the vermilion deposits4 ,the sublimed masses adhering to the lid are sorted1 ground and repeatedly washed with water4 ,according to ,callum's description of the manufacture of vermilion at ,hong ,kong1 mercury and sulphur are heated in a large iron pan1 with continual stirring at about the melting point of sulphur 7#aaa ,c471 until the whole has changed to a black mass4 ,after cooling1 this is mixed with water and mercury1 the mixture thoroughly stirred1 dried1 placed in a hemispherical dish and covered over with broken porcelain4 ,a similar dish is cemented on the top of the first1 and the dishes are heated for #af hours2 the vermilion adhering to the porcelain fragments is removed1 wet ground and dried4 ,a vermilion approaching ,chinese in beauty is said to be obtained by mixing ordinary vermilion with #a per cent4 of antimony sulphide and again subliming the mixture4 ,the dark grey sublimate produces a reddish brown powder1 which is repeatedly boiled with a solution of 8liver of sulphur0 7potassium polysulphide71 washed with water and digested for a long time with hydrochloric acid4 ,the author has repeatedly made vermilion by this process1 but could never obtain a product differing appreciably from the original vermilion4 7b7 ,,wet ,,methods4 ,the manufacture of vermilion in the wet way is founded on the conversion of metallic mercury or its compounds into mercuric sulphide by heating with alkaline sulphides1 such as ammonium sulphide and liver of sulphur4 ,the product always contains uncombined sulphur1 which is eliminated by treatment with alkalis4 ,apart from the danger to the health of the workmen caused by the poisonous mercury vapours1 which are present in rooms where mercury or its compounds are heated in apparatus even of the best construction1 and which is not to be feared in a wet process1 the vermilion prepared in the latter manner has a finer and brighter shade than that prepared by a dry process4 ,the greater cost of the wet process is covered by the higher value of the product4 ,the starting point of the wet method may be either metallic mercury1 black mercuric sulphide or another mercury salt4 ,when metallic mercury is used1 according to an old process1 #ajj parts are ground with #bc parts of flowers of sulphur and a little caustic potash solution to a homogeneous mass1 which is then heated with a solution of #ec parts of caustic potash in an equal quantity of water1 the evaporated water being continually replaced1 until the colour changes from brownish-red to the fiery red of vermilion4 ,when the colour approaches the desired shade a careful watch must be kept1 and immediately the proper shade is obtained the heating must be stopped4 ,if it is continued beyond this point for but a short time1 the vermilion at once loses its fire and cannot be again brightened4 ,an interruption in the heating is equally harmful1 a dull shade being produced4 ,when the proper shade has appeared1 the contents of the vessel are poured into a large quantity of water4 ,the vermilion is then washed with dilute caustic potash and afterwards with water until the alkaline reaction disappears4 ,it is finally dried4 ,the alkaline solutions obtained in this process contain considerable quantities of mercury in solution4 ,they are collected1 and when a sufficient quantity has accumulated the mercury is extracted4 ,barff recommends the following method3 ,mercury is rubbed with to of its weight of sulphur until a uniform grey powder results4 ,this is heated in a porcelain dish with caustic potash solution 7#acc parts of potash in #aej parts of water7 at #de ,c4 until the powder has become bright red4 ,heating above #de ,c4 is to be avoided2 it would impart a brown tinge to the vermilion4 ,a convenient process for making vermilion in the wet way is to first produce the black sulphide in the dry way and then treat this with alkalis4 ,brunner's method is founded on this procedure3 #ajj parts of mercury and #ch parts of sulphur are used to prepare the black sulphide4 ,this is heated with a solution of #be parts of caustic potash in #aej parts of water4 ,the operation is best conducted in a vessel placed in a water bath1 the temperature of which does not exceed #de ,c4 ,after heating #g to #h hours1 the mass begins to turn red1 when the change proceeds more quickly1 and the greatest care must be taken not to exceed the point at which the colour has reached its greatest brilliance4 ,as soon as the desired shade has appeared1 the temperature of the water bath is lowered1 but it is kept warm for several hours4 ,caustic solutions of different strengths produce different shades4 ,thus1 in order always to obtain the same product from the same quantities1 it is necessary to replace the evaporated water at short intervals4 ,in this process some quantity of mercury remains uncombined2 it is separated from the vermilion by a process of levigation in the washing4 ,firmenich's ,method4--,many wet methods for the manufacture of vermilion differ but little from the preceding4 ,in ,firmenich's method the production of the black sulphide is united with the formation of vermilion in one operation4 ,a solution of potassium sulphide of a certain strength is made by igniting #bj parts of potassium sulphate with #f parts of coal1 boiling the mixture with #ae time the quantity of rain water1 cooling the solution1 separating from the potassium sulphate which crystallises out1 and boiling the solution with sulphur so long as it is dissolved4 ,a mixture of #de parts of this solution1 #ajj parts of mercury1 and #b parts of sulphur is placed in flasks1 which are subjected for several hours to a shaking or rocking motion4 ,the liquid becomes greenish1 and its temperature rises in consequence of the combination of mercury with a portion of the sulphur of the potassium sulphide4 ,the latter immediately dissolves the free sulphur present1 and again gives it up to the mercury1 which in the course of a few hours is completely converted into the black sulphide4 ,the shaking is discontinued when the contents of the flasks have acquired a deep brownish-red colour4 ,the flasks are then placed in a room heated to #de ,c41 and their contents repeatedly shaken up4 ,at this temperature the transformation of the black into the red mercuric sulphide is completed4 ,the deposit in the flasks acquires more and more a scarlet shade4 ,as soon as the colour is found to have reached its greatest intensity the liquid is carefully poured off1 and the vermilion treated with caustic soda solution in order to dissolve free sulphur2 it is then very carefully washed4 ,in this process1 the temperature at which the operation commences is important4 ,the cooler the mixture which is placed in the flasks before shaking1 the paler will be the colour of the vermilion obtained4 ,it is to be supposed that the reaction1 which is but slow in the cold1 forms in consequence of its slowness a black sulphide of such character that in its subsequent transformation into the red crystalline sulphide very small crystals are produced4 ,the ,gautier-,bouchart method for the preparation of vermilion from mercury and ammonium sulphide is applied on the large scale as follows3 #a1jjj parts of mercury are shaken for #g hours with #bjj parts of flowers of sulphur and #djj parts of ammonium sulphide saturated with sulphur2 the dark-coloured mixture is exposed for several days to a temperature of #fj ,c41 when the colour changes to red4 ,in addition to the usual washings1 the mass is further treated with nitric acid4 ,the purpose of this operation is to oxidise all the free sulphur to sulphuric acid4 ,for a colour works in which1 in addition to vermilion1 are made other pigments1 especially such as are sensitive to the action of sulphuretted hydrogen1 this process1 which produces vermilion of a good shade1 although not particularly stable1 is not to be recommended on account of the evolution of sulphuretted hydrogen1 which cannot be completely prevented even by the greatest care4 ,liebig's ,process4--,the starting point in the manufacture of vermilion by this process is the compound known as white precipitate 7see below74 ,it is only necessary to heat white precipitate with a solution of ammonium sulphide saturated with sulphur1 at #dj to #ej ,c41 for a long time4 ,the operation may be conducted in well-closed flasks in a place the temperature of which is1 as nearly as possible1 #de to #ej ,c41 such as the flues leading from a furnace in constant use4 ,the change of colour is gradual2 this is an advantage1 since it is easier to obtain the correct shade4 ,by treating the product with weak caustic potash solution it may be made still brighter4 ,after washing and drying at a gentle heat the pigment is finished4 ,this method is especially adapted for manufacturers not exclusively engaged in making vermilion4 ,no special arrangement of apparatus is necessary2 the apparatus for making ammonium sulphide and a number of glass flasks are the only essentials4 ,there is another considerable advantage1 that the product cannot be completely spoiled4 ,the process of formation of the vermilion is tolerably slow2 a careful observation of the progress of the earlier operations is sufficient to determine the time required4 ,in order to be able to do this with certainty1 it is necessary to work always under exactly the same conditions2 the same quantity of white precipitate must always be used and the solution of ammonium sulphide must always have the same strength4 ,mercuric ,ammonium ,chloride1 ,infusible ,white ,precipitate1 ,hg,cl,n,h4--,this compound1 which is required in the last-mentioned process for the manufacture of vermilion1 is most cheaply made in the following way3 to a solution of #a part of common salt in #cb parts of water1 #b parts of dry mercuric sulphate are added in small quantities1 whilst thoroughly stirring4 ,it is absolutely necessary to work in this way1 because mercuric sulphate is decomposed by water into free sulphuric acid and a basic salt1 which is much more slowly converted into white precipitate than the neutral salt4 ,the liquid now contains mercuric chloride2 on the addition of ammonia to alkaline reaction it gives a heavy white precipitate4 ,the liquid is poured off and the precipitate washed with water containing a little ammonia1 until the washings give only a slight turbidity with barium chloride4 ,this process may also be commenced with mercuric chloride1 but the above method is cheaper4 ,white precipitate should volatilise without fusing when heated on platinum foil and should keep its white colour when treated with ammonia4 ,electrolytic ,process4--,in a wooden vessel #a metre in diameter and #b metres deep are placed1 at the sides1 dishes #ae centimetres wide1 containing a layer of mercury #a centimetre deep4 ,these dishes are connected with the positive pole of a dynamo4 ,the negative pole is connected to an iron plate1 electrolytically coated by copper1 placed at the bottom of the vessel1 which is filled with a solution containing #h per cent4 of ammonium nitrate and #h per cent4 of sodium nitrate4 ,a regular current of sulphur dioxide is introduced through a perforated coil4 ,the excess of gas escapes by a tube in the cover4 ,when the current is passed a precipitate of red mercuric sulphide is at once formed4 ,attempts have been made to dispense with the current of sulphur dioxide4 ,the bath then contains #ajj litres of water and #h kilogrammes each of ammonium nitrate1 sodium nitrate1 sodium sulphide and sulphur4 ,under these conditions it is only necessary to add sulphur and mercury in order to obtain1 at the end of the operation1 vermilion which is in no way inferior to that made by the first process4 ,vermilion is frequently grossly adulterated by cheaper pigments4 ,substances are often found under the name of vermilion which contain no trace of mercury1 but consist of bright orange lead mixed with a few per cent4 of ferric oxide1 and having a deceptive similarity in colour to the best vermilion4 ,mercuric ,iodide4--,when corrosive sublimate solution is precipitated with exactly the necessary quantity of potassium iodide1 mercuric iodide is obtained as a scarlet precipitate which surpasses in beauty even the best samples of vermilion4 ,unfortunately1 this substance cannot be used as an artists' colour4 ,exposure to light soon turns it brown and finally black4 ,it appears to be unaltered in the dark2 the author possesses a sample which has been so kept for #cj years without losing its shade in any way4 ,,chapter ,,xviii4 ,,antimony ,,vermilion4 ,antimony vermilion is a red pigment which will bear comparison in fineness of shade with mercury vermilion1 over which it has the advantage of cheapness4 ,in composition it is antimony trisulphide1 ,sb,s4 ,this compound is obtained by precipitating a solution of antimony trichloride with sulphuretted hydrogen4 ,however1 the precipitate1 which is a very fine red whilst wet1 loses its colour in drying1 and the product is almost worthless as a pigment4 ,in another way it can be obtained in such a condition that it loses nothing of its beauty in drying1 but retains its brilliance4 ,bttger gives the following process3 a solution of antimony trichloride is mixed with a solution of sodium hyposulphite 7thiosulphate7 and the liquid heated so long as a precipitate forms1 which is then washed on a filter with water containing acetic acid4 ,if pure water were used for washing1 the antimony chloride still present would be decomposed1 forming the white oxychloride1 which would detract from the shade of the antimony vermilion4 ,in this process particular regard is to be paid to the use of exact quantities of materials4 ,the finest product is obtained when #b parts of a solution of antimony trichloride1 which has exactly the specific gravity #ace1 are mixed with a solution of #c parts of sodium hyposulphite in #f parts of water4 ,according to ,r4 ,wagner1 antimony vermilion is obtained by dissolving #d parts of tartar emetic and #c parts of tartaric acid in #ah parts of water1 heating to #fj ,c41 mixing with a solution of sodium hyposulphite 7thiosulphate7 and heating to #ij ,c4 ,the precipitate is then carefully washed and dried4 ,pure antimony vermilion closely approaches1 as we have said1 ordinary vermilion in shade1 and for a sulphur compound shows a remarkable resistance towards chemical reagents4 ,by dilute acids1 ammonia and alkaline carbonates1 it is attacked only on long continued contact1 but it is easily decomposed by very dilute hydrochloric acid and by caustic alkalis4 ,a mixture with white lead keeps for a long time1 but there can be no question of the permanence of such a mixture1 in consequence of the oft-repeated properties of lead pigments4 ,antimony vermilion is well adapted for oil painting4 ,when ground with oil it exhibits a red of a brilliance in no way inferior to that of genuine vermilion4 ,it may also be used as a water colour1 but is not adapted for fresco work1 since it is quickly decomposed by lime4 ,in spite of these favourable properties antimony vermilion has so far been little used4 ,considering the small cost of its preparation1 especially when calcium hyposulphite1 which gives an equally good result1 is used in place of the sodium salt1 its use is to be recommended in the place of mercury vermilion4 ,it appears as if the high price demanded for this substance by several manufacturers has prevented its general employment4 ,appendix4 ,antimony ,blue4--,this fine blue pigment can be prepared by the addition of a dilute solution of potassium ferrocyanide to a clear solution of antimony in aqua regia4 ,according to ,krauss1 it contains no antimony as colouring principle1 but is a ,prussian blue obtained from the ferrocyanide1 which is decomposed by the strong acid1 with evolution of hydrocyanic acid4 ,,chapter ,,xix4 ,,ferric ,,oxide ,,pigments4 ,the pigments composed of ferric oxide are used in enormous quantity4 ,they are distinguished by a high degree of permanence4 ,large deposits of ferric oxide occur in nature1 and in places where it is found in considerable quantity iron is manufactured from it on the spot4 ,several varieties of natural ferric oxide are distinguished3 specular iron ore forms crystalline masses of brilliant lustre2 another variety in small crystals is called iron glance2 micaceous iron ore consists of shining scales2 red hmatite has the appearance of bundles of fibres2 an earthy variety of hmatite is also common4 ,the compound of ferric oxide with water1 ferric hydroxide1 is still more abundant than hmatite2 brown hmatite1 limonite and other iron ores consist essentially of this compound4 ,the pigment known as ochre is also ferric hydrate4 ,very pure red hmatite has so fine a red colour that it may often be used as a pigment after grinding or levigating4 ,the famous red of ,pompeii1 which has been found on the ruined walls of the town1 still shows1 after eighteen centuries' exposure to damp1 the brightest shade1 certainly a striking proof of the extraordinary permanence of this pigment4 ,considering its great permanence1 its easy preparation1 and its low price1 it is surprising that ferric oxide is not more extensively used by artists than it is at present4 ,it is used1 however1 extensively in colouring earthenware1 for which purpose its stability at high temperatures makes it suitable4 ,principally on account of its cheapness it is largely used in ordinary painting1 but for artistic purposes it is not used to the extent it deserves4 ,every colour maker well knows that artists justly complain that the pigments offered to them have generally but a small degree of permanence4 ,they are surprised that the paintings of the old masters show now1 after the lapse of centuries1 their colours unaltered1 whilst the pigments manufactured at the present day1 instead of corresponding to the high standard of chemical knowledge1 are often discoloured within a few months after use4 ,but it was just the restricted knowledge of chemistry which the ancients possessed which compelled them to make extensive use of the permanent earth pigments1 to which class of permanent colours ferric oxide belongs4 ,the advances of science have succeeded in preparing ferric oxide1 not only as a red pigment1 but in the different shades of red1 from yellow to brown and deep violet1 all consisting entirely of pure ferric oxide4 ,ferric oxide has the property of altering its molecular condition on protracted heating2 this change is accompanied by an alteration in colour4 ,if ferric oxide is heated for a very long time at the highest temperatures its colour changes at last to black4 ,ferric oxide can be prepared by different methods for artists' purposes4 ,the process by which it is made is not unimportant4 ,either ferrous or ferric salts can be employed as the raw material4 ,with the latter1 pure ferric oxide is at once formed1 or hydroxide1 which is converted into oxide by heating4 ,the ferrous salts are generally cheaper than ferric salts2 they are therefore commonly used for the preparation of ferric oxide1 as well as of the other iron pigments4 ,even in combination with the strongest acids1 ferrous oxide has but little stability2 when separated from its salts as ferrous hydroxide1 the greatest precautions must be taken to obtain it pure2 in contact with the air it at once takes up oxygen and changes to ferric hydroxide4 ,ferrous carbonate shows this same degree of instability2 the natural substance1 occurring in large crystals as spathic ironstone1 is no exception3 on exposure to the air it is gradually changed to ferric oxide4 ,there is another reason for the advisability of using ferrous salts to prepare ferric oxide4 ,when ferric hydroxide is made by precipitating the solution of a ferric salt with ammonia or caustic potash1 the least excess of the precipitant unites with the hydroxide to form a compound which is only decomposed by long washing with water4 ,the precipitate is1 however1 gelatinous1 and consequently very difficult to wash4 ,in order to prepare ferric oxide suitable for an artists' pigment the following process may be used3 #ag parts of soda are dissolved in #fh parts of water2 the solution is boiled in an iron pan1 and #aj parts of crystallised ferrous sulphate are added in small quantities with continual stirring4 ,the boiling and stirring are continued until the green vitriol has completely dissolved1 when the greenish white precipitate is allowed to settle1 washed several times with water1 and then exposed to the air in thin layers4 ,the precipitate1 which begins to turn yellow during washing1 becomes in a short time ochre yellow in the air1 being changed into ferric hydroxide4 ,after drying and calcining1 a fine red powder of pure ferric oxide is formed4 ,the shade depends on the temperature at which the substance is calcined3 the higher the temperature and the longer the heating is continued1 the darker is the product4 ,vogel's ,iron ,red4--,this preparation1 which is particularly brilliant and therefore highly suitable for an artists' colour1 is made by adding a saturated solution of oxalic acid to a boiling solution of green vitriol4 ,the greenish yellow precipitate of ferrous oxalate is collected on a filter and well washed with water4 ,after drying1 the precipitate is heated in a shallow iron dish to a temperature of #bjj ,c41 at which the ferrous oxalate decomposes and is converted into a soft fiery red powder consisting of pure ferric oxide4 ,by igniting this powder in covered crucibles the different shades of ferric oxide can be obtained4 ,macay's ,english ,red4--,seven hundred and four parts of ferrous sulphate1 #a1jjj parts of copper chloride1 and #a1fgh parts of common salt are dissolved1 the solution boiled and the precipitate ignited4 ,in the manufacture of fuming or ,nordhausen sulphuric acid1 ferric oxide is obtained as a residue4 ,it is then known under the names of ,english red1 caput mortuum1 colcothar1 rouge and ,indian red as a very cheap pigment4 ,it is also used as a polishing material4 ,fuming sulphuric acid is made by heating green vitriol at a white heat in retorts placed in furnaces2 sulphur dioxide and trioxide are evolved1 whilst in the retorts there remains a residue of almost pure ferric oxide1 containing small quantities of basic ferric sulphate1 which can only be decomposed by long continued violent heating4 ,the vapours of sulphur trioxide are caught in receivers containing oil of vitriol1 in which they dissolve and produce fuming sulphuric acid4 ,the residue in the retorts1 which has only a low commercial value1 can be converted into a good pigment without the expenditure of much money or labour4 ,it is ground in mills as finely as possible1 and1 if necessary1 afterwards levigated4 ,the fine powder is mixed with varying quantities of common salt1 the object of which is to prevent the temperature from rising too high in the calcining process4 ,common salt is volatile at a temperature approaching a strong red heat2 when the temperature has once risen so far1 a further rise is prevented by the heat taken up in volatilising the salt4 ,in order to make ferric oxide of a yellow tinge1 #b per cent4 of salt are added1 and the mixture heated with a moderate fire for #a hour4 ,to obtain the deeper shades1 the addition of common salt is increased even to #f per cent4 ,for a brownish-red oxide1 #d per cent4 of salt are added and the mixture heated for #d hours2 for a dark violet oxide1 #f per cent4 of salt are used1 and the mixture is heated for #f hours with the fiercest fire4 ,it has been observed that the shade of the product is finer the more completely air is excluded from the glowing mass and the more quickly the product1 after sufficient heating1 is cooled down to the ordinary temperature4 ,fire-clay tubes are used for heating the ferric oxide1 which are similar to gas retorts1 and are built one above the other in furnaces4 ,the number in one furnace may reach #fj4 ,each retort is closed by a well-fitting lid1 which is luted with clay after the retorts are filled1 a small opening being left through which the heated air may escape4 ,if the retorts were closed completely air-tight they would burst on heating4 ,ferric oxide pigments are made in very large quantity by several works1 which bring up to #bj different shades1 varying from reddish yellow to dark violet1 into the market4 ,on account of their great resistance to the action of the atmosphere and of chemical agents1 the ferric oxide pigments are particularly suitable for painting iron and other metals which are exposed to air or water4 ,they are also suited to fresco work4 ,lower qualities of iron reds are made by calcining ochres1 large deposits of which occur in nature1 and also from the residues of basic ferric sulphate obtained in the alum manufacture4 ,these varieties are at the best usable for ordinary painting1 but never for artists' pigments4 ,according to the method of ,steinau1 iron pigments can be made from wrought-iron scraps1 turnings1 etc41 by causing them to rust through alternate contact with air and water4 ,the resulting ferric hydrate is either at once used as a pigment or converted into other shades by calcining4 ,by heating in the air a red pigment is formed2 by heating with coal in the absence of air a black2 and from mixtures of red and black different shades of brown4 ,if the iron turnings can be obtained cheap1 this process should be well adapted to the manufacture of fine iron pigments4 ,indian ,red consists of ferric oxide4 ,it was originally obtained from a very pure hmatite1 occurring in ,india1 by grinding and levigating4 ,it can1 however1 also be artificially made1 in shades varying between bright red and dark brownish-red1 by heating pure ferric oxide4 ,this valuable pigment is extremely brilliant and durable4 ,the darkest brownish-red shades can be obtained from ,indian red by mixing it with varying quantities of litharge1 and heating the mixture very strongly in a covered crucible4 ,,chapter ,,xx4 ,,other ,,red ,,mineral ,,pigments4 ,chrome ,red or ,chrome ,vermilion4--,under the most varied names1 chrome orange1 ,persian red1 ,derby red1 ,chinese red1 ,indian red1 chrome vermilion1 etc41 there occur in commerce numerous pigments1 orange to dark red in colour1 which can all be made from neutral lead chromate4 ,when this salt1 i4e41 ordinary chrome yellow1 is treated with smaller or larger quantities of a strong base1 such as caustic potash or caustic soda1 8basic0 lead chromates are formed1 which exhibit a more intense red shade the more lead they contain4 ,these compounds can be made either by adding caustic potash to the solution of potassium chromate used for making the chrome1 or the precipitated chrome yellow may be treated with caustic potash4 ,the latter process readily yields good results1 so that it is generally followed4 ,recent researches have shown that differences in the shade of chrome red are due to the varying size of the single microscopic crystals of which it consists4 ,when chrome reds of the most different shades are ground the powder has almost the same colour4 ,the larger are the crystals the deeper is the shade of the red1 so that the art of making deep chrome red lies in working so as to produce large crystals4 ,as was said in describing the preparation of chrome yellow1 the lead liquors used in its manufacture contain varying quantities of acetic acid1 which affect the shade of the product4 ,the quantities of caustic potash necessary to turn a certain quantity of chrome yellow into chrome red of a certain shade can1 therefore1 only be estimated from time to time in an empirical manner4 ,this estimation may be performed by the method of ,habich with great certainty4 ,the precipitate of chrome yellow is made in the ordinary way1 and well washed #f to #h times4 ,equal portions of the paste are brought into vessels of equal height and diameter4 ,to the first of these portions caustic soda solution of a certain strength is added2 to the second rather stronger caustic soda solution2 in each succeeding vessel the strength of the solution is increased to a known extent4 ,after the addition of caustic soda the vessels are energetically shaken4 ,they are then set aside for the precipitate to settle in a place completely free from vibration4 ,in one of the vessels1 an orange or red shade will be seen very similar to that it is desired to make4 ,now1 it is known how much caustic soda solution of a certain strength has been added to this quantity of colour1 so that the quantity necessary for the whole of the chrome yellow precipitate may be found by a simple calculation4 ,in working on the large scale1 the process is exactly the same as in the preliminary test2 the calculated amount of caustic soda solution is added to the precipitate in the tub1 it is well stirred1 and left at rest for some hours4 ,when the proper shade appears1 the liquid above the precipitate1 which contains sodium chromate in proportion to the strength of the caustic soda solution used1 can be drawn off and used to precipitate fresh lead acetate solution4 ,the precipitate is washed first in the tub and then on the strainers4 ,since1 as has been said1 the depth of colour depends upon the size of the single crystals1 care should be taken in washing the precipitate not to agitate it too vigorously1 or the pigment will lose in depth by the breakage of a large number of crystals4 ,special formul for the manufacture of chrome red are abundant1 but if the above process be followed they are superfluous1 and it is only for the sake of completeness that one or two are given4 ,deep chrome red is made by the action of #be parts of caustic soda on #ajj parts of pure chrome yellow4 ,a noteworthy process is due to ,liebig4 ,saltpetre is melted in a crucible1 and heated to a temperature below that at which oxygen is evolved4 ,dry chrome yellow is introduced so long as effervescence occurs2 the fused mass appears1 whilst liquid1 deep black4 ,as soon as it is in quiet fusion it is poured on a cold plate4 ,in consequence of the rapid cooling it becomes brittle and can be easily powdered4 ,the hot mass is broken up and boiled with water1 potassium chromate going into solution4 ,the chrome red made by this process is little inferior in brilliance to vermilion4 ,according to ,prinveault a handsome chrome red is obtained by treating #be grammes of neutral lead carbonate with #aj grammes of yellow potassium chromate dissolved in #e litres of water1 boiling for half an hour1 washing the violet precipitate1 and finally treating with #a gramme of sulphuric acid diluted with #ajj grammes of water4 ,cobalt ,red consists of cobalt phosphate4 ,it was first recommended by ,salvetat4 ,it is obtained by precipitating a solution of a cobalt salt by sodium phosphate4 ,after drying at the ordinary temperature the precipitate has a beautiful rose-red colour4 ,by careful heating1 the shade becomes more violet according to the temperature used4 ,cobalt-,magnesia ,red4--,when magnesia is moistened with the solution of a cobalt salt and strongly heated1 a rose-red mass is obtained which can be used as an extremely durable artists' colour4 ,it probably consists of a compound of cobalt oxide with magnesia4 ,the method of preparation is as follows3 ,magnesium carbonate is mixed to a thin paste with a dilute solution of cobalt nitrate2 this is heated and stirred until quite dry1 when the residue is strongly heated in a covered crucible4 ,in the manufacture of this and other cobalt pigments it is of particular importance to prevent the entry of the fire gases into the crucible4 ,unless this is done a product of good colour is not obtained4 ,cobalt ,arsenate4--,by precipitating a cobalt salt with sodium arsenate1 a violet-red precipitate is obtained which leaves a fine durable red on heating4 ,the mineral erythrite has a similar composition and colour4 ,this pigment has a bright shade1 is permanent1 and although it contains arsenic is not particularly poisonous1 since after fusion it is little soluble4 ,chromium ,stannate4--,this artists' pigment1 which may be used in oil and porcelain painting1 is made in the following manner 7,gentele73 #a kilogramme of tin is converted by strong nitric acid into metastannic acid1 #ej grammes of potassium chromate are dissolved in #a litre of water1 the solution mixed with #b kilogrammes of chalk and #a kilogramme of powdered quartz1 and finally with the metastannic acid4 ,the mixture is dried and strongly heated4 ,the temperature must be raised to a white heat1 at which the mass sinters and acquires a dark rose-red colour4 ,it is then completely extracted with boiling water1 when a fine powder is left4 ,this pigment1 which is known in the market as 8pink colour10 may be used with advantage in oil painting in the place of rose madder lake1 over which it has the advantage in durability4 ,silver ,chromate4--,a solution of silver nitrate gives1 with potassium chromate1 a deep red precipitate of silver chromate1 which is occasionally used as an artists' pigment under the name of 8purple red04 ,not only is the price of this pigment high1 but it has little durability1 since1 like all silver compounds1 it is acted upon by sulphuretted hydrogen and turned dark1 owing to the formation of black silver sulphide4 ,,chapter ,,xxi4 ,,purple ,,of ,,cassius4 ,purple of ,cassius1 or gold purple1 is not a pigment for painters' use2 it is employed for colouring glass1 for porcelain painting and for coloured glazes4 ,for these last purposes we know nothing which can completely replace purple of ,cassius1 so that its preparation will be described here4 ,its costliness prevents its general use4 ,as regards the chemical constitution of purple of ,cassius very diverse views are held4 ,chemists have not yet succeeded in explaining it2 some regard it as aurous stannate1 others as stannic acid1 in which a particular form of gold of a red colour is contained in an extremely finely divided condition4 ,there are reasonable grounds for both opinions4 ,theoretical considerations are of little interest to the manufacturer1 who is chiefly interested in the method by which he can prepare a product which satisfies the demands of the consumer4 ,purple of ,cassius has been known for nearly two hundred years1 hence there are many formulas for its preparation4 ,before these are enumerated it is necessary to give an account of the conditions under which this substance is formed4 ,in order to obtain gold purple1 a solution is required which contains both stannous and stannic chlorides2 if this solution is mixed with a very dilute solution of gold chloride a precipitate is obtained which is generally brownish red1 and only acquires its fine red shade on igniting4 ,the colour shown by the purple after precipitation is no guide to the shade of the finished product2 a purple which shows a very fine colour whilst wet often produces a pigment of much less beauty than an actually ugly precipitate4 ,these differences are to be ascribed to the varying molecular condition of the purple1 for the different varieties show very small differences in chemical composition4 ,according to the directions of ,fuchs1 a fine purple is obtained by mixing a solution of stannous chloride with sufficient ferric chloride solution to give the mixture a green colour4 ,part of the ferric salt is then reduced to ferrous salt1 whilst the stannous chloride is partially oxidised4 ,at the same time a solution of gold chloride is made2 this must be quite free from nitric acid and contain #a part of the salt in #djj to #ejj parts of water4 ,the tin solution is added drop by drop to the gold solution with constant stirring2 the mixture becomes turbid1 but the precipitate requires a long time to settle on account of its fine state of division4 ,the depth of colour shown by the purple varies according to the strength of the solutions4 ,m4 ,mller states that the following process gives the best results3 ,the quantity of stannic chloride equivalent to #i grammes of stannic acid is dissolved in #bjj cubic centimetres of water2 potassium carbonate is added to alkaline reaction1 then #a gramme of gold in the form of chloride4 ,grape sugar is added to the mixture1 which is made up to #cjj cubic centimetres by water1 and warmed until the brightest shade is reached4 ,when a very gelatinous mass is formed after the addition of the potassium carbonate it is heated for a short time before adding the gold solution and grape sugar4 ,wchter gives directions for obtaining pale and deep shades4 ,to obtain the pale purple #e grammes of tin are dissolved in aqua regia1 the solution evaporated to dryness on the water bath1 the solid residue mixed with a solution of #b grammes of stannous chloride and dissolved in #aj litres of water4 ,to this liquid is added a solution of #je gramme of gold in aqua regia1 and immediately #ej grammes of ammonia to neutralise free acid4 ,the precipitate separates spontaneously from the dark red liquid2 its formation may be hastened by adding sulphuric acid4 ,the washed precipitate is mixed whilst moist by means of a silver spatula with #bj grammes of lead flux1 #b grammes of red lead1 #a gramme of quartz sand1 and #a gramme of calcined borax4 ,the mixture is then dried2 it produces a purple red colour4 ,if #c grammes of silver carbonate are added1 a clean1 pale purple pigment results4 ,the deep purple is made by mixing a solution of #je gramme of gold in #aj litres of water with #ge grammes of stannous chloride solution 7specific gravity1 #ag7 whilst stirring1 and adding a few drops of sulphuric acid4 ,the washed precipitate is mixed with #aj grammes of lead flux and #je gramme of silver carbonate4 ,a rose-red shade of gold purple is obtained by dissolving #a gramme of gold and mixing the solution simultaneously with solutions of #ej grammes of alum in #bj litres of water1 and of #ae gramme of stannous chloride 7specific gravity1 #ag74 ,ammonia is now added until all the alumina is precipitated4 ,in order to prepare from the dried precipitate the mixture which will produce the colour on fusion1 it is mixed with #ej grammes of lead flux and #be grammes of silver carbonate4 ,magnesia ,gold ,purple4--,according to ,m4 ,mller1 the colour of gold purple is produced by covering the particles of a very finely divided white substance with metallic gold4 ,thus1 when calcined magnesia is stirred up with water1 gold chloride solution added1 and the mixture warmed to #ajj ,c41 the gold is precipitated upon the magnesia2 the wet1 yellow powder acquires a reddish shade on drying1 which at a red heat becomes so beautiful a carmine-red that it surpasses purple of ,cassius in fineness of shade4 ,a purple which contains #bj grammes of gold as chloride to #hd grammes of magnesia has the most pure carmine tint2 the shade varies with the proportion of gold to magnesia4 ,the different shades of purple contain the following percentages of gold3-- ,percentage of ,gold4 ,shade of the ,purple4 #cce ,brownish-red 7excess of gold74 #bej ,deep carmine-red4 #bjj ,medium carmine-red4 #ajj ,pale carmine4 #ej ,a good rose-red4 #cj ,rose-red4 #aj ,pale rose4 #jb ,delicate rose4 #ja ,appreciable red tint4 ,alumina ,gold ,purple is obtained1 according to ,mller1 by adding gold chloride and excess of potassium carbonate to alum solution and boiling4 ,the purple obtained in this way is as deep in colour with #aj per cent4 of gold as a magnesia purple with #bj per cent4 of gold1 but has a more bluish violet shade4 ,if1 in the preparation of purple1 the alumina is precipitated by potassium carbonate and the gold chloride reduced by grape sugar1 a different shade of purple is obtained to that in the precipitation of which ammonia is used4 ,the alumina gold purple is specially adapted for the production of porcelain enamels4 ,,chapter ,,xxii4 ,,blue ,,mineral ,,pigments--,,iron-,,cyanogen ,,pigments4 ,the pigments occurring in commerce under the names of ,prussian1 ,chinese1 ,berlin or ,paris blue consist1 when pure1 of ferric ferrocyanide1 ,fe,fe7,,cn74 ,this compound is obtained as a deep blue precipitate when yellow prussiate 7potassium ferrocyanide7 is mixed with the solution of a ferric salt4 ,the precipitate shows certain differences in composition according to the exact method by which it is obtained4 ,a different result is obtained when the solution of the ferric salt is poured into that of a ferrocyanide1 to that produced by the reverse procedure1 the precipitate produced in the one case has properties which it does not possess in the other4 ,similar differences often occur in precipitating pigments4 ,if the solution of the ferrocyanide is poured into the iron solution1 the latter being in excess1 an insoluble precipitate is formed2 but if the iron solution is poured into the ferrocyanide solution of which an excess is present1 the blue precipitate is formed1 but it is soluble in pure water1 though not in water containing salts4 ,thus when this precipitate is separated from the liquid and washed1 the washings are at first quite colourless and remain so whilst salts are present1 but when these have been completely washed away1 a fine blue solution of the ferric ferrocyanide is formed1 from which the addition of a salt solution again separates the dissolved ,prussian blue4 ,before proceeding to the manufacture of ,prussian blue on the large scale1 it is necessary to consider the behaviour of ferrous salts towards yellow prussiate1 since these are commonly used instead of ferric salts4 ,when a solution of potassium ferrocyanide is mixed with a solution of a ferrous salt1 there is formed a pure white precipitate of potassium ferrous ferrocyanide1 ,k,fe,fe7,,cn74 ,in order to obtain a completely white precipitate1 it is necessary that the ferrous salt should be completely free from ferric salts and that the solutions should contain no dissolved oxygen2 the solutions would therefore have to be boiled before mixing4 ,if one of the solutions contains the smallest quantity of oxygen a bluish precipitate is formed4 ,when the white precipitate of potassium ferrous ferrocyanide is exposed to the air it immediately acquires at the surface a dark blue colour1 and is completely changed to ,prussian blue by sufficiently long contact with air4 ,in accordance with this behaviour of ferrous and ferric salts different methods may be used to obtain ,prussian blue4 ,either the process is commenced with a ferric salt from which a precipitate of ,prussian blue is at once obtained1 or the solution of a ferrous salt is converted into ferric salt by a powerful oxidising agent1 such as chlorine or nitric acid1 or a solution of a ferrous salt is precipitated with yellow prussiate and the white or bluish precipitate1 which consists chiefly of potassium ferrous ferrocyanide1 converted into ferric ferrocyanide or ,prussian blue by treatment with nitric acid4 ,prussian blue is also known1 as we have said1 as ,chinese blue1 ,berlin blue and ,paris blue2 ,brunswick blue or mineral blue is another form4 ,generally the product under the name of ,chinese or ,paris blue1 which has an intense dark blue colour1 is quite pure1 whilst under the names of ,prussian blue and ,berlin blue mixtures with starch or alumina are included1 which consequently have a more or less pale colour4 ,the pigments known as mineral or ,brunswick blue are the least valuable1 they have generally a less deep colour and are quite without the metallic lustre which distinguishes ,chinese blue and the better varieties of ,prussian blue4 ,mineral blue often contains very large quantities of alumina1 chalk1 or even barytes2 the addition of the last is to be regarded as irrational1 since it makes the pigment conspicuously heavy4 ,chinese ,blue4--,pure ,chinese blue appears in the form of deep blue masses1 characterised by a peculiar metallic lustre1 which is especially marked when the surface of a lump is rubbed with the finger nail4 ,this metallic lustre is accompanied by a copper-red shimmer which is similar to that exhibited by fine indigo4 ,in large pieces pure ,chinese blue appears very dark by artificial light2 it possesses enormous strength of colour4 ,the following test serves for the recognition of the complete purity of ,chinese blue3 ,a small quantity is powdered and rubbed in a thin layer on white paper2 if the metallic lustre shows in undiminished strength the blue may be regarded as quite pure1 for ,chinese blue quickly loses this property by additions of other substances4 ,from what has been said above concerning the different behaviour of ferrous and ferric salts1 the simplest method of making ,chinese blue would be to precipitate the solution of a ferric salt with yellow prussiate1 keeping the ferric salt in excess1 to wash and dry the precipitate4 ,ferric salts are1 however1 dearer than ferrous salts1 so that the latter are generally used4 ,in making ,chinese blue from a ferrous salt ferrous sulphate or green vitriol is generally taken4 ,this salt is dissolved in water2 it is advisable to add a small quantity of sulphuric acid1 since the water will contain carbonates1 which produce ferrous carbonate4 ,air oxidises the latter to ferric hydroxide1 which is brown1 and if present even in small quantity will spoil the shade of the blue4 ,this addition of sulphuric acid is of special importance when the white precipitate produced by the prussiate solution is to be oxidised by the air4 ,a solution of yellow prussiate is added to the iron solution in such quantity that a very small excess of iron salt is left2 there results a white or rather1 since the ferrous sulphate always contains small quantities of ferric oxide1 a pale blue precipitate4 ,this is allowed to settle1 the liquid drawn off as completely as possible from the precipitate1 and nitric acid then added1 or a solution of bleaching powder1 followed by the amount of sulphuric acid required to decompose it4 ,the nitric acid or the chlorine liberated from the bleaching powder speedily effects the oxidation1 changing the pale blue colour to the deep blue of ,chinese blue4 ,the precipitate should be left for several days in contact with the liquid in order to complete the oxidation2 it is then well washed and dried4 ,pieces of definite shape and size bearing the trade mark of the firm are often pressed from the blue when it has acquired a stiff consistency4 ,there are many formul for the preparation of ,chinese blue1 differing in regard to the quantities of green vitriol1 yellow prussiate1 and nitric acid or bleaching powder to be used4 ,it is1 however1 clear that only one formula can be correct1 that in which the quantities of materials are equivalent1 since the reactions take place between equivalent quantities4 ,in practice the equivalent quantities would not be weighed to the tenth of a gramme--there would be no object in such a proceeding1 since in works chemically pure substances are not used2 but manufacturers should work according to equivalent quantities in order to use up their materials as completely as possible4 ,no increase in labour is involved1 the same labour weighs one or another quantity4 ,the proportion of materials in which the least loss is involved is here given4 ,nine kilogrammes of green vitriol are dissolved in #ajj litres of water1 #ae kilogrammes of strong sulphuric acid are added1 and then a solution of #ae kilogrammes of yellow prussiate in #ajj litres of water4 ,the solutions are kept in constant motion during the mixing4 ,as soon as the decomposition is finished1 without waiting for the precipitate to settle1 steam is led in and #bj kilogrammes of nitric acid of #acbih specific gravity added in small portions4 ,the heating by direct steam is continued until red vapours are no longer evolved from the liquid1 which is a sign that the oxidation is finished4 ,although the use of direct steam is very convenient for heating1 since wooden vessels can be used and the heating quickly accomplished1 it may be dispensed with1 and the solutions heated in pans or even not at all4 ,in this case the oxidation lasts considerably longer than when the liquid is heated4 ,in the process recommended by ,gentele #aji parts of yellow prussiate are used to #bj parts of green vitriol1 each dissolved in much water4 ,the precipitate is heated for a short time with #ea parts of nitric acid of #abbhe specific gravity and #af parts of sulphuric acid4 ,the mixture is allowed to stand for several days to complete the oxidation before the precipitate is separated from the liquid4 ,in ,hochsttter's method1 solutions of #f parts of yellow prussiate in #ae parts of water and of #f parts of green vitriol in #e parts of water are mixed4 ,to the precipitate #bd parts of strong hydrochloric acid and #a part of sulphuric acid are added1 and then a solution of bleaching powder in #hj parts of water until the liquid smells distinctly of chlorine4 ,apart from the fact that this method does not employ equivalent quantities of iron salt and yellow prussiate1 it is also to be regarded as unsuitable1 since the addition of sulphuric acid produces calcium sulphate1 which1 being soluble with great difficulty1 will be precipitated along with the blue1 making the shade lighter4 ,the addition of sulphuric acid should be omitted and only hydrochloric acid used1 the calcium chloride formed by the decomposition of the bleaching powder being very soluble in water4 ,many formul given for the manufacture of ,chinese blue are said to produce a pigment of special beauty4 ,this1 however1 is incorrect4 ,chinese blue is a compound of fixed composition1 which is always formed when equivalent quantities of the salts are used and the precipitate converted into the blue compound by one of the oxidising agents given4 ,it is most simple to use nitric acid as the oxidising agent2 for this purpose the presence of chlorine in the acid is harmless4 ,when sufficient space and time are allowed1 a special oxidising agent may be omitted and the oxidation of the white precipitate accomplished by atmospheric air4 ,in working in this manner the precipitate is washed several times with water1 and spread in a thin layer upon boards which are placed in rows one above the other4 ,in a short time the mass turns blue on the surface1 but the pale colour remains underneath much longer1 since the access of oxygen to the interior is difficult4 ,the boards must be left until the mass has a uniform colour throughout4 ,in order that the paste shall not dry too thoroughly whilst on the boards it is desirable to make it very fluid4 ,if the precipitate has been completely washed before the oxidation the product is finished after drying1 but if a portion when completely dried shows a crystalline incrustation1 salts are still present1 which must be removed by careful washing4 ,prussian ,blue4--,as we have already stated1 ,prussian blue is identical in chemical nature with ,chinese blue1 from which it differs only by certain additions which are made in order to reduce the price4 ,prussian blue should therefore be regarded as a more or less impure ,chinese blue2 less pure materials are used in its preparation than for the fine ,chinese blue4 ,instead of pure potassium ferrocyanide1 the crude salt1 which is sold by the prussiate makers at a lower price1 is used for ,prussian blue2 in addition to the ferrocyanide this crude salt contains a considerable proportion of other salts1 including a quantity of potassium carbonate4 ,the ferrous sulphate used for ,prussian blue is mixed with alum1 which neutralises the potassium carbonate1 precipitating alumina1 by which the precipitate formed from the yellow prussiate and ferric salt is made paler4 ,if the pale blue precipitate were treated with acids they would first dissolve out the alumina2 this should be avoided1 since the alum has been added with the intention of increasing the quantity of precipitate and making the pigment paler4 ,the precipitate can therefore only be changed into the blue pigment by spontaneous oxidation2 this is accomplished by the oxygen of the air in the manner previously described4 ,the oxidation is more rapid according to the quantity of ferric salt contained in the green vitriol at the commencement2 it is convenient to prepare a large quantity of green vitriol solution and expose it in shallow vessels to the air so that the oxidation may proceed4 ,but if the solution of green vitriol were exposed alone to the action of the air a rust-coloured precipitate of basic salt would be deposited at the bottom of the vessels4 ,to prevent the formation of this basic salt1 sulphuric acid is added in small quantity1 and1 as the oxidation proceeds1 further small quantities of acid are added4 ,in this way a solution of ferric sulphate is slowly formed1 which gives with yellow prussiate a blue precipitate requiring little further oxidation4 ,mineral ,blue1 ,brunswick ,blue4--,this pigment1 the most reduced of the colours of this class1 is obtained by mixing white pigments1 barytes1 pipe clay1 etc41 with the already impure ,prussian blue4 ,soluble ,prussian ,blue4--,the modification of ferric ferrocyanide easily soluble in water is obtained by adding a solution of a ferric salt to a solution of yellow prussiate1 the latter being in considerable excess4 ,brcke gives the following method3 a solution is prepared of #bag grammes of yellow prussiate in #aa kilogrammes of water4 ,another solution contains #ajj grammes of ferric chloride in #a litre1 #a litre of which is mixed with #b litres of a saturated solution of ,glauber's salt and the mixture added to the prussiate solution so long as a blue precipitate forms4 ,the ,glauber's salt plays no part in the formation of the colour2 it is added to prevent the solution of the precipitate1 which is insoluble in salt solutions4 ,the precipitate is brought on to a filter and washed with water until the washings begin to be blue1 which is a sign that the salts have been almost completely removed4 ,the precipitate cannot be further washed without the loss of a large quantity which would be dissolved by the water2 without further washing it is slowly dried in the air4 ,soluble ,prussian blue has but a limited application2 anatomists use its solution to inject specimens1 and it was formerly used for blue writing inks1 for which purpose aniline dyes are now preferred4 ,it may also be remarked that ordinary ,prussian blue readily dissolves in a solution of oxalic acid2 the solution was also used as a writing ink1 but since it attacks steel pens1 it has now been replaced by solutions of dyes which have no action on steel4 ,special ,processes for the ,manufacture of ,chinese ,blue4--,in place of chlorine or nitric acid manganic chloride can be used to oxidise the white precipitate obtained from yellow prussiate and green vitriol4 ,this process is based upon the property of manganic chloride to readily give up part of its chlorine and be changed into manganous chloride 7the ordinary chloride of manganese74 ,the conversion of the white precipitate into the blue is thus also in this case indirectly effected by chlorine4 ,many varieties of pyrolusite contain considerable quantities of manganic oxide which are of little use in the manufacture of chlorine1 for which pyrolusite is chiefly employed4 ,if such pyrolusite be digested with crude hydrochloric acid for several days1 the manganic oxide is dissolved with the production of manganic chloride4 ,the oxidation of the white precipitate is performed in the usual way2 after running off the liquid an excess of manganic chloride solution is added1 as soon as two tests taken at an interval of a few minutes show no further increase in the depth of the colour1 the reaction is ended and the solution of manganous chloride is drawn off4 ,any powerful oxidising agent may be used to oxidise the white precipitate2 chromic acid has been proposed for this purpose1 but up to the present the chromates are too dear to be used in place of the cheap oxidising agents previously mentioned4 ,in regard to the present endeavours to utilise by-products of the chemical industries1 a method for preparing this pigment may be mentioned which would certainly be very profitable on the large scale4 ,coal gas before purification contains some quantity of ammonium cyanide1 which is decomposed by ferric oxide with the production of ,prussian blue4 ,this pigment might be made by passing coal gas over very finely divided ferric oxide1 until it was completely converted into ,prussian blue4 ,the process is1 however1 not practicable on the large scale3 the ferric oxide would have to be exposed in an extremely thin layer to be completely converted into ,prussian blue1 and the transformation would require a long time4 ,a better process is to make yellow prussiate instead of ,prussian blue4 ,a mixture of ferric oxide with coarse sawdust is spread out in thin layers1 over which the impure coal gas passes4 ,when the mass has acquired a blue colour owing to the ,prussian blue produced1 it is treated with a mixture of quicklime and potassium sulphate4 ,potassium ferrocyanide is formed2 it is obtained in crystals by the evaporation of the solution and can be used in the preparation of ,prussian blue4 ,the 8,laming's mass10 now generally used in gas works1 contains1 after use1 a considerable quantity of cyanogen compounds1 and it would only require a short trial to decide whether it was more advantageous to make this mixture by exposure to air again suitable for the purification of coal gas1 or to use it to obtain yellow prussiate4 ,turnbull's ,blue4--,when a solution of a ferrous salt is precipitated by potassium ferrocyanide1 a fine blue precipitate is formed1 identical in physical properties with ,chinese blue1 but differing in chemical constitution4 ,it is ferrous ferrocyanide1 ,fe,fe7,,cn74 ,the manufacture of ,turnbull's blue is expensive2 the pigment has no specially advantageous properties and is therefore seldom made4 ,in preparing this pigment1 a solution of yellow prussiate is transformed into red prussiate by passing chlorine through it so long as it is absorbed by the liquid2 the mother liquors from which red prussiate has been crystallised may be used with advantage4 ,when to the solution of red prussiate green vitriol solution is added so that the former remains in excess1 a soluble ,turnbull's blue is obtained1 but when excess of green vitriol is used the insoluble form is produced4 ,chinese blue and ,turnbull's blue are used both as oil and water colours1 and these handsome but not particularly durable pigments are also employed in colouring wall papers4 ,antwerp ,blue is a mixture of ,prussian blue with zinc cyanogen compounds4 ,it is obtained by precipitating a solution of #b parts of zinc sulphate and #a to #b parts of green vitriol 7according as pale or deep blue is required7 by a dilute solution of yellow prussiate4 ,,chapter ,,xxiii4 ,,ultramarine4 ,at the present time blue1 green1 red and violet pigments come into the market under the name of ultramarine4 ,the green and blue have been commercial articles for about seventy years2 the violet and red were introduced about the year #ahfj4 ,at first the name ultramarine was restricted to a natural blue pigment obtained from lapis lazuli1 which was extremely costly4 ,accounts of the payments of ,italian artists1 still extant1 show the expensive nature of the ultramarine blue used in their paintings4 ,at that time1 when artists were compelled themselves to make the majority of their pigments1 ultramarine was made in a most laborious manner from lapis lazuli1 for which incredibly high prices were paid4 ,in order to make the mineral easier to powder the lumps were heated1 and1 whilst hot1 thrown into water4 ,they were then powdered as finely as possible4 ,the powder was mixed with melted resin1 and the mixture kneaded under water for a long time4 ,the ultramarine suspended in the water by this crude method of levigation was obtained by allowing the wash waters to settle4 ,few places are known at which lapis lazuli occurs in quantity4 ,it is chiefly obtained in ,china and ,thibet1 and1 considering the little intercourse between ,europe and these distant countries at that time1 it is no wonder that the price of ultramarine was fabulously high4 ,one ounce cost about #h--;a price which is explained by the small yield of ultramarine from the best lapis lazuli4 ,by the most careful work not more than from #b to #c per cent4 of the mineral was obtained1 the residue consisted of foreign minerals4 ,the enormously high price of this pigment was the stimulus for the endeavours to make it artificially4 ,the attempts are to be regarded not only as completely successful1 but it must be allowed that science has gone a considerable step further than nature1 since the researches have made it known that there is not only a blue ultramarine1 but also a green1 and1 according to the latest researches1 there exist in addition violet1 red and white compounds1 also to be described as ultramarines4 ,with the discovery of the methods by which ultramarine can be made artificially1 the preparation of this pigment from lapis lazuli came to an end1 and has now but historic interest4 ,the discovery of artificial ultramarine is due to the ,french chemist ,guimet and to the great ,german chemist ,gmelin4 ,ultramarine was first manufactured in ,germany in the year #ahbh by ,a4 ,kttig1 as a branch of the porcelain works at ,meissen in ,saxony1 where the manufacture was continued for about fifty years4 ,the discovery of the aniline dyes is rightly called a triumph of human intellect4 ,the artificial manufacture of ultramarine deserves the same description in no less degree1 although it has not effected so great a revolution as the former4 ,attempts to make ultramarine artificially would naturally be based on the analysis of the natural product4 ,the following comparison of the compositions of natural and artificial ultramarines shows how nearly the artificial product approaches the natural3-- ,,natural ,,ultramarine4 ,clment and ,desormes4 ,gmelin4 ,silica #ceh per cent4 #dgca per cent4 ,alumina #cdh 0 #bbjj 0 ,soda #bcb 0 #abjf 0 ,lime #ca 0 #aee 0 ,sulphuric acid ---- 0 #dfh 0 ,sulphur #ca 0 #jai 0 ,water and organic matter ---- 0 #abba 0 ,,artificial ,,ultramarine4 ---------------------------------------- -------------------------- ,blue4 ,green4 ---------------------------------------- --------------------- ,observer4 ,warrentrapp4,elfen4,brunner4,pohl4 ,gentele4 ,silica #defj #djj #cbed #cffg #dgca ,alumina #bcca #bie #bebe #cbab ,soda #badg #bcj #afia #bade #ciic 7sodium silicate7 ,potash #age ---- ---- ---- #cib ,lime #jjb ---- #bch ---- #aac ,sulphuric ,acid #chc #cd ---- #bjh ---- ,sulphur #afi #da #aafc #gbb #ffb ,iron #ajf #aj #bbe trace #aie 7ferric silicate7 ,water ---- ---- ---- ---- ---- ,oxygen ---- ---- #ijd #jeh ---- ---------------------------------------- --------------------- ,i4 ,szilasi found three samples of green ultramarine to have the following composition3-- ,water #bbj #abj #aai ,aluminous residue #ahj #adb #ada ,silica #afgc #agah #afgd ,aluminium #aeib #aehg #afae ,sodium #ahdb #ahah #ahaj ,sulphur #gai #fig #fhe ,there are many other analyses in addition to those we have given and agreeing with them1 so that there is no doubt as to the composition of ultramarine1 but as to the manner in which the elements are grouped nothing is definitely known4 ,some chemists are of the opinion that the colouring principle of ultramarine is a sulphur compound of iron1 whilst others oppose this view and consider that the colour is due to the combination of a double silicate of alumina and soda with an unknown sulphide of sodium4 ,although no blue or green compound is known of corresponding composition1 the majority of chemists incline to the latter view4 ,experience has shown that the presence of iron in any of the materials used in the manufacture of artificial ultramarine is very dangerous to the success of the operation1 and at the least considerably injures the beauty of the product4 ,although the manufacture of ultramarine is now very well known1 it cannot be denied that some works produce a pigment of a shade which cannot be obtained by others4 ,these works keep their method very secret1 so that it is not possible to say with certainty whether they have introduced a process varying from that commonly known1 or whether1 by carefully watching the process1 they have achieved great technical dexterity in the manufacture of this product4 ,the latter appears the most probable1 for in order to obtain a good result1 many experiments1 and an accurate knowledge of the raw materials1 are necessary4 ,the raw materials used are as follows3 pure aluminium silicate1 sodium sulphate1 soda1 sulphur1 coal4 ,the aluminium silicate is used in the form of fine china clay or kaolin1 sodium sulphate and soda must be used in the anhydrous form1 the sulphur is the ordinary commercial substance purified by distillation4 ,charcoal or coal containing little ash can be used4 ,whilst the remaining raw materials are always of similar composition1 the china clay from different localities possesses a very varying composition4 ,this substance must be carefully chosen4 ,there is hardly any kaolin which is naturally of sufficient purity to be used without purification2 it is well known that the china clay used for porcelain is subjected to a thorough preparation before it is used4 ,kaolin1 like all clays1 has been produced by the decomposition of feldspar2 when the aluminium silicate so formed was able to deposit without foreign admixtures1 that mineral was formed which is the purest of all clays and is called kaolin4 ,the more foreign substances are mixed with the aluminium silicate the further is the clay removed from kaolin4 ,the impurities which generally accompany the aluminium silicate are quartz sand1 chalk and ferric oxide4 ,we distinguish accordingly between kaolin1 white clay or pipe clay1 clay1 and lastly marl1 a clay containing much chalk4 ,even the purest kaolin contains certain impurities1 of which quartz sand is the principal and the least harmful4 ,before kaolin can be used in the ultramarine manufacture it must always be purified by levigation2 it is then ignited at a low temperature and powdered under stamps or in mills4 ,the other materials required are generally produced by the chemical works in a condition of such purity that they can be at once used4 ,occasionally ,glauber's salt contains iron1 which would spoil the shade of the ultramarine4 ,the iron can be easily removed by dissolving the crystallised salt in water1 adding a little milk of lime and leaving the liquid for several days1 stirring frequently4 ,the lime neutralises every trace of free acid1 and at the same time produces an ochre-yellow precipitate of ferric hydrate4 ,the solution of ,glauber's salt thus freed from iron is evaporated in reverberatory furnaces1 in which the salt is then calcined4 ,this operation is not only simpler than evaporating the solution in iron pans to crystallisation and subjecting the dried salt alone to calcination1 but it also guards against fresh contamination by iron1 which might be caused by the use of iron evaporating pans4 ,the sulphur and coal are employed in a soft powder1 which is most readily obtained by placing the coarsely powdered materials in rotating drums containing a number of iron balls4 ,by continued rotation the materials are converted to any desired degree of fineness without the production of dust4 ,the powder is then put through fine sieves by which the larger particles are retained4 ,the proportions in which the raw materials are mixed vary within certain limits2 fixed quantities can only be given for a kaolin of definite composition4 ,definite formul are known by which ultramarine is made1 but these can only be regarded as approximate4 ,the proportions employed by ,french manufacturers differ considerably from those usual in ,german works4 ,this variation is chiefly due to the difference in the composition of the kaolin employed in the two countries4 ,from the composition of the different mixtures one conclusion may be drawn with certainty--sufficient sodium is always used to neutralise half the silicic acid of the kaolin and to form some quantity of sodium sulphur compounds4 ,in the successful process of the ,german makers a portion of the soda unites with the silica during heating4 ,by the action of the coal on the ,glauber's salt it is reduced to sodium sulphide1 which1 since sulphur is present1 unites with a further quantity of that element4 ,the sodium sulphur compounds then unite with the silicates of aluminium and sodium to form a green compound1 which is converted into blue ultramarine by a further treatment with sulphur in the presence of air4 ,instead of using ,glauber's salt1 which must always be decomposed in the first process1 the sodium sulphide may be formed by the action of sulphur on soda in the presence of coal4 ,this procedure is adopted in the ,french process4 ,the proportions of the mixture used in different works vary4 ,if the kaolin employed is assumed to be bisilicate of alumina--a somewhat arbitrary assumption--the following mixture can be successfully used3-- ,anhydrous kaolin #ajj 0 ,glauber's salt #db 0 soda #db ,sulphur #fj ,coal #ac ,in working by the ,french method the following formula is suitable3-- ,anhydrous kaolin #ajj 0 soda #ajj ,sulphur #fb ,coal #ad ,these formul are not to be regarded as unalterable4 ,in the different works such varied mixtures are used that it may be said with truth that each works has its particular formula for the mixture1 the composition of which depends on the nature of the clay used in the works4 ,the composition of the mixtures used in works is kept secret as far as possible4 ,the formul given above refer to a clay approximating in composition to the bisilicate of alumina4 ,it will appear from the description of the manufacture of ultramarine that certain quantities of sodium sulphide are produced4 ,the process is1 however1 conducted so that sodium sulphide shall be formed2 thus the soda and ,glauber's salt used in the mixture may be replaced by the sodium sulphide produced in previous operations4 ,the liquors in which the sodium sulphide is contained are evaporated to dryness1 and as much of the residue added to the clay as corresponds to the quantity obtained from the usual amounts of soda and ,glauber's salt4 ,assuming that these latter materials are pure1 #hj parts of the sodium sulphide residue correspond to #ajj parts of soda1 and #fj parts to #ajj parts of ,glauber's salt4 ,,chapter ,,xxiv4 ,,the ,,manufacture ,,of ,,ultramarine4 ,we have thought it necessary to an understanding of the manufacture of ultramarine to discuss the production of this important pigment in some detail1 for it is only possible to properly conduct an operation regulated by chemical laws when the processes which take place are accurately known4 ,the mixture of the materials used in making ultramarine must be most intimate in order that the constituents may act chemically upon one another4 ,in some works the mixing is performed in a very laborious manner--upon a heap of the dried1 levigated clay the remaining materials are thrown1 and the whole shovelled about till it is completely homogeneous4 ,naturally1 instead of this primitive and costly operation1 mechanical mixers may be used1 but the mixture can also be effected in a simpler manner1 which almost dispenses with the necessity for a mechanical process4 ,of the substances to be mixed only kaolin and sulphur are insoluble in water2 the others and also the by-products of previous processes are easily soluble4 ,the soluble and insoluble constituents of the charge may be mixed in a very simple way by bringing the levigated kaolin in the form of paste1 without drying1 into a pan1 adding the solutions of the salts and the powdered sulphur4 ,the pans are most conveniently heated by the fire gases from the ultramarine furnaces4 ,after mixing the solutions with the clay to a thick paste the heating is commenced1 the solid substances are prevented from sinking to the bottom by continual stirring1 the mixture is slowly evaporated1 and an extremely intimate and complete incorporation of the constituents occurs4 ,the heating is continued until a dry mass is obtained1 which may be used for the second operation without powdering4 ,the mixture of raw materials is heated for a long time at a clear red heat1 or1 in some works1 at a white heat4 ,the operation demands some care2 air must be excluded and the whole mass must acquire a uniform temperature4 ,if both these conditions are not obtained in heating it is very difficult to obtain a product of uniform colour4 ,in different works different arrangements are used for the calcining process4 ,in the older methods crucibles or dishes of fire-clay were used1 of such a shape that the bottom of one crucible formed the lid of the crucible beneath1 just as is the case with the saggers used in porcelain kilns4 ,the mixture is closely pressed into the crucibles1 of which piles are built in the furnaces4 ,these must be so arranged that each crucible is surrounded by the fire4 ,the furnaces are very similar to porcelain kilns4 ,this method of calcining is obviously attended with many drawbacks2 a large number of costly crucibles is required1 a certain proportion of which is lost at each burning1 either by breakage in the fire or in filling4 ,the pressing of the charge into the small crucibles requires much labour1 as also the placing of the crucibles in the furnace and their removal2 at the end of the nine to ten hours' calcining1 it is necessary to wait some time to take the crucibles out of the furnace1 or considerable loss will be caused by breakage of the crucibles due to rapid cooling4 ,for these reasons in most works crucibles have been abandoned in favour of muffles1 a large number of which are built in one furnace4 ,the charge is placed in the muffles2 after completion of the calcining it is quickly raked out1 and the still hot muffle at once recharged1 thus the losses of time and heat are reduced to a minimum4 ,the muffles are generally about #a metre long1 #a metre wide and #cj to #dj centimetres high4 ,they are made of fire-clay1 and1 when kept in uninterrupted use1 last a long time4 ,the muffles have a small opening at the back which communicates with the furnace1 so that the gases evolved have a free outlet without reaching the working place4 ,the front of the muffle is closed by an iron plate in which are small openings1 through which the contents can be examined without the entry of much air4 ,three muffles are generally built in a furnace1 but1 by suitable alterations in the construction1 a considerably larger number may be heated in one furnace4 ,whatever the number of muffles1 the furnace must be so arranged that the fire can be controlled at will4 ,this is best done by a good damper2 all the muffles must be uniformly heated4 ,j4 ,curtius recommends cast-iron cylinders1 lined with a thin layer of fire-clay4 ,for this purpose a covering of fire-proof cement is used to protect the retorts4 ,this covering1 as it is gradually destroyed1 may be renewed by smearing over the damaged places with fire-proof cement1 mixed with water or some binding material4 ,aluminium silicate1 graphite and coke may also be used4 ,the retorts1 a 7,fig4 #bh71 project through the wall of the furnace at one end4 ,they rest on fire-proof stone bridges1 and can be put into communication with the air by the pipe1 m1 which can be closed air-tight4 ,short pipes1 k and d1 which can be closed1 connect the interior of the retort with the cooling and collecting chambers1 ,p and g1 the latter of which is connected by r with the vessel1 h1 where the gaseous products are absorbed4 ,the porous plate1 f1 prevents the charge in the hinder part of the retort from becoming open and falling to pieces during stoking4 ,in order to obtain a regular heating of the retorts the fire gases passing through the space1 q1 are led away at two opposite places by flues into the main flue1 ,f4 ,the intimate mixture of finely-powdered materials is introduced into the hinder part of the retort1 the porous plate1 f1 placed in position1 the cover1 t1 closed up air-tight1 and the connection with the chamber1 ,p1 closed4 ,on heating1 the volatile products pass through the porous plate and the pipe1 d1 into the chamber1 g1 the more volatile portions1 without mixing with the furnace gases1 passing direct to the absorption vessel1 h1 or to a lead chamber1 whilst the sulphur which distils over remains in g4 ,when the reaction is finished1 by opening the cover1 t1 and the tube1 m1 the crude green ultramarine in the retort can be rapidly oxidised to blue by aspirating air at m1 or after closing the opening1 d1 and removing the plate1 f1 the green ultramarine can be raked into the collecting chamber1 ,p1 and there oxidised4 ,the retorts are then immediately re-filled with the mixture and the temperature raised4 ,illustration3 ,,fig4 #bh4 ,the heating of a charge lasts nine to ten hours2 the larger the quantity of sodium sulphide in the mixture the shorter is the time required4 ,the mixture is spread out in the muffles in a layer #g to #i centimetres thick1 and brought to a moderate red heat4 ,when the whole mass is uniformly hot it is more strongly heated2 the change of the constituents then becomes visible4 ,the mixture takes at first a brownish colour1 and is somewhat similar in appearance to liver of sulphur4 ,the colour soon begins to incline to green1 and finally changes to a tolerably pure green1 but always has a yellow tinge4 ,those parts of the hot mass which come into contact with air are more blue1 and occasionally change to a pure blue4 ,when crucibles are used the upper layer of the contents is always bluer than the lower1 and when crucibles crack during the heating the portions near the cracks always show distinctly a more or less blue colour4 ,when the calcination is finished the hot mass drawn out of the muffles is at once brought into washing vessels1 in which it is treated with water so long as soluble materials are extracted4 ,the compounds dissolved in the water are chiefly sodium sulphide and sulphate and a little alumina dissolved in caustic soda4 ,the presence of a larger quantity of caustic soda in the wash waters indicates too violent heating4 ,in this case the mass will not mix up easily in water2 it contains sintered lumps4 ,the washed material is strained1 spread out on boards or linen stretched across frames1 and completely dried by artificial heat4 ,at this stage the product may be described as green ultramarine and sold as such1 or it may be converted into blue ultramarine4 ,for the latter purpose it is ground to a moderately fine meal1 but green ultramarine must be ground to a very fine powder2 the finer the powder the brighter the shade4 ,in order to obtain blue ultramarine from the washed and ground substance1 it is subjected for a short time to a moderate red heat with unrestricted access of air4 ,the heating by which the blue colour is produced must be continued until the proper shade is obtained4 ,this operation is conducted in special muffles2 in many works it is customary to sprinkle powdered sulphur upon the heated mass during the roasting4 ,the sulphur burns1 forming sulphur dioxide1 which escapes into the furnace through an opening at the back of the muffle4 ,the object of the addition of sulphur may be to keep the temperature from rising beyond a certain point1 or to prevent a possible reduction of the sulphur compounds in the ultramarine4 ,the muffles used for finishing the ultramarine are similar to those used in making green ultramarine2 they are generally #ej centimetres wide and #ajj to #abj centimetres long4 ,a muffle of this size will contain #f to #ah kilogrammes of green ultramarine4 ,the temperature is gradually raised to a gentle red heat1 each muffle being provided in front with an iron plate which prevents the cooling of the contents by the external air4 ,when the charge in the muffles is carefully observed1 it is noticed that the blue colour first appears at the surface and the edges1 i4e41 at those places where the oxygen of the air has unrestricted access4 ,the mass is frequently turned over with an iron rake1 in order to expose all parts to the action of the air2 samples are frequently taken in order to observe the moment at which the colour has reached its greatest intensity1 when the heating is at once stopped4 ,by proper treatment about half an hour is required to convert the charge of a muffle of the above dimensions into ultramarine of the deepest blue4 ,the hot mass is drawn out of the muffles and spread out upon flags so that it may cool quickly4 ,during the cooling the colour is often observed to become considerably darker1 which is a sign that the ultramarine has not been heated for a sufficient length of time4 ,mechanical arrangements are often used to continually turn over the ultramarine in the muffles1 which are then made in the form of cylinders in which the ultramarine is continually turned by a stirrer provided with wings4 ,the whole arrangement is very similar to the apparatus used for roasting coffee4 ,the ultramarine is then carefully ground to a very fine meal2 it is tolerably hard1 and granite stones should be used1 ordinary stones would be too quickly worn down4 ,it is not possible1 by the most careful grinding1 to convert ultramarine into that condition of fine division which is necessary if it is to be ground into paint2 grinding must be followed by levigation4 ,the various qualities and shades brought into the market differ only in regard to the fineness of their particles2 they do not vary in chemical nature1 for the substance has always the same composition4 ,it occasionally happens in ultramarine works that a charge does not turn out a bright blue2 the product is then sold as inferior quality at a lower price1 or is mixed with a larger quantity of good material4 ,in working by a settled process the different shades of ultramarine vary in composition between narrow limits2 the difference is caused by variations in the raw materials4 ,it has been already remarked that there is no agreement as to the composition of the colouring principle of ultramarine2 some maintain that it is an iron compound1 whilst others regard the iron found in ultramarine as an accidental impurity1 which has no connection with the colour4 ,recently this point appears to have been decided from the results of many most accurate analyses of ultramarine4 ,it has been found that its chemical composition shows the greatest similarity with the mineral nepheline4 ,nepheline is a double silicate1 its composition is expressed by the following formula3 ,na,o4,si,o ,al,o4#b,si,o4 ,by a comparison of the analyses of green and blue ultramarine with that of nepheline1 it is seen that blue ultramarine may be regarded as nepheline combined with sodium pentasulphide1 whilst green ultramarine is nepheline combined with sodium bisulphide4 ,if this is the correct view1 the two species of ultramarine have the following formul3-- #b,na,o4,si,o ,al,o4#b,si,o ,na,s4 #b,na,o4,si,o ,al,o4#b,si,o ,na,s4 ,ultramarine is one of the most permanent pigments4 ,it is not altered by the substances with which a pigment generally comes in contact4 ,being a sulphur compound1 it retains its colour completely in air containing sulphuretted hydrogen4 ,by acids1 even weak organic acids such as malic1 citric or tartaric1 it is rapidly decomposed1 sulphuretted hydrogen being evolved1 and a greyish white residue left4 ,it is sometimes found that the sugar used in making lemonade produces a perceptible smell of sulphuretted hydrogen4 ,this is due to ultramarine1 which has been added to the sugar to hide its yellow colour4 ,from the preceding account of the manufacture of ultramarine it will be understood that there exist only two species of ultramarine1 green and blue4 ,in commerce a large number of different shades are found1 which are not to be regarded as pure ultramarine2 they owe their particular shade to additions4 ,by mixing in a white pigment1 such as barytes or starch1 the paler shades are obtained2 by adding a small quantity of a pure red pigment a colour with a violet tinge is produced4 ,in a similar manner any number of shades of ultramarine can be obtained4 ,the following account is taken from a new comprehensive work by ,j4 ,wunder1 on the different ultramarines4 ,preparation of ,mixtures for ,ultramarine4--,the following points are to be observed3 ,chemically pure soda and ammonia soda react with difficulty4 ,the presence of caustic soda in the soda facilitates the formation of sodium sulphide1 and gives a finer product4 ,it is also of advantage to sprinkle the soda with a strong solution of sodium sulphide4 ,the more silica the mixture contains the more difficult is the transformation into ultramarine1 but the product is deeper and better in shade1 and has more resistance to alum and weak acids4 ,the sodium sulphide must react with silica and alumina4 ,when oxygen enters during the burning1 silica is re-formed1 which with soda and alumina produces slags4 ,in order to exclude oxygen many manufacturers burn with restricted access of air2 then the carbon bisulphide and sulphur gases evolved are not burnt1 but1 together with tarry materials from the coal1 form an evil-smelling smoke1 which renders the neighbourhood objectionable4 ,the coal consumption in burning is also greater4 ,the varieties rich in silica and stable towards alum are generally dark reddish-blue4 ,in order to obtain pure blue shades from mixtures rich in silica they are burnt in closed crucibles to produce the green1 which is powdered and heated with restricted air supply1 and the admission of a little steam1 to #afj to #ahj ,c41 when pure blue or greenish-blue shades are obtained as required4 ,in this way a mixture rich in silica can be burnt to a good blue1 containing #ficb parts of silica to #cjfg parts of alumina1 or #a equivalent of ,al,o to #chd equivalents of ,si,o2 whilst ultramarine rich in silica1 made in the ordinary way1 contains at the most #ffg parts of silica to #ccc parts of alumina4 ,ultramarine ,violet was first introduced into commerce about the year #ahei by the ,nuremberg ,ultramarine ,works1 under the direction of ,leykauf4 ,by the reaction of moist calcium chloride on ultramarine blue in the warm chambers above the furnaces the blue was changed to violet4 ,by the action of air a portion of the moist calcium chloride is decomposed into lime and hydrochloric acid1 the latter of which1 together with air1 reacts on the blue4 ,in #ahgb ,wunder1 intending to apply to the estimation of sulphur in ultramarine blue a method which gives good results with metallic sulphides1 passed chlorine over heated ultramarine4 ,the pigment was converted into a brownish-red substance1 which on washing combined with water and turned violet4 ,the red substance is not produced at every temperature2 #cjj ,c4 is the most favourable4 ,on washing sodium chloride is dissolved2 the washed violet is free from chlorine1 but has taken up water1 which is expelled on heating1 when the violet turns to blue4 ,a similar brownish-red body is formed when sulphur trioxide is led over heated ultramarine blue1 and when sulphur chloride acts on warm ultramarine blue4 ,when the brownish-red chlorine compound is introduced into absolute alcohol1 a reddish-violet compound is produced1 containing organic matter4 ,ethyl chloride is formed at the same time4 ,when ammonia gas is passed over the heated chlorine compound it is absorbed2 a violet ultramarine is produced1 from which the ammonia is not removed by washing with water1 but only by heating nearly to redness1 or1 better1 by fusing with caustic alkalis4 ,aniline combines in a similar manner4 ,in order to obtain a good violet the brownish-red chlorine compound must not be formed2 the violet is produced by leading chlorine and steam over ultramarine blue at #afj to #bjj ,c4 ,blue rich in silica is most suitable for transformation into violet4 ,the violet so obtained is not decomposed by lime4 ,c4 ,mahla produced the chlorine in the blue itself by the reaction3 ,,nh,cl #b,,nh,,no #f;,h,o #e,n ,cl4 ,by heating a mixture of ultramarine blue with ammonium chloride and nitrate in crucibles at #bjj ,c4 a fine violet is produced4 ,it contains ammonia1 which cannot be removed by washing1 but only by strongly heating or heating with concentrated alkalis4 ,this violet is decomposed by the prolonged action of lime1 in three days it is changed to a grey green4 ,in the course of the manufacture it was noticed that less nitrate was required in the mixture according to the length of time it was exposed in porous crucibles to the action of air and heat2 by heating for a sufficient length of time with access of air1 a good violet is obtained with ammonium chloride alone4 ,in the manufacture of violet by means of moist chlorine hydrochloric acid is formed1 which is also the active material in its formation by means of ammonium chloride4 ,it was therefore to be expected that chlorine gas might be replaced by hydrochloric acid1 if it were accompanied by sufficient air4 ,this has been found to be the case4 ,the temperature must be maintained between #ahj and #bcj ,c4 ,below #aej ,c4 the blue is decomposed by moist hydrochloric acid gas2 at temperatures above #bcj ,c4 it is unchanged4 ,hydrochloric acid gas and air1 without steam1 give with ultramarine blue on heating a brownish red substance similar to that produced by dry chlorine2 it also is changed to violet by washing with water4 ,the violet obtained by means of moist chlorine differs from the blue from which it was formed1 in that the latter has lost one-sixth of its sodium and combined with water and much oxygen4 ,the following is the approximate formula for a blue3-- ,na,al,si,s,o1 and for the violet obtained from it ,na,h,al,si,s,o ,h,o4 ,the violet contains much thiosulphate4 ,if it is decomposed by nitric acid and silver nitrate added to the filtered solution a precipitate is obtained which changes in colour from white to yellow1 orange and brown1 just as the precipitate given by silver nitrate in solutions of thiosulphates containing nitric acid4 ,chlorine and ,steam ,process4--,chlorine does not attack iron at #aej to #bej ,c4 ,the reaction is carried out in heated iron boxes #a metre wide1 #b metres long and #fe centimetres high4 ,the blue is spread out in a layer #b centimetres thick on earthenware plates1 which stand one above another at a distance of #e centimetres1 each supported on three feet4 ,the plates are introduced by means of iron tongs through large openings in the top of the box2 after filling iron plates are screwed on to the openings1 through them pass sheet-iron tubes reaching to the bottom1 in which thermometers can be lowered on wires4 ,the iron boxes stand in heated chambers1 which have openings corresponding with the openings in the boxes1 and shut off from the interior of the furnace4 ,chlorine and steam are led into the iron boxes at both ends through lead tubes reaching to the bottom2 the parts of these tubes in the furnace and the iron boxes are protected by wide sheet-iron tubes1 the space between being filled with clay4 ,the gases evolved1 hydrochloric acid1 sulphur chloride and steam1 pass from the covers through earthenware pipes into boxes filled with limestone1 upon which water drops1 and thence to the chimney4 ,after filling1 the boxes are heated to #bhj ,c4 and steam introduced to remove sulphur2 they are then allowed to cool to #afj ,c41 when chlorine and steam are led in for three hours4 ,the violet is then finished1 and the residual gases are blown out by a fan4 ,hydrochloric ,acid and ,air ,process4--,the operation is conducted in the same iron boxes1 upon the bottoms of which1 beneath the openings1 are earthenware dishes into which hydrochloric acid can be poured through earthenware pipes4 ,the chimney draught must be strong enough to draw sufficient air through these pipes into the boxes4 ,after the temperature has been maintained for seven hours at #bbj to #bcj ,c41 hydrochloric acid being poured in from time to time1 the blue is changed to a dull violet1 which becomes brighter when hydrochloric acid is repeatedly added at diminishing temperatures1 #baj1 #bjj1 #ahj and #afj ,c4 ,more recently the iron boxes have been replaced by stone chests or by chambers above the ultramarine furnaces1 the temperature in this case being kept at about #bjj ,c4 ,ammonium ,chloride ,process4--,a mixture of ultramarine blue with #e per cent4 of ammonium chloride is heated during fourteen days in porous crucibles placed in the upper chambers of the ultramarine furnaces1 when the contents of the crucibles become a handsome violet throughout4 ,if sodium nitrate is used together with ammonium chloride1 the violet is formed in a much shorter time4 ,after washing1 the violet still contains nitrogen2 on ignition or heating with strong alkalis it loses ammonia4 ,unfortunately1 this fine violet is decomposed by the continued action of moist slaked lime4 ,the violets made by the first two processes absorb ammonia when this gas is led over them at #ahj to #bjj ,c41 and it cannot be removed by washing4 ,pale ,blue ,ultramarine4--,if the violet is heated in hydrogen at #bhj to #bij ,c41 it is converted into a pure1 bright1 pale blue4 ,this has an absorption spectrum in which the red is not absorbed1 but appears more brilliant than in the spectrum of ultramarine rich in alumina4 ,pale blue is turned violet blue by heating at #cjj ,c41 and at a red heat a dull blue4 ,it is not yet made on a commercial scale1 but on account of its great purity of shade it appears to be valuable for many purposes2 perhaps it may replace alumina cobalt blue4 ,the composition of pale blue is3-- ,calculated for ,found4 ,na #abd per cent4 #aai per cent4 ,h #jed 0 #jfb 0 ,al #aag 0 #aca 0 ,si #ahb 0 #aig 0 ,s #aci 0 #abg 0 ,o #dcc 0 #dbj 0 7by difference74 ,by a comparison of the composition of the violet and pale blue ultramarines1 it is seen that the chief difference is an increase of hydrogen in the latter4 ,ultramarine ,red4--,since ultramarine violet increases in brightness and redness of shade in the air1 ,wunder erroneously believed that this was due to oxidation1 and that1 consequently1 the violet could be converted into a red by oxidising agents4 ,nitric acid vapours led over ultramarine violet at #agj to #bjj ,c4 do not act upon it1 but where drops of nitric acid are spirted over1 the violet is changed to red4 ,wunder then reduced the temperature to #ace to #ade ,c4 and obtained the first ultramarine red4 ,iron is attacked by nitric acid at lower temperatures1 but not at #ace ,c42 the iron boxes previously described could therefore be used4 ,it was afterwards found that at a sufficiently low temperature hydrochloric acid gas converts ultramarine violet into red4 ,the iron boxes cannot be used for this operation1 as they are attacked at the temperature2 the stone chests are used instead4 ,other acids also act on ultramarine violet2 boric acid gives a reddish-violet4 ,the violet is spread out on the dishes standing on three feet mentioned before1 and heated to #abh to #acb ,c4 ,at higher temperatures the violet is unaltered1 whilst below #ajj ,c4 it is decomposed4 ,the hydrochloric acid is poured in from time to time through earthenware tubes into dishes in which it evaporates4 ,a mixture of red and blue would appear violet1 but would behave towards reagents in a different manner to real ultramarine violet4 ,ultramarine blue is decomposed at #abh to #acb ,c4 by hydrochloric acid to a gelatinous mass1 whilst at this temperature ultramarine violet is changed into a bright red4 ,from the blue no violet can be obtained by nitric acid1 but the violet gives a red at #ace to #ade ,c4 ,analysis would also indicate the difference4 ,ultramarine red has the following composition3-- ,calculated for ,found4 ,na #gi per cent4 #ha per cent4 ,h #jeg 0 #jgb 0 ,al #abc 0 #acc 0 ,si #aia 0 #aic 0 ,s #adf 0 #aeb 0 ,o #def 0 #dcd 0 7by difference74 ,it appears that in the red two more equivalents of sodium have been replaced by hydrogen4 ,the violet is apparently a sodium salt of which the red is the acid4 ,the violet made by means of ammonium chloride is also converted by hydrochloric acid gas at #abh to #acb ,c4 into a handsome red containing nitrogen1 and the red is changed by hydrogen at #bhj to #bij ,c4 into a lighter pale blue4 ,,chapter ,,xxv4 ,,blue ,,copper ,,pigments4 ,bremen ,blue and ,green4--,the pigment known as ,bremen blue or ,bremen green consists of copper hydroxide4 ,it possesses all the disadvantages of copper compounds2 it is very sensitive towards sulphuretted hydrogen and sulphur dioxide2 in contact with air containing the former gas it is quickly turned black4 ,it has also other disadvantages2 it cannot be used in oil1 for when ground in oil it is quickly discoloured1 on account of the formation of copper oleate4 ,if a wall which has not completely dried be covered with ,bremen green1 in a short time it will be covered with spots4 ,in spite of this small stability1 ,bremen green is still largely used by artists on account of its low price1 although it could be replaced by other pigments almost as cheap and considerably more durable4 ,copper hydroxide comes into the market under many names4 ,the pigments known as blue verditer1 lime blue and mountain blue contain essentially copper hydroxide4 ,the preparation of pure copper hydroxide on the large scale will be first described4 ,copper sulphate is the usual raw material4 ,in order to obtain a colour of a pure blue shade it must be free from iron1 the presence of which would result in the production of a discoloured precipitate4 ,a fairly concentrated solution of copper sulphate is warmed in a pan to about #cj ,c42 weak caustic potash solution is added until the liquid is slightly alkaline4 ,a green precipitate separates1 which consists of copper sulphate and hydroxide4 ,in order to remove the copper sulphate from the precipitate1 and impart to it the correct bluish-green colour1 it is left on a strainer until it has acquired a pasty consistency1 when it is brought into a tub and mixed with weak caustic potash solution4 ,care must be taken that this potash solution is not too concentrated1 or it will withdraw water from the copper hydroxide and produce black copper oxide4 ,in order to prevent this result1 which would render the whole mass useless1 a portion of the precipitate is tested with the caustic potash solution4 ,if it is blackened1 the solution must be diluted with the necessary quantity of water before it is used4 ,instead of diluting with water1 potassium carbonate solution is often added4 ,the addition of the caustic liquor is continued until the colour of a test portion of the precipitate is not deepened by further additions4 ,when this point is reached the colour must be at once withdrawn from the action of the alkali4 ,it is brought into a large tub filled with water1 in which it is most carefully washed with many waters4 ,basic copper chloride may also be used as the raw material for this pigment4 ,it is obtained by treating scrap copper with #fj per cent4 of common salt and #cj per cent4 of sulphuric acid4 ,the pale green basic chloride is then treated with caustic potash solution4 ,this method is now rarely used2 copper sulphate is considerably lower in price than formerly and copper hydroxide is prepared from it with the least trouble4 ,neuberg ,blue is a mixture of copper blue with ,chinese blue4 ,the larger the quantity of the latter component the deeper the colour4 ,neuberg blue can be more easily ground with oil than pure copper blue4 ,it should not be used as a distemper colour1 for the ,chinese blue is decomposed by the action of lime1 and the colour will quickly be spoiled by the separated ferric oxide4 ,lime ,blue is ordinary copper blue1 mixed with varying quantities of gypsum4 ,it is paler than pure copper blue2 different shades are obtained by increasing the quantity of gypsum4 ,this pigment is made by dissolving #ae parts of copper sulphate in #a1cjj parts of water1 adding a strong solution of #aba parts of ammonium chloride1 and then milk of lime prepared from #cj parts of quicklime4 ,the precipitate is well washed1 strained1 ground1 and finally dried4 ,lime blue is brought into the market in several forms2 in cubes obtained by cutting up the stiff paste and then completely drying1 and in irregular lumps or a coarse powder4 ,the pigments containing copper hydroxide as their colouring principle are used less as artists' colours than for distempering4 ,payen's ,mountain ,blue is a mixture of copper hydroxide with varying quantities of calcium carbonate4 ,it is prepared by adding calcium chloride to a solution of copper sulphate and stirring in dilute milk of lime4 ,a green precipitate of basic copper chloride is formed2 potassium carbonate solution mixed with milk of lime is then added4 ,the latter mixture contains caustic potash1 which decomposes the copper chloride1 copper hydroxide and calcium carbonate being simultaneously precipitated4 ,different shades may be obtained2 by increasing the quantity of lime the product is paler4 ,this pigment commonly comes into the market in the paste form4 ,when it is dried the operation must be conducted at a low temperature2 copper hydroxide is converted into copper oxide at relatively low temperatures4 ,oil ,blue4--,the pigment known under this name consists of copper sulphide 7,cu,s74 ,it can be made in several ways4 ,the simplest process1 which also gives a good product1 is here described4 ,sulphur is boiled in a glass flask with a long neck4 ,when the heavy reddish brown vapours begin to fill the neck1 copper turnings or wire free from oxide are thrown in4 ,the copper burns in the sulphur vapour with a red flame to cupric sulphide4 ,when it has once commenced to burn1 the flask requires little heating1 so much heat is produced by the combustion of the copper that the sulphur continues to boil4 ,the introduction of copper is continued until only a small excess of sulphur is left1 the flask is then closed and allowed to cool4 ,when the contents have reached the temperature of the air the flask is broken1 and the mass boiled with caustic potash solution in order to remove excess of sulphur4 ,the product obtained by this process has a handsome violet blue colour1 which must be shown by the whole mass4 ,if portions taken out of the flask are black1 an excess of copper has been used4 ,in order to improve the colour of a faulty batch1 it is mixed with sulphur and quickly heated to the boiling point of sulphur1 air being excluded4 ,the excess of sulphur is then removed by boiling with caustic potash solution4 ,oil blue is a handsome but not very durable pigment4 ,when used in varnish1 which protects it from the action of air1 it is fairly permanent4 ,copper ,hydroxide4--,by precipitating carefully a solution of a copper salt with caustic soda1 a blue precipitate of copper hydroxide is obtained1 which1 though not distinguished by any particular beauty1 is adapted for use as a distemper colour and for similar purposes4 ,the operation is conducted at ordinary temperatures2 on account of its voluminous nature the pale blue precipitate requires a long time for washing4 ,hot solutions must not be used2 at a temperature near the boiling point of water copper hydroxide is completely decomposed into black copper oxide4 ,,chapter ,,xxvi4 ,,blue ,,cobalt ,,pigments4 ,cobalt ,blue1 ,thnard's ,blue1 ,cobalt ,ultramarine1 ,king's ,blue1 ,leyden ,blue4--,the pigment known under these names is a compound of cobalt oxide with alumina1 and is prepared in a similar manner to ,rinmann's green4 ,of all the blue pigments used in painting1 cobalt blue is the most handsome and most durable4 ,it is completely unaltered by the atmosphere4 ,the most powerful chemical reagents have but a slight action upon it1 and their action is less the higher the temperature used in the manufacture4 ,cobalt blue is made by precipitating mixed solutions of a cobalt salt and alum1 washing1 drying1 and igniting the precipitate4 ,a product of pure blue colour is only obtained when alum absolutely free from iron is used4 ,if but very small quantities of iron are present1 the red ferric oxide has a very considerable influence on the shade of the product4 ,the depth of colour varies according to the proportion of cobalt salt used4 ,the variation is not so considerable as in the case of cobalt green2 as a rule1 #ej to #ajj parts of cobalt sulphate or nitrate are used to #ajj parts of alum4 ,the temperature at which the precipitate is ignited must be much higher than that used for cobalt green2 it should be raised to a white heat4 ,the crucible should be provided with a well-fitting lid--the fire gases damage the shade of the colour4 ,when cobalt sulphate is ignited with ammonia alum1 cobalt blue is obtained2 but this method is not to be recommended4 ,the ignition must be of long duration to completely drive off the sulphuric acid4 ,the author has made a cobalt blue of remarkable beauty in the following manner3 ,alumina obtained by precipitating electrolytically an alum solution 7page #di7 was mixed with a solution of pure cobalt chloride to a thin pulp1 which was quickly dried in a shallow porcelain dish4 ,the mixture1 whilst still hot1 was pressed into a crucible placed in a larger one filled with magnesia2 the crucible was heated to a good white heat1 at which it was maintained for an hour1 when it was allowed to cool4 ,the cobalt blue made by this method has the purest blue colour1 being without that admixture of red which is not rarely to be perceived in this pigment4 ,to avoid the appearance of this red tint1 certain additions are made2 a small quantity of a zinc salt is most frequently employed1 according to the quantity of which more or less pale shades are produced4 ,cruleum is a pale blue pigment consisting of a compound of the oxides of cobalt and tin4 ,it is made by converting tin by the action of nitric acid into white stannic oxide1 adding a solution of cobalt nitrate and evaporating to dryness in a porcelain dish whilst stirring2 whilst still warm the powder is strongly ignited4 ,in cruleum the chemical combination is less firm than in the compounds of cobalt oxide with zinc oxide or alumina1 strong hydrochloric and dilute sulphuric acids decompose it1 continued treatment with nitric acid extracts all the cobalt4 ,cruleum resists completely all atmospheric influences4 ,the circumstance that all the cobalt in this compound may be removed by treatment with nitric acid leads to the conclusion that the pigments composed of cobalt oxide and another oxide are not chemical compounds of the two oxides1 but that the alumina1 zinc oxide and tin oxide serve simply as bases for the blue modification of cobalt oxide4 ,that a chemical compound cannot be present follows from the fact that the quantities of the oxides uniting together may be very considerably altered and a coloured product still obtained4 ,the author has shown in #ahfh that the blue modification of cobalt oxide is obtained by heating the red4 ,the change of the red colour of cobalt chloride into the blue is not caused1 as was formerly thought1 by loss of water1 but by the transformation of the cobalt oxide contained in the compound from the red into the blue modification4 ,strong bases are able to retain the cobalt oxide in the blue form1 and strongly basic oxides are therefore used in the manufacture of this series of pigments4 ,cobalt ,zinc ,phosphate4--,this pigment is made by precipitating a solution of zinc sulphate1 free from iron1 by sodium phosphate1 adding a solution of cobalt sulphate and again sodium phosphate so long as a precipitate is produced4 ,excess of sodium phosphate is to be avoided1 otherwise a considerable quantity of cobalt remains unprecipitated4 ,in the directions given by ,gentele it is stated that the sodium phosphate must be in excess1 and that the liquid above the precipitate must possess a reddish colour4 ,the author's experiments have shown that a pigment in every respect equal to that produced by ,gentele's process is obtained when all the cobalt is precipitated4 ,the precipitate1 which consists of variable quantities of zinc and cobalt phosphates1 is dried and ignited1 when it acquires a very deep blue colour4 ,,chapter ,,xxvii4 ,,smalts4 ,this blue pigment is a very finely powdered glass1 coloured by cobalt oxide1 according to the quantity of which products of very different shades are obtained4 ,if a very small amount of cobalt oxide is used the smalts has a beautiful pale blue colour1 but by the use of larger quantities an almost black mass can be obtained4 ,although the proportion of cobalt oxide contained in smalts is so variable1 yet it is probably present as a compound of constant composition--the cobalt potassium double silicate of the formula ,co,o4 #b,si,o ,k,o4 #b,si,o4 ,the numerous published analyses of smalts lead to this conclusion4 ,the small quantities of other metallic oxides which are found in smalts are to be regarded as chance impurities4 ,being a glass free from lime smalts is easily decomposed2 in this respect it shows great similarity with water-glass1 which is completely soluble in boiling water4 ,smalts comes into commerce in the form of powder4 ,in the 0,blue ,colour ,works0 in which smalts is made a number of qualities are distinguished2 these are separated according to the fineness of the powder4 ,smalts of good quality is composed of particles of the same size and has a pure sky-blue colour4 ,a shade inclining to red is generally to be ascribed to the presence of iron2 material of this nature is of little value4 ,smalts is not easily attacked by chemical reagents4 ,it has been above stated to belong to the easily decomposed glasses1 and it is attacked by reagents which ordinary glass completely resists4 ,finely ground smalts is strongly attacked by boiling sulphuric acid1 and1 after fusion with soda1 is soluble in acids4 ,water has some action upon smalts2 by the long continued action of a large quantity the shade is injured1 the colour acquires a greenish tinge4 ,in the manufacture of smalts there are three principal operations3-- #a4 ,preparation of the charge4 #b4 ,fusion of the charge4 #c4 ,grinding the fused mass4 ,these processes are principally mechanical4 ,only as regards the composition of the charge is chemical knowledge required4 #a4 ,preparation of the ,charge4--,the cobalt is supplied by substances of different origin--as a rule1 roasted speiss cobalt and cobalt glance are used2 occasionally ores are employed without previous preparation4 ,when pure cobalt salts 7sulphate and nitrate7 are used1 a product of very fine shade is produced1 but in practice these salts are not applicable on account of their cost4 ,there remain therefore only the compounds of cobalt occurring in nature4 ,on account of the foreign substances they contain1 these require a special treatment before they can be used in the manufacture of smalts2 the treatment varies according to the other elements present in the cobalt ores4 ,ores containing bismuth are first treated in order to obtain this valuable metal2 ores containing arsenic are roasted in furnaces of special construction1 which are connected with a series of stone or wooden passages in order to condense the arsenic trioxide completely4 ,if ores are employed which contain only a small quantity of cobalt1 the same quantity of glass is melted time after time with fresh quantities of the poor ore4 ,at each operation cobalt is taken up4 ,in place of glass a mixture of potash and very fine quartz sand may be used with advantage4 ,it produces that species of glass which most easily takes up cobalt oxide4 ,the quartz sand is generally made by igniting flint and quenching in water to facilitate the grinding2 it is then powdered4 ,river sand is generally so impure that it would produce a brown or green coloured glass1 which1 when fused with cobalt ores1 would give smalts of a bad shade4 #b4 ,fusion of the ,charge4--,this process is very similar to the fusion of ordinary glass4 ,the materials1 in very fine powder1 are carefully mixed and then 0fritted10 that is1 heated until the mass sinters together without melting4 ,the real fusion is accomplished in glass furnaces4 ,the fritted mass is fused in small 0glass pots0 made of fire-clay1 in a furnace similar in principle to the ordinary glass furnace4 ,the glass pots are made rather small1 to hold about #ej kilogrammes1 in order to obtain as homogeneous a product as possible4 ,they are placed to the number of six in a furnace heated by coal1 in which a very high temperature can be obtained4 ,this is essential1 because the charge has a high melting point and must be made quite fluid in order that impurities may settle4 ,the furnace must be slowly heated at first to prevent the pots from cracking4 ,when they are once heated the temperature is raised to fuse the charge1 which is repeatedly stirred so that the residues may sink to the bottom4 ,these residues consist chiefly of metallic sulphides and arsenides4 ,after six to seven hours' fusion the stirring is discontinued1 and the temperature raised for a short time to the highest it is possible to attain1 so that the smalts may be as fluid as possible4 ,when this is the case it can be drawn out into long thin threads4 ,the melted glass is then taken out and poured into cold water4 ,the rapid cooling makes it extremely brittle1 and considerably facilitates the powdering4 ,when new pots are used for the fusion1 their walls are considerably attacked by the alkalis contained in the glass4 ,in order to prevent this a small quantity of common smalts is fused in them before the introduction of the real charge2 the inner surface then becomes covered with a protective glaze4 #c4 ,grinding the ,fused ,mass4--,the smalts is next powdered under stamps4 ,these only differ from the ordinary construction in that both stamp and trough are made of granite4 ,the coarse powder from the stamps then goes to mills of ordinary construction1 in which it is ground as finely as possible in a current of water4 ,a blue liquid runs from the mills into tubs4 ,the coarser particles which settle in these vessels constitute the article known commercially as strewing smalts1 which is of small value4 ,the quantity of this quality is fairly considerable2 it cannot all be sold2 part is fused in a later operation with a fresh quantity of the fritted mixture4 ,the liquid remaining in the tubs then gives the different qualities of smalts4 ,after having deposited the coarsest particles in the first vessel it is brought into another1 in which it stays only a few minutes1 when it is run off into another vessel1 in which also it remains but a short time4 ,the liquid goes in this manner through from three to five vessels1 and in the process deposits all the coarser particles4 ,the oftener the liquid is brought into fresh vessels the finer are the particles still suspended in it1 and the longer it should remain before being drawn off into another4 ,when the liquid has run through three or four vessels1 as the case may be1 it still retains the finest particles in suspension4 ,it is now run into a tank1 in which it remains until it is perfectly clear and has deposited all the blue4 ,the deposit in this tank has a dirty bluish-grey colour2 it is utilised by being added to a later fusion4 ,it would be expected that this last deposit would have the best shade1 since it consists of smalts in the finest state of division1 which would no doubt be the case if the smalts remained unchanged4 ,smalts is1 however1 a glass which is rather easily decomposed4 ,in grinding1 the smalts comes in contact with large quantities of water1 and in the succeeding levigation the water decomposes it2 the final residue is thus produced4 ,in view of the easy decomposition of smalts by water1 it is necessary to carry out all processes in which it is in contact with water as rapidly as possible1 in order to obtain the largest yield of smalts4 ,the smalts deposited in the successive vessels have a different degree of fineness1 and are sold under particular marks4 ,the ,saxony works1 which produce the greater part of the smalts used in ,germany1 distinguish the qualities by letters4 ,the better qualities are distinguished by the same letter1 the fineness of the quality being indicated by the repetition of this letter4 ,thus ,,fffe1 ,,ffe1 and ,,fe indicate qualities which are of lower value the less often the letter ,f occurs in the mark4 ,the qualities following those marked ,f are distinguished by ,m2 the lowest quality is marked ,,oe4 ,f indicates fine2 ,m1 medium2 and ,o1 ordinary4 ,the qualities generally designated smalts are those deposited in the third and fourth vessels2 they are also known as king's blue or azure blue4 ,the processes used in different works apparently vary4 ,the essentials of the processes are1 however1 as they have just been described2 the time during which the liquid is left in the various depositing vessels is different4 ,smalts1 being a glass1 well resists the action of the weather1 although on account of the absence of lime it has not the great chemical indifference of ordinary glass4 ,smalts is not altered by atmospheric influences1 but from analogy with the behaviour of water-glass1 to which smalts is closely related in chemical composition1 we should conclude that1 although smalts resists the action of the air for a tolerably long time1 it cannot be regarded as absolutely permanent2 in the course of time potassium carbonate and silica will be formed4 ,since the introduction of the manufacture of ultramarine1 the use of smalts has considerably decreased4 ,ultramarine is incomparably the more handsome pigment1 but it cannot be exposed to high temperatures without undergoing change of shade4 ,for purposes in which the pigment is subjected to a high temperature1 as in porcelain painting or earthware glazing1 smalts has maintained its position4 ,smalts is also used in fresco painting1 for colouring wax and tinting writing paper4 ,for the latter purpose it should be rejected4 ,it has no influence on the durability of the paper1 but it spoils steel pens4 ,any one who has written for a long time on paper coloured with smalts must have observed this2 the best steel pens are soon worn out by such paper4 ,the very fine splinters of glass present in large number in the paper act upon the steel as a very fine but very hard file1 and quickly wear it down4 ,when smalts are used for painting earthenware1 the outlines of the design are quite obliterated1 the cause of which is that smalts1 being itself a glass1 fuses with the glaze 7also a glass7 of the vessel4 ,when clean outlines are required smalts should not be used2 some other cobalt pigment resisting heat should be substituted4 ,in addition to the above blue pigments which are in common use1 there are two others to be mentioned1 rarely used and very costly--tungsten blue and molybdenum blue4 ,tungsten ,blue is made by adding excess of ammonium chloride solution to a hot solution of potassium tungstate1 collecting the precipitate resulting when the liquid has completely cooled1 drying and heating to redness in a crucible1 through the cover of which a porcelain tube reaches to the bottom4 ,when the crucible begins to glow1 hydrogen is passed through the tube2 the crucible is then heated to a full red heat for fifteen minutes1 the current of hydrogen being continued4 ,the pigment obtained in this way is a deep blue powder of velvety appearance4 ,tessi du ,motay's ,blue4--,the following is the method of preparation3 #aj parts of sodium tungstate1 #h parts of tin crystals1 #e parts of yellow prussiate1 and #a part of ferric chloride are dissolved separately and the solutions mixed4 ,the precipitate is washed and exposed to light in thin layers4 ,the blue colour develops in the course of several days4 ,according to the discoverer1 this pigment consists of a compound of tungsten oxide with a double cyanide of iron and tin2 in physical properties it is similar to good ,prussian blue1 but is distinguished by greater durability on exposure to light and also by a much higher cost4 ,up to the present this pigment has not been made commercially4 ,molybdenum ,blue4--,this fine but costly pigment is obtained by mixing a solution of sodium molybdate with a solution of stannous chloride4 ,a blue precipitate is formed1 which1 after washing and drying1 may be used as an artists' colour4 ,it is distinguished by great durability4 ,a good shade of molybdenum blue can be obtained with greater certainty by adding finely-powdered tin and a few drops of hydrochloric acid to a solution of pure molybdic acid4 ,in composition it is a mixture of stannic molybdate and the blue modification of molybdenum oxide4 ,,chapter ,,xxviii4 ,,green ,,mineral ,,pigments--,,green ,,copper ,,pigments4 ,copper ,carbonate4--,in nature two salts occur containing copper1 carbonic acid1 and water in different proportions--one1 the mineral malachite1 has a fine emerald green colour2 the other1 azurite1 is sky blue4 ,both minerals are ground and levigated1 and brought into commerce as mountain green and mountain blue4 ,compounds of copper with carbonic acid1 made artificially1 are used under different names as pigments4 ,the terms mountain blue and mineral blue are applied indiscriminately to various copper compounds2 as mountain blue1 or ,brunswick green1 pigments come into commerce containing varying quantities of copper carbonate 7made by precipitating a copper salt with soda7 mixed with barytes1 zinc white1 or another white pigment1 in order to obtain paler and deeper shades4 ,the poisonous ,scheele's green is also given the same name as that under which copper carbonate is sold1 viz41 mineral green1 so that the composition of this colour can only be decided by analysis4 ,a green pigment1 similar in composition to malachite1 is obtained by precipitating copper sulphate with soda in the cold and washing quickly4 ,if the precipitate is left in contact with the liquid1 its colour changes and it is converted into a blue mass similar in properties to ground malachite4 ,a green precipitate is obtained with more certainty by precipitating a boiling solution of copper sulphate with soda solution4 ,both green and blue copper carbonate are pigments of little depth2 as a rule ground and levigated malachite and azurite have a greater intensity of colour than the artificial pigments4 ,copper ,arsenite4--,the compounds of arsenious acid with copper are among the most handsome and bright colours which exist4 ,it is thus to be regretted that these pigments are disappearing more and more1 and indeed with every reason1 from the pigments permitted by law4 ,in the end they must fall into complete disuse4 ,it is a matter of common report that these pigments1 and particularly emerald green1 have frequently caused arsenical poisoning4 ,numbers of people have been repeatedly made ill by the dust of emerald green fixed on light fabrics1 such as are used for ball dresses1 simply by albumin or dextrine1 and brought into the air by the movements of the dancers4 ,it has been further shown that the air of rooms papered with hangings coloured by emerald green contains small quantities of the most poisonous of all arsenic compounds1 arseniuretted hydrogen4 ,although it is in the interest of colour makers to produce the brightest possible colours1 yet1 on account of their dangerous properties1 pigments containing arsenic should be quite excluded4 ,in several countries their use is forbidden by law4 ,since there are several pigments which can compete in brightness with the arsenic colours1 it is to be hoped that the latter will shortly disappear from commerce4 ,scheele's ,green1 ,swedish ,green4--,a solution of #cb parts of potash is boiled with #aa parts of white arsenic 7arsenious acid7 until the latter is completely dissolved4 ,this solution of potassium arsenite is mixed with a hot solution of #cb parts of copper sulphate free from iron4 ,the beautiful green precipitate is washed with hot water and dried4 ,these directions for the preparation of copper arsenite are due to ,scheele1 the discoverer of the pigment4 ,it can be prepared by several other methods4 ,when white arsenic and copper sulphate are dissolved together1 and caustic soda added to the boiling solution1 ,scheele's green is precipitated4 ,when made by this method the pigment must be very carefully washed2 if the excess of caustic soda is not completely removed it is very hard when dry1 and is difficult to powder4 ,in order to obtain darker greens the quantity of copper sulphate is increased4 ,a particularly bright green is obtained by dissolving copper sulphate in water1 with the addition of #ab to #ae per cent4 of white arsenic1 and precipitating by a solution of potassium zincate1 which is obtained by boiling caustic potash solution with zinc filings1 hydrogen being evolved4 ,the shade of ,scheele's green depends on the relative quantities of arsenious acid and copper sulphate employed4 ,if the arsenious acid predominates1 a pale product is obtained2 when excess of copper sulphate is used1 the colour is pure green4 ,the pigment made according to the foregoing directions possesses only small covering power4 ,a product better in this respect is obtained by precipitating a solution of #ajj parts of copper sulphate by a solution of #ij parts of potassium carbonate1 in which #ff parts of arsenious acid have been dissolved4 ,scheele's green is a bright green pigment1 which resists the action of the atmosphere tolerably well4 ,it is easily decomposed by dilute acids2 when strongly heated arsenious acid is set free1 and copper arsenate and arsenide are produced4 ,copper arsenite is the essential constituent of the pigments sold under the name of mineral green1 which is generally a mixture of copper arsenite with varying quantities of mountain green4 ,brunswick ,green1 ,green ,verditer1 is a mixture of copper arsenite1 copper hydroxide and gypsum4 ,it is prepared by dissolving #ajj parts of copper sulphate in water1 adding a solution of part of arsenious acid and #aj parts of anhydrous potassium carbonate1 and finally precipitating with milk of lime made from #bj parts of quicklime4 ,the pale to bluish-green precipitate is washed and pressed into flat cakes1 which are brought into the market and used as lime colours4 ,this pigment is not adapted for use in oil2 when applied in that medium it darkens considerably4 ,neuwied ,green is made in almost exactly the same manner as ,brunswick green1 the chief difference being that a larger quantity of arsenic is used1 and thus a product obtained inclining more to green than to blue4 ,as a rule #b to #b parts of arsenious acid are used to #ajj parts of copper sulphate4 ,the colours found in commerce under this name very often consist of mixtures of emerald green and finely ground barytes4 ,copper ,oxychloride was at one time largely used4 ,at present it is scarcely employed2 it has been replaced by handsomer and cheaper pigments4 ,copper oxychloride is made by exposing a wet mixture of copper1 copper sulphate and common salt to the action of the air4 ,to #aaa parts of copper sulphate #aabe parts of copper and the same quantity of common salt are employed4 ,the mixture is made into heaps1 which are wetted and from time to time shovelled about1 so that the air may come in contact with all portions of the mass1 and the copper chloride be converted into basic chloride4 ,it is advisable to allow the heaps to dry frequently after they have been turned over1 so that the air may more readily penetrate into the interior4 ,copper oxychloride has a pale green colour of little brilliance4 ,on this account it is hardly ever used now2 it forms the raw material for the preparation of ,bremen green4 ,,chapter ,,xxix4 ,,emerald ,,green4 ,there are many versions as to the discovery of this pigment4 ,according to one it was first made in ,schweinfurt by ,russ and ,sattler2 another version gives it that ,mitis of ,vienna first made it on the large scale4 ,it is possible1 as has been the case with many chemical products1 that this pigment was simultaneously discovered by both4 ,the method of making the pigment was at first a secret possessed by few4 ,not until the publication of a method by ,liebig in #ahbb was the preparation of emerald green generally known4 ,in recent times the industry has supplied other colours which are less poisonous4 ,the time should not be far distant in which this handsome but highly poisonous pigment shall no longer be found in commerce4 ,the circumstance that the poisonous nature of the pigment and cautions as to its use were given great publicity1 brought about the discovery of the countless names under which it has been sold4 ,it was endeavoured by re-naming the pigment to pass it off as a different substance4 ,all the pigments which have been sold under the names of ,mitis1 moss1 patent1 new1 king's green1 etc41 are either pure emerald green or mixtures of it with barytes or gypsum1 which additions were intended to alter the shade of the green and make it appear to the buyer as a new pigment4 ,in chemical composition emerald green is a compound of copper arsenite and copper acetate4 ,it has the following formula3-- #c7;,cu,o4,as,o7 ,cu7,c,h,o74 ,this compound rarely comes into commerce in the pure state2 it is generally mixed with chrome yellow or lead sulphate1 which are added with the object of producing shades between yellowish-green and dark green4 ,emerald green is a compound of constant composition4 ,when made by different processes it has the same properties4 ,under the microscope it is seen to consist of crystals2 when the pure substance is ground it becomes paler1 the intensity of the colour being diminished by the breakage of the crystals4 ,the colour of emerald green is not altered by artificial light4 ,this is a most valuable property2 the majority of green pigments appear yellowish-green in artificial light4 ,emerald green can be made on the large scale by two processes2 these differ according to the copper salt used1 which is either the acetate 7verdigris7 or the sulphate4 ,the latter is by far cheaper than verdigris1 which is now seldom used for this purpose4 ,manufacture of ,emerald ,green from ,verdigris4--,by boiling for several hours1 #gj parts of ordinary verdigris are dissolved in water2 in a second vessel #ajj parts of arsenious acid are dissolved in #a1ejj parts of hot water2 the verdigris solution is filtered through a cloth into a larger wooden vessel and mixed with two-thirds of the arsenic solution4 ,the mixture is well stirred and allowed to stand for some hours4 ,a precipitate of dull green colour is formed4 ,this consists of copper arsenite4 ,after three to four hours the remaining one-third of the arsenic solution is added2 the precipitate then changes into the double salt of which emerald green consists4 ,the use of such dilute solutions as are given in these directions is essential when a product of particularly good colour is required4 ,emerald green is a crystalline substance which is deeper in colour in proportion to the size of its crystals4 ,large crystals can only be formed from very dilute solutions2 when strong solutions are used1 the emerald green has never the deep colour possessed by the product of dilute solutions4 ,in the place of ordinary 7basic verdigris7 the so-called distilled verdigris 7neutral copper acetate7 can be used1 of which seventy-six parts are required for the quantity of arsenious acid given4 ,the emerald green made from 0distilled0 verdigris is of a yet deeper colour than that made from ordinary verdigris1 but is considerably dearer4 ,such emerald green is commercially described1 very incorrectly1 as distilled emerald green4 ,the method given by ,liebig is as follows3 #d parts of basic verdigris and #c parts of arsenious acid are separately dissolved in boiling vinegar2 the liquids are mixed and evaporated until a precipitate of emerald green separates4 ,according to ,ehrmann and ,kastner1 #gj parts of verdigris and #ef to #fc parts of arsenious acid are separately dissolved1 the boiling solutions mixed and boiled until the dirty green precipitate changes into a bright green4 ,in consequence of the rapid formation of the precipitate due to the boiling1 the colour is pale green2 if a dark-coloured product is required1 the solutions are allowed to cool before mixing4 ,after several days a very dark-coloured precipitate separates from the liquid2 it consists of comparatively very large crystals of emerald green4 ,manufacture of ,emerald ,green from ,copper ,sulphate4--,there are two processes4 ,either the solution of copper sulphate is mixed with an acetate1 by which it is converted into copper acetate1 and then with arsenious acid1 or copper arsenite is precipitated from the solution of copper sulphate and then converted into emerald green by treatment with acetic acid4 ,if acetic acid can be cheaply obtained1 the latter process is to be recommended4 ,braconnet gives the following directions3 #c parts of copper sulphate are dissolved in a little boiling water1 the hot solution is mixed with a hot solution of #d parts of arsenious acid and four parts of potassium carbonate2 the precipitate is then treated with #c parts of pyroligneous acid4 ,the dull-coloured precipitate at first formed is changed by the acetic acid to a bright green4 ,the colour is more quickly produced when the liquid is heated nearly to boiling for several hours4 ,when the desired shade appears the boiling is stopped and the precipitate at once separated from the liquid1 by long contact with which it would give up arsenious acid and thus lose in shade4 ,according to ,fuchs1 #e kilogrammes of lime and #be kilogrammes of copper sulphate are dissolved in acetic acid1 then a boiling solution of #be kilogrammes of arsenious acid is added4 ,the precipitate is at once formed2 it is immediately separated from the liquid1 washed1 and dried2 the top liquor1 with the addition of arsenious acid1 can be again used to precipitate the copper lime solution4 ,emerald green has an extremely bright colour which surpasses other green mineral pigments in beauty4 ,the larger are the microscopic crystals of which it consists the deeper is the colour4 ,in order to obtain the desired deep shade of emerald green it is necessary to use very dilute solutions2 from strong solutions the precipitate is instantaneously produced1 in which case it is impossible to obtain large crystals4 ,the covering power of emerald green1 in consequence of its crystalline nature1 is less the deeper the shade4 ,it cannot be regarded as a permanent colour3 very dilute alkalis and acids attack it4 ,by the action of sulphuretted hydrogen it is discoloured1 owing to the formation of black copper sulphide4 ,it ought not to be used upon lime1 which withdraws acetic acid and produces yellowish-green copper arsenite4 ,this pigment should not be used for distempering or for colouring wall papers4 ,by the action of the atmosphere on the arsenic it contains1 arseniuretted hydrogen is formed--an extremely poisonous gas1 very small quantities of which are sufficient to cause serious illness in the case of susceptible people4 ,in spite of its poisonous nature1 emerald green is still largely used4 ,all possible shades of green can be produced from it1 yellowish-green or pale green1 by admixtures of yellow pigments1 such as chrome yellow1 or white pigments1 such as barytes or white lead4 ,many qualities of green known as palette green1 ,basle green1 etc41 are generally composed of such mixtures4 ,mitis ,green or ,vienna ,green is obtained by dissolving verdigris in acetic acid and adding a boiling solution of white arsenic in water2 acetic acid is then added until the precipitate dissolves4 ,on boiling the clear solution a green precipitate forms1 which1 when dry1 is a deep bluish-green of characteristic shade4 ,this pigment is now practically disused because of its poisonous nature1 which is equal to that of emerald green4 ,copper ,stannate4--,this green pigment1 also known as ,gentele's green1 can be made by two methods4 ,gentele gave the following process3 #ei parts of tin are converted into stannic chloride by solution in aqua regia2 a solution of #abe parts of copper sulphate is added and copper stannate is precipitated from the mixture by caustic soda1 on washing and igniting it acquires a pretty green colour4 ,it may also be made by fusing #ei parts of tin with saltpetre2 the potassium stannate is then dissolved in dilute caustic soda and copper sulphate solution added2 the precipitate is washed and ignited4 ,copper stannate is tolerably durable1 in this respect it considerably surpasses emerald green4 ,only sulphuretted hydrogen has any considerable action upon it1 turning it to a dirty brownish-green hue4 ,kuhlmann's ,green is a basic chloride of copper1 obtained by heating #b equivalents of lime with a solution of #c equivalents of copper chloride4 ,it is important that the copper salt should be present in excess4 ,in shade ,kuhlmann's green is very similar to emerald green1 with which it agrees in retaining its colour by artificial light4 ,it is a somewhat less pure green than emerald green2 the difference is only perceived when the two pigments are directly compared4 ,when1 however1 it is considered that it is far more permanent than emerald green and cheaper1 a more extended use is indicated than is yet the case4 ,elsner's ,green is a species of lake1 made by mixing a solution of copper sulphate with a decoction of fustic1 adding a small quantity of stannous chloride and precipitating with caustic soda4 ,to #ajj parts of copper sulphate #aj to #ad parts of stannous chloride are used4 ,according as the copper salt or fustic extract predominates1 the colour of the precipitate inclines to blue or yellow4 ,elsner's green is also sold under the name of 0non-poisonous green04 ,this description is incorrect2 the pigment is indeed free from arsenic1 but is poisonous on account of the copper it contains4 ,casselmann's ,green approaches emerald green in brightness4 ,it consists of a compound of copper sulphate with copper hydroxide and water1 ,cu,s,o4#c;,cu7,,oh74,h,o4 ,this pigment is obtained by mixing solutions of #d equivalents of copper sulphate and #c equivalents of sodium acetate at a certain temperature4 ,the author's experiments have shown that the best results are obtained when the solutions are mixed at a temperature of about #ajj ,c4 ,with this object the solutions are placed in vessels standing in a pan of boiling water2 when their temperatures have risen to about #ajj ,c4 they are quickly mixed1 the mixture stirred1 and the precipitate allowed to settle4 ,when the precipitate is cautiously treated with very weak caustic soda solution a rather deeper colour is obtained4 ,this treatment should not be continued too long1 or the precipitate may acquire an ugly bluish shade4 ,lime ,green is a mixture of copper arsenite and calcium sulphate4 ,it is thus a pigment which ought no longer to be used1 on account of its poisonous properties4 ,it is made by boiling milk of lime with excess of arsenious acid so long as the latter is dissolved4 ,to this solution of calcium arsenite1 copper sulphate solution is added so long as a precipitate is formed4 ,a mixture of copper arsenite and calcium sulphate is precipitated4 ,patent ,green is similar in composition to lime green4 ,a solution of calcium acetate is made by adding quicklime or pure powdered limestone to acetic acid2 copper sulphate solution is then added1 when gypsum is precipitated and copper acetate remains in solution4 ,a hot solution of arsenious acid is next added1 and the precipitated copper salt mixed with the gypsum at the bottom of the vessel4 ,copper ,borate4--,a pale green precipitate of copper borate is obtained by adding a solution of #c parts of borax to a solution of #b parts of copper sulphate4 ,it must be dried at a very moderate temperature1 or it will decompose4 ,when perfectly dry the precipitate can be heated to a red heat without decomposition2 according to the temperature employed different shades are obtained4 ,it is most convenient to take tests out of the crucible from time to time during the ignition1 and to quickly cool the crucible when the desired shade is obtained4 ,when levigated this pigment may be used in oil1 or as a porcelain colour4 ,copper ,silicate 7,egyptian ,blue74--,when a solution of water-glass is added to a solution of copper sulphate a pale green precipitate of copper silicate is obtained1 which can be heated to redness without alteration4 ,when #gj parts of white quartz sand1 #ae parts of copper oxide1 #be parts of chalk and #f parts of soda are fused together a glass is produced which1 after pouring into water1 grinding and levigating1 exhibits a pretty blue and very permanent colour4 ,it appears from the examination of the colours of the ,egyptian mural paintings that this pigment was already known to the ancient ,egyptians4 ,,chapter ,,xxx4 ,,verdigris4 ,verdigris is little used as a pigment1 but is important to the colour maker1 because copper colours are made from it4 ,in wine-growing countries it is made from the marc at small expense and without much labour4 ,in commerce several kinds of verdigris are distinguished2 they differ in physical and chemical properties4 ,all verdigris consists of copper acetate1 either alone or combined with varying quantities of copper hydroxide4 ,blue ,verdigris is made in large quantities in ,france and is commonly known as ,french verdigris 7vert de gris naturel74 ,it has the following formula3-- ,cu7,,oh77,c,h,o74#b;,h,o4 ,the process adopted in southern ,france1 especially in the neighbourhood of ,montpellier1 is as follows3 copper plates are placed in layers in heaps of the freshly pressed grape residues1 which always contain a certain quantity of must even when the most powerful presses are used4 ,the process is conducted either in large heaps or in pots2 in the first case care must be taken that the heaps are in a room whose temperature does not lie below #ae ,c4 ,it is important to maintain this temperature1 because the formation of acetic acid takes place with sufficient rapidity only at temperatures not below #ab to #ae ,c4 ,too high a rise of temperature in the heaps must also be avoided or a considerable quantity of acetic acid will be volatilised4 ,the heaps should therefore not be made too large1 otherwise the temperature cannot be kept within the proper limits4 ,the residues contain a considerable quantity of sugar1 which can be transformed by fermentation into alcohol4 ,if air has free access1 the alcohol is at once oxidised to acetic acid1 which is recognised by the acid smell given off4 ,in order to make possible the entry of air into the interior of the heaps1 rectangular wooden bars are introduced in piling up the heaps4 ,these are carefully withdrawn when the heap is finished1 so that it is traversed by passages through which air can enter4 ,by the simultaneous action of air and acetic acid copper acetate is formed1 and since copper is always in excess1 the acetate produced is a basic salt4 ,in consequence of the chemical processes1 the temperature of the heap rises to #ce to #dj ,c42 it is endeavoured to attain this temperature by artificial heat4 ,it has already been stated that too great a rise of temperature is accompanied by a considerable evaporation of acetic acid4 ,the process is then finished in a short time1 but the loss of acetic acid is remarkable4 ,when the temperature is so regulated that it varies between #be and #cj ,c4 the process takes a normal course--four to five days may be regarded as its duration4 ,the grape residues are effective on account of the sugar1 which is transformed into alcohol and then into acetic acid4 ,residues which have been extracted with water after pressing should not be used in the manufacture of verdigris2 they contain but little sugar and hence undergo a very feeble acetic fermentation4 ,when such residues are used the verdigris is often accompanied by black spots of copper sulphide upon the plates2 this is due to incipient decomposition of the residues4 ,as a practical test for the termination of the process a strip of copper is plunged into the heap and left for some hours4 ,it should be covered by a uniform coating of verdigris2 if it is covered with small drops that is a sign that the process is not completed and the heaps must be left some time longer4 ,the course of the process can be simply and safely followed by means of a thermometer4 ,this is placed in a perforated copper tube and plunged into the interior of the heap4 ,a continuous rise of temperature indicates a steady increase of chemical action2 the temperature of the room is regulated in accordance4 ,when the temperature in the interior of the mass begins to fall the process is nearing the end4 ,more heat is now supplied to assist the chemical action4 ,the process is at an end when1 in spite of external heat1 the temperature of the heap decreases and approaches the temperature of the air of the room4 ,verdigris can also be made by placing sheet copper and grape residues in layers in pots1 which are deposited in a room of fairly uniform temperature1 such as a cellar4 ,this method has the advantage that the formation of the verdigris is finished in a shorter time1 which is more than counterbalanced by the labour and expense of filling the pots4 ,the copper plates1 when removed from the heaps or pots1 are covered by a crust of thin needle-shaped crystals of a bright green colour4 ,they are shaken to free them from the adhering grape skins and seeds1 and then treated with weak vinegar1 in which they are dipped2 they are then left standing on edge for several days4 ,this treatment with vinegar has the object of converting the neutral salt formed on the plates into basic salt4 ,the dipping into vinegar and exposure to air are repeated six to eight times1 when the originally pure green crust on the plates is gradually changed into bluish-green verdigris4 ,these processes are continued until the plates are covered uniformly by a layer of verdigris about #e centimetres thick4 ,the crust is then scraped off by copper knives and stirred with water to a paste1 which is pressed in leather bags in rectangular moulds4 ,the lumps are then slowly dried in the air4 ,plates which have been once used give a larger quantity of verdigris in a second operation1 which is to be ascribed to the fact that they possess a larger surface than unused plates4 ,new plates are made more susceptible to the further action of the acid by dipping in strong vinegar1 by which they become covered with a layer of copper acetate4 ,the verdigris obtained by this method consists of crystalline scales of a pale bluish-green colour1 which produce a pale blue powder4 ,in crude verdigris grape seeds are often found1 and occasionally stalks and pieces of metallic copper4 ,these admixtures are a consequence of the method of manufacture and cannot be regarded as adulterants4 ,gypsum is to be regarded as an adulterant4 ,verdigris often contains basic copper carbonate4 ,verdigris behaves in a peculiar manner with water4 ,in contact with a small quantity it swells to a bluish-green mass1 which becomes quite warm4 ,neutral copper acetate and the basic salts #b;,cu7,c,h,o74,cu7,,oh74#e;,h,o and ,cu7,c,h,o74#b;,cu,o4#a;,h,o are formed1 the latter of which is insoluble4 ,by the addition of a larger quantity of water the basic compounds are decomposed1 neutral copper acetate dissolves1 and a mixture remains of the compound ,cu7,c,h,o74#b;,cu,o4#a;,h,o and a brown basic acetate containing still less acetic acid4 ,on account of this peculiar behaviour of verdigris towards water some care is required when it is used as a water colour4 ,a very dilute solution is not green1 but has an indefinite shade4 ,distilled or ,crystallised ,verdigris consists of neutral copper acetate1 ,cu7,c,h,o74,h,o4 ,it can be made from blue verdigris by treating with the amount of acetic acid required to completely neutralise the copper oxide1 or by decomposing copper sulphate with the acetate of a metal which forms an insoluble or difficultly soluble sulphate4 ,crystallised verdigris is very simply made from ordinary verdigris2 the latter1 whilst still moist1 but containing only a small quantity of water1 or the acetic acid would be too largely diluted1 is brought into a pan and strong acetic acid poured over4 ,strong pyroligneous acid may be used1 its empyreumatic odour is without influence on the quality of the product4 ,the pan is heated until the contents almost1 but not quite1 boil4 ,they are frequently stirred so that the particles at the bottom are brought in contact with the acid4 ,a dark green solution is formed2 when its colour no longer increases in depth it is allowed to stand until suspended solids sink to the bottom4 ,the clear solution is then drawn off and rapidly evaporated in shallow copper pans4 ,it is important that the liquid should not contain an appreciable quantity of free acid4 ,when a crystalline skin begins to form on the surface of the solution it is drawn off into the crystallising vessels4 ,these are made of glazed earthenware2 wooden rods are placed in them1 on which the crystallisation takes place4 ,in order that large crystals shall be obtained1 it is necessary to maintain a regular temperature in the room in which the crystallising vessels are placed4 ,it is heated at the commencement1 and the temperature is allowed to sink a little towards the end of the operation4 ,from twelve to fourteen days are required to obtain large crystals4 ,the mass of verdigris crystals adhering to each rod weighs #be to #c kilogrammes4 ,the residual liquid is a saturated solution of verdigris1 and is used in the next operation4 ,it is only necessary to heat it with the residue from the first operation and some acetic acid in order to obtain a crystallisable solution of verdigris4 ,the residue in the pan contains metallic copper1 grape stems and seeds1 and basic copper acetate4 ,the copper is extracted by moistening with acetic acid and exposing to the air1 when verdigris is formed1 which is added to a later batch4 ,it is often advisable to make verdigris from a soluble copper salt2 the process varies somewhat according to the salt employed4 ,from copper sulphate verdigris is obtained by the action of calcium acetate4 ,when solutions of these compounds are mixed1 calcium sulphate separates as a white precipitate1 whilst a solution of the easily soluble copper acetate is left4 ,it is only necessary to mix the solutions in equivalent proportions1 separate the liquid from the precipitated gypsum and evaporate4 ,gypsum is somewhat soluble in water1 so that when the solution is evaporated a double salt separates out first4 ,this consists of copper calcium acetate2 it may be used as a pigment1 but is of less value than verdigris4 ,it is advisable to prevent the formation of this double salt1 which is accomplished by adding copper sulphate to a slightly acid solution of calcium acetate until a precipitate is no longer produced4 ,the solution of copper acetate is boiled for several hours to effect the separation of the dissolved gypsum2 at the same time the iron contained as impurity in the copper sulphate is also precipitated4 ,the purified solution of verdigris is concentrated and allowed to cool1 when a further quantity of gypsum separates2 the solution is then evaporated to crystallisation4 ,if barium salts and lead acetate are cheap1 barium acetate can be obtained by double decomposition4 ,when copper sulphate is added to the solution of barium acetate so long as a precipitate is formed1 a solution of verdigris is produced1 which only requires evaporation to crystallise4 ,the precipitate is barium sulphate1 and can be used as enamel white4 ,it obstinately retains a quantity of copper1 which1 though small1 is sufficient to give it a greenish tint4 ,by several washings with acetic acid this copper is removed2 the acid can be used to obtain fresh quantities of verdigris1 so that none is lost1 and the copper retained in the precipitate is regained4 ,the precipitate1 after treatment with acetic acid1 only requires thorough washing with water to produce permanent white1 satisfactory in every respect4 ,ammonia may also be used in the manufacture of verdigris from copper sulphate4 ,strong ammonia is left in contact with copper sulphate in a covered vessel for several hours2 gentle warming accelerates the formation of copper ammonium sulphate4 ,the liquid has then a fine blue colour2 it should not contain sufficient ammonia to be perceptible by the smell4 ,it is then gently warmed and acetic acid gradually added4 ,on continued heating small green crystals separate from the solution1 which is boiled with continual additions of acetic acid in small quantities until small crystals appear on the surface1 when it is allowed to cool and the crystals are strained off4 0,distilled0 verdigris forms deep bluish-green crystals1 which effloresce slightly in the air2 they dissolve in #e parts of boiling water and in #acd parts at #bj ,c4 ,when the solution is boiled for some time the tribasic acetate separates2 the liquid becomes brown and acquires an acid reaction4 ,german ,verdigris does not differ essentially from ordinary verdigris4 ,it is a compound of the following basic acetates3 #b;,cu7,c,h,o74,cu,o and ,cu7,c,h,o74#b;,cu,o4 ,the method is similar to that in which grape residues are used2 where acetic acid is cheap the process is especially appropriate4 ,in ,sweden1 where pyroligneous acid is made in large quantities and copper is also cheap1 verdigris is made by arranging copper plates and flannel in alternate layers4 ,the plates are frequently turned over and the flannel kept saturated with acetic acid4 ,the same chemical reactions occur as in the process in which grape residues are used4 ,when a layer of verdigris has formed on the copper plates they are taken apart1 exposed to the air1 and frequently wetted4 ,the formation of the verdigris is thus completed4 ,the difference between this process and that adopted in wine-producing countries lies simply in the use of pure acetic acid2 the product is free from the mechanical impurities introduced by the grape residues4 ,in properties ,german or ,swedish verdigris is completely identical with blue verdigris4 ,,chapter ,,xxxi4 ,,chromium ,,oxide4 ,chrome ,green4--,although very different substances are commercially known as chrome green1 this name is usually applied to the very valuable pigment which consists of pure chromium oxide4 ,there is hardly another pigment for the preparation of which such varied directions have been given and whose shade varies so much according to the manner of production4 ,the cheapest process is to ignite potassium bichromate with sulphur1 extract the mass with very dilute sulphuric acid and wash the residue4 ,the chromic acid is reduced by the sulphur2 when the mass is treated with sulphuric acid sulphur dioxide is evolved1 potassium sulphide and sulphate are dissolved1 whilst pure chromium oxide remains4 ,the larger the quantity of sulphur used the paler is the chromium oxide4 ,the purity of the potassium bichromate has considerable influence on the shade of the pigment2 if iron is present in any quantity a discoloured product always results4 ,convenient proportions are3 #ai parts of potassium bichromate and #d parts of sulphur1 which produce #icc parts of chromium oxide4 ,if potassium bichromate free from iron cannot be obtained1 the shade of the product is somewhat improved by treatment with dilute hydrochloric acid1 in which ferric oxide dissolves more easily than chromium oxide4 ,when the latter has been strongly ignited it is soluble with very great difficulty4 ,there are many formul for the preparation of chromium oxide by means of sulphur3 in all the above statement holds good1 that the more sulphur the paler the product4 ,according to ,a4 ,casali1 a chrome green which satisfies every requirement is obtained by strongly igniting #a part of potassium bichromate with #c parts of burnt gypsum4 ,after ignition the mass is boiled with very dilute hydrochloric acid4 ,in this process the chromic oxide is produced according to the following equation3-- #b,k,c,o ,ca,s,o #b;,cr,o #b,k,,so #b;,ca,o #c,o4 ,on boiling with hydrochloric acid the lime is dissolved2 when the liquid remains distinctly acid after long boiling it is poured off and the chromium oxide washed with hot water and dried4 ,in another method ammonium chromate is very gradually heated4 ,at a certain temperature the salt suddenly becomes incandescent and is converted into a dark green1 almost black1 mass which has a very similar appearance to dry tea-leaves4 ,the green obtained after washing and powdering is handsomer the lower the temperature of the decomposition4 ,chromium oxide may also be made in the wet way1 but the product does not compare in beauty with that obtained in the dry way4 ,when soda solution is added to a solution of chrome alum1 a greyish green precipitate of chromium hydroxide is formed2 on ignition of the washed precipitate pure chromium oxide remains4 ,in a similar manner chromium oxide is produced by precipitating with soda solution the solution of chromium chloride obtained by adding hydrochloric acid to a solution of potassium bichromate1 and then alcohol in small quantities1 so long as a reaction occurs and the green liquid becomes deeper in colour4 ,a handsome and bright chrome green is only obtained when the potassium bichromate is quite free from iron1 a very small quantity of which has a very harmful effect upon the brightness of the pigment4 ,the author has found that there is no great difficulty in rendering commercial potassium bichromate tolerably free from iron by recrystallisation4 ,as much of the salt is dissolved in boiling water as it will take up1 the boiling solution is quickly filtered and rapidly cooled with continual stirring2 the fine crystalline meal is left on a strainer until no more liquid filters through1 and then washed with a little cold water to remove the mother liquor4 ,the salt obtained by this simple operation is of great purity and always produces chrome green of a good shade4 ,when chrome green contains ferric oxide it shows a blackish colour4 ,from such chrome green1 which has little value1 a product of more pure colour can be obtained with a little care4 ,by treatment with dilute hydrochloric acid the ferric oxide dissolves1 even when it has been somewhat strongly ignited2 chromium oxide loses almost all solubility in dilute hydrochloric acid after heating at a relatively low temperature4 ,to facilitate the solution of the ferric oxide1 the green to be treated is finely powdered2 it is then covered with a mixture of equal parts of hydrochloric acid and water4 ,after several days the mass is strained and washed with pure water until the acid reaction disappears4 ,comparative analyses have shown that almost the whole of the ferric oxide can be removed from chrome green in this manner2 the brightness of the colour is considerably increased4 ,it is1 however1 advisable to employ materials free from iron in the manufacture of chrome green4 ,chromium oxide can be obtained as a colour of particular brightness1 according to the process of ,leune1 by precipitating it very slowly from a solution in which it is contained in the green modification4 ,for this purpose a solution of chrome alum is boiled until the violet colour has changed to green2 the green modification of chromium oxide is now contained in the solution4 ,it is cooled to about #aj ,c41 and either freshly precipitated alumina or zinc carbonate added1 very gradually and in small quantities4 ,a fine green shade of chromium oxide separates2 after washing and drying it is obtained in a condition in which it can be used as a pigment4 ,chromium oxide can indeed be obtained by this process1 but it is not distinguished by particular beauty2 the author has never been able to obtain1 even by using the precipitant in very small quantities1 a chromium oxide surpassing in shade that obtained by the direct precipitation of a chromium salt with an alkali4 ,the emerald green described in the following chapter is obtained in a similar manner by precipitation with zinc oxide4 ,,chapter ,,xxxii4 ,,other ,,green ,,chromium ,,pigments4 ,guignet's ,green is a chromium oxide made in the dry way2 it is obtained by grinding #a part of potassium bichromate with #c parts of pure boric acid and water1 drying and heating to a dark red heat with access of air4 ,the hot mass is brought into water2 by boiling repeatedly with water it is freed from the boric acid which it obstinately retains4 ,in order to remove the last portions of boric acid it is necessary to boil with sulphuric acid and then with caustic soda2 this treatment may be omitted for technical purposes1 since the small quantities of boric acid contained in the pigment are not harmful4 ,guignet's green is distinguished by the great resistance it offers to chemical reagents2 it is largely used in painting and calico printing4 ,pale shades are obtained by additions of barytes4 ,emerald ,green4--,this pigment must not be confounded with the more important copper compound previously described1 to which the name emerald green is usually applied4 ,it consists of chromium hydroxide obtained by precipitating a solution of the green modification of a chromium salt by zinc hydroxide4 ,after careful washing it has a dull green shade2 it is a very durable pigment4 ,chrome ,green ,lake is a mixture of chromium oxide with alumina2 it is obtained by precipitating a solution of alum and a chromium salt by a soda solution4 ,the precipitate1 which contains aluminium and chromium hydroxides1 on ignition takes a paler shade in proportion to the quantity of alumina it contains4 ,for the chromium salt a solution of potassium bichromate1 which has been allowed to stand with sulphuric acid and alcohol until if has acquired a pure green colour1 may be used4 ,turkish ,green4--,this pigment1 which retains its fine green colour in artificial light1 is prepared in a peculiar manner3 #dj parts of alumina free from iron1 #cj parts of cobalt carbonate and #bj parts of chromium oxide are thoroughly ground in a mortar4 ,the mixture is placed in a porcelain tube1 which is exposed to a strong white heat whilst pure oxygen is led through4 ,the oxygen may be replaced by air if it is previously heated and under pressure4 ,another recipe for ,turkish green is to intimately mix #d parts of freshly precipitated alumina with #c parts of cobalt carbonate and #b parts of chromium oxide1 heat the mixture in a crucible at a white heat1 powder and levigate4 ,turkish green has a characteristic bluish-green colour2 the shade is inclined to blue or green by increasing the quantity of cobalt carbonate or chromium oxide4 ,leaf ,green is a pale green1 very durable pigment similar to chrome green lake4 ,it is obtained by igniting mixtures of chromium oxide with pure aluminium hydrate2 the paleness of the shade is in proportion to the amount of alumina4 ,chromium ,phosphate ,pigments4--,several chromium phosphates are used as pigments2 the more important are described here4 ,arnaudan's ,green is chromium metaphosphate2 it is obtained by intimately mixing #abh parts of neutral ammonium phosphate with #adi parts of potassium bichromate by long grinding1 and carefully heating the mixture at #agj to #ahj ,c41 but not higher1 until the mass is pure green4 ,it is then brought into hot water and thoroughly washed2 it has a very handsome green colour1 which is not altered in artificial light4 ,ammonium arsenate may be used in the place of ammonium phosphate2 a handsomer green is then obtained1 which is1 however1 very poisonous4 ,plessy's ,green is essentially a chromium phosphate mixed with variable amounts of chromium oxide and calcium phosphate4 ,it is obtained by boiling a solution of #a part of potassium bichromate in #aj parts of water with #c parts of a solution of acid calcium phosphate and #a part of sugar1 until the whole has become deep green4 ,the chromic acid is reduced by the sugar1 so that the precipitate contains chromium phosphate1 chromium oxide and neutral calcium phosphate4 ,these two chromium phosphate greens are very stable towards chemical reagents1 and very durable towards atmospheric influences4 ,schnitzer's ,green4--,thirty-six parts of sodium phosphate are melted in its water of crystallisation1 #ae parts of potassium bichromate and #ad parts of ,rochelle salt are then added4 ,a large dish must be used for the fusion1 since the mass effervesces4 ,the colour changes gradually from yellow to green4 ,when it is pure green the heating is stopped1 and1 after cooling somewhat1 as much hydrochloric acid is added as the mass will absorb2 then1 after standing some time1 it is washed with cold and finally with boiling water4 ,on account of their great durability1 the chromium phosphate pigments are well adapted for paperhangings1 calico printing and oil painting4 ,chromaventurine is a glass coloured green by chromium oxide4 ,it is hardly used as a painters' colour in the ordinary sense of the term2 it is applied in porcelain painting as an under-glaze colour1 and is largely used for colouring glass4 ,chromaventurine is most simply made by the process of ,pelouze3 #bej parts of quartz sand1 #ajj parts of soda1 #ej parts of calcium carbonate and #dj parts of potassium bichromate are fused together4 ,the presence of iron would have a very harmful effect on the shade of the product4 ,quartz sand generally contains a small quantity of ferric oxide1 which should be extracted by treatment with strong hydrochloric acid when a product of the best colour is required4 ,the calcium carbonate should also1 as far as possible1 be free from ferric oxide4 ,chrome ,blue 7,garnier74--,a mixture of #dhfb parts of potassium chromate with #fe parts of fluorspar and #aeg parts of silica is fused in a crucible lined with coal-dust4 ,,chapter ,,xxxiii4 ,,green ,,cobalt ,,pigments4 ,from mixtures of chromium oxide1 cobalt carbonate and alumina in different proportions a series of pigments can be obtained varying in shade between pale blue and bluish-green4 ,on account of the great stability of these colours at the highest temperatures they are of great importance in porcelain painting1 for which they are principally used4 ,it is necessary that the porcelain should be free from iron1 since ferric oxide forms a black compound with chromium oxide1 very small quantities of which would be sufficient to considerably damage the fineness of the colour4 ,cobalt ,green1 which is also known as ,rinmann's green or zinc green1 is a compound of the oxides of cobalt and zinc4 ,it is always produced when a cobalt compound is ignited with zinc oxide4 ,rinmann's green has not so deep a colour as the poisonous emerald green1 but it is distinguished by extraordinary durability1 and deserves to be more largely used than it is at present4 ,this pigment is most simply made by precipitating the mixed solutions of a zinc salt and a cobalt salt4 ,it is also formed by moistening pure zinc oxide with a cobalt solution and igniting4 ,in precipitating the mixed solutions of zinc and cobalt salts products of different shades are obtained1 according to the proportions in which the salts are used4 ,if equivalent quantities are used1 an almost black product is obtained1 quite useless as an artists' colour4 ,the best result is obtained by mixing intimately pure precipitated cobalt carbonate with zinc oxide and igniting the mixture2 a mixture of #i to #aj parts of zinc oxide with #a to #ae part of cobalt carbonate gives colours between pale green and dark green4 ,especially fine ,rinmann's green is obtained by igniting cobalt arsenate with zinc oxide and arsenious acid4 ,the addition of the last-named substance can only have the object of preventing the temperature from rising too high1 which might injure the beauty of the colour2 arsenious acid is volatile at a fairly low temperature4 ,cobalt green is also obtained by evaporating a solution of cobalt nitrate and zinc nitrate and igniting the residue1 or by igniting a mixture of the sulphates4 ,in the latter case a tolerably high temperature is necessary in order that the sulphates may be decomposed4 ,the author has found that a particularly handsome product is obtained by mixing pure zinc oxide with a dilute solution of cobalt chloride1 drying and then slowly heating to redness in a crucible with a well-fitting lid4 ,towards the end of the operation the heat is considerably increased and maintained for a short time1 after which the mass is rapidly cooled4 ,,chapter ,,xxxiv4 ,,green ,,manganese ,,pigments4 ,manganese ,green1 ,rosenstiehl's ,green4--,this pigment1 which is handsome but difficult to produce1 consists of barium manganate4 ,it can be obtained by several methods1 all of which produce a good green1 but with very unequal properties4 ,manganese green made from barium nitrate has little durability2 when made from barium hydrate it is more costly1 but very durable4 ,barium manganate is most easily obtained by precipitating a boiling solution of potassium manganate by barium chloride4 ,the almost blue precipitate becomes nearly white when washed and dried1 but when it is gradually heated on a porcelain plate to a dark red heat it acquires a fine green colour4 ,the heating must be carefully conducted2 if the temperature rises too high1 the colour changes to a dirty greyish brown1 owing to the reduction of the manganic acid4 ,this pigment is also made by heating #ad parts of manganic oxide1 #hj parts of barium nitrate and #f parts of barytes with access of air until the desired shade appears4 ,the mass is then ground in a continuous current of water until it is changed into a very fine powder and nothing more is dissolved by the water4 ,the best result is obtained by ,rosenstiehl's process3 #d parts of barium hydrate1 #b parts of finely-powdered barium nitrate and #je part of artificial manganese dioxide are rapidly mixed2 the mixture is moistened and heated to a dark red heat4 ,the fused mass is boiled out with water and the residue dried under a bell jar1 under which are dishes of sulphuric acid and caustic potash1 the former of which absorbs the water1 whilst the latter keeps the air free from carbonic acid1 which would injure the shade of the moist substance4 ,manganese green is amongst the pigments more recently discovered4 ,on account of its high price it has found but limited use up to the present4 ,it may be used in any vehicle1 and is distinguished by great permanence4 ,in regard to the preparation of this colour by ,rosenstiehl's method1 which of all gives the best results1 it should be observed that the shade largely depends on the quantity of barium hydrate used2 the greater this is the more the shade inclines to blue4 ,if it is desired to produce a colour of a greener tone than is produced by the fusion1 this can be accomplished by boiling for a very long time with very weak hydrochloric acid1 which extracts a portion of the base from the compound and produces a deeper shade4 ,bttger's ,barium ,green4--,a beautiful green is obtained by the process given by ,bttger1 as the author has found4 ,it consists of barium manganate4 ,the process is1 however1 somewhat costly1 so that the pigment would only be available for artists' purposes4 ,a solution of potassium manganate is first made by gradually adding #b parts of very pure pyrolusite1 finely powdered1 to a fused mixture of #b parts of caustic potash and #a part of potassium chlorate1 bringing the mass to a low red heat after the introduction of the whole of the pyrolusite1 and finally extracting with water1 in which the potassium manganate dissolves to a fine emerald green solution4 ,this process is unattended by difficulty if the pyrolusite contains a sufficient quantity of manganese peroxide and is in a sufficiently fine powder1 which is most important4 ,potassium manganate is a very unstable substance4 ,cold water must be used to dissolve it1 and the solution should not long stand exposed to the air1 but should at once be used to obtain barium manganate4 ,when the solution of potassium manganate is mixed with a solution of a barium salt1 a handsome violet precipitate immediately forms4 ,this is washed with water and quickly ground with to #a part of its weight of barium hydrate4 ,the mixture is heated in a copper dish with constant stirring to a low red heat2 the colour changes gradually to a very fine green4 ,when the mass has reached the proper shade it is treated with cold water to remove excess of barium hydrate1 until the washings show no trace of alkaline reaction4 ,manganous ,oxide is occasionally used as a green pigment1 especially for painting metal work2 it is obtained in the following manner3 ,manganese sulphate solution is precipitated by soda solution1 and the manganous carbonate obtained strongly ignited in a crucible4 ,in order to avoid oxidation of the manganous oxide1 which would readily occur in the process1 it is necessary to prevent air from reaching the substance4 ,with this object the crucible in which the heating is conducted is covered by another from which the bottom has been removed and which is filled with coal4 ,the air entering the crucible on cooling must pass through the layer of glowing coals1 by which it is deprived of oxygen4 ,manganese ,blue is obtained1 according to ,g4 ,bong1 by igniting a mixture of #c parts of quartz1 #f parts of soda ash1 #e parts of limestone and #c parts of manganese oxide1 or of #c parts of quartz1 #h parts of barium nitrate and #c parts of manganese oxide1 air being admitted and reducing gases excluded4 ,all materials must be free from iron4 ,the quantity of manganese oxide regulates the depth of the colour1 but not its shade2 by increasing the soda a greener1 by increasing the quartz a more violet1 shade is obtained4 ,,chapter ,,xxxv4 ,,compounded ,,green ,,pigments4 ,mixtures of a yellow and a blue pigment produce a green2 according as one or the other predominates colours are obtained inclining to yellow or blue4 ,in some cases the mixing can be accomplished in the actual production of the pigments1 so that a green precipitate is directly produced4 ,this is1 however1 rarely the case2 generally the compound pigments are obtained by simply mixing the two colours4 ,the mixing can be done either in the dry or the wet way2 colours in the wet state are more easily mixed than when dry1 so that even when dry colours are employed the mixing is done with the addition of water4 ,although the mixture then requires a second drying1 this method is still to be recommended1 in the first place1 because the mixing can be more quickly done in consequence of the greater mobility of the mass1 and in the second1 because the formation of poisonous dust is completely avoided4 ,the mixing is generally accomplished by mechanical arrangements4 ,if dry colours are to be mixed1 rotating cylinders may be used2 these are filled with the materials to be mixed1 well closed and rotated about the axis as long as may be necessary4 ,it should be observed that when colours which have a very different specific gravity1 such as chrome yellow and ,prussian blue1 are to be mixed1 the cylinders must be rotated for a much longer time than when colours of approximately equal specific gravity are to be united4 ,in working in the wet way1 which is to be preferred1 sufficient water is added to the colours to make a paste thin enough to be mixed by spatulas2 the mixture is thoroughly stirred and the pulp ground in ordinary mills until the mixture is quite uniform4 ,already whilst on the mills the pulp becomes thicker in consequence of evaporation2 when the grinding is finished it is spread out in thin layers so that it may dry as quickly as possible4 ,this is important in the case of mixtures whose constituents have very different specific gravities1 otherwise the heavier pigment may sink to the bottom of the paste and the mass thus lose its uniformity4 ,the compound green pigments come into the market under most varied names1 which are often entirely without connection with their chemical composition4 ,such names are3 mineral green1 ,english green1 oil green1 green vermilion2 the most common are chrome green and ,brunswick green4 ,it should be noted that these names are more strictly applied to simple colours previously described4 ,chrome ,green is generally made by mixing deep chrome yellow and ,prussian blue2 it can naturally be obtained in all possible shades4 ,the brightness of this already handsome pigment can be considerably increased by the addition of a small quantity of indigo carmine4 ,in this case the mixing is best done by adding a solution of the indigo carmine to the stiff paste and again sending the mixture through the mill4 ,by additions of white substances paler shades of chrome green are obtained2 levigated terra alba or white pipe clay can be advantageously employed4 ,elsner's ,chrome ,green is obtained by preparing a solution of yellow prussiate of potash and potassium chromate and another solution of lead acetate and ferric chloride4 ,the two liquids are mixed with vigorous stirring2 according to the proportions of the materials a blue or a yellow shade of green is produced4 ,silk ,green4--,forty-one parts of lead nitrate are dissolved in #bj to #cj times the weight of water1 the solution is boiled in a copper pan1 and1 according to the shade required1 #aj to #cj parts of fine ,chinese blue are added4 ,after well stirring1 a solution of #aj parts of potassium bichromate and #a part of nitric acid is poured into the boiling liquid1 the mixture is again well stirred1 the precipitate allowed to settle1 washed and dried4 ,the green pigment obtained in this way has a peculiar silky lustre1 hence the name 0silk green04 ,natural ,green is a mixture of ,guignet's green with picric acid2 it is used in making artificial flowers instead of emerald green4 ,non-arsenical ,green was proposed as a substitute for emerald green1 which1 however1 it does not equal in brilliance4 ,it is obtained by mixing copper blue 7basic copper carbonate7 with chrome yellow1 chalk and ferric oxide1 in somewhat variable proportions4 ,it usually contains #hj to #hb per cent4 of the copper compound and #ac to #ae per cent4 of chrome yellow4 99 99 99 99 99 ,in making mixtures of pigments it is to be remembered that chemical actions may occur in the mixture2 colours which act upon one another should not be mixed3 the mixture would contain the cause of its own destruction4 ,for example1 a lead pigment should not be mixed with one containing sulphur in the form of a sulphide or sulphate4 ,by following this important rule the number of pigments which may be mixed together is considerably diminished2 the advantage is that durable colours are produced1 which do not change in a short time to an unrecognisable shade4 ,,chapter ,,xxxvi4 ,,violet ,,mineral ,,pigments4 ,chromic ,chloride4--,the violet modification of chromic chloride is a compound which is little used1 but deserves the highest attention on account of its durability and beauty of shade4 ,up to the present chromic chloride has been almost exclusively used for colouring paper hangings under the name of chrome bronze1 which it has received in consequence of its property of imparting a peculiar metallic lustre to paper upon which it is rubbed4 ,it is also possible to fix this substance upon fabrics1 which thus acquire a similar metallic lustre4 ,pure chromic chloride forms beautiful peach-blossom coloured scales1 which can only be obtained by treating chromium oxide in a certain manner with chlorine4 ,the pure substance is practically insoluble in water1 but if the water contains but a trace of chromous chloride the chromic chloride readily dissolves to a green solution4 ,in the preparation of this compound it is necessary to avoid the least trace of chromous chloride1 otherwise the product will begin to change when it comes into contact with moist air4 ,pure chromic chloride is obtained by proceeding according to the method first given by ,whler3 the simple apparatus necessary is depicted in ,fig4 #bi4 ,pure chromic oxide is first made by any suitable process2 this is made into a paste with charcoal1 starch paste and water1 and formed into small balls which are heated in a crucible to a white heat4 ,the residual intimate mixture of chromic oxide and carbon is loosely placed in a crucible which stands in a furnace2 a porcelain tube is cemented into the bottom of the crucible1 it passes through the ashpit to connect with a chlorine apparatus4 ,upon the crucible another larger one is placed1 which has a small opening in the bottom and serves as a receiver for the sublimed chromic chloride4 ,the heating and current of chlorine are started at the same time1 the fire is regulated so that the lower crucible glows brightly4 ,this is continued for an hour1 during which a rapid current of chlorine must pass into the crucible2 the fire is then removed and a slow current of chlorine passed through the apparatus until it is quite cold4 ,illustration3 ,,fig4 #bi4 ,if the operation has succeeded the lower crucible is found empty and the interior of the upper covered with the magnificent peach-blossom crystals of chromic chloride4 ,a small quantity of the chromic chloride is tested as to its behaviour towards water2 if it remains unaltered the whole may be washed1 but if it dissolves to a green solution it must be again ignited in a current of chlorine4 ,the washing is necessary to remove small quantities of aluminium chloride formed by the action of chlorine on the clay of the crucible4 ,manganese ,violet1 or ,nuremberg ,violet1 consists of manganic phosphate4 ,it is obtained by fusing glacial phosphoric acid with pure pyrolusite1 boiling the melt with ammonium carbonate1 filtering the solution1 evaporating to dryness1 and again fusing the residue4 ,after boiling with water this forms a handsome violet powder2 it is suitable for use as a very durable artists' colour4 ,shades of this pigment inclining to blue are obtained when a ferric compound is added in the first fusion2 the more iron ore is used the more intense is the blue tone4 ,tin ,violet or ,mineral ,lake is obtained as a violet mass by igniting an intimate mixture of #ajj parts of tin dioxide with #b parts of chromic oxide4 ,this pigment is completely permanent in air2 it is suitable for printing paper hangings and for colouring faience4 ,copper ,violet1 ,guyard's ,violet4--,according to ,j4 ,depierre1 this pigment is obtained by precipitating a solution of copper ammonium sulphate with potassium ferrocyanide1 washing and drying the precipitate and heating in a porcelain dish4 ,at #agj ,c4 cyanogen and ammonia are evolved1 the mass takes up oxygen and becomes violet2 it then resists the action of dilute acids and alkalis1 and as a pigment has great covering power4 ,on heating to #bjj ,c4 it turns blue1 and at #bdj to #bej ,c4 becomes greenish4 ,,chapter ,,xxxvii4 ,,brown ,,mineral ,,pigments4 ,lead ,brown4--,when red lead is treated with nitric acid1 lead monoxide is dissolved1 whilst deep brown lead peroxide remains4 ,when the action of the nitric acid is finished the residue is well washed and dried4 ,lead peroxide is now extensively used for lucifer matches2 it readily gives up oxygen on heating1 and thus accelerates the ignition of the composition4 ,brown match-heads owe their colour to lead peroxide4 ,manganese ,brown consists of manganic oxide2 it occurs in nature1 but seldom in a state of sufficient purity to be used as a pigment2 it is1 therefore1 generally made artificially4 ,the process is very simple4 ,a solution of manganese sulphate is precipitated by caustic soda solution1 the manganous hydroxide produced is quickly changed by the action of the air into manganic hydroxide4 ,the colour is most rapidly developed when the precipitate is spread out in thin layers2 it is well washed after it has changed to brown4 ,pyrolusite ,brown is manganese peroxide in a state of fine division4 ,it can be made from the residual liquors of the preparation of chlorine by adding sodium hypochlorite4 ,a brown precipitate results1 which is kept in contact with the liquid until it no longer changes in colour4 ,it is then washed with water slightly acidified with sulphuric acid1 and finally with pure water4 ,when finely powdered1 manganese peroxide has a very fine brown colour4 ,it is quite unaltered by the air and thus1 in consideration of its cheapness1 deserves a much greater use than it has yet found4 ,prussian ,brown4--,when ,prussian blue is heated in air it soon begins to glow1 and is converted into a brown mass1 the shade of which depends on the amount of impurity in the ,prussian blue4 ,it is desirable to use ,prussian blue quite free from impurities1 so that a brown of the same shade is always obtained4 ,the brown obtained can be shaded by additions of indifferent substances4 ,iron ,brown4--,by igniting a mixture of #ajj parts of finely levigated natural yellow ochre with #e parts of common salt a brown product is obtained1 which is pale or deep according to the temperature used4 ,it is a cheap and durable colour4 ,copper ,brown4--,according to ,cartheuser solutions of #b parts of copper sulphate and #a part of ,epsom salts are mixed1 and a strong solution of potassium carbonate gradually added so long as a precipitate forms4 ,the precipitate is washed1 dried and ignited1 when copper brown is obtained as a brown powder of great permanence in air4 ,according to ,schreger solutions of #b parts of copper sulphate1 #b parts of alum and #je to #a part of ferrous sulphate are mixed1 potassium carbonate solution added1 the precipitate dried and ignited4 ,the redness of the shade is proportional to the quantity of ferrous sulphate4 ,hatchett ,brown is copper potassium ferrocyanide4 ,it is obtained by precipitating a soluble copper salt with potassium ferrocyanide4 ,copper salts behave towards potassium ferrocyanide in the same manner as iron salts2 different compounds result according as the ferrocyanide or the copper salt is in excess4 ,hatchett brown is somewhat largely used for painting wood4 ,chrome ,brown4--,when solutions of potassium chromate and a copper salt are mixed a precipitate of the composition ,cu,cr,o4#b;,cu,o4#b;,h,o is obtained4 ,on drying it acquires a fine brown colour2 it forms a very stable pigment4 ,chrome brown can also be made by dissolving #aj parts of potassium bichromate in #bj parts of water1 heating to boiling1 adding #ace parts of solid copper chloride and then gradually a boiling solution of #aj parts of soda in #bj parts of water1 until effervescence no longer takes place4 ,on cooling1 chrome brown separates as a soft brown precipitate4 ,cobalt ,brown is a very durable compound pigment of a pleasing shade4 ,it is obtained in various hues by adding ferric oxide to the mixture of alumina and a cobalt salt used for making cobalt blue4 ,the process may also be carried out by igniting ammonia alum with cobalt sulphate and ferrous sulphate4 ,the temperature required in this case to obtain a bright colour is very high1 and must be maintained for a long time to decompose the whole of the ferrous sulphate4 ,the pigment can be obtained at a far lower temperature when ferric chloride is used in place of ferrous sulphate4 ,the mixture is made by grinding together #e parts of cobalt hydroxide and #be parts of ammonia alum1 then adding a solution of ferric chloride1 rapidly drying the whole to a powder1 and whilst still hot filling it into the crucible in which the ignition is performed4 ,when small quantities of ferric chloride are used chocolate brown shades inclining to violet are produced2 the larger the quantity of the iron compound the more pure is the brown4 ,it has been stated that it is important1 in the preparation of cobalt pigments1 to prevent the entry of fire gases to the heated mixture2 the reducing action of the gases would materially damage the beauty of the colour4 ,it has been proposed to place a small quantity of mercuric oxide at the bottom of the crucible4 ,this would decompose on heating1 and create an atmosphere of pure oxygen in the crucible4 ,apart from the cost of the mercuric oxide1 which is considerable1 it would only be effective at the commencement of the operation1 since it is completely decomposed at a low red heat4 ,the author has found an addition of pyrolusite considerably more effective4 ,this may be applied by spreading a small quantity1 about #e per cent4 of the mixture to be heated1 on the bottom of the crucible and covering it with powdered glass1 upon which the colour mixture is placed4 ,an alternative course is to place the crucible in a second1 filling the space between the crucibles with powdered pyrolusite4 ,at a strong red heat oxygen is slowly evolved from the pyrolusite2 the entry of fire gases into the crucible is thus prevented4 ,in using the first method the crucible is frequently spoilt1 whilst in the second method the surrounding pyrolusite protects it1 so that it can be used again4 ,,chapter ,,xxxviii4 ,,brown ,,decomposition ,,products4 ,humins4--,wood decomposes1 like many other substances of organic origin1 to form compounds of a deep brown colour1 which are known as humins1 on account of their occurrence in the humus of tilled soil4 ,the numerous compounds found in humus have all a deep brown colour1 which1 together with their great stability1 makes them very suitable for use as pigments4 ,by various methods substances can be made so rich in humins that they can be used as pigments4 ,for this purpose sugar1 starch1 young plant fibres and beet-sugar molasses may be used1 which are converted into humins with great rapidity when they are heated with water4 ,in this way the author has obtained handsome colours from sawdust4 ,these humins are most easily made by the following process3 ,thick beet-sugar molasses are cautiously heated with #e per cent4 of caustic soda in a very capacious iron pan4 ,the already dark mass soon becomes quite black when seen in thick layers1 and evolves a considerable quantity of gas2 if the heating is too rapid the soft mass may boil over out of a very large vessel4 ,when the evolution of gas diminishes the heat is increased and the mass frequently stirred4 ,with some practice it is possible to tell when the action is finished from the smell1 which is at first sweetish but later of a characteristic nature4 ,at first tests should be repeatedly taken from the mass2 these are considerably diluted with water until the liquid begins to be transparent4 ,when two tests taken at an interval show no difference of colour the heating is stopped4 ,the whole mass is then poured into water in order to dilute the alkali1 so that it will not destroy the strainer2 the soft mass1 which in the wet state appears quite black1 is washed with water until the washings are neutral4 ,the humin brown made in this way1 when ground with oil or gum solution1 produces a very handsome brown of great covering power and warmth of shade1 also distinguished by complete indifference towards chemical reagents4 ,the pigments we have designated humins contain a very large quantity of carbon1 to which they owe their dark colour4 ,when peat or lignite is treated with caustic soda in a similar manner1 good shades of brown are obtained2 they are1 however1 surpassed in beauty by the brown from molasses4 ,a handsome but costly brown is obtained when crude spirits of wine are heated with fuming sulphuric acid4 ,equal volumes of alcohol and sulphuric acid are used2 the mixture is heated in a retort connected to a condenser1 which is required on account of the combustible vapours evolved from the mixture4 ,when the mass is quite black the heat is withdrawn2 the residue is diluted with water1 and soda solution added so long as effervescence occurs4 ,on filtering a very soft brown powder is left1 which forms a very handsome and durable pigment4 ,bistre4--,when soot is produced at a very low temperature it is very lustrous1 and1 in addition to carbon1 contains a notable quantity of the products of dry distillation4 ,when this soot is powdered and treated with water the latter substances are dissolved2 boiling water should be used4 ,when water is no longer coloured the soot is suspended in a large quantity of water and subjected to a process of levigation4 ,the fine powder obtained by repeated levigation has1 when dry1 an ugly brown colour1 but when ground it acquires an extremely warm shade4 ,,chapter ,,xxxix4 ,,black ,,pigments4 ,carbon occurs in nature in many different forms--the diamond1 graphite 7black lead71 and purified lamp black are1 from the chemical point of view1 one and the same substance1 namely1 carbon4 ,in colour making the non-crystalline form of carbon1 which is pure black1 is alone used2 almost all black pigments used in painting are composed of tolerably pure carbon4 ,in whatever way and from whatever materials carbon is made for use as a pigment1 the manufacturer must always endeavour to obtain it as pure as possible1 and in a condition of the finest division2 the depth of colour and the covering power depend on these two conditions4 ,carbon only shows a pure black colour when it is pure2 if it contains relatively small quantities of impurities1 it has a more or less brown shade4 ,at first sight it appears to be a very simple matter to obtain black pigments from organic materials2 it is simply necessary to expose them in the absence of air to a temperature high enough to decompose them1 carbon is then left as a residue4 ,in spite of the apparent simplicity of this operation there are many difficulties4 ,the preparation of good black pigments demands considerable practice4 ,there are two methods by which carbon can be made for use as a pigment4 ,one has been indicated1 the heating of organic materials in the absence of air1 i4e41 their dry distillation2 the second1 which produces the best qualities of black1 consists in burning substances very rich in carbon with a very small supply of air4 ,the product of this process1 commonly known as soot1 is very different in external appearance from carbon made by dry distillation4 ,the latter forms an easily powdered mass1 which only acquires lustre by grinding with oil1 whilst soot consists generally of very light flocks1 which1 in consequence of their greasy nature1 exhibit a peculiar velvety lustre4 ,in commerce there are many qualities of black1 the names of which are generally chosen quite arbitrarily4 ,the so-called ivory black is an example of this4 ,at some period it was observed that ivory produced a very fine black when carbonised2 this black was made for a long time from refuse ivory4 ,when it was found that a similar black could be made quite as well from much cheaper materials1 it was no longer made from ivory4 ,the name1 however1 remains in trade to the present day3 it has come to be regarded as a description of quality4 ,by the name of ivory black a fine black pigment is understood2 it is immaterial to the consumer whether it is made from ivory or not3 to him the quality of the pigment1 but not its source1 is important4 ,according to the method of production1 the black pigments can be divided into charcoal blacks and soot blacks4 ,,charcoal ,,blacks4 ,this term is applied to the pigments obtained by heating organic substances in the absence of air4 ,the charcoal blacks have two valuable properties3 they are easily made1 and they exhibit a pure black shade which it is far more difficult to obtain with the soot blacks4 ,it is very difficult to convert these pigments into the requisite state of fine division4 ,they cannot be levigated on account of their low specific gravity1 which causes them to settle very slowly in water4 ,it only remains to convert the charcoal into a very soft powder by grinding1 but even then the pigment has but little covering power1 because it is not possible to destroy the organic structure of the substance carbonised4 ,when the finest charcoal powder1 made by carbonising any organic substance1 is examined under a powerful microscope the structure of the particles is at once recognised1 so that it is almost always possible to decide whether the charcoal is of plant or animal origin4 ,a very careful examination may show what particular part of the plant has been carbonised4 ,if a manufacturer succeeded in producing by direct carbonisation a black with the covering power of a soot black1 that black would soon be the only one found in commerce4 ,the charcoal blacks come on the market under various names--ivory black1 bone black1 vine black1 ,frankfort black1 ,paris black1 etc4 ,the ivory blacks are the best quality1 but recently true vine black1 i4e41 made from grape residues1 has come into use4 ,true ,charcoal ,black4--,in charcoal-burning wood is burned in great piles with restricted air supply2 the greater part of the carbon contained in the wood remains behind as charcoal1 which is used for fuel4 ,the charcoal made from hard wood1 such as maple or beech1 is not well suited for pigments2 the lighter and more porous the wood1 the more pure is generally the shade of the charcoal1 and the more easily it can be ground4 ,when1 therefore1 charcoal is to be used as a pigment it should be made from wood of a porous nature2 the wood of the lime1 black-alder and spindle tree is particularly adapted for this purpose4 ,spent tan-bark is a very cheap1 and at the same time suitable material for this purpose4 ,it generally consists of oak bark1 and has lost the greater part of the salts it contained by long contact with water2 also the woody substance of the bark has suffered a change which is favourable to carbonisation4 ,this is especially the case when the bark has been stored for some time2 a considerable quantity of the humins previously mentioned has formed in it1 and these are easily decomposed at a low temperature4 ,the charcoal1 however obtained1 is ground to a soft powder4 ,when it has reached the proper degree of fineness it should be repeatedly washed with water to remove the salts4 ,when instead of pure water a very dilute acid1 such as hydrochloric1 is used1 practically all the salts dissolve1 and the residue consists of nearly pure carbon4 ,vine ,black4--,in wine-producing countries a good and cheap black can be made from the residues of the wine manufacture2 this is the so-called vine black4 ,either the pressed grapes or the lees separated in the fermenting vessels may be used4 ,vine ,black from ,wine ,lees4--,the lees always contain a considerable quantity of liquid1 they must be thoroughly dried before they are carbonised2 this is most simply done by spreading out the pasty mass in a thin layer1 and exposing it to a temperature of about #ajj to #abj ,c4 ,in drying the volume considerably diminishes4 ,the lees are changed into a brown mass which is easily powdered2 it is packed into barrels while still warm1 and can be kept for a considerable time without alteration4 ,fresh lees can be kept but a short time2 they are quickly destroyed by a rapid fermentation4 ,the dried lees are carbonised in iron tubes1 protected from the fire by a thin coating of clay mixed with chopped hair so that the coat more readily adheres to the iron4 ,old stove pipes or cast-iron gas or water pipes may be used4 ,the tubes are about one metre long2 they are closed with well-fitting covers1 in one of which is a small opening through which the gases produced on heating can escape4 ,these covers are fastened on air-tight with clay4 ,the process begins by affixing the unperforated lid1 and packing with a wooden rammer the dry lees as tightly as possible into the tube2 the second lid is then luted in place4 ,the tubes are placed near one another in a suitable furnace and first slowly heated at the back1 i4e41 the end closed by the unperforated cover4 ,at the commencement of the operation heat must be gradually applied4 ,with too large a fire the products of dry distillation might be evolved in sufficient quantity to force the covers from the tube2 air would then enter and the contents be burnt4 ,when the hinder part of the tube is red-hot1 the heating is conducted forward1 and finally the whole length of the tube is brought to a good red heat4 ,the termination of the operation is shown by the disappearance of the pointed flame of the products of distillation which protrudes from the opening in the cover of the tube4 ,when this occurs1 the fires are drawn2 the tubes are left to cool in the furnace until they can be taken out by the hands protected by wet cloths4 ,the covers are at once taken off and the hot contents emptied into a large tub filled with water1 which is thus soon raised almost to boiling point4 ,the time required for washing is thus considerably shortened4 ,the charcoal falls from the tubes in lumps1 which soon fall to a fine powder in the water4 ,wine lees consist of a mixture of yeast cells and small crystals of tartar 7a mixture of the tartrates of potassium and calcium74 ,on ignition these salts are converted into carbonates1 by which the particles of carbon are united4 ,potassium carbonate is very readily soluble in water2 in contact with the warm water it dissolves in a very short time1 the carbon particles then fall apart4 ,when the charcoal has settled to the bottom of the vessel the liquid is drawn off4 ,it can be utilised in a colour works1 since it is a fairly strong solution of potassium carbonate4 ,the charcoal is mixed with calcium carbonate1 arising from the decomposition of the calcium tartrate1 and with the other insoluble salts which yeast ashes contain in some quantity4 ,these salts would prevent the proper grinding of the charcoal2 they are therefore removed by treatment with hydrochloric acid after the water has been drawn off as completely as possible4 ,a small quantity of hydrochloric acid1 diluted with an equal volume of water1 is poured over the charcoal1 an effervescence of carbonic acid follows1 the easily soluble calcium chloride is formed and the remaining salts are also dissolved4 ,the charcoal made in this way is very pure4 ,after washing1 grinding and drying1 it forms a pigment whose shade leaves nothing to be desired4 ,the drying must be conducted at a low temperature2 charcoal in such a fine state of division is very easily inflammable4 ,vine ,black from ,pressed ,grapes4--,the material contains the stems and pressed remains of the grapes after the must has been expressed4 ,after-wine1 spirits or vinegar can be obtained before it is used for vine black4 ,the process is exactly the same as for wine lees4 ,the charcoal taken from the tubes has rather more coherence than that made from lees and must be ground4 ,the black is a very useful pigment1 but is inferior to the black from lees4 ,in regard to the latter1 it should be stated that it is a particularly good black pigment1 and when finely ground is as well suited for the preparation of the finest blacks1 such as are used in copper-plate printing1 as the far more costly soot black4 ,the black from grape residues1 or from grapes themselves 7the poor grapes removed in pruning the vine are used71 can be employed with advantage for many purposes for which the best black is not necessary4 ,the greater number of the pigments sold under the names of ,frankfort and ,paris black consist of this substance4 ,bone ,black or ,ivory ,black4--,bone black1 for of ivory black only the name now exists1 is distinguished by a peculiar quality which it owes to the structure of the raw material from which it is made4 ,this raw material is animal bones1 which largely consist of incombustible materials 7bone ash72 these form a delicate framework whose interstices are filled by organic matter4 ,when bones are carbonised1 the carbon resulting from the decomposition of the organic matter is deposited on the incombustible framework of bone ash and thus acquires a very great surface4 ,carbon is well known to possess very powerful absorptive properties1 which are especially developed in bone black1 in consequence of its fine division4 ,the use of granular bone black 7known as 0char07 in sugar works1 and generally for decolourising liquids1 is due to the peculiar state of division of the charcoal4 ,for these purposes bone black is used in enormous quantities2 it is made in special works4 ,it does not fall within the scope of this work to give a detailed description of the manufacture of bone black1 and we must here restrict ourselves to matters of special interest to the colour maker4 ,the bones are coarsely powdered and freed from fat by boiling2 they are then generally carbonised in iron retorts1 a number of which are built in a furnace in a vertical position2 a valve at the bottom serves to empty the retorts4 ,in a well arranged apparatus the products of the dry distillation of the bones1 chiefly consisting of ammonium carbonate1 are collected4 ,the retorts are carefully closed so that air cannot enter1 otherwise a portion of the carbon would burn and the black would acquire a grey shade instead of the pure black which it should possess4 ,bone black makers who work for sugar factories carbonise by preference the densest bones2 these produce a black of the most powerful decolourising properties4 ,this property is of no advantage to the colour maker1 who simply requires a very dense black4 ,the bones of young animals1 and especially certain bones1 contain a larger proportion of cartilage than the hollow bones which produce the best 0char04 ,in making bone black to be used as a pigment just those bones should be chosen which are of less value for 0char04 ,on the small scale1 bone black can be made by carbonising in crucibles2 these hold about #af kilogrammes of bones1 they have a projecting rim1 so that when one is placed upon the other it serves as a lid for the first4 ,piles of these pots are formed1 the top one being covered by a well-fitting lid4 ,the piles are heated in a furnace in such a manner that the flames can freely circulate between them4 ,at first a small fire is applied2 as soon as dry distillation of the bones begins1 which is recognised by pale white flames at the rims of the crucibles1 the fire is damped1 because the burning products of distillation produce so much heat that the crucibles are soon at a good red heat4 ,when the flames disappear the fire is maintained for about fifteen minutes longer1 and when the crucibles have cooled to some extent they are taken out of the furnace and immediately emptied into a sheet-iron cylinder1 in which the charcoal remains until quite cold4 ,if the black comes in contact with air whilst still hot a portion of the carbon burns and the product has little value either as a pigment or for decolourising purposes4 ,when quite cold the black is ground and levigated4 ,the bone ash it contains makes these operations easy4 ,bone black contains at the most #ab to #ac per cent4 of carbon2 the remainder consists of bone ash and water absorbed by the hygroscopic carbon from the air4 ,bone black which has been partially burnt in the process has a greyish tinge2 it may also have an ugly shade of brown3 this is the case when it has not been heated to a sufficiently high temperature1 so that it still contains some quantity of organic matter4 ,such black can be made usable by again heating1 but it would always be desirable to test a small portion before the whole was ground and levigated2 a uniform heating of the finely-powdered black would be attended with difficulty4 ,finely ground bone black has numerous uses as a pigment2 by a simple process it can be converted into almost pure carbon1 which can be used as an excellent black pigment for all purposes for which blacks are employed4 ,bone black consists of bone ash upon which fine particles of carbon are deposited4 ,bone ash is easily soluble in hydrochloric acid2 if finely ground bone black is treated with this acid and the residue washed with water until the washings are neutral1 a residue of extremely soft and pure carbon is obtained1 which has a deep black colour and1 in consequence of its fine division1 very great covering power4 ,,chapter ,,xl4 ,,manufacture ,,of ,,soot ,,pigments4 ,the soot which is formed in the incomplete combustion of organic substances containing a large proportion of carbon is a mixture of different substances1 of which carbon is the chief2 in addition to this1 we find in soot almost all the products which result by the dry distillation of the substance from which it is formed4 ,soot from hard wood contains different compounds to soot from soft wood2 again1 rosin soot is of a different nature to that obtained in the incomplete combustion of fats4 ,we can thus define soot as very finely divided carbon1 mixed with the products of dry distillation4 ,the soot of hard woods1 which contain little or no resin1 has a deep black1 though dull hue2 it is a gritty powder1 and has little value as a pigment4 ,wood containing much resin1 such as the wood of the pine1 rosin1 fish oil1 asphaltum1 in short1 all bodies which are at the same time easily combustible and rich in carbon1 produce on the contrary a handsome1 glistening soot1 which forms a valuable pigment4 ,in addition to this difference in composition1 soot from different sources differs also in the size of its particles4 ,soot forms light flocks1 which adhere to projections in the flues through which the products of combustion pass2 the larger the flocks the sooner they are deposited1 the smaller they are the longer they remain suspended4 ,the finest particles of soot are called 0flying soot10 which is very highly prized on account of its fine division4 ,the manufacture of soot blacks is a very important industry3 black printing ink1 which is used in such enormous quantities1 is made from a soot black2 in addition1 all the best black paints and lacquers4 ,soot black was formerly made in the most primitive manner1 and is still1 to some extent1 as will be seen from the account of the manufacture of rosin black4 ,the process used for printing blacks is more rational1 but is still capable of great improvements4 ,the principles of a rational manufacture of soot blacks will be briefly indicated4 ,the ,manufacture of ,soot ,blacks on the ,large ,scale4--,the principle of the arrangements necessary for making soot blacks is very simple4 ,an apparatus is required in which substances very rich in carbon can be burnt at the lowest possible temperature2 this apparatus must be connected with suitable arrangements for retaining the soot carried away with the products of combustion4 ,the soot works as at present arranged are developments of the crude arrangements still used in districts in which there is an abundant supply of pine wood containing much resin4 ,the apparatus used in such localities consists of a low masonry flue connected with a long pipe built of wooden boards4 ,in order to give this pipe a rough surface upon which the soot can readily deposit1 it is lined in several places with coarse linen1 to the projecting fibres of which the soot adheres4 ,in the flue the very resiniferous wood is burnt1 especially the roots of pines1 which are very rich in resin2 these burn with an unrestricted air supply with a bright flame1 but when the air is restricted1 they give off a large quantity of a very heavy smoke4 ,the operation is commenced by first making a good fire of dry split wood1 the object of which is to heat the flue and thus prevent the deposition of soot in it in the later part of the process4 ,if a deposit of soot formed in the flue it might take fire1 the fire would then spread further into the wooden flue and a considerable loss of soot would occur4 ,when the stonework has become so hot that deposition of soot in it is no longer to be feared1 the materials are introduced from which the soot is to be made4 ,as has been said1 pine roots are generally used1 the chips of pine wood are also used in some districts1 and in general such combustible materials as produce a large quantity of smoke4 ,the combustion in the flue must be conducted with care1 it should proceed at the lowest possible temperature1 but this should not sink below a certain minimum4 ,if the fire is too strong the greater portion of the carbon is burnt1 which would otherwise be obtained as soot2 the yield of soot is very small1 and generally only 0dust soot0 would be obtained1 without any quantity of 0flying soot04 ,on the other hand1 if too little air enters1 so that the combustion takes place at too low a temperature1 a large yield of soot is obtained1 but it is of poor quality4 ,soot obtained by combustion at too low temperatures has not a pure black but a perceptibly brown colour2 it has not the flocculent nature of the best product1 a small weight of which occupies a very large volume1 but is greasy and has a high specific gravity4 ,the lower the temperature used in producing soot black1 the further is the chemical change removed from that of ordinary combustion1 and the nearer to that of dry distillation4 ,soot produced with an insufficient supply of air contains a considerable quantity of liquid and solid products of dry distillation1 which give it a brown colour and the above-mentioned greasy nature4 ,in many soot works the air supply is regulated in a most primitive manner3 the workman places against the openings by which air is admitted to the burning materials a larger or smaller number of bricks according as the combustion appears to be too rapid or too slow4 ,unfortunately there is no clear sign to indicate the temperature most favourable for the production of the greatest quantity of soot1 the appearance of the flame alone can be taken as a guide4 ,if the flame appears pure white and very luminous and shows at its end no thick black smoke the combustion is very complete1 and but a very small yield of soot is to be expected4 ,on the other hand1 if the flame continually threatens to go out the air supply is too small and a liberal amount of soot will be formed1 but mixed with a large quantity of the products of dry distillation4 ,as far as it can be described in words the flame should appear as follows3 ,the colour should be a murky red1 similar to that of the flame of a bad tallow candle2 in shape the flame should be a long drawn out tongue1 from the point of which a thick black smoke is clearly seen4 ,the soot deposits in the long board flues in the form of flocks or dust4 ,the properties of the soot which is deposited in the different parts of the long flue vary according to the distance from the place of combustion1 near to which a good black soot is deposited1 requiring1 however1 long grinding with oil or gum solution to form a good paint4 ,at a greater distance the soft and very fine 0flying soot0 is deposited2 it is the most pure black and is regarded as the best quality4 ,the soot deposited farther on is more and more brown1 and has a more greasy nature the greater the distance from the place of combustion4 ,the flue for the reception of the soot must be made so long that hardly any smoke is perceptible at the end1 which it is convenient to connect with a chimney with a good draught1 regulated by a damper4 ,in this case the combustion and the speed at which the products enter the flues are twice regulated4 ,the material of which the flues are constructed through which the products of combustion are led influences the manner in which the soot is deposited2 the portions nearest to the grate must be of stonework1 but when the smoke has cooled to a certain extent different materials can be used in addition to wood2 flues made of sacking stretched over laths are used4 ,the fine flying soot adheres to the roughnesses of the coarse sacking1 and is easily loosened by striking the wall of the flue4 ,as we have said1 the arrangements of most soot works are very primitive2 they obtain only a fraction of the quantity of soot which they could produce by a proper regulation of the draught in the combustion chamber and in the flue in which the soot deposits4 ,we shall now briefly describe the conditions which should be regarded in constructing a soot works2 these conditions have not been found to be observed in any works we have seen1 in this branch of chemical industry so-called practical experience is alone regarded1 and consequently the 0practical0 soot burner loses large sums1 literally up the chimney4 ,a black works can be properly designed by any one who knows sufficient chemistry to understand the process of combustion4 ,of this most educated men have some understanding1 but the practical soot burner appears to have but hazy ideas on the subject1 for one occasionally finds the arrangements for making soot in direct opposition to the proper disposition4 ,for the sake of the uniformity of the product and of safety against fire1 the flues in which the soot is deposited should be entirely of masonry2 the joints of the bricks should be smoothly cemented over1 so that soot cannot collect in quantity in them4 ,the end of this flue should be connected with a high chimney provided at the top with a well-fitting damper1 so that the draught in flues and chimney can be regulated at will or completely stopped4 ,such an arrangement1 perhaps somewhat costly1 has many important advantages3 it is fire-proof1 and when once warm remains so for a long time1 since bricks are bad conductors of heat4 ,when the flue is hot no water condenses in it2 all the water formed in the combustion remains in the form of vapour1 and is carried away by the chimney4 ,a further advantage is that it is not often necessary to enter the flue to collect the soot2 burning may be continued for a long time1 and a large quantity of soot taken at once from the flues or soot chambers4 ,the soot collects on the walls of the chambers in flocks1 which finally become so heavy that they fall off and collect on the floor4 ,the entry to the soot chambers should be through a single iron door1 tightly closed whilst the chambers are in use1 and cemented round4 ,if this door does not fit air-tight the combustion cannot be exactly regulated by the damper on the chimney4 ,the soot is removed from the chambers by a workman1 who sweeps off with a soft brush into a sheet-iron vessel the soot adhering to the walls and lying on the ground4 ,it is extremely important that soot and nothing else should be collected2 the brush used for loosening the soot should be so soft that it does not rub off mortar from the brickwork2 the workman's shoes should be provided with felt soles1 so that no particles are loosened from the floor of the chamber and mixed with the soot4 ,the admixture of the smallest quantity of sand would be extremely harmful in the ensuing grinding of the soot2 the mills would be damaged4 ,the flues for collecting the soot in well arranged works are very similar1 but the apparatus used for burning the materials which produce the soot varies greatly according to the nature of the material4 ,some quantity of the soot black used in the arts is still made by burning pine roots and chips1 but for the finer qualities ,american rosin is largely employed4 ,earth-wax or ozokerite and the hydrocarbons obtained from petroleum and in the distillation of shale are materials frequently used in making soot blacks of very good quality4 ,for the finest qualities1 such as are used for fine printing inks1 copper-plate inks and black lacquers1 soot obtained by burning fish oils or cheap fatty oils is most commonly used4 ,the great differences in the physical nature of these materials demand the use of different apparatus for their combustion4 ,the space allotted to soot blacks in this work would be far exceeded if the construction of all the forms of apparatus were described2 the most important only will be given4 ,illustration3 ,,fig4 #cj4 ,when rosin is the raw material1 the combustion can be conducted in flat spoon-shaped vessels placed before a narrow opening into the flue4 ,fig4 #cj shows an arrangement very successful in practice4 ,the spoon-shaped iron vessel1 ,g1 stands in a second1 ,g1 which is filled with water3 this prevents the fused rosin from becoming too hot4 ,if the temperature in ,g rose too high1 dry distillation would take place along with the combustion of the rosin1 and the soot would be largely contaminated by the products of this distillation4 ,this may proceed so far that in place of the fine flocks of soot a greasy mass is deposited in the flues1 consisting of a mixture of soot with products of distillation1 from which the soot could be obtained only with great difficulty4 ,the soot and gaseous products of combustion pass through the opening1 ,o1 into the flues1 ,r ,r4 ,this opening is only several centimetres wide1 but is nearly as long as the combustion vessel4 ,above the vessel1 ,g1 is a movable iron cover1 ,d1 in which are slides by which the air supply is regulated4 ,the cover is only taken off when fresh material is introduced4 ,the air supply cannot be sufficiently regulated by the slides in the cover2 these must be used in conjunction with the chimney damper4 ,the combustion is observed through a thick glass plate let into the cover4 ,at the commencement of the operation slides and damper are completely opened4 ,when the chimney is seen to emit a thick black smoke the flues are filled with the products of combustion1 and the speed with which they pass through the flues must be regulated4 ,the current of air is decreased until only a little visible smoke escapes from the chimney1 and the flame is no longer white1 but a murky red4 ,it should be noted that the first soot obtained from a new works is never of the best quality1 the production of this is only gradually attained4 ,the cause of this is that the new masonry is damp and gives up water to the hot gases1 so that they are cooled and their velocity disturbed2 the soot will also be damp4 ,thus a greasy soot is obtained4 ,it is of very little use to allow the installation to remain unused for some months after it is completed2 the brickwork would only dry superficially1 and when it was first heated the presence of the water would become evident4 ,in order to dry the whole erection to such an extent that the moisture from the brickwork has no effect on the regular course of the operation1 it is advisable to commence with materials of little value and to allow a portion of them to be lost by the use of a stronger draught than is generally used1 so that the flues can be freed from all moisture as soon as possible4 ,this applies equally to all kinds of arrangements for this purpose4 ,illustration3 ,,fig4 #ca4 ,lamps are used to burn liquid fats and mineral oils4 ,these lamps naturally have a different construction to those used for lighting1 which are constructed with the object of burning all the carbon in the oil1 so that the temperature may rise as high as possible and the carbon burn at a high white heat4 ,the lamps used in the soot black manufacture are designed to burn only as much carbon as is absolutely necessary to maintain the flame1 at the same time the temperature of the flame must be kept low1 so that no portion of the soot is again burnt4 ,these lamps have flat burners and are enclosed in a sheet-iron casing provided with an air regulator1 which must work very accurately1 otherwise air will enter between the joints and the working of the regulator will be deceptive4 ,so that the material to be burnt shall not be too strongly heated1 which would be accompanied by great loss when mineral oil is used1 the reservoir should be placed outside the iron casing which surrounds the burner4 ,fig4 #ca shows the construction of a soot lamp4 ,the flat burner1 ,b1 is placed in the cylindrical sheet-iron mantle1 ,h1 which is bent above at not too sharp an angle4 ,the products of combustion are led into a chamber1 ,k1 from which they pass into the flues where the soot is deposited4 ,the form of the upper portion of the cylinder is of importance2 if this is bent at right angles1 soot accumulates on the angle1 and when a mass has formed it falls off1 and is partly burned in the flame4 ,if the cylinder is given a proper bend no soot is deposited in it1 but it is all carried away into the soot chambers4 ,the air regulator1 ,s1 is placed at the bottom of the cylinder2 it must turn easily4 ,the larger the slits are made by the rotation of this regulator1 the more oxygen enters the flame1 and the more vigorous is the combustion4 ,a small1 well-fitting door is placed in the lower part of the cylinder1 through which the wick can be reached2 opposite to this a glass plate is inserted1 so that the flame may be observed without opening the door4 ,the wick is raised or lowered by means of the screw1 ,r4 ,the oil reservoir1 ,o1 must be outside the cylinder3 in the older arrangements it is so placed that the wick sucks up the oil2 the workman who is in charge of the lamps must then take particular care that the reservoirs always contain the proper quantity of oil1 if he neglects to keep the oil at the proper level the wick is charred2 it then sucks up too much oil1 which cannot completely burn and is chiefly distilled1 so that the soot is oily and cannot easily be treated afterwards4 ,the most diligent and attentive workman who is in charge of a large number of lamps may easily allow one of them to run short of oil4 ,with the oil reservoir above depicted1 a new quantity of oil flows only when the level of the liquid sinks below the line1 ,u4 ,as soon as a small quantity is used air enters the reservoir1 ,o1 in place of which oil runs out until the opening1 ,u1 is again closed by the liquid4 ,this construction of lamp only works well when thin oils are burned1 and great care must be taken that the lamps are kept constantly clean4 ,lamps of all constructions have some drawbacks1 they must always be cleaned1 and losses of oil occur in filling4 ,these defects are obviated when1 instead of providing each lamp with its own reservoir1 a single one is used for a large number of lamps1 which are automatically fed from it4 ,in this case the attendant has only to regulate the air supply to the lamps1 and to see that the mechanical arrangement by which the oil flows to the different lamps is working properly4 ,when the lamps are automatically fed1 the burners must be firmly fixed1 and all in the same horizontal plane4 ,a pipe connects each burner with a main pipe running under the lamps1 which latter pipe is connected with the reservoir1 and this in its turn is connected with another reservoir placed a little higher4 ,in the pipe connecting the two reservoirs is a tap1 which is opened by a float in the lower vessel as soon as the level of the liquid in it sinks a little1 and which remains open until the level of the liquid has again risen to a certain height4 ,the float in the reservoir connected with the lamps is arranged so that the level of the liquid is slightly higher than the burners4 ,under the slight pressure oil continually flows to the burners1 and it is not difficult to regulate its flow so that all which reaches the burner is burned4 ,in using a new oil it is not easy at first to regulate the flow so that absolutely all is burned without any dropping off the burner2 to prevent the loss of this portion1 the lower end of the air regulator is conical1 at the apex of the cone is a small tube and under this a vessel in which the unburnt oil is caught4 ,in ,fig4 #cb1 ,s is the air regulator1 ,t the vessel to catch the unburnt oil1 ,l the pipe leading from each burner to the common pipe ,h1 ,g the vessel in which a float regulates the flow from a larger reservoir1 so that the liquid always remains at the same level4 ,when tar oils are used1 or thin mineral oils1 the pipes which convey the oil to the burners may be made tolerably narrow1 but when viscous oils or fish oils are burned1 narrow tubes would offer too great resistance to the flow1 so that it is always advisable to use fairly wide pipes4 ,viscous oils become considerably more fluid at higher temperatures1 it is therefore well to place the reservoirs in the same room as the lamps2 in winter the temperature of this room is kept fairly high by the burning of the lamps1 and thus the oils remain fluid4 ,,fig4 #cb4 ,in recent years hydrocarbons of very low boiling point have been placed on the market at low prices2 these produce a black of very good quality4 ,on account of the low boiling point of these very inflammable liquids1 particular care is necessary in burning them2 they are very fluid and retain their fluidity at a low temperature4 ,the reservoirs for them should be placed for safety outside the lamp room1 and should be closed by an air-tight lid1 with only one small opening through which air can enter4 ,when these low boiling liquids are used1 particular care must be taken to regulate the flow to the lamp1 or large quantities will evaporate without being burnt4 ,the materials used in the manufacture of soot black differ considerably in chemical constitution4 ,rosin1 animal and vegetable fats1 distilled oils and volatile hydrocarbons are used4 ,each of these substances gives different decomposition products when heated1 to which proper regard must be had1 since the quality of the black is dependent on them4 ,the more difficultly volatile are the products of distillation1 the higher must be the temperature at which the combustion is conducted1 otherwise the soot will contain a considerable quantity of these products of distillation4 ,in consideration of the great variety of materials used for making soot black1 it is impossible to say exactly in what manner each should be treated3 this must be left to the practical experience of the manufacturer4 ,,chapter ,,xli4 ,,manufacture ,,of ,,lamp ,,black4 ,the variety of soot black known as lamp black is the best2 it is used for making copper-plate inks and black coach paints4 ,its price is much higher than that of ordinary soot black2 for the best qualities1 twenty times the price of an ordinary black is paid4 ,the materials already mentioned are used for making lamp black1 fish oils and rancid vegetable oils1 and in recent times mineral oil and tar oils4 ,in regard to vegetable oils it is to be observed that it is advisable to use very rancid oil1 which gives a larger yield of soot2 experience has shown that a very rancid oil requires a larger quantity of oxygen to burn without a smoky flame than a sweet oil4 ,this indicates that a portion of the carbon in the rancid oil is present in such a form that it requires a higher temperature to burn it than is required for the carbon in sweet oils4 ,the use of rancid oils for making soot blacks has thus two advantages1 it is much cheaper and produces a larger yield4 ,the only disadvantage1 and not a very important one1 attending the use of rancid oil is that the free fatty acids in these oils strongly attack the metallic parts of the lamps4 ,this is especially the case with copper and brass2 only such portions of the lamps as is absolutely necessary should be made of these metals2 all other parts1 and in particular the oil reservoirs1 should be made of tin plate4 ,since the development of the coal-tar industry oils distilled from coal tar have come into commerce at low prices4 ,these oils consist of carbon and hydrogen and are equally volatile with the essential oils1 to which class turpentine belongs4 ,there are two kinds of these tar oils1 light and heavy2 they differ both in specific gravity and in the boiling temperature1 which ranges between tolerably wide limits4 ,when the burning qualities of these oils are examined1 they show a great difference in the quantities of oxygen necessary for complete combustion with a white flame without smoke4 ,the more oxygen an oil requires to burn with a non-smoky flame1 the more suited it is for the manufacture of blacks4 ,generally speaking1 the difficulty of completely burning these oils is in proportion to their specific gravity and the height of their boiling point4 ,by the distillation of rosin1 oils are obtained which also consist of carbon and hydrogen and form a useful material for the manufacture of soot blacks4 ,the mineral known as earth-wax or ozokerite1 a substance intermediate between asphaltum and petroleum1 can also be used1 but since it is a solid it must be burnt in troughs4 ,in burning light oils the arrangements can be very simply made2 wicks are not required and thus a considerable outlay is spared4 ,in place of the burner1 shallow dishes are used into which the oil enters from below1 replacing that burnt away4 ,it is necessary to cool these dishes continuously from below1 otherwise they would soon become so hot that the greater part of the oil would evaporate without burning1 and it would also be very difficult to regulate the flame properly4 ,black can be obtained from very resiniferous coal by burning in furnaces with a regulated air supply4 ,the product is1 however1 generally largely contaminated by ash1 and can only be used for common purposes4 ,very resiniferous lignite gives a better product than coal2 the black can be partially separated from the ashes by shaking upon water and then stirring1 when the particles of ash sink to the bottom and the light black floats on the top4 ,however carefully the manufacture of soot black is conducted1 it will always contain1 in addition to carbon1 varying quantities of the products of distillation1 partly solid and partly liquid4 ,in consequence of these admixtures the soot will not be pure black1 but will show a more or less brown tinge1 which is clearly observed when the black is smeared on white paper4 ,at a certain thickness of the layer of soot it will be seen that the colour is not black1 but an impure brown4 ,when such soot1 as it is taken from the chambers1 is chemically examined1 it is found that it gives up a large quantity of soluble matter to different chemical reagents4 ,by proper treatment it is possible to remove the admixtures almost completely1 so that nearly chemically pure carbon remains4 ,such pure carbon can be made by boiling lamp black with strong caustic soda solution so long as the liquid is coloured1 and when caustic soda can dissolve nothing more1 the residue is boiled with aqua regia until this no longer takes up soluble matter4 ,the black is then washed with water until free from every trace of acid1 and the residue dried4 ,by this treatment the soot is converted into a powder of the purest black hue which it is possible to obtain4 ,it is now no longer soot1 but chemically pure carbon in the non-crystalline form2 heated upon platinum foil it burns to pure carbonic acid without producing smoke or smell4 ,in practice the purification of the soot is not carried to the extent of producing pure carbon2 this would be accompanied by a diminished yield of the pigment without increasing the commercial value of the product3 the aim of the manufacturer is simply to produce a substance of a pure black appearance from the brown soot4 ,to remove the brown substances present in the crude soot the solvent action of caustic soda solution can be used4 ,the soot is several times boiled in iron pans with strong caustic soda solution in order to dissolve the products of dry distillation4 ,it is superfluous to repeat this operation until fresh caustic soda remains colourless4 ,the treatment may be stopped when the solution acquires a slight brownish colour4 ,when the soot has been purified so far it has lost its brown shade and now appears as a velvety black powder1 very soft and very light1 and distinguished by extraordinary covering power4 ,it is not so easy as it appears at first sight to judge of the quality of a black pigment by its appearance4 ,to the unaccustomed eye a pigment may appear to be of an unexceptionable black1 which to the expert appears decidedly brown2 only long practice can give the eye the requisite keenness4 ,in addition to the test already given--of smearing on white paper--there is another especially to be recommended to the inexperienced for discriminating between pigments4 ,a small quantity of the black under examination is intimately mixed with a white pigment2 white lead or zinc white is very suitable4 ,if the mixture has a pure grey shade1 the black may be regarded as of good quality1 but if it contains brown substances the mixture has an indefinite1 dirty shade instead of a pure grey4 ,this is a sure sign that the black requires further purification4 ,although caustic soda is now very cheap1 its use for the purification of soot black is tolerably costly1 because it entails much labour4 ,this process is therefore only used for the finest qualities which are to be employed for copper-plate inks and black coach colours4 ,for inferior qualities the method of calcination is used1 which produces1 when properly carried out1 a black of such purity that it can be used for the preparation of even the finest black paints4 ,calcination of the ,soot4--,the substances which give the soot its brown colour are products of dry distillation1 and hence are all volatile at a certain temperature2 they can be separated from the soot by heating it in the absence of air4 ,the temperature necessary completely to volatilise these compounds is fairly high4 ,the soot must be heated to a good red heat to obtain a safe result4 ,when the soot is heated too quickly or to too high a temperature it undergoes an alteration which affects the quality of the product4 ,by too long or too vigorous ignition the soot changes its flocky consistency to a sandy nature2 it will then require much longer grinding with oil to produce a uniform mixture than is the case with the light flocculent soot1 which very readily mixes with oil4 ,the soot is ignited in sheet-iron boxes with a coating to protect the metal from burning4 ,this coating is best made from clay and hair4 ,a very thin paste of clay and water is painted uniformly over the boxes with a brush2 when the first coat is dry a second and third are given4 ,when once the metal is completely covered with clay1 several coats are given of clay mixed with chopped tow until the layer is several millimetres thick4 ,the coating carefully made in this manner is very durable1 and the boxes can be used for a long time1 whilst without the coating they would very soon be burnt4 ,particular care must be given to the manufacture of the boxes themselves2 the bottoms must fit very accurately1 and should be coated with clay in order to ensure an air-tight joint4 ,the lids also must fit accurately1 and when they are closed must equally be made tight by clay4 ,the soot is at first loosely packed into the box and each portion then pressed with a rammer so that it tightly fills the boxes4 ,in the lid is a very small opening1 through which the volatile products can escape4 ,the heating begins quite gently at the back1 and proceeds gradually to the front2 the boxes are finally brought to a good red heat1 at which they are maintained for about half an hour2 at this temperature the substances mixed with the carbon are almost entirely volatilised1 and the soot acquires its true black appearance4 ,the soot itself attains a red heat in the boxes and in consequence of its loose nature it very readily burns4 ,the precautions given above must be observed in order to protect completely the soot against the action of the air4 ,the boxes should not have the smallest opening besides that in the cover necessary for the escape of the volatile matters2 through an opening invisible to the naked eye so much oxygen may enter during the cooling of the boxes that a considerable quantity of carbon will burn to carbonic acid4 ,to avoid losses through the carbon burning precautions must equally be taken in the cooling of the boxes4 ,when the ignition is finished they are drawn out of the furnace by tongs and placed upright on a stone floor2 as the cool air enters1 and in contact with the red-hot carbon would burn a portion of it4 ,this can be prevented by a simple artifice3 a red-hot coal is placed on the small opening in the lid2 this converts the oxygen of the air which enters the boxes into carbonic acid4 ,when all the boxes are taken out of the furnace the doors of the room in which they are placed are opened1 so that they are cooled in the draught4 ,finely divided carbon takes fire at a temperature far below a red heat1 so that the boxes should not be opened until their contents are quite cold4 ,if they were opened whilst hot the soot might take fire4 ,pine ,black4--,under this name a poor quality of black comes into the market1 which is much used for ordinary black paints1 etc4 ,the pine black formerly brought into the market was what its name purported2 it was made from the roots of the pine in the primitive fashion already described4 ,the black was sold without further purification3 it was a soft light powder1 very variable in shade on account of the absence of control over the process3 it varied from pure black to a dark brown4 ,at present1 under the name of pine black many substances are sold1 generally without purification1 made from the most different materials1 frequently from rosin1 rosin residues1 and other cheap materials4 ,,chapter ,,xlii4 ,,the ,,manufacture ,,of ,,soot ,,black ,,without ,,chambers4 ,a certain temperature is necessary for the combustion of every substance2 if a cold body is placed in the flame of a candle or an oil lamp it becomes covered with soot1 because it cools the flame to such an extent that the carbon is no longer heated to the temperature necessary for its combustion1 and is1 therefore1 separated in a finely divided condition4 ,use is made of this phenomenon in a method of making soot black which has many advantages1 of which the most important is that expensive buildings are not required1 and the manufacture can be conducted in restricted space4 ,illustration3 ,,fig4 #cc4 ,a convenient arrangement for obtaining black by this process is represented in ,fig4 #cc4 ,the thin-walled hollow cast-iron cylinder is turned smooth on the outer surface1 and is surrounded by a sheet-iron cover at the distance of a few centimetres2 it rotates in bearings1 which1 like the spindles1 are hollow2 cold water is thus led through the cylinder from a tank at a higher level4 ,below the cylinder are placed1 near to one another1 smoking lamps1 and at the side of the cylinder is a broad brush of soft hair which continuously removes the soot deposited on the surface1 which then falls over an inclined plate into the collecting vessel4 ,the cylinder is kept in slow rotation by any mechanical arrangement4 ,the lamps are devised not to produce a hot flame1 but when this comes in contact with the cold surface of the cylinder1 it deposits a ring of soot on the rotating cylinder which is then removed by the brush4 ,the cylinder is kept cooled by the water which runs through it4 ,the soot which is collected shows a tolerably strong brown shade in consequence of the rapid cooling of the flame1 which causes the formation of a large quantity of products of distillation2 the soot will always require ignition4 ,illustration3 ,,fig4 #cd4 ,it has been proposed further to simplify the manufacture of soot black by this method1 by burning coal gas under the cylinder from numerous small openings in a pipe4 ,coal gas indeed gives a very fine deep black1 but the yield is so small that this process could never be adopted with advantage4 ,the apparatus constructed by ,thalwitzer for the manufacture of oil black 7,fig4 #cd7 consists of a plate1 ,a1 with a rim1 a1 fastened to a vertical axis1 b4 ,this is carried by bearings in ,b1 and is kept in rotation by the cog-wheels1 d and f1 moved from the shafting1 ,o4 ,the plate is cooled by water supplied by the pipe1 g1 it flows away by h and the annular vessel1 ,d4 ,the lamps1 e1 are connected with the common oil reservoir by n4 ,h is a scraper fastened to ,b by x4 ,,chapter ,,xliii4 ,,indian ,,ink4 ,indian ink consists of purified soot mixed with gum1 as binding medium1 and a little camphor and musk4 ,it is generally believed that ,indian ink is made in ,china by a process which is still a secret2 this opinion is supported by the fact that the ink made in ,europe is almost always inferior to the ,chinese4 ,it is quite possible that a substance which produces a particularly fine black is used in ,china to prepare the soot used for the ink1 and which we do not yet know or do not use on account of its high price4 ,but it appears that the difficulty of producing an ink equal in quality to the ,chinese lies less in the quality of the soot --for by the methods of purification already given we can make almost chemically pure carbon--than in the extremely careful mechanical treatment of the soot with the other constituents of the ink4 ,the genuine ,chinese ink has a peculiar smell1 which1 when not hidden by musk1 distinctly recalls the smell of burning camphor2 the camphor tree is a native of ,china1 so that it is not impossible that the soot of the wood of this tree is used for the ink4 ,the soot from camphor alone would be too expensive1 so that it is probable that camphor wood is used from which camphor has been prepared1 or that camphor soot is mixed with the soot of a cheaper substance4 ,in fact several varieties of ,chinese ink show distinctly the smell peculiar to soot produced by fat4 ,the binding material is animal glue1 which is most thoroughly ground with the carbon2 the secret of making good ,indian ink lies in the careful grinding with the binding medium4 ,according to ,piou1 who lived for a long time in ,china and learned the process there used1 the black employed for the ink is made from the resins of the pine and other trees4 ,the soot is sieved through silk1 boiled with glue and water1 and kneaded by hand with a little oil until the mass has become completely homogeneous4 ,it is then left for some days1 heated1 and pressed into the moulds4 ,this description is not very satisfactory2 the products obtained are far inferior to those made by the ordinary ,european process4 ,the viscous mass obtained by long treatment of the black with the binding medium is slowly dried1 and again ground when it has become thick4 ,when a completely homogeneous paste has been obtained it is made into sticks which are pressed into moulds1 and then very slowly dried so that they do not crack4 ,small cracks always occur2 they are filled in by a brush dipped in the thick paste1 finally the sticks are entirely or partially covered with gold leaf4 ,in order to impart to the ink the odour characteristic of the ,chinese ink1 it is sufficient to use good lamp black1 made odourless by extraction with caustic soda1 and to add a little solution of camphor in turpentine during the grinding4 ,if it is desired to impart the musk smell which several ,chinese varieties possess1 a small quantity of a spirit extract of genuine musk may be added4 ,the size solution is made by long boiling isinglass with water2 it must be so concentrated that it forms a strong jelly on cooling4 ,a small quantity of acetic acid is added1 so that the grinding may not be hindered by the viscous nature of the size1 which the acid prevents from gelatinising4 ,when the mixture has been made by long grinding1 the mortar is warmed to #dj or #ej ,c41 whereupon the acetic acid is soon volatilised1 and the mass rapidly becomes very thick4 ,neutral ,tint ,black4--,a mixture of ,indian ink1 ,chinese blue1 and a very small quantity of madder lake forms the colour known as 0neutral tint10 the shade of which is a peculiar greyish violet4 ,by alterations in the proportions of the constituents different shades of 0neutral tint0 are produced4 ,,appendix4--,,black ,,mineral ,,pigments4 ,chrome ,copper ,black4--,when copper chromate is strongly ignited in air and then treated with boiling nitric acid a glittering black compound is obtained1 which shows up well when printed on fabrics with albumin4 ,this and all similar pigments are distinguished by great durability4 ,chrome ,black4--,when a mixture of chromium oxide with varying quantities of ferric oxide is strongly heated1 pigments are obtained of all shades from dirty yellow and green to the deepest black4 ,this pigment is largely used in porcelain painting to produce a black1 which also can be obtained by other but much more costly methods4 ,the best mixture to produce a deep black contains one part of chromium oxide to four parts of ferric oxide4 ,,chapter ,,xliv4 ,,enamel ,,colours4 ,an enamel is a glass distinguished from ordinary glazes by a much lower melting point1 and generally by opacity4 ,most enamels are coloured by additions of metallic oxides4 ,without going in detail into the art of enamelling1 some observations may here be given which appear indispensable for an understanding of the manufacture of enamel colours4 ,the enamels are glasses1 but not every glass can be used for an enamel1 since the constituents of the glass react with the substances by which the enamel is coloured1 and with certain colouring matters quite different shades to the intended might be produced4 ,of equal importance with the composition of the glass used in the preparation of the enamel is the temperature at which the glass melts4 ,many colours bear but a low heat2 they decompose at a somewhat higher temperature and produce quite the wrong colour4 ,this is especially the case with the enamels coloured purple red by gold4 ,the enamel colours are fixed by mixing them with an easily fusible glass 7the flux71 applying them to the object to be enamelled1 whether metal1 glass1 or porcelain1 and heating the painted article in muffles until the glass melts1 and either dissolves the colouring matter or encloses it unaltered4 ,according as the enamel melts as a whole1 or the flux alone melts and encloses the colouring matter1 so transparent or opaque enamels are produced4 ,the former are really coloured glasses1 the latter are glasses in which is enclosed the sintered colouring substance4 ,whilst enamels were formerly of importance only for artistic purposes1 they have recently attained great industrial employment2 not only is earthenware now covered with enamel1 and thus made to resist the attack of chemical reagents1 but boiler tubes are lined with enamel to prevent the formation of scale4 ,the colours used for enamels must in all cases be metallic oxides2 for yellow1 silver and antimony oxides2 for red1 gold1 copper oxide and ferric oxide2 for blue1 cobalt compounds2 for green1 copper oxide or chromium oxide4 ,two operations are required in the production of enamel colours1 the preparation of the flux and its fusion with the real colouring substance4 ,in most cases the latter operation takes place simultaneously with the fixation on the enamelled article1 but the enamels may be melted and cast into lumps1 which are then powdered4 ,white ,enamels4--,these are always ordinary crystal glass1 to which tin dioxide or potassium antimoniate has been added4 ,particular care must be taken that only pure raw materials are used1 for almost unweighable quantities of iron compounds are sufficient to impart to the enamel a yellow tinge4 ,in almost all cases the glass must be decolourised by the addition of pure pyrolusite 7manganese dioxide71 which at a red heat gives up a portion of its oxygen to the ferrous oxide contained in the glass1 producing ferric oxide1 which has much less colouring power4 ,too large a quantity of pyrolusite imparts a blue tinge to the enamel4 ,the tin dioxide used in the glaze is made by direct oxidation of tin in air4 ,it has been found that tin burns much more easily in air when it is mixed with lead2 #bj to #dj parts of tin are melted with #ajj parts of lead1 and the alloy heated in shallow vessels in the air2 it takes fire at a certain temperature1 and it is only necessary to remove continually the layer of oxide in order to oxidise the whole of the metal within a short space of time4 ,the mixture of oxides obtained in this manner is freed from particles of metal by grinding and levigation2 when it is fused with the glass1 the lead oxide enters into combination1 whilst the tin oxide is embedded in the colourless glass4 ,when paste enamels are required the mass is melted in shallow crucibles1 poured into water and broken up to a coarse powder1 which is again fused4 ,in some cases this operation must be repeated several times to obtain a quite homogeneous product1 for tin dioxide is very heavy and sinks to the bottom of the fluid glass2 this is readily seen if the fused enamel is allowed to cool in the crucible4 ,when the crucible is broken the lower portions of the fused mass are dense white1 whilst the upper are merely milky white4 ,by repeatedly fusing the mass it is endeavoured to obtain it uniform4 ,in fusing the enamel care must be taken that it is heated in a vessel from which the fire gases are completely excluded1 since the smallest quantity of coal or of ferruginous ashes coming into contact with the melted mass would injure its colour4 ,if the melting point of the enamel is too high it can be lowered by the addition of a small quantity of pure quartz sand4 ,a fine white enamel is obtained by using litharge or red lead4 ,the mixture contains #fj parts of quartz sand1 #cj of alum1 #ce of common salt and #ajj of red lead4 ,it is advisable to add a small quantity of finely-powdered talc to the sand4 ,in consequence of the considerable proportion of alumina contained in this enamel it is difficult to melt1 and can be heated to very high temperatures without injury to the shade4 ,when antimony oxide is used a glass free from lead must be taken2 lead glass does not give a pure white with antimony oxide4 ,a very good white enamel is obtained by fusing #c parts of crystal glass with #a part of sodium antimoniate4 ,coloured ,enamels owe their colour to metallic oxides4 ,enamels coloured by metallic oxides1 in which the oxygen is firmly united1 can be fired without great precaution1 but if they contain oxides easily decomposed1 great care is required to obtain a fine colour4 ,in enamelling metals a white under-glaze is generally used beneath the coloured enamel2 it consists of a refractory white enamel4 ,by this means it is more easy to obtain pure colours4 ,yellow ,enamels are coloured by silver1 antimony oxide combined with litharge1 or ferric oxide2 from the latter a red can also be obtained4 ,to produce a yellow enamel by means of silver the article is first enamelled white at a low temperature2 silver oxide is then applied where required1 and the article again heated4 ,it then frequently happens that the surface has a metallic appearance owing to the reduction of a part of the silver oxide to metallic silver4 ,when this coating is scraped off the enamel beneath is found to be coloured a fine yellow4 ,the antimony yellow is obtained by mixing #a part of antimony oxide1 #a part of alum and #a to #c parts of white lead1 according to the depth of colour required4 ,these finely-powdered materials are intimately mixed with #a part of sal ammoniac1 and heated in an open vessel with stirring until the yellow colour appears4 ,the vapours of the ammonium chloride indicate the proper temperature for the operation4 ,when this substance is completely volatilised the temperature should not be further raised1 or the mixture would fuse4 ,by means of ferric oxide a fine and durable yellow is produced2 the quantity employed must not be too large1 or a red colour will result4 ,a very high temperature is required for burning in this colour4 ,the alum used in making the yellow enamel colours serves to prevent the oxides from fusing4 ,red ,enamel4--,ferric oxide is generally used4 ,when a purple red is required it is obtained either directly from metallic gold or from purple of ,cassius4 ,red iron enamel is made by slowly heating #bj to #be parts of pure ferrous sulphate with #aj parts of aluminium sulphate until all the water of crystallisation is expelled1 when the temperature is gradually raised to an intense heat4 ,the shade depends upon the temperature3 the higher it is the darker is the colour4 ,tests are taken from time to time of the mixture1 and rapidly cooled4 ,hot ferric oxide is black1 consequently the shade can only be judged with complete certainty in a cooled portion4 ,although the temperature required for the preparation of this colour is very high1 yet it ought not to rise so far that the magnetic oxide is produced1 a small quantity of which would cause the enamel to appear dirty red1 since it gives to the flux a blackish green colour4 ,the red ferric oxide colour should not be dissolved in the glass of the enamel1 but should be embedded in it4 ,thus1 when the enamel is burnt on1 the temperature should not rise so high that ferric silicate is formed1 otherwise a yellow or even completely black enamel results4 ,purple red is obtained by means of gold2 formerly purple of ,cassius was exclusively employed for this purpose1 but an equally bright red can be obtained from gold chloride4 ,the colour obtained from gold will bear only a very low heat2 it must be mixed with a very fusible glass1 brought on to the article to be enamelled1 and heated just sufficiently to melt the mass4 ,the following mixture is used for gold red and other delicate colours3 #c parts of calcined borax1 #c parts of quartz sand and #a part of chalk4 ,a very small quantity of gold is sufficient to produce a deep red1 the amount of gold preparation used for a pale red or a medium purple must be carefully weighed4 ,blue ,enamels are always coloured by cobalt oxide4 ,any cobalt compound can be used1 since at a red heat the silica of the glass displaces other acids1 and produces cobalt silicate4 ,it is most simple to take cobalt nitrate4 ,this salt is readily obtained completely pure1 and absolute purity is of great importance1 for only thus is a pure blue produced4 ,cobalt oxide produces a more or less deep blue when fused with varying quantities of glass4 ,in order to produce shades similar to turquoise and forget-me-not1 a white enamel must be used beneath the blue1 or bone ash must be mixed with the blue enamel2 this produces a paler colour1 which is also opaque4 ,green ,enamel is coloured by copper oxide or chromium oxide4 ,in the former case #a part of copper oxide is used to #cj to #ej parts of glass1 according to the depth of shade required4 ,the enamel made with copper oxide alone has never a pure green colour2 it exhibits a blue tinge4 ,a pure green is obtained by adding a very small amount of ferric oxide1 which produces a yellow and compensates for the blue shade1 so that a pure green is formed4 ,chromium oxide produces a beautiful emerald green without any addition4 ,the enamel may be exposed to very high temperatures without injury4 ,green enamels may also be made by mixing blue cobalt enamel with a yellow enamel3 an unexceptional shade results1 but this method is seldom used1 since green enamels are obtained in a simpler manner from copper and chromium oxides4 ,violet ,enamel4--,manganese dioxide is used exclusively to produce violet enamel2 an extremely small quantity is sufficient to colour a considerable quantity of glass4 ,a pure violet shade is only obtained when very pure manganese dioxide is used2 the artificially prepared substance should be used to produce the finest violet3 the cost is considerably greater than that of the mineral pyrolusite1 but equally good results can rarely be obtained from pyrolusite4 ,black ,enamel4--,when a large quantity of ferric oxide1 copper oxide or cobalt oxide is fused with a glass1 a deep black enamel is obtained4 ,generally mixtures of these oxides are used2 experience has shown that a much deeper black is thus obtained than from any one alone4 ,now that enamels are not used exclusively for artistic purposes1 but in considerable quantities for earthenware and other technical purposes1 the manufacture of enamel colours has attained considerable importance2 works already exist occupied almost exclusively with this special branch of manufacture4 ,by ,lacroix' process enamel colours are made which can be applied to porcelain without further admixture with a flux2 for example1 a very fine blue is made by dissolving #cjj parts of pure alumina and #ajj parts of cobalt carbonate in nitric acid1 evaporating the solution to dryness1 igniting the residue and fusing it with #cjj parts of quartz sand free from iron1 #ijj parts of crystallised boric acid and #a1hjj parts of red lead4 ,a blue glass is obtained which easily melts1 but is difficult to powder2 but if poured when fluid in a thin stream into cold water1 it forms thin threads1 which are very brittle in consequence of the rapid cooling1 and may be easily converted into a soft powder4 ,,chapter ,,xlv4 ,,metallic ,,pigments4 ,metallic pigments do not always consist of metals2 the name is also applied to compounds which possess a pronounced metallic lustre2 mosaic gold1 the preparation of which has been previously described1 is an example of such a pigment4 ,another variety of metallic pigment is made by heating finely-powdered alloys2 a layer of oxide is thus produced upon the surface of the metallic particles1 this layer produces a shade of the colour of the metal or alloy4 ,metallic pigments are only unalterable when they are composed of metals which are not changed by the action of the air4 ,as a matter of fact1 this property is not possessed by any of the metals used for this purpose2 even gold and silver are blackened by the action of the sulphuretted hydrogen in the air4 ,this alteration proceeds1 however1 very slowly when the metal is enveloped by a layer of a binding medium1 which is always the case when the metallic powder is used for painting4 ,there are many manuscripts1 the initial letters of which have been coloured by gold or silver1 in which the metals retain their peculiar lustre after the lapse of centuries4 ,metallic paints made from yellow alloys have never much durability3 they always contain copper1 which readily alters2 articles painted with imitation gold soon lose their lustre1 and in the course of time become green4 ,shell-,gold4--,this very expensive artists' paint is made by rubbing gold-beaters' refuse with gum solution upon a stone slab until a completely homogeneous mixture results1 which is then rapidly thickened over the fire and generally allowed to dry in small shells4 ,the preparation so made is known as shell-gold3 it is sold at very high prices4 ,the operation of grinding the gold is very lengthy2 it considerably increases the cost of the already expensive material4 ,the process may be considerably shortened if the gold is obtained in a very finely divided state by a chemical operation4 ,for this process coins or broken jewellery is heated in hydrochloric acid1 and nitric acid gradually added4 ,the gold dissolves in the mixture4 ,if it was alloyed with silver a white precipitate of silver chloride is formed1 which is filtered off after largely diluting with distilled water4 ,the solution is boiled for some time to remove excess of nitric acid4 ,a solution of ferrous sulphate is then added2 the liquid at once becomes bluish black1 and in a short time deposits a brown precipitate composed of chemically pure gold1 which is so finely divided that it is almost without the characteristic glitter of gold4 ,the precipitate is filtered off1 dried and preserved in stoppered bottles4 ,in order to prepare shell-gold from this gold powder it is simply necessary to grind it with thick gum solution in a porcelain mortar2 under the pressure of the pestle the gold rapidly acquires its natural glitter4 ,the grinding need only be continued until the gold and gum solution are uniformly mixed4 ,the mixture so made should be at once filled into the shells1 since on standing the gold would soon separate from the gum solution in consequence of its high specific gravity4 ,shell-,silver4--,genuine shell-silver can be made by rubbing silver leaf with gum solution upon a slab exactly as genuine shell-gold4 ,in this case also the labour may be considerably lessened by converting the silver into a state of fine division by a chemical process4 ,silver is dissolved in nitric acid1 which must be quite free from hydrochloric acid1 or insoluble silver chloride would be formed4 ,in the operation brown suffocating fumes are evolved which attack the respiratory organs2 it should therefore be conducted in the open air or under a flue with a good draught4 ,the silver solution1 which is generally coloured blue by admixed copper1 is diluted with a large quantity of distilled water4 ,a sheet of copper is then dipped into the liquid and rapidly moved about in it4 ,the silver then separates as a dark grey powder2 after washing it is chemically pure1 and when ground with gum solution it produces genuine shell-silver4 ,shell-silver and shell-gold are rarely used in painting on account of their cost2 they are chiefly used for illuminated manuscripts4 ,when these metallic pigments are to be used in oil painting1 in place of gum they must be ground with a liquid which mixes with boiled oil or essential oils4 ,for this purpose copaiba balsam is to be recommended4 ,imitation ,silver4--,the imitation silver pigments are made from an alloy of tin and bismuth1 or from a tin amalgam4 ,the latter is most easily made by melting tin in a porcelain dish and adding one quarter of its weight of mercury2 the mixture is then well stirred1 and allowed to cool4 ,it quickly solidifies to a crystalline mass1 which is tolerably brittle and can be powdered without difficulty4 ,to obtain a substance of a true silvery appearance the amalgam must be converted to a powder of a certain degree of fineness4 ,if the powdering is carried too far the product loses a great part of its metallic lustre1 and acquires a dull grey colour4 ,the bismuth alloy is made by fusing #ajj parts of tin1 adding #ajj parts of bismuth1 and then #aj parts of mercury4 ,it is not absolutely necessary to add mercury1 but the addition has the advantage that the solid alloy is far more easily powdered4 ,the imitation silver made by this process has a white metallic colour approaching that of genuine silver1 but not equal to it1 especially in lustre4 ,it is1 however1 largely used in the industries on account of its low price2 for example1 for paper hangings4 ,,chapter ,,xlvi4 ,,bronze ,,pigments4 ,it would be anticipated from the name that bronze pigments were composed of an alloy of copper and tin2 in reality the alloy is composed of copper and zinc1 i4e41 brass4 ,the bronze pigments are made by a similar process to that described for genuine gold and silver pigments4 ,the waste produced in the manufacture of imitation gold leaf is ground with a solution of dextrine upon a slab until the mixture is uniform and separate metallic particles can be perceived only through a lens4 ,whilst genuine gold and silver paints are always made in small quantities1 on account of the expensive nature of the material1 and machinery is not employed1 the bronze pigments are in different case2 the use of mechanical arrangements is necessary for producing the fine subdivision1 otherwise the bronze would be very dear on account of the great cost of grinding4 ,the mechanical arrangements required to divide the alloy are of the ordinary nature1 but special machines have been constructed for the manufacture of bronze pigments1 by which the metal is far more quickly converted into powder than by means of grinding machinery4 ,these machines consist of metal drums studded on the interior with a large number of fine needles and capable of very rapid rotation4 ,when a metal powder already tolerably fine is brought into these drums1 it is rapidly brought to such a condition of fine division as would be attained by hand grinding only by prolonged and laborious exertion4 ,the raw material for the manufacture of bronze powders is produced in making imitation gold and silver leaf2 the waste metal obtained in beating the sheets is used4 ,the employment of this waste has two advantages3 the metal is already in very thin sheets and is composed of alloys varying in colour from silver white1 through gold1 to a bright copper4 ,in making leaf metal the waste of each colour is kept carefully separate1 so that it simply requires to be broken up to produce bronze powders of different shades4 ,before this waste is brought into the drums mentioned above it must be subjected to a preliminary grinding in a mortar with a small quantity of a fatty oil1 which serves to bind together the mass4 ,sufficient oil should be used to give the mass some degree of coherence2 if too much oil is added the space between the needles of the drum would be coated with the mass and the process in the drum would require a much longer time4 ,the uniform mixture of oil and bronze waste is then brought upon a wire sieve of the finest possible mesh1 and the mass is rubbed through by means of a fine metal brush into a vessel below2 thus the larger particles are retained by the sieve and only those which are smaller than the mesh pass through4 ,the product of this process is then brought into the drums1 which are rapidly revolved2 the small particles of metal are thrown with great force against the side and are converted by the fine points with which it is studded into a very fine powder4 ,the time required for this process depends on the rate of revolution and on the quantity of powder treated at once4 ,the drums are stopped from time to time and the contents examined4 ,when the powder is sufficiently fine it is taken out of the drum4 ,this is most easily accomplished if the drum is arranged to take apart into two halves4 ,in most works it is usual to free the bronze powder from the admixed oil by subjecting the mass to the greatest pressure that can be produced by a very powerful hydraulic press4 ,the oil which flows from the press is always green1 which shows that chemical action has taken place4 ,in consequence of the large surface imparted to the oil it becomes speedily rancid1 and then contains free fatty acids which attack copper very energetically4 ,illustration3 ,,fig4 #ce4 ,the use of hydraulic presses may be avoided by removing the oil by means of a solvent4 ,fatty oils dissolve very readily in carbon bisulphide1 but this solvent cannot be used in this case1 because commercial carbon bisulphide always contains dissolved sulphur1 which would blacken the bronze powder4 ,petroleum ether and benzene are very suitable solvents for this purpose4 ,on account of the volatility of these inflammable liquids lights must be absolutely excluded from the room in which they are used1 and in order to avoid loss of solvent the bronze powder must be treated in closed vessels4 ,the safest plan is to use a special apparatus of simple construction to dissolve the oil4 ,fig4 #ce shows the construction of an arrangement suitable for this purpose4 ,it consists of a cylindrical vessel of tin plate surrounded by a rim into which fits the edge of the cover4 ,when the lid is placed on and the rim filled with water1 the contents of the vessel are closed in air-tight and cannot evaporate4 ,the lower portion of the vessel is conical1 and is joined to a pipe in which is a tap1 and which communicates at the side by a tube with the glass vessel in which the solvent is contained2 another tube connects the neck of this vessel with the cover4 ,when this apparatus is used for extracting the oil from bronze powder1 a filter of strong blotting paper is placed in the conical portion of the vessel1 care being taken that it fits accurately so that it is not torn by the weight of the bronze4 ,the oily bronze powder is placed on this filter1 the cover set on1 and the rim filled with water4 ,by opening the tap attached to the solvent reservoir the liquid is allowed to enter the cylinder from below1 the air in the latter passing through the tube in the cover to the reservoir4 ,after some hours the oil is dissolved1 the tap in the cover is then opened and the liquid run off by opening the lowest tap4 ,if the bronze powder is not quite free from oil after one treatment with the solvent1 the operation is repeated with a fresh quantity4 ,when free from oil the powder and filter are removed from the apparatus and dried2 the dry mass forms a solid cake1 which is broken up in a mortar and by a little grinding changed into a fine powder4 ,the colour of the bronze powder is the same as that of the alloy used1 but the shade is always rather paler than that of the coherent metal2 regard must be paid to this circumstance in making a bronze of a determined colour3 the alloy employed must have a rather deeper colour than the shade the bronze is to possess4 ,the manufacture of leaf metal and bronze powder is frequently conducted in the same works1 which also often prepare the requisite alloys2 we1 therefore1 give a few examples of the composition of the alloys which produce certain shades4 ,the more zinc the alloys contain the lower is their melting point1 the greater their brittleness and hardness and the paler their colour4 ,an increase in the copper causes the colour of the alloy to approach more nearly to that of gold1 and increases the malleability1 a property useful in making leaf metal1 but not desirable in making metallic powder4 ,a zinc copper alloy which contains between #a and #g per cent4 of zinc has an almost pure red1 or even a dark red colour2 an alloy containing #gd to #ach per cent4 of zinc has a pure golden yellow colour1 between #aff and #be per cent4 of zinc a yellow appears4 ,an increase of the percentage of zinc above this point produces the colour of brass2 it is noteworthy that an alloy containing still more zinc1 #cc to #da per cent41 again shows a reddish colour1 which is most developed when the alloy contains equal parts of zinc and copper4 ,if the zinc is increased still further the shade gradually goes over to white2 this change is already observed in an alloy containing #ea per cent4 of zinc1 which shows a pure golden yellow colour1 and is very brittle4 ,when the zinc rises to #ec per cent4 the colour is reddish white2 at #ef per cent4 it is yellowish white1 at #fd per cent4 bluish white1 and between #ge and #ij per cent4 the alloy is bluish-grey4 ,the alloys for bronze powders of different shades have the following composition1 according to ,r4 ,wagner3-- ,copper1 ,zinc per cent4 per cent4 ,pale yellow #hc #ag ,red #id-ij #f-aj ,deep red #ajj ,bronzes from ,english1 ,french and ,bavarian works contain the following percentages of copper3-- ,,english ,,bronzes4 ,orange #ihb per cent4 ,deep yellow #hbcg 0 ,pale yellow #hjdb 0 ,,french ,,bronzes4 ,copper red #igcb per cent4 ,orange #iddd 0 ,pale yellow #habi 0 ,,bavarian ,,bronzes4 ,copper red #ihib per cent4 ,violet #ihhb 0 ,orange #iecj 0 ,straw yellow #haee 0 ,speiss yellow #hbcd 0 ,in each case the remainder of the alloy consists entirely of zinc4 ,alloys containing from #a to #ce per cent4 of zinc are only malleable in the cold4 ,the malleability is at the greatest with a content of zinc between #ae and #bj per cent42 such alloys are the most suitable for making leaf metal4 ,alloys containing between #cf and #dj per cent4 of zinc may be hammered either cold or hot1 whilst the former alloys become brittle on heating4 ,when the percentage of zinc is still further increased the malleability decreases4 ,the most brittle alloys contain #fj to #fg per cent4 of zinc4 ,the alloys are made in a furnace with a good draught1 for copper liquefies at a very high temperature4 ,to prevent loss of copper by oxidation the molten metal should not come in contact with air2 it should be covered by a layer of redhot coal1 which prevents oxygen from reaching it4 ,when the copper is completely melted1 which is ascertained by stirring with a piece of wood1 the whole of the zinc is added4 ,some skill is required in this operation1 otherwise a large proportion of the zinc will be volatilised1 and the vapours will burn when they come in contact with air1 in which case dazzling bluish white flames are seen over the crucible4 ,the best method is to throw the zinc into the crucible and immediately stir it into the molten metal with a wooden rod4 ,the products of the dry distillation of the wood1 which are given off in great quantity at this high temperature1 keep the air from the surface of the metal and prevent the oxidation of the zinc vapours4 ,the zinc is thoroughly mixed with the copper by stirring with the wooden rod1 the crucible is then slowly cooled1 with the precaution that the surface of the metal is kept covered by red-hot coals so long as the metal is fluid4 ,when sufficiently cool the metal is poured into shallow iron moulds1 in which it quickly solidifies2 it is then rolled into sheets1 which may be converted into thin leaves by hammering in a similar manner to that in which the gold-beater makes gold leaf4 ,to obtain bronze powders of different shades alloys of different colours may be used2 the bronze powders may also be shaded by two methods--either by adding certain colouring matters of very great colouring power or by partially oxidising the finely divided metallic powder4 ,in the first process the finely ground colouring matter is mechanically mixed with the bronze powder4 ,the use of manual labour would involve a great loss of time2 even when quite small quantities of bronze and colouring matter are mixed in a mortar it is necessary to grind diligently for a very long time before a mixture of homogeneous appearance is obtained4 ,in working on a somewhat larger scale it is therefore advisable to adopt mechanical mixing arrangements4 ,a very simple apparatus suffices4 ,a sheet-iron cylinder is used which can be revolved1 and provided with a well-fitting slide4 ,in this cylinder are placed the bronze powder and the colouring matter until it is about half full2 then1 after tightly closing the slide1 it is set in slow rotation1 which is continued until a test taken out shows a uniform colour4 ,when bronze powder is slowly heated in a shallow vessel the colour begins to darken at a temperature not much above the boiling point of water4 ,in consequence of the fineness of the particles of the metallic powder the copper readily takes up oxygen1 and is superficially converted into copper oxide4 ,this oxide is of a darker colour1 and thus by this method the shade of the bronze can be deepened as desired4 ,this simple operation requires a certain amount of practice to produce a product of a determined shade4 ,the desired result is most safely attained when the bronze is spread out quite uniformly in a thin layer upon a metal plate1 which is gently heated from below4 ,the powder soon begins to darken2 by cooling the plate the progress of the oxidation may be arrested at any moment4 ,recently bronze powders have come into the market showing all possible colours in the deepest shades1 by the aid of which very remarkable colour effects can be produced4 ,these bronzes are made by dissolving an aniline dye in a little alcohol1 pouring this solution over the powder1 and mixing the dye uniformly through the whole of the bronze by working the mass for a sufficient length of time4 ,in this way bronze powders are produced which possess a green1 red1 blue or violet lustre1 according to the colour of the dye used4 ,these colours with metallic lustre can also be produced by bronzing the article with a white 7zinc7 bronze1 and then coating it with a varnish in which the required aniline dye is dissolved4 ,a bronze with a fine golden red glitter is produced by applying a golden yellow bronze and then a varnish in which a little aniline red is dissolved4 ,it should be observed here that these effects1 produced by a coat of varnish in which an aniline dye is dissolved1 only turn out well when the dye is used in very small quantity1 for these colours are the strongest with which we are acquainted1 and in colouring power far surpass cochineal carmine1 which is renowned for this property4 ,when bronze is coloured by dyes the most varied shades can be obtained with a metallic lustre4 ,according to ,conradty a very fine blue bronze is obtained by boiling white bronze for some hours with a weak alum solution1 washing and drying1 and then mixing in a mortar with a strong solution of aniline blue in alcohol until the solvent has evaporated4 ,this operation is repeated until the desired depth of shade is obtained4 ,the bronze is then washed with pure water4 ,conradty also recommends that the coloured bronze should be ground with a little petroleum1 and then exposed to the air to allow the petroleum to evaporate4 ,this operation1 for which no chemical reason can be given1 is quite unnecessary4 ,if other dyes or mixtures of them are used in place of aniline blue1 bronzes of corresponding colour are obtained4 ,however handsome are the bronzes coloured by this process1 nearly all have the disadvantage that the colours have little permanence1 and quickly fade when exposed to light4 ,this is especially the case when the bronzed article is coated with an oil varnish2 if1 however1 a spirit varnish is used1 or indeed any varnish composed of a resin and a volatile solvent1 the colour of the bronze1 protected by the layer of resin1 remains quite unaltered for a long time4 ,electrolytic ,copper ,bronze4--,electrolytically precipitated copper may be used as a bronze pigment2 it is most simply made by adding pieces of metallic zinc to a solution of copper sulphate free from iron and violently shaking the flask for a long time4 ,the liquid becomes warm1 and the copper separates in the form of a very fine precipitate1 which is collected on a filter and washed with air-free water 7boiling water is best7 and then quickly dried4 ,the upper portions of the precipitate in the filter1 which are exposed to the air1 have generally a brownish colour due to the incipient oxidation of the finely divided metal4 ,they are removed1 and the lower portions show the characteristic colour of pure copper4 ,in the same way silver can be precipitated from a solution of silver nitrate in a finely divided state1 but the particles of the silver powder are so very small that they reflect very little light1 and consequently the powder has an unsightly grey colour4 ,when a surface painted with this silver is rubbed gently with a hard body1 the metallic lustre appears4 ,tungsten ,bronze ,pigments are expensive and rarely employed4 ,they are obtained by fusing sodium or potassium tungstate in a porcelain crucible and gradually adding tungstic acid until the mass has an acid reaction4 ,tin dioxide is then added in quantity sufficient to neutralise the tungstic acid2 the mass is cooled and finely powdered4 ,according as potassium or sodium tungstate is used1 a violet or reddish pigment is obtained which exhibits the peculiar metallic lustre of a bronze powder4 ,still more costly is vanadium bronze1 which is made by adding ammonium vanadate to a solution of #b parts of copper sulphate and #a part of ammonium chloride with continual stirring1 until the precipitate no longer re-dissolves on stirring4 ,the liquid is then heated for several hours to about #ce ,c41 when vanadium bronze separates in golden yellow scales4 ,these are collected on a filter1 washed and dried ,when ground with oil or gum solution they can be used as a red gold bronze4 ,the colour is unaltered by the air4 ,,chapter ,,xlvii4 ,,vegetable ,,bronze ,,pigments4 ,under this apparently contradictory term1 substances come into the market which produce a peculiar metallic lustre4 ,when applied under certain conditions1 the appearance is similar to that produced by real bronze4 ,the vegetable bronze pigments are lakes as pure and free from foreign admixtures as possible4 ,the lakes obtained from red wood or logwood can be used for this purpose4 ,from the red woods 7see p4 #chd7 a magnificent bronze pigment can be obtained1 which is either pure golden yellow or possesses a greenish golden metallic lustre not unlike the colour of the wing cases of the rose-bug4 ,to obtain either shade a pure lake is first made by extracting red wood with boiling water1 adding a little carbolic acid to the decoction 7#jja per cent4 of the quantity of liquid7 and allowing to stand for several weeks4 ,the liquid is syphoned off from the deposit1 heated1 and alum added equal in quantity to #aj per cent4 of the wood used4 ,the mixture is then allowed to stand for about a week1 the precipitate is filtered off1 washed1 and1 if necessary1 dried4 ,if the bronze is to be used in the form of water colour1 the precipitate is dried to a thick paste and mixed with about #aj per cent4 of its volume of thick gum solution1 so that a viscid mass is obtained which can just be applied with the brush4 ,when the coating is made so thick as to hide the surface of the bronzed article1 it has when dry the golden green colour4 ,in using this lake to prepare a pigment similar to gold bronze it must be almost completely dried1 and then mixed with the liquid obtained in the following manner3 ,white soap is melted on the water bath with the smallest possible quantity of water1 and when completely dissolved the same quantity of white wax is stirred in1 finally water is added1 so that the cooled liquid has the consistency of a moderately thick varnish4 ,when this liquid is ground with the requisite quantity of the still damp lake and the mixture applied to paper1 wood1 or leather1 and after drying rubbed with a glass ball1 it gradually acquires a very fine golden bronze colour4 ,this method of bronzing is largely used in the manufacture of wall papers and for colouring fancy leather4 ,to protect this coating against the action of water1 it should be varnished when dry4 ,these bronze pigments may also be used in varnish4 ,the lake is then completely dried and ground with varnish in such quantity as to give a thick mass which can just be brushed on4 ,the vegetable bronze is obtained from logwood in a similar manner1 a solution of stannic chloride being generally used to precipitate the lake when a deep bronze is required1 and alum for a pale gold shade4 ,by using mixtures of the two salts intermediate shades are produced4 ,the precipitate produced by alum may be shaded by means of potassium bichromate4 ,hmatoxylin forms with chromium oxide a deep bluish black compound which has such intense colouring power that it is used to colour writing ink4 ,the ink is prepared by adding a little potassium bichromate to a decoction of logwood4 ,if a very small quantity of this dark precipitate is mixed with the lake precipitated from logwood extract by alum solution1 colours are produced possessing the peculiar metallic lustre and a shade depending upon the quantity of potassium bichromate added4 ,the addition of this salt must be very carefully made1 as a very small excess is sufficient to render the colour so dark that it is useless as a bronze4 ,the shade of the precipitate depends upon the concentration of the liquid and other conditions1 so that it is impossible to give precise quantities4 ,in practice1 the safest and most convenient method is to dissolve the bichromate in a large quantity of water and add very small quantities of the dilute solution to the logwood extract along with the alum4 ,after each addition a portion of the precipitate is rapidly mixed with the above-mentioned solution of soap and wax1 to which a little size has been added1 and then spread upon paper4 ,if the desired shade has not yet appeared1 a little more bichromate is added and another test made1 and the process repeated until the proper shade is attained4 ,pigments for colouring wall papers and fancy leather are not easily made which produce such fine effects at so small a cost as the vegetable bronze pigments1 which deserve the greatest regard from the colour maker and leather and paper manufacturers4 ,appendix--,the ,brocade ,pigments 70,brocatfarben074--,under this designation powders have been recently introduced characterised by a strong metallic or glassy lustre1 and very suitable for certain purposes1 such as the manufacture of wall papers1 since they enable remarkably fine effects to be produced4 ,they consist of mica in a tolerably fine state of division4 ,mica is a mineral which occurs frequently in nature and which very readily splits into thin sheets2 it occurs in various colours4 ,in thin sheets mica is colourless and completely transparent2 in somewhat thicker pieces it generally shows a distinct metallic lustre similar either to that of gold or silver4 ,when ground to fairly fine powder1 it has the same gold or silver lustre1 and gold or silver brocade colours are distinguished in commerce4 ,they are made by grinding mica which has been previously sorted according to its appearance4 ,the powdered mica can be sold as powder or may be mixed with a binding substance in order to be ready for use4 ,gum ,arabic is generally used as the binding medium1 but it can be replaced by the cheaper dextrine4 ,when printed upon paper the brocade pigments produce the effect of a bronze1 and in addition to their cheapness they have the great advantage of being completely unaltered by the air4 ,,pigments ,,of ,,organic ,,origin4 ,,chapter ,,xlviii4 ,,lakes4 ,the pigments commercially designated lakes generally consist of an organic colouring matter united with a metallic oxide4 ,in isolated cases other compounds of colouring matters are included under the term1 such as indigo sulphonic acid1 and yet more rarely pure colouring matters are included1 for example carthamine red4 ,but the overwhelming majority of lake pigments are compounds of a colouring matter with the oxide of a metal4 ,for this purpose the oxides of tin1 lead and aluminium are commonly used4 ,lakes are generally made by mixing the solution of the colouring matter with the solution of a salt of the metallic oxide1 and precipitating the oxide by an alkali4 ,the colouring matter is separated along with the oxide and forms with it a substance known as a lake4 ,it has not yet been decided whether the lakes are true chemical compounds of the colouring matter with the metallic oxide1 or whether the colouring matter is simply held fast by the surface attraction of the finely divided oxide4 ,in favour of the latter view is the fact that a larger or smaller quantity of the colouring matter can be united with a given quantity of the oxide4 ,the lakes vary greatly in durability2 some1 such as the madder lakes1 can be counted among the most durable pigments1 whilst others have very little permanence1 as for example1 the logwood lakes4 ,the majority of the colouring matters used in the preparation of lakes are of vegetable origin1 but several are derived from animal sources4 ,the properties of the colouring matters used for this purpose vary greatly2 each material demands a special treatment for the production of lakes4 ,therefore1 in describing the methods by which lakes are made1 we shall give first the properties of the colouring matter in question1 and then proceed to the preparation of the lake4 ,in the preceding portion of the book the pigments have been arranged according to their colour2 the lakes will be described in the same order4 ,the yellow1 red or green lakes of different origin will be treated in the same section in order to facilitate reference to any particular pigment4 ,white lakes are not known1 neither are there lakes which can be described as black4 ,with these exceptions lakes of all colours can be made and also of all shades4 ,as an example of this madder lake may be given1 which is found in commerce in a great variety of shades2 it can be made from the palest rose-red to the deepest purple red1 or1 more properly1 madder red1 which is a characteristic shade4 ,the shades of any lake are obtained by mixing in a white pigment just as in the manufacture of mineral pigments4 ,whilst1 however1 in the latter case the white pigment must often be mechanically mixed with the colour1 the shading of the lakes is accomplished in their preparation4 ,generally speaking1 a pale shade of a lake is obtained by increasing the amount of the salt1 the oxide of which is used to precipitate the colouring matter4 ,the oxides in question are white 7with the exception of lead oxide72 thus in the pale shades a small amount of colouring matter is precipitated upon a large amount of oxide1 whilst in the deep lakes the reverse is the case1 a large quantity of colouring matter is precipitated upon a small quantity of oxide1 and the shade thus appears very deep4 ,apart from the nature of the colouring matter contained in a lake1 and considering only the metallic oxide with which the colouring matter is united1 it appears that lakes containing lead oxide have little durability4 ,the combination between the colouring matter and the metallic oxide in a lake is so loose that it is easily destroyed by sulphuretted hydrogen2 if a lake containing lead is exposed to the action of air containing that gas the colour will1 in the course of time1 inevitably blacken4 ,the lakes containing tin are also susceptible to sulphuretted hydrogen2 in air containing but a trace of this gas they quickly lose their brilliance and in time are quite discoloured4 ,alumina is not affected by sulphuretted hydrogen1 and must thus be regarded as the most suitable oxide for the preparation of lakes4 ,it is generally applied in the form of alum1 in the selection of which great care is necessary if fine colours are to be produced4 ,commercial alum frequently contains ferric oxide2 when the alumina is precipitated simultaneously with the colouring matter the ferric oxide is also thrown down1 and is mixed with the lake1 its dark colour influencing the shade of the lake greatly to its disadvantage4 ,the effect of the ferric oxide upon the colour of the lake is so important that it is impossible1 for example1 to obtain a pale red lake with alum containing iron4 ,to avoid the bad results given by alum containing iron it should be examined before it is used1 and if it is found to contain any considerable quantity of iron it should be rejected for this purpose4 ,after alum a solution of stannic chloride is most commonly used to precipitate lakes1 but it must be free from stannous chloride2 it produces as a rule darker lakes than alum4 ,care must be taken that the stannic chloride solution is free from iron4 ,the ordinary process for making lakes is very simple3 a clear aqueous solution of the colouring matter is obtained2 to this alum or stannic chloride solution is added in proportion to the amount of colouring matter dissolved by the water2 the metallic oxide is then precipitated by an alkali4 ,sodium or potassium carbonate or caustic alkalis may be used2 ammonia is very suitable for this purpose1 since it is free from iron4 ,the precipitant must be cautiously added1 it is introduced in drops when the greater part of the colouring matter has been precipitated2 an excess of the alkaline solution would have considerable effect on the shade of the precipitate4 ,the precipitated lake rapidly settles to the bottom of the almost colourless liquid2 the settling is particularly rapid when stannic chloride has been used4 ,the liquid is then drawn off1 the pasty residue brought upon a strainer1 washed several times with water1 and dried in the air or in stoves4 ,when dry1 a properly prepared lake forms a mass of little coherence1 and can be readily ground to a soft powder1 which may then be ground with oil or gum solution to produce oil or water paints4 ,at the same time the materials are added to the pure lake which are used to shade its colour2 white pigments are generally employed for this purpose--the paleness of the shade is proportional to the amount of white pigment introduced4 ,certain lakes are shaded by small quantities of other colouring matters2 for example1 the admixture of a small quantity of a blue pigment with a pure red lake produces a much deeper colour inclining to purple4 ,if a small quantity of a red or blue colouring matter is added to a yellow pigment there is produced a deeper yellow inclining to orange1 or a yellow inclining to green1 in proportion to the quantity of the added colouring matter4 ,it should be observed that it is of great importance for the colour maker to have a practised eye1 sensitive to fine differences of colour4 ,he may then produce colours faultless in shade1 for if by chance a colour does not turn out well it may be improved by judicious admixtures4 ,it is quite impossible to give definite rules for the mixing of colours2 the estimation of a shade cannot be taught in words1 it demands long practice4 ,by the use of a system1 provided the user has normal eyes1 very slight differences of colour can be readily estimated4 ,a scale of colours should be made from pigments of pure and definite shades1 in which scale successful mixtures are gradually inserted1 so that a series is produced in which the separate pure colours blend regularly into one another4 ,then1 when it is required to produce a pigment corresponding to a certain shade on the scale1 with a little practice the shade can be readily produced1 for the scale indicates which colour predominates4 ,the so-called sap colours are generally characterised by very pure shades4 ,they are produced by decomposing a lake by an acid or a strong base1 evaporating the solution of the colouring matter so obtained at a gentle heat and mixing with gum1 starch1 or some other thickening material to produce a mass of such consistency that it can be formed into balls or sticks4 ,the decoctions of the dye-woods always contain other substances in addition to the colouring matters1 which are precipitated with the colouring matter1 and somewhat injure its shade4 ,when such a lake is decomposed the colouring matter is obtained in a purified form1 thus showing its full beauty4 ,this solution of the purified colouring matter might be again precipitated with a salt solution and lakes be produced which would be much brighter than the original1 but the losses incidental to this double precipitation would be so great that the lake would be made much too expensive4 ,,chapter ,,xlix4 ,,yellow ,,lakes4 ,yellow colouring matters are widespread in nature2 from them are obtained many yellow pigments used in dyeing and in the manufacture of colours4 ,the colours produced by the yellow vegetable colouring matters are not particularly bright2 thus the yellow lakes are used chiefly to produce cheap pigments1 whilst the inorganic pigments are used for bright yellows4 ,dutch ,pink4--,several species of buckthorn 7,rhamnus7 contain a yellow colouring matter--xanthorhamnin--which is obtained pure by extracting the yellow berries with hot alcohol4 ,on cooling1 the impure colouring matter separates2 by repeated recrystallisation from alcohol it is obtained in the form of crystalline needles1 which are soluble in water and alcohol4 ,the yellow lake known as ,dutch pink is prepared from yellow 7,persian7 berries1 by boiling the crushed berries with water and mixing the extract with a solution of alum4 ,the lake is then precipitated by the addition of powdered chalk4 ,as a rule1 #ejj parts of water are used to #ajj parts of berries1 #bj parts of alum are added to the decoction1 and the mixture poured upon #ge parts of finely powdered chalk4 ,the liquid is decanted off1 the residue filtered1 washed and dried4 ,commercial ,dutch pink is made from a mixture of the decoctions of yellow berries1 quercitron bark and turmeric1 to which the alum solution is added1 and then chalk4 ,the precipitate is made into conical lumps1 which are sold as ,dutch pink1 and used for ordinary painting and for colouring leather4 ,weld ,lake4--,the dyers' weld 7,reseda luteola7 contains a yellow colouring matter formerly much used in dyeing2 a yellow lake can also be obtained from it4 ,when weld is boiled with water a deep yellowish green decoction is obtained1 from which yellowish-green flocks separate on cooling4 ,the lake can be obtained from all parts of the plant except the root1 the flowering shoots giving the largest yield of colour2 the lake is generally precipitated by alumina4 ,equal parts of weld and alum are boiled with water until the latter is dissolved and the liquid is coloured deep yellow2 the hot solution is quickly filtered through a thick linen cloth and soda solution gradually added in small quantities with continual stirring so long as effervescence follows4 ,alum entirely free from iron is required to produce a bright yellow lake2 a small quantity of iron has great influence on the shade4 ,weld contains more or less tannin1 which gives very dark blue or green compounds with iron salts1 the production of a very small quantity of which suffices to convert the yellow shade into an ugly dirty colour4 ,chalk may be used instead of soda to precipitate the alumina2 in this case the precipitate will contain calcium sulphate in addition to the alumina compound of luteolin4 ,weld lake may be used in oil1 or size1 or as a water colour4 ,gamboge ,lake4--,crude gamboge is the dried sap of certain ,east ,indian trees2 it is used as an artists' colour1 but only in water2 for use in oil it is converted into a lake4 ,a particular treatment is necessary to obtain a handsome lake4 ,gamboge is treated for several days with water and the soft mass ground on the slab or in a mill until it forms a uniform paste1 which is mixed with water to a thick liquid1 which is then put through a fine sieve4 ,a hot solution of alum is then added in the proportion of three parts of alum to one part of gamboge1 the mixture is boiled in a wooden vessel and two parts of nitric acid added whilst well stirring2 finally a dilute solution of potash is added in small quantities until the liquid solidifies to a jelly1 which is spread out in thin layers on filter cloth1 well washed with water and dried at a gentle heat4 ,prepared ,gamboge4--,crude gamboge cannot be used in oil painting because it never gives a uniform shade1 but when the colouring matter is freed from admixtures and ground with oil1 it gives a deep durable colour of great beauty4 ,the colouring constituent of gamboge is a resin which is fairly soluble in strong alcohol1 whilst the impurities are insoluble4 ,the pure colouring matter is obtained without great expense in the following manner3 ,coarsely powdered gamboge is placed in a large flask with strong alcohol2 the flask is well closed1 placed in a warm position and repeatedly shaken2 the deep yellow solution is carefully poured off from the sediment1 water is then added1 when the colouring matter separates in flocks4 ,only sufficient water should be added to precipitate all the colouring matter2 test portions of the liquid should be examined from time to time1 the alcohol can then be recovered by distillation and used again4 ,the colouring matter separated from the alcoholic solution forms a hard mass on drying2 it must be very finely powdered before it is ground in oil4 ,there are many other yellow lakes which can be obtained by adding alum to an aqueous decoction of the colour-bearing material and neutralising the liquid4 ,such decoctions are obtained from fustic1 quercitron 7,quercus tinctoria71 young fustic 7,rhus cotinus71 the root of barberry 7,berberis vulgaris71 annatto 7the fruit of ,bixa orrellana71 turmeric 7the root of ,curcuma longa71 etc4 ,the yellow lakes obtained from these sources are seldom used in painting1 the mineral pigments are preferred on account of their finer appearance4 ,these colouring matters are largely used in dyeing to produce shades varying from yellow to brown1 the majority are also used in calico printing4 ,fustic ,lake4--,of the colouring materials mentioned above fustic produces a lake which is so handsome that it deserves larger use in painting than it has yet found4 0,old fustic0 is chipped immediately before use and extracted with boiling water2 whilst still hot the extract is mixed with a hot solution of alum2 on cooling a fine yellow precipitate is formed1 which when dry is frequently sold under the name of ,dutch pink4 7,genuine ,dutch pink is made from a decoction of yellow berries2 the majority of the pigments sold under this name are made from decoctions of mixtures of the different yellow dye wares47 ,to obtain the best lake from fustic the alum used must be completely free from iron1 otherwise only a dirty green lake is produced4 ,since the least trace of iron damages the shade of the colour1 fustic lake is more frequently made by means of lead oxide4 ,to obtain the lead fustic lake the decoction is allowed to stand for several days1 so that the morin1 which together with maclurin forms the colouring principle of fustic1 may separate2 the liquid is filtered from the precipitate1 and lead acetate solution added which has been boiled with litharge to saturation1 so that the most basic acetate is produced4 ,the lead fustic lake has a deep yellow colour2 it is well adapted for use in painting1 but1 like all lead pigments1 is not specially permanent in air4 ,by admixtures of levigated chalk or starch paler shades of the dull yellow lake are obtained4 ,quercitron ,lake4--,lakes are seldom made from quercitron alone1 although they possess a deep yellow colour2 they are more frequently employed in dyeing when they are produced directly upon the fibre4 ,quercitron lake can be made by treating the aqueous decoction of the ground bark with tin crystals and a little alum solution4 ,with tin crystals alone a darker yellow lake is obtained than when alum is used at the same time4 ,different shades may thus be produced4 ,extract of quercitron bark comes into commerce as a greyish yellow powder under the name of flavine1 which has great colouring power1 and may be used with advantage in the place of aqueous extracts of the bark4 ,since the discovery of the aniline dyes the applications of all lakes have been largely extended1 since the dyes enable brighter shades to be obtained without the many processes necessary when natural colouring matters are used1 and do not require so much skill on the part of the workman4 ,this applies not only to yellow colouring matters1 but to the many other colouring matters formerly used by the dyer4 ,the principal reasons which have so quickly brought the new dyes to the front lie in their greater beauty and in the diminished labour required in their use4 ,purree or ,indian ,yellow must not be confounded with the yellow cobalt pigment known also under the latter name4 ,it is a compound of magnesia with an organic acid--euxanthic acid4 ,it is obtained from the urine of cows fed upon mango leaves4 ,it comes into commerce in lumps weighing about #ej to #fj grammes1 which are dark brown on the exterior1 but on fracture show a fine orange yellow colour4 ,indian yellow is little used1 and is not likely to attain importance4 ,many cheaper colouring matters equal in shade are known4 ,the ,colouring ,matter of ,saffron4--,the dried stigma of the flowers of the saffron1 a species of iris1 has been long used for colouring foods4 ,it contains a very handsome yellow colouring matter of a characteristic shade2 formerly this was largely used in silk-dyeing1 and especially for dyeing glove leather4 ,it is practically now no longer used2 considerably cheaper aniline dyes produce an equally good shade4 ,on account of its high price 7#a kilogramme of saffron contains about #fj1jjj stigmata7 this material cannot be used for lakes1 although they leave nothing to be desired in fineness of shade1 but they have no great permanence4 ,the ,colouring ,matter of ,gardenia ,grandiflora4--,the fruits of this plant1 which are imported from ,southern ,asia1 contain a beautiful dark yellow colouring matter1 which1 according to ,rochleder1 is identical with the colouring matter of saffron4 ,it is readily soluble in water2 lakes of various shades can readily be obtained by the addition of salts to the aqueous solution4 ,alum gives a pure yellow1 lead acetate a yellowish red1 and stannous chloride a dark orange red lake4 ,,chapter ,l4 ,,red ,,lakes4 ,,cochineal ,,and ,,carmine4 ,the purple of the ancients was obtained from the shellfish purpura2 it was so costly that it was regarded as an attribute of royalty4 ,according to history the ,tyrians discovered this colour2 at any rate they were able to use it for dyeing4 ,in the writings of the ancients ,tyrian purple garments were regarded as the greatest luxury4 ,the art of obtaining a purple from this source was lost2 more recently it has been re-discovered1 but the colour is found in no way to correspond with what we regard as a bright shade4 ,when the ,spaniards conquered ,mexico they found an insect cultivated which produced a splendid red colouring matter4 ,this insect1 the cochineal1 is parasitic upon certain cacti1 especially ,cactus coccinellifer and ,cactus opuntia4 ,the females only are used as colouring material2 the males are very small1 and much fewer in number4 ,the cultivation of the proper species of cactus and of the cochineal has spread to most tropical countries4 ,the females1 which are attached in enormous numbers1 are brushed off and killed by heating upon hot plates4 ,they then appear as grains of the size of millet seeds1 with a wrinkled surface covered with a silvery grey dust4 ,this variety of cochineal is the best4 ,black cochineal also comes into commerce2 it has a brownish black colour4 ,it is produced by killing the insects in boiling water1 by which the grey dust which covers the living insect is removed4 ,cochineal produces when ground an ugly reddish brown powder4 ,the animal nature of cochineal cannot be recognised by the naked eye1 it is seen on examination under the microscope2 this has given opportunity for the most incredible adulterations of the costly substance4 ,cases have been known in which a paste chiefly composed of flour has been pressed into the form of cochineal1 the grains coloured by some cheap red colouring matter1 powdered with the dust from boxes in which cochineal has been packed1 and placed upon the market as cochineal4 ,the expert would not be deceived by this gross fraud1 but another method of adulteration is far more difficult to recognise2 genuine cochineal is brought into commerce from which the greater part of the colouring matter has been extracted1 and which has been again powdered with the grey cochineal dust4 ,such extracted cochineal does not produce the same brownish-red powder as the fresh substance4 ,in the cochineal insect there is a very large quantity of colouring matter3 it may reach #ej per cent4 of the weight of the dry insect4 ,the colouring matter1 which is known as carmine 7the same name is also applied to its lake71 is soluble in water with a fine red colour4 ,when cochineal is extracted with water the operation must be often repeated1 and each time fresh quantities of colouring matter are dissolved4 ,the cochineal may be exhausted by repeated boiling with water1 but a large quantity of liquid containing little colouring matter is then produced4 ,in order to obtain a strong solution of the colouring matter the cochineal must be powdered2 this is difficult on account of the softness of the material1 which does not give a fine powder1 but a pasty mass4 ,the object is best attained by grinding the cochineal through a mill similar to a coffee mill1 but since the grooves of the steel cone1 which effects the crushing1 may be easily clogged1 the mill must be arranged so that the cone can be taken out and cleaned4 ,the colouring principle of cochineal is an acid1 carminic acid1 which was obtained by its discoverer1 ,warren de la ,rue1 in the following manner3 #a part of powdered cochineal is boiled with #dj parts of water for #bj minutes2 after standing1 the liquid is poured off from the sediment1 and mixed with a solution of #f parts of lead acetate1 acidified by #a part of acetic acid4 ,the precipitate1 which consists of impure lead carminate1 is filtered from the colourless liquid and carefully washed2 whilst still wet it is suspended in water1 through which sulphuretted hydrogen is passed2 the lead carminate is decomposed into lead sulphide and carminic acid1 which dissolves in the water4 ,the colouring matter is not yet quite pure2 the treatment with lead acetate and sulphuretted hydrogen must be repeated1 the solution then obtained is evaporated at a low temperature1 the residue dissolved in boiling alcohol1 phosphoric acid added to decompose traces of lead carminate still present1 then ether1 finally the clear liquid is separated from the precipitate and evaporated4 ,by this process carminic acid is obtained in a state of complete purity2 unfortunately the process is too complicated for practical application4 ,pure carminic acid is a purple red mass1 which transmits red light at the edges and forms a pure scarlet red powder when ground4 ,the aqueous solution gives1 with alum and ammonia1 a characteristic precipitate1 the colour of which is the purest carmine-red2 lead1 zinc and copper salts produce purple red precipitates4 ,the composition of carminic acid is expressed by the formula ,c,h,o4 ,,chapter ,,li4 ,,the ,,manufacture ,,of ,,carmine4 ,the colouring matter of cochineal is used in the form of a lake under the name of carmine1 the finest and most expensive colour used in painting4 ,however simple the preparation of carmine may appear1 it is not easy to obtain a product of great beauty2 certain conditions1 still unexplained1 play an important part in the process4 ,until not long ago the manufacture of fine carmine was regarded as a secret2 this it is no longer1 and with proper care any one may produce an entirely satisfactory product4 ,many recipes have been given1 some of the best will be mentioned4 ,whatever method is used to obtain carmine certain precautions must be taken1 without which it is impossible to obtain a bright colour4 ,alkalis and alkaline earths in very small quantity affect the shade of carmine1 so that spring water should never be used in its preparation4 ,pure rain water1 or1 still better1 distilled water1 should be employed4 ,the decoction of cochineal is difficult to filter4 ,paper cannot be used1 because the pores are so rapidly stopped up that new filters would be continually required4 ,fine silk is the most serviceable2 it should not be washed with soap--the alkalinity of the small quantity of soap the fabric would retain would affect the colour4 ,the decoction is made in a well-tinned copper pan1 all other vessels should be of glass or porcelain1 which are most easily cleaned1 and great cleanliness is the prime essential to the success of the process4 ,the greatest care is required to prevent the contact of the liquid with iron during the whole process1 the smallest trace of this metal would result in a discoloured product4 ,the essentials of the manufacture of carmine on the large scale are that the colouring matter is dissolved in water1 and precipitated by the addition of an aluminium salt1 generally alum1 absolutely free from iron4 ,the more slowly the carmine separates the finer is its colour4 ,it is generally observed that the last portions to precipitate show the brightest shade4 ,this is because the foreign substances occurring with the carminic acid in the decoction are thrown down with the first portions of the precipitate4 ,in the process of ,frau ,cenette1 famous for the beauty of the product1 a solution is made from which the whole of the carmine is separated in about three weeks4 ,during this long time the majority of the substances which have been dissolved in the water together with the carminic acid are decomposed2 the liquid acquires an unpleasant smell1 and is covered with mould4 ,in the author's opinion so good a product is obtained by this process because the greater part of the impurities is decomposed3 the nearer the product approaches the pure compound of carminic acid and alumina1 the purer and brighter will be the shade of the carmine4 ,it is known that light has considerable influence on the beauty of carmine4 ,during dull winter days it is quite impossible to produce so fine a product as in summer4 ,instead of alum a tin solution may be used to precipitate the colouring matter2 the shade of the product is different to that of alumina carmine4 ,,cenette',s ,,method4--#a kilogramme of finely powdered cochineal is boiled with #ge litres of water for two hours2 #ij grammes of saltpetre are added1 the liquid boiled for three minutes1 then #abj grammes of salt of sorrel 7acid potassium oxalate7 are added and the liquid again boiled for ten minutes4 ,the liquid is then completely clarified by standing1 drawn off from the residue by a syphon1 and brought into shallow glass dishes which are placed1 protected from dust1 in a bright light in a uniformly warm place4 ,during several weeks the carmine separates1 the last portions being always brighter than the first4 ,the addition of potassium oxalate has the object of assisting the separation of the carmine1 for acid salts separate the carmine from solutions2 the saltpetre may reasonably be omitted4 ,the majority of the recipes for carmine1 which are frequently sold at a high price1 differ but little from the above2 acid potassium tartrate is used instead of the oxalate1 but the latter is to be preferred because of the slight solubility of the tartrate4 ,it is important not to use too strong decoctions of cochineal1 and to add only small quantities of alum4 ,the clear liquid is placed in shallow glass dishes4 ,after a few days the nature of the deposit should be examined3 if a considerable quantity of a red precipitate has formed1 the liquid is poured off into other dishes1 in which carmine again separates during the following days1 and usually of a brighter colour than the first4 ,for example1 #abe grammes of cochineal are boiled with #e litres of water during fifteen minutes1 #cj grammes of very finely powdered alum are added to the boiling liquid1 which is again boiled for a few minutes1 allowed to clarify and cool4 ,the greater part of the carmine is then obtained in a few hours1 but the liquid still separates carmine after several days4 ,according to another formula #ejj grammes of cochineal are boiled with #cj litres of water1 #fj grammes of cream of tartar are added1 then #cj grammes of alum1 boiling is continued for several minutes1 and the liquid then allowed to cool4 ,carmine may be obtained in a very short time by means of tin solution4 ,the process is similar to that just given4 ,the liquid which would be set aside for the spontaneous deposition of the carmine is1 however1 returned to the pan1 and a solution of pure stannous chloride added in drops1 so long as the solution is still clearly red4 ,the carmine separates at the bottom of the pan2 the liquid drawn off1 even when it appears almost colourless1 produces a further small quantity of carmine in a few days4 ,according to ,j4 ,j4 ,hess1 a brighter carmine is obtained when the fat of the cochineal is previously extracted by ether or benzene4 ,proposals have often been made to deepen the colour of prepared carmine2 this must be done with the greatest care1 for it is very easy to produce a less handsome instead of a finer pigment4 ,the carmine is moistened with distilled water containing about #e per cent4 of ammonia solution4 ,carmine readily dissolves in ammonia4 ,this property may be applied to test its purity1 pure carmine should dissolve without residue in #e to #f times its quantity of ammonia4 ,any considerable residue denotes an intentional addition of some adulterant4 ,starch1 vermilion1 and cheaper lakes are used for this purpose4 ,the red solution obtained by treating carmine with the above quantity of ammonia may be used as a red ink4 ,this solution can also be used to purify carmine2 when it is allowed to stand in an uncorked bottle for some time the ammonia escapes1 and the greater part of the carmine is deposited as a very fine powder4 ,carmine solution is made by dissolving carmine in the necessary quantity of ammonia1 adding glycerine equal in quantity to the ammonia1 driving off the latter by heat and diluting the liquid4 ,this solution is well adapted for colouring confectionery1 but cannot be employed in painting and writing1 since the glycerine would prevent it from drying4 ,carmine is extensively used in painting1 and for many purposes cannot be replaced by another pigment1 e4g41 the cosmetic known as vegetable rouge can be made from no other pigment4 ,carmine may be used in all methods of colouring2 it is quite harmless for confectioners' purposes4 ,munich1 ,vienna1 ,paris1 or ,florentine ,lake4--,this fine deep red lake differs from carmine in containing a much larger quantity of alumina1 thus possessing the character of an ordinary lake4 ,occasionally carmine lake is intentionally mixed with light white substances1 such as magnesia1 to obtain paler shades or cheaper pigments4 ,whilst only the finest varieties of cochineal can be used to make fine carmine1 the cheaper sorts can be used for ,florentine lake4 ,the cochineal used for carmine is boiled but a short time with water1 so that the residue contains considerable quantities of colouring matter1 which may amount to half of that originally present4 ,the same materials are used as in the preparation of carmine1 and in this case1 too1 stress should be laid upon their purity4 ,the weight of the alum is usually #aj to #ae times that of the cochineal2 a little stannous chloride and cream of tartar are also added to brighten the shade4 ,all these materials are boiled with the cochineal1 soda is added to the clear solution until effervescence no longer occurs1 the separated lake is then washed4 ,the lake may be made with magnesia instead of alumina1 it is added in the form of magnesium sulphate2 the more magnesia is used the paler is the lake4 ,the proportions in which the materials are employed vary with each manufacturer4 ,the following quantities have always given the author a favourable result3 ,cochineal #aj parts1 alum #aej parts1 water #bej parts2 or cochineal #aj parts1 magnesium sulphate #e parts1 alum #je part4 ,in making ,florentine lake a fairly deep colour should be produced4 ,this may be mixed without difficulty in the wet or the dry state with a white pigment1 thus producing any desired shade1 even to the most delicate rose-red4 ,ammonia-,cochineal4--,this preparation1 which is chiefly used by dyers1 is obtained by treating cochineal in a well-closed flask with strong ammonia1 which dissolves the colouring matter4 ,after about a month alum equal to about #c per cent4 of the amount of cochineal is added without separating the undissolved residue from the solution1 and the whole is evaporated at a gentle heat in a tinned pan until it becomes a stiff paste on cooling4 ,the mass solidifies more readily if a small quantity of starch paste is added4 0,cochineal paste0 is cochineal which has been treated in this manner2 it is generally brought into the market in the form of cakes or small slabs4 ,in addition to the true cochineal other species of the same insect contain a red colouring matter and have a restricted use in dyeing4 ,the most important of these is the ,polish cochineal 7,coccus polonicus71 which lives on the roots of the scleranthus4 ,it has not been proved that these insects contain the same colouring matter as true cochineal1 but it is certain that the colouring matters of ,polish and also of ,russian cochineal 7,coccus euv ursi7 are far inferior in beauty to that of true cochineal4 ,,chapter ,,lii4 ,,the ,,colouring ,,matter ,,of ,,lac4 ,from the punctures of the insect ,coccus lacca on certain ,east ,indian trees1 especially those belonging to the genus ,ficus1 flow at the same time resin and colouring matter in such quantities that the insects are frequently enclosed and large red masses are formed on the trees4 ,the insects live in some measure in these masses1 the females lay their eggs in the spaces and the larv are said to feed on the red sap contained in the mass4 ,when the larv have left the incrustation1 generally in ,november1 it is broken off from the branches and collected4 ,it is now known as stick-lac2 it consists of large masses of resin of a fine deep red colour4 ,in the interior the cells of the insects may still be perceived4 ,on chewing1 it becomes soft and colours the saliva a deep violet4 ,when stick-lac is boiled in water a portion of the colouring matter dissolves4 ,good stick-lac contains #aj per cent4 of colouring matter and #hj per cent4 of resin4 ,seed-lac has the same origin as stick-lac1 but frequently the greater part of the colouring matter has been extracted2 it rarely contains more than #be per cent41 and is consequently of little value for colouring purposes4 ,lac ,dye4--,the colouring matter of stick-lac is generally separated from the resin in ,india and comes into the market under the name of lac dye4 ,it is made by stirring coarsely powdered stick-lac in large vessels for several hours with warm water4 ,almost the whole of the colouring matter dissolves1 whilst the resin remains as a ruby red mass which is melted and brought into the market under the name of shellac4 ,the solution of the colouring matter is evaporated in shallow vessels in the sun or boiled down in pans2 the residue is made into cakes4 ,at present soda solution is used instead of pure water to extract the colouring matter2 a larger yield is obtained4 ,lac dye usually contains #de to #ej per cent4 of colouring matter1 #be per cent4 of resin1 and1 in addition1 earthy substances which are to be regarded as intentional admixtures4 ,in the preparation of lac dye by ,stephen's method coarsely powdered stick-lac is boiled with soda1 and the remainder of the colouring matter contained in the resin extracted by repeated boiling with water4 ,all the extracts are then united and precipitated by alum4 ,the colouring matter separates as a lake which still contains a large quantity of resin4 ,according to the patented process of ,henley1 the colouring matter of seed-lac is extracted by hydraulic presses4 ,the lac is filled into press bags which are placed between iron boxes heated by steam4 ,on applying pressure the melted resin1 shellac1 comes through the bags1 whilst the colouring matter remains behind4 ,if this method were employed on the large scale1 presses similar to those used in stearin candle works would be suitable4 ,when lac dye is treated with hydrochloric acid the colouring matter dissolves2 the solution can be used to dye wool1 which it colours a beautiful red4 ,the colouring matter is very similar in appearance to that of cochineal1 but has the appearance of much greater fastness4 ,it appears also to be similar in composition to carminic acid1 but little is known as to its chemical constitution4 ,when lac dye is to be used for painting it must be freed from resin2 this is accomplished by treating the finely powdered mass for a long time with boiling alcohol and separating the solution of resin from the undissolved colouring matter1 which is then dried4 ,in this way a lake is produced known commercially as ,vienna red and little inferior to carmine lake4 ,unfortunately the price of lac dye1 although it is imported in large quantities from ,india to ,england1 is so high that it can only be used for artists' colours4 ,,chapter ,,liii4 ,,safflower ,,or ,,carthamine ,,red4 ,the safflower or bastard saffron 7,carthamus tinctoria7 grows wild in ,southern ,europe1 and is also cultivated4 ,it contains two colouring matters1 yellow and red4 ,the former is not used in dyeing1 but is employed for colouring liqueurs1 since it is innocuous4 ,the red colouring matter is used for colouring artificial flowers and for fine cosmetics2 formerly it was employed in dyeing1 but is now rarely used for this purpose1 since carthamine red has little permanence and can be replaced by cheaper dyes4 ,the yellow colouring matter1 which is not used1 is generally removed by treating the corolla of the safflower1 which contains the colouring matter1 with water4 ,after this treatment it is known as washed safflower4 ,in the dried corolla of the flower up to #cf per cent4 of the yellow colouring matter is found1 whilst only #jd to #jf per cent4 of the red is contained4 ,it appears that the colouring matter of the safflower has been used from the most ancient times4 ,the ,chinese employ it to obtain a handsome cosmetic1 the ,tyrians are said to have used it in dyeing4 ,in ,europe it was not cultivated before the seventeenth century1 when it came into use for dyeing4 ,in order to obtain pure carthamine red--and this is the form in which it is generally used--safflower is treated for a long time with water containing a little acetic acid until a yellow solution no longer results4 ,the residue is then treated with soda solution for several hours1 when the colouring matter dissolves2 the solution is filtered and neutralised with acetic acid4 ,cotton is then introduced4 ,carthamine red is a colouring matter which at once dyes animal and vegetable fibres when these are brought in contact with its solution4 ,thus the whole of the colouring matter is precipitated on the cotton1 which is coloured a deep red4 ,after twenty-four hours the cotton is taken out1 washed1 and treated with soda solution1 in which the colouring matter dissolves4 ,when this solution is carefully neutralised with citric acid the colouring matter separates in the form of fine flocks4 ,these are collected1 dissolved in strong alcohol1 the solution evaporated to a small volume1 the colouring matter again precipitated by the addition of a large quantity of water1 and washed with pure water until the wash waters begin to be coloured red4 ,the pure carthamine thus obtained is spread upon small cups1 in which it dries to a beautiful red mass which in somewhat thicker layers has a fine green lustre4 ,it is brought into commerce as 0cup red0 or 0plate red04 ,the small quantity of colouring matter contained in the safflower1 as well as the complicated process for obtaining it1 make it evident that this colouring matter will be among the most expensive found in commerce4 ,the high price is1 however1 neutralised by its great colouring power1 and by the fact that nothing can in all cases replace it for colouring the best artificial flowers4 ,safflower ,carmine4--,this substance1 used by dyers1 is a solution of carthamine red in soda solution4 ,it is only necessary to add an acid after once introducing the fabric in order to fix the colouring matter at once upon the fibre4 ,the shades produced by carthamine red are distinguished by a delicacy of tint not produced by other dyes2 all shades between the deepest red and the palest rose-red may be obtained from it4 ,unfortunately it is very susceptible to the action of alkalis2 one careless washing of an article dyed with carthamine is sufficient to remove the greater part of the colour4 ,on account of its cost and little durability carthamine red is not used in painting4 ,it is principally employed in the artificial flower industry for colouring flowers4 ,pure carthamine or a mixture with finely powdered steatite is applied by rubbing4 ,alkanet4--,the roots of alkanet 7,alkanna tinctoria7 contain in the bark a fine red colouring matter1 from which also a violet lake can be obtained1 though this is rarely made4 ,the plant is largely grown in ,southern ,europe and also around ,vienna4 ,the colouring matter is obtained pure by macerating the root for a long time with water and then treating with strong alcohol1 which dissolves the colouring matter1 together with a large quantity of resin4 ,the alcohol is distilled off1 the residue extracted with ether1 and the ethereal extract treated with a large quantity of water1 which extracts the colouring matter4 ,this is left in the pure state1 when the solution is slowly evaporated4 ,according to ,carnelutti and ,r4 ,nasini alkannin is obtained by extracting the root of ,anchusa tinctoria with petroleum ether1 evaporating1 treating the residue with weak caustic potash1 filtering1 and shaking the filtrate several times with ether4 ,the solvent is removed1 the colouring matter precipitated by carbonic acid1 dried over sulphuric acid1 and dissolved in ether4 ,the filtered solution is then allowed to evaporate4 ,alkannin is then obtained as a dark brownish-red mass1 which is easily powdered4 ,it has a metallic lustre1 and readily dissolves in alcohol1 glacial acetic acid and chloroform4 ,when alum is added to the aqueous solution of the colouring matter a beautiful violet precipitate separates1 which when dry is very suitable for artistic purposes4 ,alkanet is little used4 ,it is completely replaced by much cheaper colouring matters4 ,,chapter ,,liv4 ,,madder ,,and ,,its ,,colouring ,,matters4 ,the root of the madder 7,rubia tinctoria7 contains a red colouring matter which is distinguished over all other colours of vegetable origin by great fastness1 on account of which it occupies a most important position in dyeing and colour making4 ,the use of madder in dyeing has been much restricted by the discovery of artificial methods of making alizarine1 the most important colouring matter of madder4 ,thus the following account of madder and its products is chiefly of historical interest only4 ,madder is cultivated in many countries4 ,the roots1 which vary from the thickness of a quill to that of a finger1 are cleansed from adherent earth1 carefully sorted according to size1 and dried4 ,in commerce a distinction is made between stripped and unstripped madder4 ,the cortex of the root contains but little colouring matter and is generally removed by mill-stones moving at some distance apart4 ,the stripped roots are finely ground1 and are then known commercially as madder4 ,merchants distinguish a large number of varieties1 which are designated according to the place of production4 ,in addition to ground madder there are a number of madder preparations which contain the colouring matter in concentrated form1 and are consequently used in smaller quantity4 ,the most important of these preparations are garancin1 garanceux1 and the madder extracts4 0,refined madder0 is made from the natural substance by subjecting it to a process of fermentation1 by which the substances accompanying the colouring matters are largely decomposed1 and the product becomes relatively richer in colouring matter4 0,flowers of madder10 which have double the colouring power of madder1 are made by treatment with very dilute sulphuric acid4 ,madder is stirred with five or six times its quantity of water to which about #a per cent4 of sulphuric acid has been added4 ,after leaving the mixture in a fairly warm place for five to six days alcoholic fermentation takes place1 and many substances which would be injurious in dyeing are decomposed4 ,the residue becomes in consequence richer in colouring matter4 ,when the fermentation is finished the residue is filtered off1 subjected to powerful hydraulic pressure1 and the mass broken up and very thoroughly dried at a temperature of #fj to #gj ,c4 ,if it is not thoroughly dried it soon becomes mouldy4 ,this method of treating madder1 due to ,julians1 is simple1 and has the advantage that from the alcoholic liquid spirit may be obtained4 ,in some respects this process is more rational than the one immediately following3 certain substances which are destroyed in the manufacture of garancin are made useful1 and also the process requires little outlay4 ,garancin is obtained from madder by treatment with sulphuric acid1 which decomposes the glucoside1 and also sets free the colouring matter united to lime and magnesia1 which would otherwise be lost4 ,in addition1 the warm acid radically attacks the nitrogenous compounds1 the greater portion of which is destroyed4 ,thus the residue contains relatively more colouring matter1 and the removal of substances which accompany the colouring matter considerably facilitates the dyeing process4 ,although the preparation of garancin was recommended in #ahbh1 it was much later before the prejudice which prevented its general employment was completely overcome1 and garancin recognised as a very valuable material for the dyer4 ,the simplest process for preparing garancin is as follows3 ,madder is several times washed with water1 then pressed1 and the residue mixed with dilute sulphuric acid in a lead-lined vessel4 ,to #ajj parts of madder #ej parts of sulphuric acid and #ej parts of water are taken1 the mixture is heated by steam to #ajj ,c41 and maintained at this temperature for half an hour4 ,by the action of sulphuric acid of this strength considerable charring occurs1 and in particular the cell walls of the madder are attacked1 so that in the succeeding process the colouring matter is readily dissolved2 in consequence of the charring1 the garancin acquires a deep brown to black colour4 ,when the action of the acid is finished1 it is drawn off and the residue washed with water until it is free from acid1 when it is dried4 ,the process here described is the original method2 it has been much modified1 hydrochloric acid1 zinc chloride1 alkalis1 soap solution1 etc41 being used in the manufacture of garancin4 ,the colour maker will rarely require to make garancin himself1 so that it is sufficient for our purpose to indicate what is understood by garancin1 and in what manner it is made4 ,garanceux4--,madder which has been once used in dyeing still retains some quantity of colouring matter2 this is utilised by treating it by the same process which is used to obtain garancin from fresh madder4 ,the treatment with sulphuric acid almost entirely destroys the cellular structure1 so that the residual colouring matter is made accessible to solvents1 and consequently the garanceux may be again used for dyeing4 ,madder ,extract4--,the fixation of the colouring matter of madder upon the fibre is attended with many difficulties2 attempts were made to present it in the purest form possible1 or in such a condition that the operation of dyeing was simplified4 ,the commercial madder extracts consist either of liquid extracts of madder1 or of the more or less pure colouring matter itself4 ,among the numerous solid or liquid madder extracts1 without doubt the most important is the crude alizarin 7the principal colouring matter of madder71 made by the process discovered almost simultaneously by ,rochleder and ,pernod4 ,this is produced by extracting either madder or garancin with hot water containing sulphuric acid2 about #e grammes of acid are mixed with #a kilogramme of water and the madder boiled with this dilute acid in a lead-lined vessel4 ,the liquid separated from the solid residue becomes turbid on cooling1 and yellow flocks separate which consist of impure alizarin2 no further purification is required for practical purposes4 ,crude alizarin is also obtained by treating madder with superheated steam4 ,these preparations are important1 not only to the dyer and calico printer1 but also to the colour maker2 from them the madder pigments can be made in a very simple manner4 ,the ,constituents of ,madder4--,madder has been most thoroughly investigated3 its colouring matter1 alizarin1 is now made artificially4 ,in addition to woody fibre1 madder contains sugar1 mucilage1 resin1 a glucoside 7i4e41 a substance which can be decomposed into a sugar and another substance71 and1 in particular1 two colouring matters known as alizarin and purpurin4 ,alizarin occurs ready formed in madder1 and is also produced by the decomposition of the madder glucoside into alizarin and sugar4 ,to obtain pure alizarin finely ground madder is extracted with boiling water2 on the addition of sulphuric acid to the decoction alizarin separates together with other substances4 ,the moist precipitate is boiled with a solution of aluminium chloride1 and1 after filtering1 hydrochloric acid is added to the filtrate1 when deep red flocks separate1 consisting of a mixture of alizarin and purpurin4 ,the colouring matters are further purified by dissolving in alcohol and adding freshly precipitated alumina1 which unites with them2 the alumina compounds are then boiled with strong soda solution1 in which the purpurin dissolves4 ,the residue consists of aluminium alizarinate mixed with resin1 the latter is extracted with ether or benzene1 and the residue then decomposed with hydrochloric acid1 when alizarin is set free and is purified by recrystallisation4 ,alizarin has the formula ,c,h,o7,,oh74 ,it forms fine red crystals which are very little soluble in cold but more easily in hot water2 they dissolve readily in strong alcohol to a yellow solution4 ,alizarin dissolves in alkaline liquids1 the solution is dichroic2 it appears dark purple by transmitted light and pure blue by reflected light4 ,when the alkaline solution of alizarin is brought in contact with freshly precipitated alumina the colouring matter is completely thrown down and a beautiful red lake is formed4 ,the second madder colouring matter is purpurin4 ,this is more soluble in water than alizarin1 it also dissolves in alum solutions2 its alkaline solutions are not dichroic4 ,the formula of purpurin is ,c,h,o7,,oh74 ,in addition to these two colouring matters1 madder contains a third1 known as rubiacin1 which also forms red compounds4 ,it appears to be fixed upon fabrics dyed with madder in company with the other colouring matters4 ,dyeing and printing with the colouring matters of madder are among the most difficult processes in dyeing2 a long series of operations is required to fix the colour permanently on the fabric4 ,the beautiful deep red colour known as ,turkey red is produced by madder2 it is distinguished from other vegetable colours by its great fastness4 ,by means of madder various other shades besides pure red may be produced4 ,this very valuable substance is largely used in dyeing and calico printing to produce permanent colours4 ,,chapter ,,lv4 ,,madder ,,lakes4 ,the madder lakes are equally as permanent as the madder colouring matters dyed upon fabrics4 ,on this account and because of their handsome colour they are highly prized by painters4 ,the best qualities of madder are necessary to produce fine lakes2 it is more convenient to use garancin or madder extract4 ,only when the colouring matter is tolerably free from the foreign substances which accompany it can a pure red madder lake be produced2 the poorer qualities of madder produce a lake which is not a pure red and is never bright4 ,the good repute of the madder lakes of certain makers is in great part due to careful choice of the raw materials4 ,this choice and care in the process are the secrets of the manufacturers who produce good madder lakes4 ,the author has found that the finest lakes can be obtained without difficulty from the alizarin1 separated in the before-mentioned manner from madder by means of sulphuric acid4 ,the small cost of obtaining crude alizarin by this process enables it to be used on a commercial scale4 ,the labour involved in the process is far outweighed by the excellent qualities of the lakes produced4 ,a very bright lake is obtained directly from madder by treating with sulphuric acid 7thus garancin is really used71 digesting the mass for several hours with a solution of alum absolutely free from iron1 filtering and adding at first a small quantity of soda solution2 a little madder lake is precipitated which is of the finest shade4 ,when this lake has settled the liquid is poured off and again mixed with a little soda solution4 ,the lake now precipitated is inferior to the first1 if the madder is not of specially fine quality4 ,by this fractional precipitation of the colouring matter1 madder lakes varying in beauty are produced2 the separate fractions often differ considerably in shade1 this is because the later portions are more and more contaminated by the foreign substances contained in the madder4 ,from inferior madder lake1 which could only be sold at a low price1 a lake of the best quality can be produced in the following manner3 ,the lake is finely powdered1 mixed with acetic acid and left to stand twenty-four hours2 the madder lake dissolves in the acid to a fine red solution1 whilst the impurities remain on the filter when the solution is filtered4 ,the clear solution is mixed with a large volume of water free from lime1 and the acetic acid neutralised by soda1 when pure madder lake separates4 ,the addition of soda is not continued until all the lake is precipitated1 but only until the liquid is still slightly red4 ,hydrochloric acid may be used instead of acetic2 it is much cheaper1 but must be absolutely free from iron4 ,it has already been stated that the crude alizarin prepared as described above is well suited as a source of madder lake1 since it is free from the majority of the substances which injure the purity of the shade4 ,it is treated with a boiling solution of alum and filtered whilst hot2 madder lake is then precipitated by cautious additions of soda1 the first portions precipitated being the best4 ,madder ,carmine is not often found in commerce2 it consists of the almost pure lakes of alizarin and purpurin4 ,the process by which this valuable pigment is produced is based upon the great stability of the madder colouring matters4 ,the following is the process on the large scale3 ,good madder1 very finely ground1 is spread out in small heaps in a room1 the temperature of which is about #af to #ah ,c42 the heaps are moistened with water and left for several days4 ,the mass ferments and gives off a peculiar smell2 in the fermentation not only is the glucoside decomposed1 but also many of the other compounds contained in the madder1 consequently the mass becomes dark and considerably diminishes in weight4 ,the end of the fermentation process may be recognised by a little practice with tolerable certainty by the disappearance of the peculiar smell2 the mass is broken up and transferred to a lead-lined vessel1 in which it is mixed with three or four times its weight of ordinary sulphuric acid4 ,the acid is allowed to act for several hours1 the plant fibres are almost completely charred1 and the mixture becomes black4 ,when the charred residue has settled1 the liquid is filtered through pure quartz sand or powdered glass1 and mixed with a large quantity of water4 ,the carmine1 which is insoluble in water1 separates as a red powder2 it is then washed and dried4 ,the colour of madder carmine is of such beauty that it can only be compared with that of good cochineal carmine1 but it is incomparably more permanent than the latter and may be used in all varieties of painting4 ,,chapter ,,lvi4 ,,manjit 7,,indian ,,madder74 ,the roots of the ,east ,indian ,rubia mungista contain purpurin and another characteristic colouring matter1 manjistin4 ,this material is a rarity in ,german commerce1 but is imported into ,england from ,india in tolerable amount and used in dyeing4 ,manjistin may be extracted by boiling manjit repeatedly with a solution of aluminium sulphate1 uniting the liquids and acidifying strongly with hydrochloric acid4 ,in twenty-four hours a red precipitate forms in the liquid2 it is dried and treated with boiling carbon disulphide1 which extracts purpurin and manjistin and leaves undissolved a dark resin4 ,the residue1 after distilling off the carbon bisulphide1 gives up purpurin to dilute acetic acid1 manjistin remaining undissolved4 ,when the purpurin has been completely extracted1 the residue is treated with a little boiling alcohol and repeatedly recrystallised2 manjistin is finally obtained in golden yellow crystals of the composition ,c,h,o7,,oh74,,co,h4 ,when a solution of manjistin in a little alcohol is mixed with water no precipitate occurs2 on then adding aluminium hydrate and long boiling an orange red lake is produced4 ,lead acetate produces a deep orange red lake when used in just sufficient quantity2 with excess a fine scarlet lake is obtained4 ,if manjit were a common article in the ,german market1 it would be used in the preparation of fine pigments with as much advantage as madder and the various madder preparations4 ,chica ,red1 ,curucuru1 ,carajuru4--,the colouring matter known under these names rarely comes into commerce2 it forms brownish-red masses which acquire a peculiar golden glitter on rubbing4 ,it is obtained from the leaves of ,bignonia chica1 a native of tropical ,america4 ,the leaves are superficially dried and then covered with water2 in the warm climate the macerated leaves soon ferment1 and a deep red powder separates at the bottom of the vessel3 this is the colouring matter2 it is dried1 made into small cakes and brought into the market4 ,chica red is only partially soluble in strong alcohol1 the residue chiefly consists of plant cells4 ,alum and stannous chloride precipitate beautiful red lakes from the solution1 which are distinguished by great permanence when exposed to light4 ,on account of the present high price1 this colouring matter has not yet obtained admission into the colour industries1 though it would be a valuable recruit4 ,chica red has been little studied2 an investigation would certainly considerably increase our knowledge of the organic colouring matters4 ,towards reducing agents it behaves in a similar manner to indigo2 in contact with caustic soda1 grape sugar and water in closed flasks1 a violet liquid is produced2 when exposed in an open vessel the violet at once changes to brown1 but if the liquid is syphoned off into dilute hydrochloric acid a pure red precipitate separates1 which is to be regarded as the pure colouring matter4 ,,chapter ,,lvii4 ,,lichen ,,colouring ,,matters4 ,many lichens contain compounds from which colouring matters can be obtained by appropriate treatment2 the colouring matters known as cudbear1 archil and litmus were formerly much more extensively used in dyeing than at present3 like so many natural colouring matters they have been replaced by coal-tar dyes4 ,the lichens which produce colouring matters live upon trees and rocks1 chiefly on the sea-shore2 the colouring matters are thus generally manufactured in places near the coast4 ,the species principally used for this purpose are ,lecanora1 ,rocella and ,usnea4 ,the lichens contain colourless compounds1 which by treatment with acid or alkalis produce orcinol4 ,in contact with moist air and ammonia1 orcinol is decomposed into water and orcein1 which is the colouring matter4 ,the lichens are treated so as to produce the largest quantity of orcinol1 which is then converted into orcein4 ,there is not space here to enumerate and describe the many compounds obtained from lichens1 only the most important can be mentioned2 these are erythric1 lecanoric and usnic acids4 ,lecanoric acid produces1 under certain conditions1 orsellic acid1 which is again changed to orcinol4 ,pure orcinol1 ,c,h,o4 ,h,o1 is a crystalline substance of sweet taste2 it is soluble in ether1 alcohol1 water1 etc4 ,in damp air containing ammonia1 orcinol gradually acquires a fine red colour1 being converted into orcein1 ,c,h,,no1 according to the following reaction3-- ,c,h,o ,,nh #c,o ,c,h,,no #b;,h,o4 ,when pure1 orcein is a brownish-red amorphous powder1 soluble in alcohol to a scarlet solution and in alkalis to a purple solution4 ,on the addition of water to the ammoniacal solution or of salt to the alkaline solution1 orcein is again separated2 this procedure may be used to completely purify the colouring matter4 ,archil is principally obtained from the lichens ,lecanora and ,rocella4 ,these lichens have a wide geographical distribution2 archil is made in ,sweden1 ,italy and ,spain4 ,it is obtained in a simple manner3 the powdered lichen is mixed with decomposing urine to a paste1 which is allowed to lie in the air until the colour has changed through red to violet2 on the average fourteen days are required for the transformation4 ,more recently the process has been made less disgusting by replacing urine by ammoniacal gas liquor4 ,when the mixture is violet all through the process is finished2 the wet mass is packed into barrels1 which are well closed to prevent it from drying4 ,the presence of alkalis accelerates the formation of orcein2 in many districts it is customary to add a little lime to the mixture of lichen and urine2 alum is also added to retard putrefaction1 which readily occurs in warm climates4 ,instead of using lichens to produce the colouring matter1 they may be extracted by boiling water1 the solution considerably evaporated and then exposed to the air with the addition of ammonia1 until the violet colouration appears4 ,slight additions of sulphuric acid give a more purple tint2 soda produces a deeper violet4 ,french ,purple is a compound of the archil colouring matter with lime1 i4e41 a lime lake4 ,this beautiful substance is obtained by treating the lichen for some minutes with ammonia1 pressing out the liquid and neutralising it exactly with hydrochloric acid4 ,the precipitate obtained consists of the lichen acids2 it is again dissolved in ammonia and the solution exposed to the air until it has become cherry red4 ,when this is the case the liquid is quickly boiled and placed in large shallow dishes1 which are kept at a temperature of #ge ,c4 until the colour is purple-violet4 ,calcium chloride is then added2 a garnet red precipitate is produced1 which1 when washed and dried1 constitutes ,french purple4 ,archil and ,french purple produce shades of great beauty and purity1 but they have little durability and are quickly altered by exposure to light4 ,they are1 therefore1 seldom used as pigments4 ,the same is the case with cudbear and litmus4 ,cudbear is a dirty purple powder with an ammoniacal odour and salt taste4 ,it is made on a large scale in ,holland4 ,it differs from archil only in containing the colouring matter in the solid form4 ,litmus is generally made from lichens of the genus ,variolaria1 though varieties of ,rocella and ,lecanora are often used4 ,it is not made in quite the same manner as archil and cudbear4 ,together with the ammonia1 potash is added to the powdered lichen4 ,the mixture is left until it has become violet1 when urine1 potash and lime are added at intervals to continue the decomposition until the colour is changed to blue and the whole mass has become a paste4 ,gypsum and lime are then added1 the mixture formed into rectangular plates1 and brought into the market1 described by a number1 according to the amount of gypsum added4 ,pure litmus should leave little solid residue when dissolved in water1 the solution should be a fine violet4 ,on account of its want of stability this colouring matter is not used in dyeing4 ,it can be used for colouring foods since it is innocuous2 but indigo carmine has much greater colouring power and at the same time gives fine shades4 ,the only use of litmus at the present time is as an indicator to decide whether a solution is acid1 neutral or alkaline4 ,in a quite neutral solution litmus is violet4 ,acids turn the solution to red and alkalis to pure blue4 ,in preparing litmus tincture regard must be given to the fact that the aqueous solution of the colouring matter is always alkaline2 acid must be cautiously added until the colour is violet1 and the least addition of acid or alkali suffices to change it to red or blue4 ,,chapter ,,lviii4 ,,red ,,wood ,,lakes4 ,red wood is obtained from species of ,csalpinia growing in ,south ,america4 ,the following varieties are distinguished3 ,fernambuco or ,brazil wood1 ,bahia wood1 ,st4 ,martha wood1 ,lima wood and ,sapan wood1 all of which contain the same colouring matter1 but in different quantities4 ,red wood comes into commerce either as thick logs of a fine red colour or as finely-rasped chips4 ,fernambuco and ,sapan woods are accounted the best varieties4 ,although the colouring matters contained in these woods have been investigated for a long time1 an accurate knowledge of them has only recently been obtained4 ,the pure colouring matter of red wood1 brasilin1 forms orange-coloured needle-shaped crystals1 soluble in water1 alcohol and ether4 ,on careful heating it partially sublimes undecomposed4 ,brasilin most probably results from the alteration of a substance contained in the inner less coloured portion of the wood2 this compound1 brasilen1 has been obtained in colourless needles2 its solution acquires a red colour on boiling1 and produces the pure colouring matter4 ,brasilin is a weak acid of the composition ,c,h,o4 ,it forms handsomely coloured compounds with most metallic oxides1 which are much used in dyeing4 ,a decoction of red wood gives with alum and soda solution a handsome lake of a pure red colour4 ,with a solution of stannic chloride it at once produces a red precipitate4 ,when a solution of potassium chromate is added to a decoction of redwood1 a dark brown precipitate separates1 which is a compound of chromium oxide with the partially altered colouring matter4 ,the decoction produces a brownish red compound with ferric oxide4 ,the decoctions of red wood contain1 in addition to the colouring matter1 a number of other substances which would injure the shade of the lake obtained from the decoction4 ,the greater portion of these substances may be separated by allowing the decoction to stand for several days1 when a dirty reddish brown mud forms at the bottom of the vessel4 ,this simple method of purification is attended with the disadvantage that1 especially in summer1 the decoction rapidly becomes mouldy4 ,this may be prevented by the addition of a little carbolic acid2 not more than #jja per cent4 of the quantity of liquid is required4 ,the foreign matters may also be separated by adding milk or a solution of glue to the decoction1 but the simpler process of allowing it to stand gives the best result4 ,from the behaviour of brasilin towards the metallic oxides1 as given above1 it follows that compounds of different colours can be made from red wood4 ,these are utilised in dyeing1 but in colour works red wood is only used for the preparation of red lakes4 ,the lakes are found in commerce under numerous names1 the most common of which are ,venetian lake1 ,vienna lake1 ,florentine lake1 ,berlin lake1 etc4 ,according as the colouring matter is combined with alumina alone or with stannic chloride in addition1 pale or deep lakes are obtained4 ,the different shades of red wood lakes found in commerce are obtained by additions of a white pigment4 ,for this purpose levigated chalk1 gypsum1 lycopodium powder1 and other white pigments light in weight are used4 ,in preparing red wood lakes the decoction should always be purified by the process mentioned above2 there is then more certainty of obtaining a bright lake4 ,it is advisable to dilute the decoction considerably with pure water before precipitating the lake2 experience has shown that brighter colours are thus obtained4 ,to #ajj parts of wood #acj to #aej parts of alum are used4 ,the latter is dissolved alone and mixed with the decoction1 the lake is then precipitated by soda solution4 ,as the lake separates the liquid becomes lighter2 portions should be taken out of the vessel in order to see when all the colouring matter is thrown down4 ,if too much soda solution is added the lake takes a violet shade4 ,a particularly fine lake is obtained from ,fernambuco wood when the extract is acidified with a weak acid1 such as acetic1 and stannic chloride used together with alum in precipitating the lake4 ,one hundred parts of rasped wood are boiled with #cjj parts of water to which acetic acid has been added2 the extract is then boiled with #acj parts of alum until the latter is dissolved4 ,to the filtered liquid #bj to #be parts of stannic chloride are added whilst stirring well1 and the lake is at once precipitated by soda solution4 ,if the lake from ,fernambuco wood does not turn out well1 a better product may be obtained by treating the lake with such a quantity of hydrochloric acid that a small portion remains undecomposed4 ,this is filtered off1 and the colouring matter reprecipitated in combination with alumina by neutralising with soda solution4 ,by adding a little ,dutch pink more orange shades of the ,fernambuco lake are obtained4 ,in this manner any intermediate shade between pure red and pure yellow can be produced4 ,it is important to lay down a standard series of shades1 and always to make pigments which exactly correspond with one of them4 ,it is not possible to make a determined shade of red wood lake or any other lake obtained from a decoction by working with accurately weighed quantities4 ,in general the result will be near the desired shade1 but only by chance will it be hit exactly4 ,this is because different samples of the dye-wood do not always contain the same quantity of colouring matter4 ,it is indeed possible with practice to estimate approximately from the colour of the decoction the shade of the lake which will be obtained from it2 but this can only be done exactly by comparing the shade of a small batch of the lake with the standard shades4 ,thus in the case of a ,fernambuco lake it will be seen by comparison with the standard shades whether the colour of the small batch is too deep1 too violet1 etc42 then by using more alum or more tin solution the defects can be removed4 ,,chapter ,,lix4 ,,the ,,colouring ,,matters ,,of ,,sandalwood ,,and ,,other ,,dye-,,woods4 ,in addition to the dye-woods in more common use1 the tropics furnish a number of woods which contain fine colouring matters1 but which are only in restricted use1 either on account of their cost or because they are not always to be bought4 ,to these belong the camwood or barwood of ,madagascar1 the ,east ,indian sandalwood1 and other woods which have not yet been used for colouring purposes even in the tropics4 ,the most commonly used of the rarer dye-woods is sandalwood1 obtained from ,pterocarpus santalinus4 ,it is garnet red in colour1 sinks in water1 and produces a fine red meal1 which rapidly becomes brown in air owing to oxidation of the colouring matter4 ,according to recent researches1 sandalwood contains two colouring matters1 one obtained from the other by oxidation4 ,only one of these1 santalin1 is known with certainty4 ,sandalwood contains about #af per cent4 of santalin1 which when pure forms a crystalline powder1 differing from other wood colouring matters in being almost insoluble in water4 ,up to the present it has only been used in dyeing to obtain handsome and fast red colours4 ,from it very bright lakes may be obtained1 which may be used equally as well as the red wood lakes4 ,the aluminium and tin lakes are especially fine4 ,the extract of sandalwood is obtained by boiling very fine chips with water1 then adding alcohol and leaving the mixture4 ,when stannic chloride or alum1 or a mixture of the two1 is added to the solution of the colouring matter a red precipitate is produced which1 after washing and drying1 furnishes a bright red lake4 ,,chapter ,,lx4 ,,blue ,,lakes4 ,indigo4--,the colouring matter of the indigo plant is distinguished by great resistance to the action of light1 air1 and chemical reagents4 ,it is thus often cited as a particular example of a fast and durable colour4 ,it is very largely used in dyeing1 and in certain combinations is important as a painters' colour4 ,indigo comes into commerce in a great variety of qualities1 all imported from the tropics1 in which alone the plant grows4 ,the principal varieties are ,indian1 ,java1 ,egyptian1 ,american and ,african1 but in these merchants make numerous subdivisions which are often to be distinguished from one another only by very small differences4 ,good indigo1 whatever its source1 has the following characteristics3 ,it appears in almost cubical lumps1 but may also form irregular masses4 ,the lumps must show a small specific gravity1 a higher might be caused by intentional additions of sand or earth4 ,it is without taste and smell1 and the colour of the finest varieties is not particularly bright1 but when rubbed with a hard substance1 or even by the pressure of the finger nail1 it acquires a peculiar coppery lustre1 which is the more intense the purer the indigo1 and is thus regarded as a common test of quality4 ,indigo is completely insoluble in almost all solvents2 in hot oils a small quantity dissolves1 which again separates on cooling4 ,the following are the principal signs by which the quality of indigo is recognised in commerce3 ,it forms a dull-coloured1 loose1 light mass of earthy nature1 a fresh fracture of which has a completely uniform appearance4 ,it must be so porous that it at once adheres to the tongue4 ,uniformity of colour1 light weight and fine fracture are the most important of the practical tests for good indigo4 ,the composition of indigo is well known2 we shall glance rapidly over the most important substances which occur in indigo in varying quantity4 ,the ,constituents of ,indigo4--,indigo contains the following compounds3 ,indigo blue1 indigo red1 indigo brown1 indigo gluten1 water and salts4 ,the single important constituent for the purposes of the colour maker is indigo blue1 or indigotin4 ,pure indigo blue can be obtained from indigo only by a lengthy process4 ,the indigo is boiled in turn with dilute sulphuric acid1 caustic potash1 and strong alcohol4 ,the gluten dissolves in the acid1 the indigo brown in the potash solution1 and the indigo red in the alcohol4 ,by these operations indigo blue is finally obtained in a state of almost complete purity1 it now contains only a small quantity of inorganic substances4 ,the quantity of pure indigo blue obtained in this manner varies1 according to the purity of the indigo employed1 from #bj to #ge per cent4 ,indigo blue can also be obtained by direct sublimation from indigo1 but the yield is very small1 since a large proportion is decomposed by dry distillation4 ,the most important constituent of indigo1 indigo blue1 can be obtained in quite pure form by a peculiar chemical process4 ,when finely powdered indigo is brought in contact with a reducing agent in the presence of a strong alkali1 the indigo blue is converted into indigo white1 which forms a soluble compound with the alkali1 which compound is stable only so long as it is protected from the action of the air4 ,in contact with air indigo white is at once oxidised1 and is reconverted into indigo blue1 which separates from the liquid as a soft deep blue powder2 after washing and drying it is quite pure4 ,whilst sublimed indigo blue forms needles with a splendid coppery lustre1 when precipitated from a solution of indigo white by the action of oxygen it is obtained as an amorphous powder1 which acquires the coppery lustre only when rubbed4 ,the process of the reduction of indigo blue by a reducing agent in the presence of a strong base is not only of theoretical interest1 but is largely used in practice4 ,fabrics are generally dyed with indigo by immersing them in a solution of indigo white 7known as the indigo vat71 and then exposing them to the air4 ,the oxidation of the indigo white then takes place on the fibre1 upon which the indigo is deposited in a very finely divided form2 the blue colour is not immediately formed1 there is an intermediate green stage4 ,indigo is used principally in dyeing4 ,certain of its compounds are used as pigments2 the starting point in the preparation of these is a compound of indigo blue with sulphuric acid4 ,when indigo is treated with sulphuric acid1 according to the duration of the reaction and the temperature at which it is performed1 either the monosulphonic acid or disulphonic acid is formed4 ,the reactions proceed according to the following equations3-- ,c,h,n,o ,h,,so ,h,o ,c,h,n,o4,,hso ,c,h,n,o #b;,h,,so #b;,h,o ,c,h,n,o47,,hso7 ,when indigo is treated with eight times its weight of strong sulphuric acid1 and the solution considerably diluted1 indigotin monosulphonic acid separates as a fine blue precipitate1 which dissolves with difficulty in water and alcohol1 and is insoluble in dilute acids4 ,in order to obtain the disulphonic acid #a part of indigo is digested with #ae partsof sulphuric acid at #ej to #fj ,c4 for several days4 ,if fuming sulphuric acid be used the solution is effected in a shorter time4 ,the solution is diluted with a large quantity of water1 when a little monosulphonic acid separates2 the clear solution is drawn off and a piece of wool immersed in it4 ,the sulphonic acid is soon fixed by the animal fibre2 the wool is washed with water and then treated with a solution of ammonium carbonate1 when a deep blue solution of ammonium indigotin disulphonate is produced4 ,this solution is evaporated at a low temperature and treated with strong alcohol1 which leaves a residue of the pure disulphonate1 which is dissolved in water1 the solution precipitated with lead acetate and the lead indigotin disulphonate treated with sulphuretted hydrogen4 ,the colourless solution becomes blue on evaporation2 finally pure indigotin disulphonic acid is left as an amorphous deliquescent mass4 ,the solution became colourless owing to the reducing action of the sulphuretted hydrogen2 when this was driven off by heating the blue colour reappeared4 ,,chapter ,,lxi4 ,,indigo ,,carmine4 ,indigo carmine is used in the laundry1 for blue inks and as an artists' pigment2 in chemical composition it is a mixture of the sodium salts of the two indigotin sulphonic acids described in the last chapter4 ,in working on the large scale it is particularly important that the indigo should be finely powdered and completely free from moisture4 ,it is a laborious process to powder indigo in mortars1 and loss always occurs through the formation of dust4 ,thus when large quantities of indigo are to be powdered it is advisable to use rotating cylinders4 ,these are strong casks bound with iron hoops and provided with a well-fitting slide1 through which the indigo and a number of iron balls are introduced4 ,when these casks are rotated for a sufficient length of time the indigo is converted into the finest powder without any loss4 ,indigo ,mills4--,special mills have been designed for powdering indigo4 ,they may be advantageously employed for other materials also4 ,the construction of a well-designed colour mill is represented in ,fig4 #cf1 in which indigo may be very finely powdered without loss4 ,it consists of a cast-iron pan1 which can be closed by a well-fitting cover4 ,through the cover passes the axis of the rotating part1 which is moved by the bevel cog-wheels and the handle4 ,above the cog-wheel fastened to the axis is a cross piece carrying heavy balls at the ends1 which serve to keep the motion regular4 ,in the interior of the pan four vertical rods are attached to the axis2 these are placed at such a distance that they drive before them the heavy balls in the circular depression of the pan4 ,the action of this apparatus is very simple4 ,after the introduction of the indigo through an opening in the cover the axis is put in rotation1 the vertical rods attached to the axis roll the balls before them1 and thus break up the lumps of indigo4 ,the larger pieces of indigo oppose considerable resistance to the rotation1 which should at first be slow4 ,when the lumps have been broken down the speed of rotation can be considerably increased4 ,after the operation has been continued for a sufficient length of time the indigo is converted into an impalpable powder4 ,illustration3 ,,fig4 #cf4 ,to facilitate the removal of the ground indigo1 an arm carrying a brush of fine hair should be attached to the horizontal arm of the axis4 ,if this brush is placed so that it sweeps the bottom of the circular depression in which the balls move1 all the indigo powder in this depression will be carried in one direction4 ,in the depression is an opening closed by a slide during the grinding4 ,the brush expels the ground indigo through this opening when the axis is slowly rotated2 it is collected in a vessel below4 ,the larger and heavier are the balls in this mill1 the more rapidly will a given quantity of indigo be powdered1 and the greater will be the power required to drive the machine4 ,by means of a pulley on the axis of the cog-wheel the mill can be driven by mechanical power4 ,the powdered indigo is exposed for a long time to a temperature of #abj ,c41 to completely dry it4 ,for this purpose it is spread out on sheets of tin plate in a thin layer and heated so long as a test portion decreases in weight4 ,the powder whilst still warm is at once mixed with the sulphuric acid2 #de kilogrammes of fuming sulphuric acid and #a kilogramme of ordinary sulphuric acid 7#ff ,b7 are used to #a kilogramme of indigo4 ,heat is developed in the operation1 and in order to prevent the indigo from being charred the vessel in which the mixture is made is placed in a larger vessel filled with cold water4 ,the mixture is stirred with a glass spatula until it is quite uniform4 ,the vessel is then maintained at a temperature of about #ej ,c4 7not more than #fj ,c47 for #g to #h days4 ,after the lapse of this time the indigo is completely dissolved1 and the vessel is found to contain two distinct layers1 the upper fluid and the lower a paste4 ,the contents are mixed with cold water1 about #aj kilogrammes of water to #a kilogramme of indigo4 ,a solution of #aj kilogrammes of common salt is then added in small quantities at a time4 ,indigo carmine is insoluble in strong salt solutions2 it separates as a deep blue precipitate1 which is allowed to settle and then filtered4 ,if it were attempted to wash out the remainder of the salt solution retained by the carmine1 a considerable quantity of the latter would dissolve as soon as the salt solution became diluted to a certain extent4 ,to avoid such loss the precipitate is allowed to drain completely on the filter1 and then spread out upon bricks1 which absorb the water1 so that the carmine forms a stiff paste4 ,indigo carmine1 from which the salt has not been completely washed out1 dries completely when exposed to the air4 ,this may be prevented by the addition of glycerine1 which is a very hygroscopic substance1 and so keeps the carmine always moist1 thus preventing the crystallisation of the salt4 ,indigo carmine easily dissolves in water to a deep blue liquid4 ,it has tremendous colouring power1 in which respect it is only equalled by genuine cochineal carmine4 ,as mentioned above1 indigo carmine is extensively employed in the manufacture of ink4 ,the so-called alizarin inks show a very pale colour as they flow from the pen1 and only become deep black after some time4 ,to make these inks equally visible at the first indigo carmine is added1 by which they acquire a handsome blue colour4 ,indigo carmine may also be made by digesting #a part of dry powdered indigo for #bd to #cf hours with #d parts of strong sulphuric acid1 diluting with water1 quickly filtering through a linen cloth1 and adding #d parts of common salt4 ,the precipitate is then collected and dried on gypsum or clay plates4 ,blue ,lake4--,when alum is added to a solution of indigo sulphonic acid1 and then soda solution1 a blue precipitate is formed1 which1 when dry1 resembles ,chinese blue in appearance4 ,it is used in painting4 ,this indigo blue lake is superior to other blue lakes by reason of its fastness to light4 ,it is rather dear1 and is mixed with starch1 so that it may be sold at low prices2 the mixture is formed into slabs and sold as 0new blue10 0indigo extract10 etc4 ,it is chiefly used in the laundry4 ,under various names a number of blue pigments are sold consisting of ordinary qualities of indigo mixed with ,prussian blue1 smalts1 chalk1 etc4 ,these are used in the laundry1 and also for distempering4 ,,chapter ,,lxii4 ,,the ,,colouring ,,matter ,,of ,,logwood4 ,the wood of ,hmatoxylon campechianum 7logwood71 a native of ,south ,america1 comes into the market in small logs of a red colour2 it contains a colouring matter whose properties are fairly well known4 ,before the discovery of the coal-tar dyes logwood was a most important colouring material2 by means of it red1 blue1 violet and black colours can be obtained4 ,at present it still plays an important part in dyeing4 ,many varieties of logwood come into commerce4 ,the most important are ,campeachy wood1 ,honduras1 ,jamaica and ,st4 ,domingo logwood2 the first named is the best1 and the last the poorest quality4 ,to facilitate the extraction of the colouring matter by water logwood is frequently sold in chips4 ,many dye-wood grinders moisten logwood with lime water2 this gives the powder a better colour1 but diminishes the yield of colouring matter4 ,since the only useful constituent of logwood can be extracted by treatment with water1 and the wood is only a carrier of the colouring matter1 which is only useful for fuel when exhausted1 logwood extracts are largely used in place of the wood4 ,the extracts are black resin-like masses1 which easily dissolve in water2 they are very hygroscopic1 and should therefore be kept in closed vessels4 ,logwood ,extract4--,solid extracts can be obtained from the majority of dye-woods4 ,the use of these is a great convenience to the dyer and the colour maker2 the method by which extracts are made is therefore briefly described4 ,dye-wood extracts can be made on the small scale1 by washing out the finely divided wood until soluble matters are no longer taken up by the water1 and cautiously evaporating the united extracts4 ,when the extract becomes concentrated the greatest care must be taken to prevent burning on the bottom of the vessel2 a burnt extract is always darkened by the presence of products of decomposition1 and its solution has a brown colour4 ,apart from this1 the complete extraction of the colouring matter requires much time1 and such dilute solutions are produced that they cannot be evaporated1 but at the best can be used in the place of water to extract fresh quantities of wood4 ,when steam is utilised to extract dye-woods these defects are removed4 ,a burnt extract is not to be feared1 and a small quantity of water is sufficient to extract the colouring matter completely4 ,the apparatus illustrated in ,fig4 #cg is very suitable for the extraction of dye-woods1 and in general for obtaining vegetable extracts4 ,the extraction vessel is pear-shaped1 its two hollow axes move in hollow bearings4 ,thus it may be turned upside down1 and steam and water can be introduced into the interior through the axes1 which are connected with the pipes1 ,e1 ,w1 and ,r4 ,the opening at the pointed end of the pear is closed by the screw1 ,s2 through it the substances to be extracted are introduced4 ,in the lower portion of the vessel is a sieve upon which the materials are spread out4 ,the opening of the pipe connected with ,e and ,w is below the sieve4 ,illustration3 ,,fig4 #cg4 ,the process is commenced by introducing the materials through the upper opening1 fastening the cover down steam-tight by the lever1 ,b1 and the screw1 ,s1 and then running in water through ,w until it flows out through the lower of the two narrow pipes which are shown somewhat paler in the shaded portion of the drawing4 ,all the taps are then closed with the exception of that on the upper of the two small pipes4 ,by opening the cock on ,r steam is led in4 ,as a rule1 steam at a low pressure is used1 not more than half an atmosphere4 ,the contents begin to boil in #ae to #cj minutes1 steam then issues from the open tap4 ,according to the nature of the material to be extracted1 boiling is continued from #dj to #fj minutes4 ,the side tap is then closed1 and the tap on the pipe ,e opened4 ,the pressure of the steam now forces the liquid up the pipe ,e2 the pressure of half an atmosphere is sufficient to raise it about #d metres4 ,in this way it can be forced into a tank above4 ,the rest of the liquid can be run off through the cock1 h1 at the bottom of the vessel4 ,when quite empty the cover is taken off1 the vessel turned over1 and the solid residue removed4 ,one extraction of dye-woods is not sufficient to remove the whole of the colouring matter2 in most cases the wood is treated a second time before the apparatus is emptied4 ,even then some quantity of colouring matter remains in the wood4 ,the twice extracted wood is brought into a tub filled with water1 and the solution resulting from the long contact of the water with the wood is used in the next operation to extract new quantities of wood instead of fresh water4 ,the dimensions of the extraction vessel vary according to the size of the works4 ,a large apparatus costs not much more than a smaller1 since in both cases the labour is the same1 so that it is advisable to use a large apparatus4 ,when the copper extraction vessel is made to have its greatest diameter about #a metre1 it can be charged with about #ej kilogrammes of rasped wood at once4 ,illustration3 ,,fig4 #ch4 ,the extraction apparatus of ,hnig and ,o4 ,reinhard is shown in ,fig4 #ch4 ,it can be turned over by means of cog-wheels4 ,in the cover are an air valve1 e1 and safety valve1 f2 below the cover is a coil1 k1 fed with cold water from c4 ,in the extraction1 by opening the valve v1 steam enters through a at l2 it is condensed by the cooled cover1 the condensed water flows through the material on the sieve1 and collects in the space ,b4 ,after some time v and z are opened1 the liquid is then boiled by the steam in the coil1 s4 ,steam rises through the material1 is condensed on the cover1 and again drops down4 ,at the end of the operation the solution is drawn off through the cock1 h4 ,illustration3 ,,fig4 #ci4 ,kohlrausch's ,process for ,obtaining ,concentrated ,extracts of ,colouring ,matters and ,tannins4--,when dye-wood or tan-bark is continually brought in contact with fresh quantities of water1 after some time it is exhausted2 if the solution containing a certain quantity of the soluble matters is brought in contact with fresh material not yet extracted1 it takes up more soluble matter1 and thus becomes more concentrated4 ,the substances contained in tan-bark are very soluble in water1 so that by the appropriate treatment of a certain quantity of bark1 divided amongst different vessels1 with a certain quantity of water1 on the one hand the bark can be exhausted completely1 and on the other very concentrated solutions 70bark extracts07 obtained4 ,the process patented by ,kohlrausch is based upon the principles just stated2 it can be used to obtain tannin extracts from tan-bark and colour extracts from dye-wood4 ,in this process the raw materials need not be finely ground in order to be completely extracted2 they may be used in large pieces4 ,it will be understood from the following description that fine bark meal or finely-rasped dye-wood could not be worked4 ,illustration3 ,,fig4 #dj4 ,the apparatus consists of a number of #aj to #bj extractors connected together1 also with a water tank above1 and with a boiler4 ,a single extractor is represented in section in ,fig4 #ci1 together with the necessary pipes and valves by which it is connected with the neighbouring extractors1 the water tank and the boiler4 ,fig4 #dj is a plan of three extractors connected together4 ,the extractors consist of wooden or copper vessels1 slightly conical in shape1 and of sufficient strength to resist the pressure of one atmosphere4 ,on the top is a copper dome closed by a lid1 through which the raw material is introduced1 and also steam and water4 ,immediately above the bottom is an opening1 also closed by a screw1 which serves to remove the exhausted materials4 ,an inclined sieve is placed at some distance above the bottom2 upon this the material rests4 ,the extract collects below the sieve1 and may be run off by the pipe or brought into another extractor4 ,all the metallic portions of the apparatus which come in contact with the liquid must be made of a metal such as copper1 which does not act upon tannic acid4 ,iron cannot be used2 it forms deep bluish or greenish black compounds with tannic acid1 which would cause the extract1 instead of being pale and clear1 to resemble ordinary writing ink4 ,in a range of #aj extractors the process is carried out in the following manner3 ,the extractors numbered #a to #aj are filled with bark or dye-wood and closed2 #a is then filled with water from the tank1 and heated by steam to #ej to #gj ,c4 ,after some time the contents of #a are forced into #b1 and #a is again filled with water1 so that the material in #b is in contact with the solution from #a1 whilst the material in #a is warmed with a fresh quantity of water under pressure2 the extract in #b is transferred to #c1 that in #a to #b1 and #a is again filled with water1 and so on4 ,finally from #aj a very strong extract of tannin or colouring matter is obtained4 ,the quantity of water required to fill one extractor has come ten times in contact with fresh bark or dye-wood4 ,the material in #a has been treated with ten times the quantity of water2 it is now exhausted1 and is replaced by fresh material4 ,the sequence of the vessels is now changed4 ,the original extractor #b is to be regarded as #a1 and #a as #aj4 ,after ten repetitions the original order of the extractors re-obtains4 ,ninety-nine per cent4 of the tannic acid of bark is extracted in this way4 ,the concentrated extracts obtained in this apparatus should be mixed with a little carbolic acid to prevent decomposition2 they may then be filled into barrels4 ,the extracts may also be so far concentrated by evaporation that they become syrupy4 ,the tannins are readily decomposed2 they would be considerably altered if their solutions were evaporated in open vessels4 ,the extracts are therefore evaporated at a very low temperature under diminished pressure in vacuum pans1 which are now much used for the concentration of solutions of substances1 such as sugar1 which would be injured by heating above a certain temperature4 ,essentially1 a vacuum pan is a thick-walled copper vessel1 in which the liquid is warmed by a steam coil4 ,it is connected with an air pump1 which exhausts the air at the commencement of an operation1 and afterwards steam4 ,the liquid is thus constantly evaporated under a low pressure4 ,extracts of tan-bark and dye-woods boil briskly under these conditions at temperatures below #fj ,c41 at which no decomposition of the tannin or the colouring matter is to be feared4 ,when the solutions have been evaporated to the proper strength they are run off directly into the packages in which they are to be despatched1 and in which they become syrupy or even solid masses1 according to the extent to which the evaporation has been driven4 ,the packages should be at once closed2 the thick extract is thereby most simply and safely prevented from decomposing1 to which risk it would be exposed by the access of mould spores4 ,if these were already present in the barrels or were communicated to the extract by the air1 they would either be killed by the hot liquid or would be prevented from developing for a long time4 ,in the closed vessels the extracts remain completely unaltered4 ,the concentrated solution of colouring matter obtained by extracting dye-woods in the above apparatus can be at once used1 after dilution1 in the preparation of lakes and in dyeing1 but it is not an extract in the ordinary commercial sense of the term1 i4e41 it does not solidify on cooling4 ,to obtain solid extracts the concentrated solutions must be evaporated2 concentration with fire heat would be attended with danger to the quality of the extract1 steam heat is therefore used4 ,the liquid to be evaporated is brought into shallow steam-jacketed pans1 in which the operation is continued until the liquid solidifies into a resin-like mass when dropped on cold stone4 ,when sufficiently evaporated the extract is allowed to solidify1 broken into lumps1 and these packed whilst still warm into barrels lined with paper4 ,the lining is necessary on account of the hygroscopic nature of the extracts2 when they are exposed to the air they absorb water and form a viscous fluid which soon becomes mouldy4 ,a properly prepared dye-wood extract should dissolve in water without residue1 and the solution when largely diluted should show the characteristic colour of the wood with no brownish shade1 and when the colouring matter is precipitated from such a solution by a metallic salt the residual solution should be almost colourless4 ,if the extract dissolves incompletely in water and the solution is brown after precipitation of the colouring matter1 the extract has been burnt in the evaporation4 99 99 99 99 99 ,logwood and logwood extract contain two substances of importance in dyeing and colour making4 ,these are hmatoxylin and hmaten4 ,hmatoxylin is found in logwood in greatest amount shortly before the wood is cut4 ,when pure it forms colourless crystals of a peculiar sweet taste1 which are soluble in cold water with difficulty1 more easily in hot1 and readily soluble in alcohol or ether4 ,the composition of hmatoxylin is expressed by the formula ,c,h,o4 ,hmatoxylin is not a colouring matter4 ,it is important because from it is obtained the essential colouring matter of logwood--hmaten4 ,when a trace of ammonia is added to the colourless solution of hmatoxylin1 the liquid at once becomes dark red owing to the formation of hmaten4 ,when a larger quantity of ammonia is added the liquid acquires a deep red colour1 and then contains only hmaten 7its ammonia compound71 which is formed according to the following equation3-- ,c,h,o ,,nh ,o ,c,h,o4,,nh #b;,h,o4 ,to obtain hmaten in the pure state it is then only necessary to add sufficient acetic acid to decompose the hmaten ammonia compound4 ,hmaten separates as dark violet crystals1 which readily dissolve in water and alcohol2 its aqueous solution gives blue precipitates with the majority of the metallic salts4 ,this behaviour of hmatoxylin towards ammonia explains the increase in colouring power of logwood1 which has been exposed for a long time to the action of the air in the rasped state4 ,through the action of the ammonia in the air a larger quantity of the hmaten ammonia compound has been formed4 ,it has been proposed to facilitate the formation of this ammonia compound by moistening rasped logwood with a very dilute glue solution and allowing it to lie in the air4 ,this process can only have the object of utilising in the formation of hmaten the ammonia resulting from the decomposition of the glue1 but in this decomposition deep-seated reactions occur1 which might affect the hmaten itself4 ,it thus appears more suitable to effect the formation of hmaten by the direct use of ammonia4 ,this can be done with little cost by watering heaps of rasped logwood with ammonia and repeatedly shovelling about the wood so that it comes into contact with the air4 ,the author has found that the conversion of hmatoxylin to hmaten is very complete in this process2 care should be taken not to make the layer of rasped wood too deep1 and to take its temperature frequently4 ,in the transformation of hmatoxylin to hmaten the temperature rises1 the rise might be injurious if it proceeded too far4 ,thus if the temperature of the interior of the heap is found to be high the wood should be turned over4 ,the solution of the logwood colouring matter produces handsome lakes1 all of which have1 however1 the inconvenient property of acquiring an ugly grey colour on long standing4 ,the finest and most durable of the logwood lakes is known as violet lake1 which is made with alumina salts4 ,the best result is obtained when a solution of aluminium acetate1 obtained by precipitating alum with lead acetate1 is mixed with a logwood decoction or a solution of logwood extract4 ,the precipitate is pale or deep violet according to the amount of aluminium salt added4 ,after drying to a certain point at a gentle heat it can be mixed with gum solution to a paste1 which is then completely dried4 ,logwood is most valuable in dyeing and calico printing1 in which it serves to produce a fine and durable black4 ,when potassium chromate is added to a decoction of logwood a deep black liquid results1 which can be used as a good and cheap writing ink4 ,if somewhat stronger solutions are used a greenish precipitate first separates1 which soon acquires a pure black hue2 it is the chromium lake of hmaten4 ,this compound is very durable and is largely used in dyeing to produce fast blacks4 ,the black precipitate might be dried and used as an artists' black pigment if the carbon blacks were not cheaper and more durable4 ,,chapter ,,lxiii4 ,,green ,,lakes4 ,the yellow colouring matters produce green compounds with copper salts4 ,these are important because they can be produced without great cost1 and are not as poisonous as the arsenic pigments1 although copper compounds are far more poisonous substances than should be used for certain purposes4 ,their employment might be attended with danger if used to colour children's toys and pictures4 ,these green copper lakes are simply made by adding copper sulphate solution1 free from iron1 to a hot decoction of yellow berries or weld until the liquid is emerald green1 and then adding caustic soda solution in small quantities to precipitate the lake4 ,the temperature of the liquid should not be more than #ej to #fj ,c4 when the caustic soda is added4 ,it has been maintained that these lakes turn out well only when the precipitation is so conducted that the residual liquid is quite colourless4 ,the author has1 however1 found it more satisfactory to discontinue the addition of caustic soda when the liquid is somewhat coloured1 since when the precipitation is complete other substances besides colouring matter may be precipitated4 ,chlorophyll4--,all the higher plants contain the same green colouring matter--chlorophyll4 ,it has a very fine shade1 is fairly fast1 and the raw material from which it is produced is to be obtained at nominal cost4 ,special attention should1 therefore1 be paid to this colouring matter4 ,chlorophyll is very easily obtained4 ,grass of a good green1 green leaves1 or any green portion of a plant is allowed to stand with weak caustic soda solution in a large vessel for twenty-four to thirty hours4 ,the liquid is poured off1 brought to the boil for a moment1 at once filtered and neutralised with hydrochloric acid4 ,the chlorophyll1 which has been dissolved by the caustic soda1 is then thrown down as a grass green precipitate2 after washing and drying it can be used as a pigment4 ,a chlorophyll lake can be obtained by dissolving the colouring matter in caustic soda and adding alum solution4 ,the green precipitate is a compound of chlorophyll and alumina4 ,tschirch gives the following method for obtaining chlorophyll3 ,green leaves 7grass71 not containing tannin1 are extracted with boiling alcohol1 the extract cooled1 filtered and evaporated until a sticky mass remains4 ,this is washed with hot water until the washings are colourless1 and the residue extracted with cold alcohol4 ,the solution is evaporated to half its volume1 the separated crystals are dissolved in alcohol1 and the solution heated on the water bath with zinc dust4 ,a deep emerald green solution with a red fluorescence is obtained2 it can be preserved unaltered for a long time in blue glass bottles4 ,it retains its colour in diffused daylight also for a lengthy period4 ,a beautiful green chlorophyll lake is obtained by boiling this solution with the solution of an aluminium salt and precipitating with soda4 ,unfortunately1 the lake is not fast4 ,the chlorophyll solution obtained by this process is quite innocuous1 and is well adapted for colouring liqueurs and confectionery4 ,sap ,green4--,this lake1 also known as bladder green1 is obtained from unripe yellow 7,persian7 berries4 ,it can be used as a water colour1 but not in oil painting4 ,this pigment differs from the ordinary yellow berry lake in colour and chemical composition2 the yellow lake is a compound of xanthorhamnin with the metallic oxide1 whilst sap green contains an uncrystallisable bitter substance1 rhamnocathartin4 ,the lake is obtained from yellow berries which are not quite ripe4 ,they are broken up and left in a warm place4 ,the mass soon ferments2 after about ten days it is pressed4 ,four parts of the liquid are then mixed with #je part of alum and #je part of potassium carbonate4 ,the salts are dissolved in boiling water1 and the solutions added to the hot sap4 ,the mixture is then evaporated to the consistency of a thick syrup1 which is generally packed in animal bladders1 hence the name of 0bladder green04 ,some care is necessary in the evaporation to prevent the burning of the soft mass on the bottom of the vessel4 ,if the evaporation is carried somewhat further the mass solidifies on cooling2 it is then black1 and only transmits green light at the edges4 ,the use of potash in preparing sap green is attended with the disadvantage that the hygroscopic nature of the salt prevents the colour from drying4 ,if magnesia is used instead of potash the lake dries far more rapidly1 but has much less covering power4 ,sap green is principally used for colouring paper and leather4 ,orange-coloured lakes also can be obtained from yellow berries by precipitating the decoction with stannic chloride4 ,these lakes are not directly employed1 but are produced immediately upon the fabric in dyeing4 ,chinese ,green1 ,lokao4--,under this description a green lake has recently been imported from ,china4 ,it is a valuable pigment4 ,chinese green is sold in flat cakes1 which are blue1 with a green or violet lustre4 ,the powdered lake is pure green and partially soluble in water2 it contains colouring matter1 water and inorganic matter consisting chiefly of clay and lime4 ,chinese green is made in ,china in a peculiar manner from the twigs of certain species of ,rhamnus4 ,according to report1 the bark is boiled with water and a cotton cloth immersed in the decoction4 ,the fibre fixes a colourless substance which becomes green on exposure to air4 ,the cotton is repeatedly dipped into the decoction until it has absorbed a large quantity of colouring matter4 ,it is then washed with cold water and boiled with water upon which cotton yarn is laid4 ,the colouring matter suspended in the liquid adheres to the yarn1 which is washed with a little cold water1 and the colouring matter then collected upon paper and dried4 ,if ,chinese green is really made by this process1 it is not a lake but a vegetable colouring matter1 to which clay has been added to increase its weight or to make it plastic4 ,very fine lakes can be obtained from ,chinese green by dissolving it in a solution of alum1 and adding soda solution4 ,when ,chinese green is dissolved in acetic acid and ammonium chloride and a zinc salt added1 a blue lake is produced on the further addition of sodium acetate4 ,a bluish violet lake is obtained by treating ,chinese green with a strong reducing agent and adding calcium acetate4 ,charvin's ,green4--,the very high price at which genuine ,chinese green was sold whilst it was still a novelty1 gave rise to attempts at imitation4 ,charvin1 of ,lyons1 succeeded in producing a pigment from ,rhamnus which has the characteristic property of ,chinese green of retaining its colour in artificial light4 ,he plunged the bark of common buckthorn into boiling water1 boiled for a few minutes1 and allowed the whole to stand for twenty-four hours4 ,lime water was added to the brown liquid1 which was then exposed to the action of the air in shallow vessels1 when it gradually turned green and deposited a green precipitate4 ,when this appeared1 the liquid was brought into glass vessels and potassium carbonate solution added so long as a precipitate resulted1 which after drying had all the properties of genuine ,chinese green4 ,although for some time ,chinese green was a very fashionable colour1 its use is now almost discontinued1 although it can be used with advantage as an artists' pigment1 and its preparation by ,charvin's method is neither difficult nor specially costly4 ,,chapter ,,lxiv4 ,,brown ,,organic ,,pigments4 ,asphaltum is found in large deposits in several regions of the earth4 ,it is a compound of carbon and hydrogen1 and varies in appearance from cobblers' wax to tar4 ,asphaltum is of organic origin and is closely related to the mineral oils4 ,among the pigments usually employed by artists asphaltum plays an important part2 it produces very warm shades between brown and deep black4 ,the preparation of asphaltum for artists' use is very simple4 ,good uniform lumps1 free from sand and other impurities1 are coarsely powdered and mixed with a solvent in a well-stoppered flask4 ,asphaltum readily dissolves in essential oils1 and also1 though with more difficulty1 in fatty oils4 ,it dissolves slowly at the ordinary temperature1 but quickly on warming4 ,on account of the inflammability of the essential oils generally used1 certain precautions must be taken4 ,the asphaltum is mixed with turpentine in a large flask which is well closed and heated by hot water4 ,in a short time a viscous mass is formed which is mixed with the solvent by shaking4 ,asphaltum may also be prepared1 without dissolving1 by powdering and grinding with oil exactly as a mineral pigment4 ,sepia4--,this brown pigment has a warm hue which is not readily surpassed4 ,it is an animal product2 the cuttle-fish1 a species of cephalopod which abounds in all warm seas1 produces a peculiar colouring matter which is stored in a sac1 commonly called the ink-bag4 ,it is used by the animal for protection1 when pursued it ejects the contents of the bag1 and thus makes the surrounding water so dark that it is enabled to escape4 ,sepia is made almost exclusively in ,italy4 ,the contents of the ink-bag are quickly dried1 and then rubbed with strong caustic lye to a thick pulp4 ,more caustic lye is then added1 and the mixture heated almost to boiling2 from the filtered solution sulphuric acid precipitates the pure colouring matter4 ,as one of the most handsome brown pigments1 sepia is largely used1 but unfortunately it can only be used as a water colour4 ,on account of its cost1 sepia is frequently imitated4 ,vegetable substances are charred1 extracted1 and the extract concentrated until it solidifies on cooling2 it is then finely powdered1 made into a paste with gum ,arabic or tragacanth1 and formed into cakes4 ,all such imitations are1 however1 so imperfect that they are at once recognised4 ,on comparison with genuine sepia1 none of them is found to possess the warm shade peculiar to sepia4 ,brown colouring matters can be obtained by heating all soft portions of plants4 ,the products have a deep brown shade in consequence of the high proportion of carbon they contain4 ,when the young twigs of soft woods are exposed in closed cylinders to a temperature of about #cjj to #djj ,c41 and the residue powdered1 colours ranging from a dark rust brown to almost pure black are produced4 ,the higher the temperature employed the more nearly the shade approaches to black4 ,parts of plants which contain sugar or similar compounds become deep brown at comparatively a low temperature4 ,the colour1 which varies from brown to hyacinth red1 is due to caramel4 ,this substance is produced when coffee1 beetroot1 or chicory root1 all of which contain a large proportion of sugar1 are heated4 ,such pigments are little used2 they cannot be ground with oil1 and in water can rarely be mixed with other colours4 ,,chapter ,,lxv4 ,,sap ,,colours4 ,under the designation of 0sap colours0 several pigments are brought into the market in the condition in which they are ready for immediate use in printing4 ,the term is practically restricted to lake pigments which form a transparent layer when dry1 thus the sap colours may be defined as dissolved lakes mixed in a viscous medium1 such as thick gum solution4 ,in general the sap colours are not much used1 since when wetted with water they again dissolve1 which is not the case with pigments ground in oil4 ,yet for certain purposes they are commonly used1 as in the manufacture of playing cards4 ,in the manufacture of these pigments only colouring matters soluble in water can be used1 the number of which is restricted4 ,according to a particular method a tin lake is first made1 which is decomposed by a strong base1 such as ammonia1 so that the colouring matter again goes into solution4 ,the very deep coloured liquid is then mixed with a thickener and an indifferent white substance such as flour or starch1 formed into thin sticks1 and sent into the market4 ,a decoction of buckthorn berries is used for the yellow sap colours4 ,it is considerably evaporated1 and then mixed with #b to #c per cent4 of alum1 after which starch paste or gum ,arabic and sugar are added in proper quantity1 and the mixture evaporated at a low temperature so that it is not browned by over-heating4 ,when a tin lake is employed in the preparation of a sap colour1 the precipitate obtained by adding stannic chloride to the solution of the colouring matter is washed1 and1 without drying1 treated with a small quantity of strong ammonia2 generally about #aj per cent4 of the volume of the precipitate is sufficient to dissolve the lake4 ,it is always better to leave a portion of the precipitate undissolved than to modify the colour by the addition of too much ammonia4 ,the precipitate should be dissolved in a glass vessel2 the liquid is well stirred1 covered over1 and allowed to stand until the undissolved portion of the precipitate has settled4 ,the ammoniacal solution of the colouring matter cannot be concentrated by evaporation4 ,thus1 before the precipitate is dissolved it must be well freed from water by long draining4 ,to give the solution the proper consistency about an equal quantity of thick gum solution is added1 and then sufficient starch to form a paste which can be rolled into thin sticks1 which are then dried upon boards at a gentle heat4 ,sap colours are made in exactly the same way from any other colouring matter adapted to the purpose4 ,in using these colours it is simply necessary to bring them into water2 if they contain only gum and sugar in addition to colouring matter they completely dissolve1 but if they contain starch the solution is incomplete4 ,as a rule starch is only added to give the colour the consistency requisite for printing4 ,red sap colours can be made either from red wood lake or from cochineal carmine2 the former is used in ammoniacal solution1 the latter as a solution of the pure carmine in ammonia4 ,the colour is prepared from red wood by allowing a decoction to stand for several days1 adding #b to #c per cent4 of alum1 evaporating and thickening with gum solution4 ,this colour is cheap1 but cannot compare in beauty with that obtained by treating red wood tin lake with ammonia4 ,the solution of genuine carmine in ammonia produces a sap colour which leaves nothing to be desired in regard to shade1 but on account of the cost of carmine it can but rarely be used4 ,a solution of pure indigo carmine mixed with gum solution is used as a blue sap colour2 it can be shaded by additions of red or yellow colours4 ,chinese blue may be used instead of indigo carmine2 it dissolves in a solution of oxalic acid4 ,when ,chinese blue1 which has been thoroughly washed1 is mixed whilst still moist with a little saturated oxalic acid solution1 the blue dissolves1 and the solution may then be made into a paste by the addition of thickening materials4 ,green sap colours are made1 as a rule1 by mixing yellow and blue4 ,all shades can be thus obtained4 ,a green colour of different composition is obtained by boiling the violet solution of chrome alum with gum solution until the colour changes to green4 ,violet colours are obtained by mixing red and blue4 ,sepia produces a brown sap colour4 ,it has been proposed to use glucose in place of the much dearer gum ,arabic1 and also to use malt extract as thickener4 ,these substances absorb water from the air1 and thus the colours prepared with them never become quite hard1 but always remain pasty4 ,for some purposes this is a decided advantage1 since such colours can be readily taken up by the brush and easily rubbed up with water1 but they cannot be formed into cakes as is usually done with water colours4 ,when the colours are to be made into cakes they must be thickened with gum ,arabic alone1 without glucose or malt extract4 ,the cakes must be dried with great care2 if they are dried too quickly they will crack or even fall to pieces4 ,,chapter ,,lxvi4 ,,water ,,colours4 ,the colours thus called are so prepared that they easily mix with water to such a condition that they can be applied with the brush4 ,special pigments are not required for this purpose1 ordinary dry colours are simply mixed with a binding medium soluble in water1 and the paste is generally pressed into cakes4 ,in commerce very different qualities of water colours are found1 ranging from cheap children's playthings to the most costly colours used by painters in water colour4 ,those pigments which are not already in very fine powder1 in consequence of the process by which they are made1 such as chrome yellow1 must be subjected to a very careful process of levigation4 ,to simplify as far as possible this laborious process1 it should be conducted by grinding the pigment as finely as possible1 well stirring it in a tub with water1 allowing to rest for several minutes1 and then running off the liquid into a second tub1 from which it is again drawn off into a third after several1 minutes4 ,the liquid remains in the last vessel until it is quite clear1 when the deposit is collected4 ,this is now so fine a powder that a powerful microscope is required to distinguish the separate particles4 ,the residue in the first and second vessels consists of the coarser particles2 it is again ground with fresh material4 ,in this process regard must be given to the specific gravity of the material3 the higher it is the shorter is the time during which the liquid is allowed to remain in the tubs1 since the coarser particles of heavy substances settle very rapidly4 ,in dealing with the light lakes1 such as the alumina lakes1 the liquid in which the lake is suspended must remain much longer at rest4 ,two vessels may be used instead of three1 without danger of the precipitate containing coarse particles4 ,gum ,arabic and tragacanth are used as binding materials for the pigments4 ,dextrine is also much used in place of the expensive gums2 for this purpose only pure white dextrine should be used1 since the brown colour of ordinary dextrine would injure the shade of the colours1 especially of pale colours4 ,gum ,arabic and dextrine1 which are readily soluble in water1 require no special preparation before their solutions are mixed with the pigments4 ,the solutions are made by treating with water2 they are then allowed to stand for several days in a tall vessel so that impurities may settle4 ,if the solutions are very turbid1 they are filtered through closely woven linen4 ,gum tragacanth requires rather different treatment4 ,it is not completely soluble in water1 in which it only swells up to a great extent4 ,it is prepared by leaving it for several days in water1 and when it has swollen1 rubbing the slimy mass in a mortar until it is completely uniform4 ,the levigated pigments are allowed to dry in the air to a soft paste1 which is mixed with the proper quantity of gum ,arabic and tragacanth solutions4 ,as a rule the two gums are used together4 ,the colouring matter and binding medium may simply be ground together1 but long grinding would be required to produce a completely homogeneous mixture4 ,the costly manual labour is therefore as far as possible replaced by machinery1 by which means a cheaper and also more uniform product is obtained4 ,the machines by which the pigment is ground with the binding material are of simple construction4 ,they consist of rollers placed in pairs one above the other and moving in opposite directions4 ,the two rollers of each pair are connected by cog-wheels1 in such a way that the lower moves more slowly than the upper4 ,in consequence of this arrangement1 the rollers1 in addition to crushing1 exert a grinding action upon the viscous mass passing between them4 ,as a rule1 after the colour has passed through one pair of rollers1 it goes through a second and third1 from the last of which it is taken off by a scraper4 ,it is now completely uniform4 ,the binding medium must be of such consistency that1 after grinding with the pigment1 a fairly stiff paste results which is suitable for pressing4 ,the cakes of colour are pressed out in an ordinary spindle press1 which should be so constructed that the stamp in the down stroke comes upon the paste beneath it and stamps out cakes upon which the engraving of the die is clearly shown4 ,if the cakes crack when slowly dried1 the medium contains too much gum ,arabic4 ,if the impression of the die upon the cakes is not sharp1 and if they remain rather elastic when completely dry1 too much tragacanth has been used4 ,it is rather difficult to grind a stiff paste1 many manufacturers prefer to grind the colour in a rather more fluid condition1 and then to allow the paste to thicken by drying to the consistency necessary for the production of good cakes4 ,the moulds in which the cakes are made must be very carefully worked in metal1 so that the description and trade mark print clearly upon the cakes4 ,the cakes should be dried at the ordinary temperature or but little higher4 ,they are placed upon smooth boards1 and care is taken that the temperature of the drying room remains uniform1 which is the condition requisite for the production of the fewest cracks4 ,when it is intended to place on the market only faultless and well-stamped cakes they must be sorted when dry1 and the cracked ones rejected2 these can be worked up in the next operation4 ,the dry cakes are given a good appearance by coating them with a weak solution of gum1 and then drying4 ,according to the price at which these colours are to be sold the cakes are given a different character4 ,the finest colours are generally made into larger cakes and packed in handsome boxes1 whilst ordinary cheap colours are made into small lumps or circular plates1 flat on one side and somewhat convex on the other1 and packed in boxes of soft wood4 ,moist ,water ,colours4--,instead of grinding water colours with gum ,arabic or tragacanth and bringing them on the market in the dry state1 they may also be sold in a condition resembling that of oil paints4 ,this may be accomplished by using very viscid glucose syrup instead of gum ,arabic1 and grinding the pigments in this exactly as in oil4 ,glucose is very hygroscopic1 the colours prepared with it remain moist1 and may be spread out upon the palette like oil colours4 ,it is then only necessary to wet the brush in water and mix the mass with it in order to obtain colour of the proper consistency4 ,moist water colours have also been known as 0honey colours10 since this mixture of sugars was formerly used for their preparation2 it also is hygroscopic4 ,honey is no longer used2 the much cheaper glucose answers the same purpose4 ,on account of their semi-fluid nature1 moist water colours are put up in tubes just as oil colours4 ,they are thus rather dear1 but are little used4 ,,chapter ,,lxvii4 ,,crayons4 ,crayons are coloured pencils by which pictures may be1 so to speak1 0dry painted04 ,at present this method of painting is little used1 though it was in vogue in the last century1 but coloured pencils1 especially blue and red1 are much used for writing4 ,crayons are now used in a very convenient form1 being generally made in the same manner as lead pencils4 ,the coloured mixture from which the crayon is made is produced in the form of a paste containing a soft1 finely ground mineral1 well mixed with the colouring matter and an amount of binding medium just sufficient to hold the powders together4 ,gypsum is generally used as the soft white mineral forming the base of the coloured mass4 ,it is much better to use steatite 7soap-stone71 which is not much dearer1 and has many advantages over gypsum4 ,the preference given to steatite is based upon a comparison of the properties of the two minerals2 gypsum is crystalline1 steatite is non-crystalline4 ,powdered gypsum has essentially a dry character1 whilst powdered soap-stone is of a peculiar greasy nature1 and consequently can be readily smeared upon a flat surface2 it also imparts a pleasing lustre to the colours with which it is mixed4 ,the manufacture of crayons consists in preparing and moulding the coloured mass4 ,the process is commenced by mixing the powdered colour and soap-stone in a closed rotating cylinder4 ,the rotation is continued until the mixture is uniform in colour4 ,the quantity of colour to be mixed with the soap-stone depends upon the shade to be produced4 ,manufacturers who make a speciality of crayons prepare a number of shades of each colour4 ,the artists who use crayons1 however1 usually require only those of a pure shade1 since they themselves can produce the intermediate shades from the essential colours4 ,on this account it is advisable to make crayons of distinct and deep colours4 ,the mineral pigments are the most suitable3 for yellow1 deep chrome yellow2 for red1 vermilion or deep madder lake2 for green1 one of the pure green pigments1 such as chrome green2 for blue1 ,chinese blue or ultramarine2 for brown1 burnt sienna or manganese bistre4 ,for white and black crayons levigated chalk is used1 alone or mixed with a sufficient quantity of fine vine black or some other good black4 ,either gum ,arabic or size may be used as binding material4 ,when the former is employed the crayon becomes so brittle when dry that it breaks when pointed with the knife1 in spite of the greatest care4 ,size produces a less brittle crayon1 and is also much cheaper1 so that it is preferred4 ,the paste from which the crayons are to be formed is made by mixing thin size with the colouring matter and steatite to a soft pulp1 which is then kneaded to secure uniformity4 ,the process then proceeds in a different manner according as the crayon is to be pressed or sawn out4 ,for producing the crayons by pressing1 a simple apparatus is required4 ,it consists of a horizontal metal cylinder with a well-fitting piston4 ,the front of the cylinder is closed by a metal plate in which is an orifice of rather greater diameter than the crayons to be made4 ,in front of the cylinder is an endless band which moves away from it4 ,in using this apparatus to shape the crayons1 the paste is made of such consistency that a slight pressure forces it out of the orifice in the front of the cylinder in a coherent rod4 ,when the cylinder is filled with the paste1 care must be taken that it includes no air bubbles1 for these would cause the rod to break4 ,the piston is then put in position and the mass forced by uniform gentle pressure out of the narrow opening4 ,the endless band must move away at the same rate as the rod proceeds from the cylinder1 so that a long stick of the crayon mass rests upon it4 ,this stick is cut up by a blunt knife into uniform lengths1 which are dried upon boards covered with blotting paper1 and are then enclosed in casings similar to those of the ordinary lead pencil4 ,the rods must be given a rather greater diameter than they are to possess when dry1 since they shrink somewhat in drying4 ,the second method consists in producing a thick paste which is moulded into blocks of the length of the crayons4 ,these blocks are very slowly dried at a uniform temperature1 and when completely dry1 are cut by a fine saw into thin rods1 which are then enclosed in a wooden case4 ,the powder produced in sawing is used in the next operation4 ,this simple process has many drawbacks4 ,in the first place it is difficult in drying large blocks of the crayon mass to avoid cracks1 which must be carefully filled with thin paste4 ,also in sawing up the blocks a large number of rods will be broken1 even with the most careful treatment 7these are again worked up with the powder produced in sawing74 ,thus1 generally1 the formation of crayons by pressure is preferred4 ,it is important to dry the crayon rods so far that they do not shrink further after they are placed in the case2 otherwise they would break up when sharpened4 ,at times it is quite impossible to make a usable point on such a faulty crayon4 ,crayons for ,earthenware4--,crayons for this purpose are made1 according to ,m4 ,rsler1 by finely powdering colours suitable for glass and earthenware1 and mixing them to a paste with a solution of #b parts of gum ,arabic and #a part of ,marseilles soap4 ,pencils are then moulded from the paste and wrapped in a strip of paper just previously dipped in a paste of gypsum4 ,upon unglazed articles or ground glass these crayons can be used like a lead pencil4 ,the colour is fixed by burning in the usual manner4 ,,chapter ,,lxviii4 ,,confectionery ,,colours4 ,confectioners employ several colours4 ,yellow1 brown and black are usually obtained by means of caramel2 the other colours1 red1 green and blue1 which are also largely used1 must be made from harmless compounds4 ,unfortunately1 colour makers have been known to offer the consumer for this purpose colours which by no means correspond to this requirement2 even the poisonous arsenic pigments have been used for colouring sweets4 ,in such a case the user of the colours is less to be blamed than the manufacturer1 who should sell for this purpose only colours in no way injurious to health4 ,fortunately we possess among the pigments of organic origin a sufficient number to satisfy these requirements3 for green1 either sap green or leaf green may be used without hesitation2 for red1 cochineal carmine is well suited1 and for blue1 indigo carmine4 ,the two pigments last named are indeed expensive1 but since they possess great colouring power they can still be used for colouring cheap sweets4 ,for colouring liqueurs equal care must be taken to choose non-injurious colours4 ,those mentioned above may also be used for this purpose4 ,recently these colours have been largely displaced by the aniline dyes1 which are particularly adapted by their beauty and great colouring power for the colouring of confectionery or liqueurs4 ,there should be some hesitation in using these dyes for colouring articles of food4 ,some of them are made by means of arsenic compounds1 and it is very difficult to free them absolutely from every trace of arsenic4 ,but supposing the dye to be free from arsenic1 there may still be objections to its use1 for the pure dyes themselves may possess poisonous properties1 and thus ought not to be used for colouring articles of food4 ,for colouring foods the colours above mentioned are sufficient4 ,orange is obtained by mixing caramel with red1 violet by mixing red and blue1 and the shades thus produced are quite sufficient for the purpose in question4 ,the colour maker should sell the colours in such a condition that they can be used without further preparation4 ,the colours for confectioners and liqueur makers should be put on the market in a semi-fluid or pasty condition4 ,for this purpose carmine should be ground with a very thick sugar syrup4 ,leaf green and indigo carmine require no further preparation2 they are already semi-fluid1 they readily diffuse1 and are also soluble in alcoholic liquids4 ,,chapter ,,lxix4 ,,the ,,preparation ,,of ,,pigments ,,for ,,painting4 ,according to the purpose for which they are to be used pigments require a different method of preparation4 ,the preparation of pigments for certain special purposes1 such as sap colours1 cake colours and water colours1 has been already described4 ,the present chapter deals with the preparation of those pigments which are used in large quantities by artists and for ordinary painting4 ,colours for artistic purposes require different treatment to those used for ordinary painting4 ,it is important that both should be ground to a completely homogeneous mixture with the binding medium4 ,at first sight this appears to be a simple operation1 but in practice there are difficulties which are not too easily overcome4 ,artists' colours are generally ground with a drying oil4 ,the drying oils are vegetable oils which1 when exposed to the air in a thin layer1 in a short time become very viscous1 and finally completely resinify2 linseed1 poppy1 and nut oils possess this property4 ,as a rule1 artists' oil paints are ground with poppy oil4 ,to prevent the paint from drying to a solid mass by exposure to air it is enclosed in protecting vessels4 ,formerly the ground paint was sold in small bags of bladder4 ,these are now no longer used2 instead1 collapsible tubes made of a soft tin alloy are employed4 ,they are closed at one end2 the other has a neck upon which a metal cap screws down4 ,pigments ground with just sufficient oil to form a thick paste may be preserved in these air-tight tubes without altering in consistency4 ,cheaper pigments1 such as white lead1 white zinc1 chrome yellow1 etc41 which are principally used in ordinary painting1 are ground with raw or boiled linseed oil4 ,ordinary boiled oil is made by boiling linseed oil with litharge2 it contains a certain quantity of lead in solution4 ,it has been repeatedly stated in this work that lead compounds are very sensitive to sulphuretted hydrogen4 ,pigments which are not themselves altered by sulphuretted hydrogen acquire a dark shade when they are ground with ordinary lead-boiled oil1 because the lead is slowly but certainly converted into black lead sulphide on exposure to air4 ,thus1 in order to retain the original beauty of colour1 lead-boiled oil should be replaced by oil boiled with manganese borate1 which is at least as cheap and has the advantage that the oil does not darken in air4 ,now that zinc oxide is so cheap it is more and more used in place of white lead1 it is not sensitive to sulphuretted hydrogen1 and does not even change its colour in an atmosphere of the pure gas4 ,it seems to be quite illogical to use this pigment with a lead-boiled oil4 ,a coating would be quite discoloured in the course of time1 whilst1 if used with manganese-boiled oil1 it would retain its white shade unaltered4 ,the dry pigment was formerly mixed with the oil by manual labour4 ,the pigment was spread out upon a smooth stone slab1 the oil poured over1 and the two substances rubbed to a uniform paste by means of a glass or stone rubber known as a muller4 ,paint ,mills are constructed in various ways4 ,the mixture of colour and oil is ground either between two metal plates or between two rollers pressed close together4 ,illustration3 ,,fig4 #da4 ,fig4 #da represents the construction of a paint mill in which the grinding is accomplished by a rotating disc4 ,the mixture of pigment and oil stirred together is brought into the hopper1 ,t1 from which it must pass between the rotating grinding disc1 ,m1 and the lower surface of the hopper4 ,the two substances are thus mixed together4 ,the ground paint flows out of the ring-shaped vessel surrounding ,m into a receiver below4 ,the grinding disc is driven by means of horizontal and vertical toothed wheels1 the latter of which is connected with a pulley driven by power4 ,by means of a screw on the lower part of the plate in which is the bearing of the axle of the grinding disc1 the distance of the latter from the lower surface of the hopper can be adjusted4 ,the process begins by adjusting the disc at a considerable distance from the hopper4 ,when the paint has once gone through the apparatus the disc is raised so that the colour is more finely ground4 ,the ground paint is returned to the hopper until it is quite uniform4 ,this form of mill can be made in different sizes4 ,fig4 #db shows the construction of a form for grinding by hand4 ,the actual grinding arrangements are exactly the same as those previously described2 the difference lies simply in the use of a fly-wheel turned by a handle4 ,the illustrations are due to the kindness of ,w4 ,sattler of ,schweinfurt1 who makes paint mills as a speciality in different sizes and of excellent quality4 ,illustration3 ,,fig4 #db4 ,in the second form of paint mill the paint is passed between smooth rollers moving in opposite directions with different speeds1 which thus exert a grinding action in addition to the crushing effect4 ,the two rollers are provided with cog-wheels with a different number of cogs in order to give the different speeds4 ,in order that the paint may be sufficiently ground in one operation1 roller mills are made with several pairs of rollers1 one above the other1 the lower rollers being somewhat nearer together than the upper4 ,the paint is fed on to the top pair of rollers1 and1 after going through these1 passes to the next1 and finally1 after going between all the pairs of rollers1 collects in a receiver below in a finished condition4 ,by the use of such mills the paints can be ground sufficiently fine in one operation1 if a proper number of rollers is used4 ,when only two or three pairs are used and the paint is to be very finely ground1 it must be passed through the whole mill two or three times4 ,,chapter ,,lxx4 ,,the ,,examination ,,of ,,pigments4 ,when an accurate examination of a pigment is required1 the only course is to conduct an exact chemical analysis1 which can only be done by an expert chemist in a well-equipped laboratory4 ,but often it is necessary in the course of trade to decide rapidly the nature of a pigment or to detect the adulteration of a dear pigment with a cheaper1 and for this purpose it is important to have a method of examination which can be conducted without much apparatus1 and which requires no great chemical knowledge4 ,it is quite possible to test the majority of pigments in a simple manner4 ,few reagents are necessary4 ,for an examination of the mineral pigments the following are generally sufficient3 hydrochloric1 nitric and sulphuric acids1 caustic soda solution and ammonium sulphide4 ,the examination of a pigment containing organic compounds is somewhat more difficult1 especially when it is necessary to ascertain the nature of the colouring matter4 ,in this case additional reagents are required--stannous chloride1 alum solution1 etc4 ,since the present work is intended to meet the requirements of the practical man1 the behaviour of the different pigments towards ordinary reagents is given in tabular form1 the pigments of the same colour being taken together4 ,since the colouring matters of organic origin1 as they occur in the lakes1 require a rather more detailed examination1 the testing of pigments composed of inorganic materials only is first given1 afterwards the properties of the organic colouring matters1 so far as is necessary1 will be added4 ,mineral ,pigments4--,if the substance to be examined is in the form of a dry powder1 it may at once be tested with the reagents mentioned1 but if it is a paint or water colour1 the oil or gum must be first removed1 otherwise it would not be possible to recognise with certainty the action of the reagents4 ,from water colours1 which are ground with gum ,arabic or tragacanth solution1 it is easy to separate the pigment from the binding medium4 ,the colour is allowed to stand in a tall narrow beaker with a somewhat large quantity of water4 ,after some time the lumps become soft1 they are then repeatedly stirred up1 the pigment allowed to deposit1 and the water1 which now contains the binding medium1 poured off4 ,the removal of oil from a paint is somewhat more difficult4 ,a quantity of the paint is placed in a flask with a mixture of equal parts of strong alcohol and ether1 or with benzine4 ,the flask is lightly corked1 and1 after frequent shaking1 allowed to stand4 ,the liquids mentioned are good solvents for oils4 ,after a day or two the pigment will generally have deposited at the bottom of the flask4 ,the solution is then poured off1 the residue mixed with a small quantity of the solvent and transferred to a filter1 where another small quantity of solvent is poured over it4 ,the solvent is allowed to drain off1 and the residue is dried4 ,a powder without coherence should be left2 this is the pigment free from oil4 ,it can be treated like an originally dry colour4 ,the pigments are most conveniently examined in test tubes4 ,if these are not at hand the reactions may be carried out on a plate of glass lying on white paper4 ,the powder is placed on the glass and the reagent dropped on to it from a glass rod dipped in the liquid4 ,examination with the ,blowpipe4--,from the behaviour of pigments at high temperatures important conclusions may be drawn as to their nature4 ,for this purpose small porcelain crucibles are used2 broken pieces of porcelain or an iron spoon may also be employed4 ,an ordinary spirit lamp is generally sufficient as a source of heat4 ,in some cases a higher temperature is required1 which is obtained by means of the blowpipe4 ,the blowpipe is an invaluable instrument in the examination of mineral pigments4 ,by means of it1 almost without reagents1 the nature of the pigment can generally be ascertained4 ,the reagents necessary in using the blowpipe are soda1 borax1 and the solution of a cobalt salt4 ,the following method should be observed in examining pigments by means of the blowpipe4 ,a quantity of the substance1 about equal in volume to two grains of rice1 is placed in a small hole cut by a knife in a piece of charcoal1 where it is heated by the blowpipe flame4 ,the behaviour of substances is different in the oxidising and reducing flames of the blowpipe4 ,when a flame is blown out to a point by means of the blowpipe it may be seen that the flame consists of two conical portions1 one inside the other4 ,the inner is known as the reducing flame1 because metallic oxides heated in it produce a bead of metal1 or1 as the change is chemically expressed1 are reduced to metal4 ,the outer cone has the opposite properties2 metals melted in it are quickly changed into oxides by the action of the oxygen of the air1 which has unrestricted access4 ,in examining a pigment with the blowpipe the reducing flame is first used4 ,the nature of the bead of metal1 such as is readily obtained from lead pigments1 often allows the composition of the substance to be recognised with certainty4 ,if the behaviour of the bead of metal is not conclusive it is further heated in the oxidising flame4 ,the metal is thus converted into oxide1 which deposits on the charcoal1 and by its colour and volatility or want of volatility enables the metal contained in the pigment to be determined4 ,a solution of cobalt nitrate or chloride is used in testing for certain metallic oxides4 ,the substances are moistened with a very dilute solution of one of these substances before heating4 ,after they have been heated they show characteristic colours if certain oxides are present4 ,several metallic oxides give a characteristic colour when fused with borax4 ,for this purpose a small loop is made at the end of a thin platinum wire2 this is moistened and dipped in powdered anhydrous borax4 ,on heating in the blowpipe flame the borax adhering to the wire melts to a colourless glass4 ,in testing a pigment the transparent bead of borax is then dipped into the powder1 and again fused in the blowpipe flame4 ,it is of great importance in this test to fuse but a very small quantity of material in the borax bead2 some metallic oxides have such great colouring power that1 when too much is used1 the bead appears quite black1 so that its colour cannot be recognised4 ,,reactions ,,of ,,the ,,white ,,pigments4 ,on ,heating on ,charcoal3--,lead pigments give a lead bead in the reducing flame1 which is converted in the oxidising flame to lead oxide1 forming a deposit on the charcoal surrounding the hole4 ,antimony white gives a brittle metallic bead in the reducing flame4 ,this burns in the oxidising flame with the evolution of white vapours1 and is at the same time covered by small shining crystals4 ,bismuth white in the oxidising flame gives a rainbow-coloured incrustation spreading far over the charcoal4 ,tin white gives a malleable metallic bead1 converted by nitric acid into a white powder4 ,zinc white is converted into a green mass when moistened with cobalt solution and heated in the oxidising flame4 ,the more expensive white pigments are frequently mixed with cheaper substances1 e4g41 white lead with finely powdered barytes1 chalk or gypsum4 ,such admixture is distinctly to be regarded as adulteration1 since the added substances have not the covering power of white lead4 ,in the case of coloured pigments an addition of a white material is not to be regarded as adulteration1 since the addition is made in order to impart a paler shade to the colour4 ---------------------------------------- ----------------------- ,pigment4 ,hydrochloric ,caustic ,ammonium ,on ,heating4 ,acid4 ,soda4 ,sulphide4 ---------------------------------------- ----------------------- ,antimony white ,dissolves1 ,dissolves4 ,turns ,turns yellow solution reddish and melts4 on turbid yellow4 adding water4 ,white lead ,dissolves with,dissolves4 ,turns ,becomes effervescence1 black4 permanently solution gives yellow4 crystalline lead chloride4 ,lead ,dissolves ,dissolves ,turns ,turns yellow4 oxychloride without on boiling4 black4 effervescence4 ,lead sulphate ,insoluble4 ,dissolves ,turns ,unaltered4 on boiling4 black4 ,permanent white,insoluble4 ,insoluble4 ,unaltered4,unaltered4 7barium sulphate7 ,bismuth white ,insoluble4 ,insoluble4 ,turns ,evolves black4 reddish brown fumes1 which redden litmus paper4 ,zinc white ,dissolves ,dissolves4 ,unaltered4,turns yellow1 without becomes white effervescence4 again on cooling4 ,tin white ,dissolves4 ,dissolves4 ,turns ,unaltered4 yellow4 ---------------------------------------- ----------------------- ,,reactions ,,of ,,the ,,yellow ,,pigments4 ---------------------------------------- ---------------------- ,pigment4 ,hydrochloric ,caustic ,soda4 ,ammonium ,on ,heating4 ,acid4 ,sulphide4 ---------------------------------------- ---------------------- ,chrome ,green solution ,becomes ,blackened4,fuses to a yellow above a white orange on yellow mass4 and residue1 which boiling and chrome redis soluble on dissolves4 largely diluting4 ,cassel ,unaltered1 ,becomes paler,blackened4,melts4 yellow becomes white on boiling1 on boiling4 liquid yellow4 ,naples ,on boiling ,reddish ,turns ,melts at yellow orange1 then yellow4 brownish a high white4 black4 temperature4 ,massicot ,turns white4 ,partially ,blackened4,melts soluble on with some boiling4 difficulty4 ,lead iodide,turns white4 ,dissolves4 ,blackened4,melts4 ,barium ,yellow solution,unaltered4 ,unaltered4,unaltered4 yellow which 7chromate7 gives white precipitate with sulphuric acid4 ,cadmium ,dissolves with ,unaltered4 ,unaltered4,melts with yellow evolution of difficulty4 sulphuretted hydrogen4 ,zinc ,yellow ,yellow ,unaltered4,melts with yellow solution4 solution1 difficulty4 white residue4 ,cobalt ,red solution4 ,colourless ,unaltered4,becomes yellow solution1 blackish greyish blue at high precipitate4 temperatures4 ,orpiment ,unaltered4 ,colourless ,yellow ,volatilises4 solution4 solution4 ,turpeth ,dissolves4 ,unaltered4 ,blackened4,turns red4 mineral ---------------------------------------- ---------------------- ,on ,heating on ,charcoal3--,chrome yellow1 chrome red1 ,cassel yellow1 massicot and lead iodide give lead beads in the reducing flame4 ,chrome yellow and red when fused with soda give red masses soluble in water4 ,naples yellow gives a lead bead and white fumes without smell4 ,orpiment gives an odour of garlic4 ,cobalt yellow1 when heated with alumina1 is turned blue4 ,cadmium yellow produces a brown incrustation on the charcoal4 ,the examination before the blowpipe serves especially for the recognition of lead1 chromium1 antimony and arsenic4 ,if a pigment blackens on heating1 the presence of an organic colouring matter is indicated1 such as ,dutch pink1 weld lake1 etc4 ,the adulteration of pigments free from lead by colours containing that metal is recognised by the blackening produced by ammonium sulphide4 ,,reactions ,,of ,,the ,,red ,,pigments4 ---------------------------------------- ---------------------- ,pigment4 ,hydrochloric ,acid4 ,caustic ,ammonium ,on ,heating4 ,soda4 ,sulphide4 ---------------------------------------- ---------------------- ,chrome ,green solution1 ,yellow ,turns ,fuses4 red white residue solution greenish soluble on and white black4 largely diluting4residue4 ,red lead ,chlorine is ,almost ,turns ,turns yellow evolved1 white unchanged4 black4 and finally residue4 melts4 ,ferric ,slowly dissolve to ,unaltered4 ,slowly ,become dark oxide yellow solution4 blackened4blackish pigments brown4 ,antimony ,dissolves with ,dissolves to,becomes ,melts4 vermilion evolution of colourless darker1 sulphuretted solution4 partially hydrogen4 soluble4 ,mercury ,unaltered4 ,turns ,unaltered4,volatilises1 vermilion yellowish4 sulphur dioxide evolved4 ,mercuric ,dissolves to ,dissolves to,blackened4,fuses and iodide colourless yellowish then solution4 solution4 volatilises4 ,realgar ,unaltered4 ,dissolves to,dissolves ,volatilises4 colourless to yellow solution4 solution4 ---------------------------------------- ---------------------- ,on ,heating on ,charcoal3--,chrome red and red lead give lead beads in the reducing flame4 ,the former gives a red mass when fused with soda1 which dissolves to a yellow solution4 ,ferric oxide pigments become darker1 but give no incrustation4 ,antimony vermilion burns with production of sulphur dioxide and white fumes without smell when heated in the oxidising flame2 when fused with soda before the blowpipe1 it gives a white brittle bead of metallic antimony4 ,vermilion volatilises in the oxidising flame and gives a smell of sulphur dioxide4 ,mercuric iodide readily fuses and volatilises4 ,realgar volatilises4 ,when heated with soda in the reducing flame1 white fumes with an odour of garlic are produced4 ,,reactions ,,of ,,the ,,blue ,,pigments4 ---------------------------------------- ---------------------- ,pigment4 ,hydrochloric ,caustic ,ammonium ,on ,heating4 ,acid4 ,soda4 ,sulphide4 ---------------------------------------- ---------------------- ,prussian1 ,dissolve to ,decolour- ,liquid ,blackened4 ,chinese1 green solution1 ised1 yellowish ,paris1 then yellow4 brown green4 ,turnbull's1 residue4 and ,brunswick blue ,mountain blue ,dissolves to ,blackened4,blackened4,blackened4 yellowish-green solution4 ,ultramarine ,rapidly ,unchanged4,unchanged4,unchanged4 decomposed with evolution of sulphuretted hydrogen4 ,smalts ,almost ,unchanged4,blackened4,fuses at unaltered1 a high greenish temperature4 solution on long boiling4 ,cobalt blue ,unchanged4 ,unchanged4,unchanged4,infusible and unchanged4 ---------------------------------------- ---------------------- ,on ,heating on ,charcoal3--,prussian1 ,chinese1 ,paris1 ,turnbull's and ,brunswick blue are turned black1 the residue colours the borax bead pale brown in the oxidising flame1 and pale green in the reducing flame4 ,ultramarine is unaltered at a high temperature4 ,smalts1 on long heating in the reducing flame with borax1 gives a dark blue bead4 ,cobalt blue is infusible2 it colours the borax bead blue4 ,the bead loses its fine colour on long heating in the reducing flame4 ,mountain blue is blackened before the blowpipe4 ,when the residue is moistened with hydrochloric acid and again heated1 the flame is coloured bright green4 ,when fused with borax in the oxidising flame1 an emerald green bead is formed4 ,,reactions ,,of ,,the ,,green ,,pigments4 ---------------------------------------- ----------------------- ,pigment4 ,hydrochloric ,caustic ,ammonium ,on ,heating4 ,acid4 ,soda4 ,sulphide4 ---------------------------------------- ----------------------- ,verdigris ,dissolves ,unaltered4,blackened4 ,blackened 7all varieties7to green with solution1 evolution smell of of peculiar acetic acid4 odour4 ,bremen green1 ,green ,unaltered4,blackened4 ,blackened4 ,brunswick greensolution and white residue4 ,emerald green1 ,dissolve to ,gradually ,become ,blackened ,scheele's greengreenish coloured brownish and evolve solution4 brownish black4 garliclike yellow4 odour4 ,copper borate ,dissolves to ,black ,becomes ,fuses4 greenish residue4 brownish solution4 black4 ,rinmann's green,dissolves to ,unaltered4,blackened4 ,unaltered4 rose-red solution4 ,chromium oxide ,almost ,unaltered4,becomes dark,unaltered4 unaltered4 dirty green4 ,chrome green ,becomes deeper ,unaltered4,becomes dark,unaltered4 lake in colour4 dirty green4 ,manganese green,dissolves to ,dissolves ,discoloured4,unaltered4 green to green solution4 solution4 ,green ,is decolourised,unaltered4,unaltered4 ,unaltered4 ultramarine with evolution of sulphuretted hydrogen4 ---------------------------------------- ----------------------- ,on ,heating on ,charcoal3--,verdigris1 ,bremen and ,brunswick greens give black residues on charcoal1 which produce a bluish-green bead when fused with borax in the oxidising flame4 ,emerald green and ,scheele's green behave in a similar manner1 but on heating evolve an odour of garlic4 ,rinmann's green gives a blue borax bead4 ,manganese green is discoloured in the reducing flame4 ,,reactions ,,of ,,the ,,brown ,,pigments4 ---------------------------------------- -------------------- ,pigment4 ,hydrochloric ,caustic ,ammonium ,on ,heating4 ,acid4 ,soda4 ,sulphide4 ---------------------------------------- -------------------- ,lead brown ,white ,dissolves4 ,blackened4,turns residue1 yellow chlorine and fuses4 evolved4 ,manganese brown ,dissolves ,unaltered4 ,becomes ,unaltered4 to yellow flesh solution4 coloured4 ,pyrolusite brown,dissolves ,unaltered4 ,becomes ,unaltered4 to yellow flesh solution1 coloured4 chlorine evolved4 ,prussian brown ,dissolves ,unaltered4 ,blackened4,turns to to yellow reddish solution4 brown4 ,iron brown ,dissolves ,unaltered4 ,blackened4,unaltered4 to yellow solution4 ,chrome brown ,dissolves ,yellow ,blackened4,blackened4 to greenish solution1 yellow black solution4 residue4 ,cobalt brown ,dissolves ,unaltered ,blackened4,unaltered4 to reddish or yellow blackened4 solution4 ,hatchett brown ,unaltered4 ,becomes ,blackened4,blackened4 greenish blue4 ,humins1 ,bistre ,unaltered1 ,give yellow,unaltered4,burn4 yellow liquid4 liquid4 ---------------------------------------- -------------------- ,on ,heating on ,charcoal3--,lead brown gives a lead bead in the reducing flame4 ,manganese brown and pyrolusite brown1 when fused with saltpetre on platinum foil at a high temperature1 give a bluish-green mass4 ,prussian brown and iron brown give a pale green borax bead in the reducing flame1 which turns yellowish brown in the oxidising flame4 ,chrome brown heated1 moistened with hydrochloric acid1 and again heated1 colours the flame green4 ,it also gives a green borax bead4 ,cobalt brown produces a blue borax bead4 ,humin substances burn when heated on charcoal4 ,,reactions ,,of ,,the ,,black ,,pigments4 ,almost all black pigments consist of carbon1 upon which reagents have no action4 ,they should be at once heated on charcoal4 ,if they burn away completely in the oxidising flame they consist of lamp black or carbon obtained by some process of incomplete combustion2 if a white1 infusible residue is left1 the pigment is bone 7ivory7 black2 if the residue is black the substance under examination must be 0neutral tint10 chrome black1 or chrome-copper black4 ,the two former give a pale green borax bead1 whilst chrome-copper black gives a deep green bead1 and when heated1 moistened with hydrochloric acid1 and again heated1 it colours the flame green4 ,,chapter ,,lxxi4 ,,examination ,,of ,,lakes4 ,in examining lakes it is necessary to ascertain the nature of the organic colouring matter1 the base with which this is united1 and also the nature of the substances mechanically mixed with the lake to lighten its shade4 ,it is most convenient to examine the pigment first for mechanical admixtures4 ,if an effervescence follows the addition of hydrochloric acid1 denoting the presence of a carbonate1 this is generally calcium carbonate4 ,white lead is rarely used1 since it is very heavy and is more expensive4 ,gypsum and magnesia are occasionally added to lakes2 they are recognised by examining the residue left on ignition4 ,in testing for the metallic oxide which is united with the colouring matter a small quantity of the lake is heated in a little porcelain crucible until all organic substances are completely destroyed4 ,the residue is then examined for aluminium and tin oxides1 by means of which lakes are most frequently prepared4 ,,reactions ,,of ,,the ,,organic ,,colouring ,,matters4 ---------------------------------------- --------------- ,colouring ,dilute ,caustic ,lime ,strong ,alum4 ,matter4 ,acids4 ,soda4 ,water4 ,nitric ,acid4 ---------------------------------------- --------------- ,,yellow4 ,buckthorn ,slight ,yellowish ,slight ,reddish ,pale berry turbidity4 red4 greenishbrown4 yellow4 extract precipi- tate4 ,dutch pink,yellow ,brown4 ,brownish,reddish ---- solution4 brown4 ,weld ,slight ,golden ,greenish,golden ,slight extract turbidity4 yellow4 yellow4 yellow4 yellow precipi- tate4 ,weld lake ,yellow ,unaltered4,greenish,golden ---- solution4 yellow4 yellow solution4 ,gamboge ,unaltered4,deep ,deeper ,deep ---- reddish yellow4 yellow4 yellow4 ,gamboge ,yellow ,deep ,deeper ,deep ,yellow lake solution4 reddish yellow4 yellow4 precipi- yellow4 tate4 ,fustic ,becomes ,dirty ,deeper4 ,slight ,pale paler4 brownish precipi- yellow red4 tate4 precipi- tate4 ,quercitron,becomes ,deeper4 ,deeper4 ,paler4 ,paler1 paler4 slight precipi- tate4 ,young ,slight ,purple ,reddish4,greenish4,slight fustic greenish red4 greenish precipi- precipi- tate4 tate4 ,turmeric ,carmine ,brown4 ,brown4 ,carmine ,yellow4 red4 red4 ,,blue4 ,indigotin ,unaltered4,yellowish ---- ,yellow4 ---- brown solution4 ,indigo ,unaltered4,yellowish ---- ,yellow4 ---- carmine brown blue lake solution4 ,litmus ,turns red4,unaltered4 ---- ---- ---- ,logwood ,red4 ,violet4 ,blue4 ,yellow4 ,dirty violet4 ,,red4 ,cochineal ,becomes ,violet4 ,becomes ,yellow4 ,red decoction paler4 darker4 flocks4 ,carmine ,red ,violet ,becomes ,yellow4 ---- solution4solution4 darker4 ,lac1 ,yellowish ,violet ---- ,yellow4 ,red lac dye red4 solution4 precipi- tate4 ,safflower ,unaltered4,red ---- ---- ---- red solution4 ,madder ,red ,red ---- ,yellow4 ,red lake solution4precipi- precipi- tate4 tate4 ,red wood ,pale red4 ,violet4 ,carmine ,yellow4 ,red red precipi- precipi- tate4 tate4 ,red wood ,red ,violet ---- ,yellow4 ---- lake solution4solution4 ,the remaining red colouring matters give such uncertain reactions that it is almost impossible to distinguish between them by ordinary means2 they are therefore not included here4 ,,green4 ,sap green ,reddish ,brownish ,becomes ,reddish ---- brown4 green4 deeper4 yellow4 ,leaf green,green ,green ---- ,reddish ---- solution4 solution4 yellow4 ,,brown4 ,sepia ,unaltered4,brown ---- ---- ---- solution4 ,catechu ,paler4 ,reddish ,reddish ,yellowish,reddish solution brown4 brown4 brown4 yellow color- ation4 ---------------------------------------- --------------- ---------------------------------------- --------------------- ,colouring ,stannous ,ferric ,copper ,gelatine ,matter4 ,chloride4,chloride4 ,acetate4 ,solution4 ,remarks4 ---------------------------------------- --------------------- ,,yellow4 ,buckthorn ,slight ,olive ,dirty ,slight ---- berry greenish green4 yellow4 precipi- extract yellow tate4 precipi- tate4 ,dutch pink ---- ---- ---- ---- ,chars when heated on platinum foil4 ,weld ,consider-,greenish4,reddish ,slight ,gives yellow extract able yellow turbid- scales yellow precipi- ity4 some time precipi- tate4 after adding tate4 potassium bichromate4 ,weld lake ---- ---- ---- ---- ---- ,gamboge ---- ---- ---- ---- ,readily melts and burns4 ,gamboge ,yellow ---- ---- ---- ---- lake precipi- tate4 ,fustic ,yellow ,blackish ,brownish ,consider-,lead acetate precipi- green yellow able gives an tate4 precipi- precipi- precipi- orange red tate4 tate4 tate4 precipitate4 ,quercitron,yellowish,becomes ,yellowish ,reddish ---- red green1 green precipi- precipi- green precipi- tate4 tate4 precipi- tate4 tate4 ,young ,orange ,brownish ,brown ,yellowish,ammonia fustic red green flocculentred gives red precipi- precipi- precipi- precipi- coloration4 tate4 tate4 tate4 tate4 ,turmeric ,yellow4 ,brown4 ---- ,fairly ,very large sensitive precipi- to alkalis4 ,,blue4 tate4 ,indigotin ---- ---- ---- ---- ,on heating gives peculiar odour and purple red vapours4 ,indigo ---- ---- ---- ---- ,on heating carmine gives blue lake peculiar odour and purple vapours4 ,litmus ---- ---- ---- ---- ,unpleasant smell on heating1 white ash4 ,logwood ,dirty ,dark ---- ,very ,black with violet4 coloured turbid4 potassium solution4 bichromate4 ,,red4 ,cochineal ,reddish ---- ---- ---- ,completely decoctionviolet soluble flocks4 in ammonia4 ,carmine ---- ---- ---- ---- ---- ,lac1 ,red ---- ---- ---- ---- lac dye precipi- tate4 ,safflower ---- ---- ---- ---- ,rapidly red decomposed by boiling with alkalis4 ,madder ,red ---- ---- ---- ---- lake precipi- tate4 ,red wood ,deep ,violet ,violet ---- ---- red precipi- red precipi- tate4 precipi- tate4 tate4 ,red wood ---- ---- ---- ---- ,much ash lake on ignition4 ,the remaining red colouring matters give such uncertain reactions that it is almost impossible to distinguish between them by ordinary means2 they are therefore not included here4 ,,green4 ,sap green ---- ---- ---- ---- ,white ash on ignition4 ,leaf green ---- ---- ---- ---- ,white ash on ignition4 ,,brown4 ,sepia ---- ---- ---- ---- ,burns with peculiar smell4 ,catechu ,brownish ,brownish ,brown ,consider- ---- solutionprecipi- green precipi- able tate4 precipi- tate4 precipi- tate4 tate4 ---------------------------------------- --------------------- ,it is not easy to decide which colouring matter is united with the metallic oxide1 because the organic colouring matters do not give1 as a rule1 decided reactions4 ,in examining pigments of this kind it is always advisable to test at the same time a pigment of known composition1 and to compare the reactions of the two4 ,the colouring matter of the lake is first brought into solution4 ,this is accomplished by the action of dilute hydrochloric acid1 which decomposes the compound of metallic oxide and colouring matter1 the latter dissolving4 ,a portion of the lake should remain undecomposed1 so that the solution has no strong acid reaction by which the action of the reagents to be used would be modified4 ,when the lake has been treated for some time with dilute hydrochloric acid1 water is added and the solution of the colouring matter filtered from the residue4 ,small quantities of this solution are then treated with the different reagents4 ,by a comparison of the reactions given by the solution and by a solution of the pure colouring matter1 the nature of the colouring matter under examination may be decided4 ,in deciding in the first place if a colour is of organic origin1 it is treated with hydrochloric acid in the above manner4 ,if a coloured solution results1 an organic colour is probably present4 ,chlorine water is then added to a portion of the solution2 if the latter is quickly decolourised an organic colouring matter is certainly present1 for they are all decomposed by the continued action of chlorine4 ,the following reagents are used in testing organic colouring matters3 dilute sulphuric or hydrochloric acid1 caustic soda solution or lime water1 strong nitric acid1 which1 in consequence of its oxidising properties1 gives different reactions to the other acids4 ,of the metallic salts1 alum1 stannous chloride and ferric chloride are used1 and occasionally copper acetate4 ,glue solution is also used in the pure form of isinglass or gelatine solution1 with which several colouring matters give characteristic precipitates4 ,the foregoing tables give the behaviour of the colouring matters contained in the organic pigments towards the reagents mentioned above4 ,,chapter ,,lxxii4 ,,the ,,testing ,,of ,,dye-,,woods4 ,in the manufacture of pigments from dye-woods or other organic substances1 the value of the raw material is in proportion to the amount of colouring matter it contains1 other things being equal4 ,it is specially desirable to estimate accurately the colouring matter in expensive materials such as indigo and cochineal4 ,there are a number of methods which permit an accurate estimation of the indigo blue in indigo4 ,one good process is founded upon the decomposition of indigo blue by chlorine1 when the colour of the solution changes from blue to yellow4 ,since a definite amount of chlorine is required to decompose indigo blue1 from the quantity of chlorine required by a sample of indigo1 its content in indigo blue can be ascertained4 ,whilst the percentage of indigo blue contained in indigo can be found with tolerable accuracy1 though by a rather elaborate process requiring special apparatus1 there is no convenient method for examining the other organic colour materials by which their content in active constituents can be readily found4 ,in practice a process is particularly valuable which requires little time and no complicated apparatus4 ,colouring materials can be rapidly tested by a physical process which requires little time and an inexpensive apparatus4 ,under similar conditions the extract of a dye-wood is deeper in colour in proportion to the colouring matter it contains4 ,if therefore the intensity of the colour of the extract can be accurately measured1 there is no difficulty in drawing a certain conclusion as to the amount of colouring matter in the raw material4 ,illustration3 ,,fig4 #dc4 ,the ,colorimeter is the apparatus adapted for the purpose in question4 ,there are many forms of colorimeter4 ,the instrument devised by ,dubosq is distinguished by simplicity and accuracy of results before other apparatus of similar construction4 ,dubosq's colorimeter consists of the following parts 7,fig4 #dc73 two glass cylinders1 ,c and ,c1 the bottoms of which must be perfectly plane both inside and outside 7the accuracy of the results depends upon this71 stand upon a sheet of plate glass4 ,two glass cylinders of smaller diameter1 ,t and ,t1 are suspended in ,c and ,c4 ,the bottoms of these cylinders must also be quite plane4 ,it would be very expensive to make glass cylinders of this kind in one piece4 ,the same result is obtained by providing each cylinder with a metal ring upon which screws another ring in which is cemented a circular piece of plate glass4 ,light should only reach the eye of the observer in a direction parallel with the axis of the cylinders4 ,c and ,c are therefore blackened on the outside4 ,the inner cylinders1 ,t and ,t1 are fastened to racks moving vertically4 ,the distance through which the cylinder is moved is measured by a scale on one of the racks4 ,above the cylinders ,t and ,t are ,fresnel's prisms4 ,below ,c and ,c is a mirror1 ,s1 which can be adjusted to throw light vertically upwards4 ,beams of light pass through the plate glass and the bottoms of the cylinders ,c and ,t1 ,c and ,t1 unrefracted1 they are then deviated by the ,fresnel's prisms so that the observer looking down through the telescope1 ,f1 has a circular field of view1 one half of which is illuminated by the light passing through the cylinder ,c1 and the other by the beam passing through ,c4 ,the intensity of the light which has passed through the two cylinders can thus be accurately compared4 ,in order to use this apparatus to compare the intensity of colour of two liquids1 the following process is performed3 ,a liquid is made1 the colour intensity of which is taken as #ajj4 ,the colour intensity of the liquid under examination will then be represented by a number indicating the relation between its intensity and that of the standard liquid4 ,a solution of caramel in water is generally used as the standard1 since this substance has very great intensity of colour4 ,the preparation of absolutely pure caramel is difficult1 and it is therefore advisable1 in order always to have the standard solution of the same intensity1 to prepare a large quantity of caramel solution at once1 to add carbolic acid to prevent it from decomposing1 and to keep it in well-closed bottles4 ,when the standard solution is almost used up the colorimeter is employed to prepare a fresh quantity of equal intensity4 ,to render possible an exact comparison of two substances they must be tested under the same conditions1 that is1 the solutions of the colouring matters must be made in exactly the same manner4 ,finely-powdered materials dissolve more readily than coarse powders4 ,in making the solutions which are to be examined for intensity of colour1 the raw materials must be brought into a condition of fine division by the same instrument1 for example1 a rasp4 ,the colour solution is made by boiling #ajj grammes of the dye-wood with exactly a litre of distilled water for precisely thirty minutes4 ,the liquid is then filtered into a #a-litre flask4 ,the dye-wood absorbs water1 and some is lost by evaporation1 so that considerably less than #a litre of liquid is collected in the flask4 ,distilled water is added to make up the volume to #a litre4 ,if two samples of logwood are treated in this manner1 solutions are obtained which contain the colouring matter in the same proportions in which it exists in the two samples4 ,the intensity of colour of the solutions is then estimated in the following manner3 ,the cylinder ,c is filled with the standard caramel solution up to a mark on the outside of the cylinder4 ,the cylinder ,c is filled with the decoction to the same height4 ,the distance between the bottoms of the cylinders1 ,r and ,t1 ,r and ,t1 must be made smaller in proportion to the intensity of colour of the liquid between them4 ,if now the amount of light which penetrates a layer of caramel solution of a certain thickness be taken as unity1 the depth of a layer of the decoction must be greater1 the smaller the quantity of colouring matter it contains1 in order that the two halves of the field of view may be equally illuminated4 ,the cylinder ,t must be raised to a greater height the smaller the quantity of colouring matter in the liquid1 in order that the two halves of the field may be illuminated to the same extent4 ,if the colouring power of the caramel solution is taken as #ajj1 the colouring power of the decoction can be readily calculated from the height to which the cylinder1 ,t1 is raised4 ,the heights of the layers of liquid between the bottoms of the cylinders ,c and ,t1 ,c and ,t1 are inversely as the quantities of colouring matter contained in the respective cylinders4 ,when caramel solution is used as the standard the intensity of the light in the two halves of the field can be judged1 but not the intensity of colour4 ,in order to estimate the latter a solution of that colouring matter must be used as a standard which is the principal constituent of the decoction under examination4 ,thus1 in a careful examination of logwood a solution of hmatoxylin would be used1 and in the examination of red wood a solution of pure brasilin1 as the standard4 ,in this case a saturated solution of the colouring matter would be taken as the standard4 ,if the intensity of its colour were represented by #ajj1 the colour intensity of the wood under examination would always be less than #ajj1 and would1 with tolerable accuracy1 represent the percentage of colouring matter in the wood4 ,the result would not be quite accurate1 because the dye-wood contains other substances which dissolve in water on boiling and affect the colour of the decoction1 but the results are of such accuracy that for practical purposes no material mistake will be made by taking them as percentages of colouring matter4 ,although at first sight the estimation of the colouring matter in a dye-wood by means of the colorimeter appears somewhat complicated1 yet it yields the most accurate results with the smallest expenditure of labour and time4 ,the value of a colouring material may also be estimated by preparing the pure colouring matter from a weighed quantity4 ,this process is lengthy1 demands considerable practice1 and only gives good results when it is carried out with the most painful accuracy4 ,the colouring matters in question are precipitated by lead salts4 ,if the dye-wood extract contained colouring matter alone its amount could be found by observing the volume of a lead solution of known strength required to precipitate the colouring matter completely4 ,the decoctions1 however1 contain other substances which form lead compounds1 and are precipitated together with the colouring matter1 so that if the precipitate were regarded as the pure lead compound of the colouring matter a very inaccurate result would be obtained4 ,in order to obtain results with some pretensions to accuracy the lead compound of the colouring matter must be purified4 ,the impure precipitate is washed and suspended in water1 through which sulphuretted hydrogen is passed until all the lead is precipitated as lead sulphide1 which is filtered off1 excess of sulphuretted hydrogen expelled by boiling1 and the solution again precipitated by a lead salt4 ,this precipitate may be regarded without considerable error as the lead compound of the colouring matter4 ,the weight of colouring matter contained in the quantity of wood used can be calculated from the weight of the dry precipitate4 ,this method is somewhat complicated and tedious2 the results are inferior in accuracy to those obtained by means of the colorimeter1 which instrument furnishes the most suitable method for testing dye-woods for practical purposes4 ,a thorough knowledge of chemistry is indispensable to the colour manufacturer who wishes to carry on his business on any extensive scale4 ,it enables him to match any sample of colour submitted to him and to test his raw materials with ease4 ,we have indeed given in a section of this book simple methods by which the majority of commercial pigments can be tested with tolerable accuracy by means of a few reagents1 and for ordinary purposes these methods are sufficient4 ,but when an accurate examination of a pigment is required1 it must be conducted by the ordinary processes of analytical chemistry4 ,the colour manufacturer has not only to carry out these occasional examinations1 but has frequently to test certain raw materials which he uses in large quantities4 ,soda may be taken as an example4 ,an estimation of the percentage of sodium carbonate in this substance is an exceedingly simple matter to the chemist1 but can hardly be carried out without a knowledge of chemistry4 ,a manufacturer without chemical knowledge1 who is carrying on an industry which1 like the manufacture of colours1 rests entirely upon a chemical foundation1 will constantly be compelled to seek advice from a scientific chemist4 ,many pigments can be made according to a settled formula1 but the results of working strictly according to the formula1 without a knowledge of the reasons for the operations1 can only be satisfactory whilst no irregularity occurs4 ,the least irregularity places those who work blindly in a completely helpless position1 for they do not know what is wrong and cannot remove the hindrance4 ,in the manufacture of pigments certain by-products are produced4 ,these can be utilised by a manufacturer possessed of chemical knowledge1 whilst they are simply thrown away by many1 thus making the manufacture of the particular pigment far more expensive than when the by-product is also made valuable4 ,strictly speaking1 there are no worthless by-products in making pigments1 every liquid obtained in precipitating a colour might be further utilised4 ,salt solutions can only be regarded as worthless by-products when the cost of separating the salt from the solution would be greater than the value of the product4 ,thus we cannot conclude this section of the work without again insisting that the study of chemistry is indispensable to the colour maker1 since his industry is chemical from beginning to end4 ,the colour maker who works simply by recipes will never raise himself above the position of an ordinary workman1 who does what he is told without thinking of what he is doing4 ,the smallest mistake in carrying out the process generally results in the complete failure of the whole operation and thus causes the manufacturer material loss4 ,,chapter ,,lxxiii4 ,,the ,,design ,,of ,a ,,colour ,,works4 ,in the establishment of a colour works several conditions are necessary4 ,the most important is the supply of water in sufficient quantity and purity4 ,it has already been stated that many pigments cannot be made with water containing much organic matter or salts1 since the dissolved substances affect the shade4 ,this action not only takes place in the formation of the colour1 but is also unpleasantly manifest when it is washed4 ,the delicate lakes are discoloured by organic matter in the water1 and are so changed by any considerable quantity of lime that the alteration in shade is clearly perceptible after continued treatment4 ,if the water contains but a very small quantity of iron1 the preparation of some pigments is made quite impossible1 since--and this is especially the case with the lakes--the ferric oxide is precipitated together with the pigment1 and in consequence of its characteristic colour imparts to it an ugly shade4 ,thus in choosing a site for a colour works the available water supply must be carefully examined4 ,if it is not sufficiently pure or in sufficient quantity1 the position must be regarded as unsuitable4 ,no colour maker1 although working on the largest scale1 is in a position to make all the materials he requires4 ,with the continual development of the chemical industries1 the number of these substances which can be made economically in the colour works continually diminishes4 ,it is far more advantageous to obtain them from works in which they are made on the large scale4 ,many of these substances are required in large quantity1 so that a site should be chosen in direct communication with the railway1 so that the cost of carriage is diminished1 and also the cost of distributing the manufactured materials4 ,this is especially necessary for materials which have a low value and consequently can bear no high cost of carriage4 ,in regard to the space required by a colour works1 no actual dimensions can be given1 since these vary with the extent of the business1 and with the pigments produced4 ,in the price lists of large colour works all the commercial pigments are generally quoted1 but they are rarely if ever actually made in one works1 but are obtained at a lower price from other establishments1 which make a speciality of certain pigments1 and by working on a large scale can produce them at such a cost that the smaller manufacturer is not in a position to compete with them4 ,thus there are works in which only white lead or ultramarine is made4 ,if a colour manufacturer is in the fortunate position of placing his works on a river1 he has not only an unrestricted water supply1 but may also be able to use water power1 the cheapest of all powers4 ,when water power is available1 it will be used to raise the large volumes of water required and to move the machinery for grinding the raw materials1 rasping dye-woods1 etc4 ,in a colour works of any size a boiler is required2 if water power is not used1 it must be of sufficient power to give steam for driving the engine1 for boiling liquids and for heating the drying stoves4 ,the boiler is of great advantage in providing steam for dissolving salts1 extracting dye-woods and boiling liquids4 ,when liquids are boiled by steam there is considerable economy in that the majority of the boiling tubs can be of wood1 which is provided with a protective coating for liquids which attack wood4 ,thus there is economy in dispensing with large metal pans and with the fireplaces in which they would be built1 and also in the course of time there is considerable saving in fuel4 ,for a well-equipped colour works a drying stove1 in which the pigments can be thoroughly dried1 is important4 ,it is most convenient to heat drying stoves with steam4 ,the temperature can be easily regulated by increasing or diminishing the supply of steam4 ,for drying pigments which would not be injured by considerable increase of temperature1 the drying stove may be heated by a fire4 ,in a colour works in which many pigments are made sulphuretted hydrogen is frequently required4 ,since all lead pigments are blackened by this gas1 the greatest care is required in using it4 ,also the poisonous nature of sulphuretted hydrogen is generally under-estimated4 ,in working with sulphuretted hydrogen1 the apparatus depicted in ,fig4 #c should be used4 ,it should be placed in a position1 such as a closed yard1 in which escaping gas will be harmless4 ,if this cannot be done the precipitation should be accomplished in closed vessels1 from which a pipe should carry the gas to a fire1 where it will be burnt to sulphur dioxide and water4 ,in most cases the manufacturer of colours makes but a certain number of pigments and rarely or never all which are mentioned in his price lists4 ,the dimensions of the establishment will be in accordance4 ,in commencing a new colour works it is advisable from purely financial reasons to produce at first a limited number of colours1 but these in perfection4 ,by many experiments and diligent study of chemistry a colour manufacturer may hope to compete successfully in so difficult a branch of chemical technology as the manufacture of colours4 ,,chapter ,,lxxiv4 ,,commercial ,,names ,,of ,,pigments4 ,in commerce the pigments are found under the most different names1 the most common of which have been given together with the description of the pigment4 ,no regularity can be found in the names chosen for the different pigments2 quite arbitrary designations have been taken4 ,pigments are most commonly named after places--for example1 ,prussian blue1 ,paris blue1 ,bremen green2 also after the discoverer--,turnbull's blue1 ,hatchett brown4 ,whilst these names give the place of production or the name of the discoverer1 and thus have some foundation1 there are many others for which no reason can be assigned1 e4g41 ,king's yellow4 ,certain names are based upon the chemical composition of the pigment4 ,these should be used by preference1 but now that the expressions white lead1 chrome yellow and ,chinese blue have become common no one would think of speaking of basic lead carbonate1 lead chromate or ferric ferrocyanide4 ,the confusion in the nomenclature of colours is increased by placing pigments which possess ,english names upon the market under ,french1 ,german or ,latin names1 which are often sadly mutilated4 ,this is more the case in ,germany than in ,england4 ,it may easily happen that a reader of a work on colour making might search in vain for a pigment whose name he had somewhere heard1 whilst the book contained a description of the colour and its properties1 but under another name4 ,to remove this difficulty it has been thought necessary to collect the names of the different pigments1 which are contained in the following table4 ,the ,french and ,german names are also given4 ,the most usual names are printed in italics4 ,,white ,,pigments4 ,basic ,lead ,carbonate4--,white lead1 flake white4 ,cruse1 blanc de plomb1 blanc d'argent1 blanc de neige1 fleur de neige1 blanc de ,venise4 ,bleiweiss1 ,schieferweiss1 ,schneeweiss1 ,silberweiss1 ,kremserweiss1 ,kremnitzerweiss1 ,berlinerweiss1 ,venetianerweiss1 ,hollanderweiss1 ,hamburgerweiss4 ,lead ,oxychloride4--,pattison's white lead4 ,blanc de ,pattison1 blanc d',angleterre4 ,bleiweiss1 ,pattisonweiss1 englisches ,patentweiss4 ,lead ,sulphate4--,lead bottoms4 ,cruse de ,mulhouse4 ,bleiweiss1 ,vitriolweiss4 ,barium ,sulphate4--,enamel white1 permanent white1 blanc fixe1 baryta white4 ,blanc fixe1 blanc permanent4 ,permanentweiss1 ,barytweiss1 ,schneeweiss1 ,mineralweiss1 ,neuweiss4 ,zinc ,oxide4--,zinc white1 permanent white1 flowers of zinc4 ,blanc de zinc1 oxyde de zinc1 fleur de zinc4 ,zinkweiss1 ,zinkblumen1 weisses ,nichts1 ,ewigweiss4 ,basic ,bismuth ,nitrate4--,pearl white1 bismuth white1 ,spanish white4 ,blanc d',espagne1 blanc de bismuth1 blanc de fard4 ,wismuthweiss1 ,spanischweiss1 ,perlweiss1 ,schminkweiss4 ,,yellow ,,pigments4 ,lead ,chromate4--,chrome1 ,chrome yellow4 ,jaune de chrome1 jaune d'or4 ,chromgelb1 ,knigsgelb1 ,citronengelb1 ,neugelb1 ,parisergelb1 ,leipzigergelb1 ,klnergelb1 ,zwickauergelb1 amerikanisches ,gelb4 ,lead ,oxide4--,litharge1 massicot4 ,bleigltte1 ,gltte1 ,massicot4 ,lead ,oxychloride4--,patent yellow4 ,jaune minral1jaune brevet1 jaune de ,montpellier4 ,casselergelb1 ,veronesergelb1 ,mineralgelb1 ,patentgelb1 ,englischgelb1 ,parisergelb1 ,montpelliergelb4 ,lead ,antimoniate4--,naples yellow4 ,jaune de ,naples1 jaune d'antimoine4 ,neapelgelb1 ,antimongelb4 ,giallolino1 ,giallo di ,napoli4 ,barium ,chromate4--,lemon yellow1 baryta yellow1 yellow ultramarine1 permanent yellow4 ,barytgelb1 gelbes ,ultramarin1 ,chromgelb4 ,zinc ,chromate4--,zinc yellow1 zinc chrome4 ,jaune de zinc1 jaune permanent1 jaune bouton d'or1 jaune de chrome inaltrable1 jaune d'outremer4 ,zinkgelb1 ,chromgelb4 ,cadmium ,sulphide4--,cadmium yellow1 aurora yellow4 ,jaune brillant4 ,cadmiumgelb4 ,basic ,mercuric ,sulphate4--,turpeth mineral1 mercury yellow4 ,jaune de mercure4 ,mercurgelb1 ,knigsgelb1 mineralischer ,turpeth4 ,cobalt ,potassium ,nitrite4--,aureolin1 cobalt yellow4 ,jaune indien4 ,kobaltgelb4 ,arsenic ,disulphide and ,trisulphide4--,realgar1 orpiment1 ,king's yellow4 ,orpiment1 jaune royal4 ,realgar1 ,auripigment1 ,rauschgelb1 ,rauschroth1 ,knigsgelb1 ,chinagelb1 ,persischgelb1 ,spanischgelb4 ,stannic ,sulphide4--,mosaic gold4 ,musivgold4 ,,yellow ,,lakes4 ,dutch pink1 ,french yellow1 stil de grain1 jaune d',avignon1 jaune franais1 ,schttgelb4 ,yellow lake1 jaune de gauche1 ,waulack4 ,indian yellow1 jaune indien1 ,purre1 ,indischgelb4 ,gamboge1 gomme-goutti1 ,gummigutt1 ,gummigutti4 ,,red ,,pigments4 ,basic ,lead ,chromate4--,chrome red1 orange chrome1 ,persian red1 ,derby red1 ,chinese red4 ,jaune d'or1 jaune orange1 pte orange4 ,chromroth1 ,chromorange4 ,mercuric ,sulphide4--,vermilion1 cinnabar4 ,vermillion1 cinabre4 ,zinnober1 ,vermillon1 ,chinesischroth1 ,patentroth4 ,mercuric ,iodide4--,scarlet4 ,ecarlate4 ,jodinroth1 ,scharlachroth4 ,ferric ,oxide4--,rouge1 colcothar1 ,indian red1 ,venetian red1 crocus1 caput mortuum1 ,mars red4 ,rouge des ,indes1 rouge de ,mars1 rouge d',angleterre4 ,englischroth1 ,engelroth1 ,berlinerroth1 ,knigsroth1 ,kaiserroth1 ,neapelroth1 ,indischroth1 ,persischroth1 ,eisensafran1 ,todtenkopfroth1 ,marsroth4 ,cobalt ,phosphate or ,arsenate4 ,chaux mtallique4 ,kobaltrosa4 ,,red ,,lakes4 ,cochineal ,lakes4--,carmine1 crimson lake4 ,laque carmine4 ,carmin1 ,cochenilleroth1 ,mnchenerlack1 ,wienerlack1 ,florentinerlack1 ,pariserlack4 ,lac ,dye4 ,lack-lack1 ,lack-dye4 ,madder ,lakes4--,rose madder1 purple madder1 madder carmine4 ,laque de garance4 ,krapplack1 ,wienerlack1 ,krappcarmin1 ,garancincarmin4 ,red ,wood ,lakes4--,rose pink1 ,florentine lake4 ,laque en boules1 laque de ,vienne1 laque de ,venise1 laque de ,florence4 ,kugellack1 ,mnchenerlack1 ,wienerlack1 ,berlinerlack1 ,florentinerlack1 ,venezianerlack1 ,neulack4 ,carthamine4--,safflower1 ,spanish red4 ,rouge de carthame1 rouge de ,chine1 rouge d'or1 rouge en cailles1 rouge vgtal1 rouge de ,portugal4 ,safflorcarmine1 ,safflorroth1 ,tassenroth1 ,tellerroth1 ,vegetalroth4 ,,blue ,,pigments4 ,ferric ,ferrocyanide4--,prussian blue1 ,chinese blue1 ,paris blue1 ,berlin blue1 ,brunswick blue4 ,bleu de ,prusse1 bleu de ,paris1 bleu de ,berlin1 bleu d',anvers4 ,pariserblau1 ,berlinerblau1 ,preussischblau1 ,schsischblau1 ,neublau1 ,oelblau1 ,wasserblau1 ,mineralblau1 ,erlangerblau1 ,zwickauerblau1 ,waschblau1 ,louisenblau1 ,raymondblau4 ,ferrous ,ferricyanide4--,turnbull's blue4 ,bleu de ,turnbull4 ,turnbull's ,blau4 7,the names given under ferric ferrocyanide are also used47 ,ultramarine4--,lime blue1 ,royal blue4 ,outremer1 bleu d'azur4 ,ultramarin1 ,azurblau1 ,lazurblau1 ,lapis lazuli-,blau4 ,copper ,hydroxide or ,carbonate 7singly or together74 --,blue verditer1 lime blue1 mountain blue4 ,bleu de montagne1 bleu de chaux1 bleu de cuivre1 cendres bleues1 bleu de ,payen4 ,bergblau1 ,mineralblau1 ,oelblau1 ,kalkblau1 ,neubergblau1 ,kupferblau1 ,bremerblau1 ,steinblau1 ,hamburgerblau1 ,neuwiederblau1 ,casselerblau4 ,cobalt ,oxide ,alumina ,compound4--,cobalt blue1 ,thnard's blue4 ,bleu de ,thnard1 bleu de cobalt4 ,kobaltblau1 ,thnard'sches ,blau1 ,kobalt-ultramarin1 ,knigsblau1 ,leydenerblau1 ,leithnerblau1 ,wienerblau1 ,cruleum4 ,cobalt ,potassium ,silicate4--,smalts4 ,bleu de smalt1 bleu d'azur1 bleu de ,saxe4 ,smalte1 ,schmalte1 ,blaufarbenglas1 ,schsischblau1 ,streublau1 ,knigsblau1 ,kaiserblau1 ,azurblau1 ,eschel4 ,,blue ,,organic ,,pigments4 ,indigo ,sulphonates4--,indigo carmine1 soluble indigo4 ,bleu de ,saxe4 ,indigocarmin1 ,carminblau1 prcipitirter ,indigo1 ,carminblau4 ,indigo ,lake4--,bleu d',angleterre1 bleu de ,hollande4 ,neublau1 ,waschblau1 ,hollnderblau1 ,englischblau1 ,tafelindigo4 ,,green ,,pigments4 ,copper ,carbonate4--,mountain green1 ,hungarian green1 lime green4 ,vert de montagne1 vert minral1 vert de cuivre1 vert de ,hongrie4 ,berggrn1 ,kupfergrn1 ungarisches ,grn1 ,tirolergrn1 ,malachitgrn1 ,mineralgrn1 ,schiefergrn1 ,glanzgrn1 ,staubgrn1 ,wiesengrn1 ,apollogrn1 ,wassergrn1 ,oelgrn1 ,alexandergrn4 ,copper ,arsenite4--,scheele's green1 verditer1 lime green1 mineral green4 ,vert de ,sude1 vert de ,scheele4 ,scheel'sches ,grn1 ,schwedisches ,grn1 ,mineralgrn1 ,braunschweigergrn1 ,neuwiedergrn1 ,erdgrn1 ,aschengrn4 ,copper ,aceto-,arsenite4--,emerald green4 ,vert de ,vienne1 vert de ,mitis1 vert brevet4 ,schweinfurter ,grn1 ,mitisgrn1 ,wiesengrn1 ,englischgrn1 ,patentgrn1 ,hrmann's ,grn1 ,papageigrn1 ,kaisergrn1 ,knigsgrn1 ,wienergrn1 ,kirchbergergrn1 ,leipzigergrn1 ,zwickauergrn1 ,baslergrn1 ,parisergrn1 ,neuwiedergrn1 ,wrzburgergrn1 ,originalgrn1 ,jasngergrn4 ,copper ,stannate4 ,gentele's ,grn1 ,zinngrn4 ,copper ,oxychloride4-- ,kuhlmann's ,grn1 ,elsner's ,grn1 giftfreies ,grn4 ,copper ,borate4 ,borgrn1 ,kupfergrn1 giftfreies ,kupfergrn4 ,copper ,acetate4--,verdigris1 distilled or crystallised verdigris4 ,vert de gris1 vert de gris naturel1 vert de gris distill1 vert de gris en grappes4 ,grnspan1 destillirter1 franzsischer1 deutscher1 prcipitirter or krystallisirter ,grnspan4 ,chromium ,oxide and ,hydroxide4--,guignet's green1 chrome green1 lime green1 viridian4 ,vert de chrome1 vert ,pannetier1 vert ,guignet1 vert de soie1 vert meraude1 vert naturel1 vert virginal4 ,chromgrn1 grner ,zinnober1 ,laubgrn1 ,smaragdgrn1 ,deckgrn1 ,myrthengrn1 ,permanentgrn1 ,amerikanergrn1 ,neapelgrn1 ,gothaergrn1 ,guignet's ,grn1 ,mittler's ,grn1 ,pannetier's ,grn1 ,chromgrn in ,lack1 ,tkisgrn1 ,seidengrn1 ,naturgrn4 ,the green produced by mixing chrome yellow with ,prussian blue is known in ,england as chrome green1 ,brunswick green1 oil green1 etc41 and on the continent by the names given above for chromium oxide4 ,chromium ,phosphate4--,arnaudan's green4 ,vert ,arnaudan1 vert de ,plessy4 ,arnaudan's1 ,plessy's1 ,schnitzer's ,grn4 ,cobalt ,oxide-,zinc ,oxide4--,cobalt green1 ,rinmann's green4 ,vert de ,rinmann1 vert de cobalt4 ,kobaltgrn1 ,rinmann's ,grn1 ,zinkgrn1 permanenter grner ,zinnober4 ,barium ,manganate4--,rosenstiehl's green4 ,vert tiges de roses4 ,mangangrn1 ,rosenstiehl's ,grn1 ,bttger's ,grn4 ,,violet ,,pigments4 ,chromic ,chloride4 ,chrombronze1 ,permanentbronze1 ,tapetenbronze4 ,manganese ,phosphate4--,nuremberg violet4 ,manganviolett1 ,nrnberger ,violett4 ,,brown ,,pigments4 ,lead ,peroxide4 ,bleibraun1 ,flohbraun4 ,manganic ,oxide and ,peroxide4--,manganese brown4 ,brun de ,mangane1 bistre minral4 ,manganbraun1 ,bisterbraun1 ,mineralbister1 ,kastanienbraun1 ,braunsteinbraun4 ,copper ,potassium ,ferrocyanide4--,hatchett brown4 ,brun de ,prusse4 ,hatchett's ,braun1 ,kupferbraun1 ,chemischbraun1 ,breslauerbraun4 ,ferric ,oxide4--,brown ochre1 ,mars brown4 ,eisenbraun1 ,van ,dyck ,braun1 ,ockerbraun1 ,sienabraun4 ,prussian brown is ,prussian blue decomposed by heat 7see page #bhj74 ,chrome brown and cobalt brown 7see pages #bhj1 #bha74 ,,black ,,pigments4 ,carbon4--,ivory black1 bone black1 ,frankfort black1 vine black1 vegetable black1 drop black1 carbon black1 lamp black4 ,noir d'ivoire1 noir de ,frankfort1 noir de ,cologne1 noir d',allemagne4 ,kienruss1 ,flatterruss1 ,russschwarz1 ,rebenschwarz1 ,hefeschwarz1 ,beinschwarz1 ,spodium1 ,elfenbeinschwarz1 ,frankfurterschwarz1 ,pariserschwarz1 ,wienerschwarz1 ,lampenschwarz1 ,oelschwarz1 ,spanischschwarz1 ,drusenschwarz4 ,carbon mixed with ,other ,substances4 ,neutral tint1 composition black1 neutral black4 ,teint neutre1 noir de composition4 ,compositionsschwarz1 ,neutraltinte1 ,naturaltinte4 ,indian ink4 ,encre de ,chine4 ,tusche4 ,,appendix4 ,,the ,,conversion ,,of ,,metric ,,into ,,english ,,weights ,,and ,,measures4 ,the conversion of metric into ,english weights and measures can be readily accomplished by means of the following relationships3-- ,,measures ,,of ,,length4 #a metre #ajj centimetres #cicg inches4 #a foot ,o#ccha metre4 ,,measures ,,of ,,capacity4 #a litre #a1jjj cubic centimetres #bbji gall4 #a gall4 #dedcf litres4 ,,measures ,,of ,,weight4 #a kilogramme #a1jjj grammes #bbje lb4 #a gramme #aeddc grains4 #a cwt4 #ejhjb kilogrammes4 ,,centigrade ,,and ,,fahrenheit ,,thermometer ,,scales4 ,to convert temperatures expressed in ,centigrade degrees to ,fahrenheit degrees multiply by #i1 divide by #e1 and add #cb4 ,to convert temperatures expressed in ,fahrenheit degrees to ,centigrade degrees subtract #cb1 multiply by #e1 and divide by #i4 ,,index4 ,acid1 acetic1 #cj4 -- carbonic1 #cj4 -- hydrochloric1 #be4 -- nitric1 #bh4 -- oxalic1 #ca4 -- sulphuric1 #bg4 -- tartaric1 #ca4 ,acids1 #be4 ,alizarin1 #cgb4 ,alkalis1 #cb4 ,alkanet1 #cfh4 ,alum1 ammonia1 #dh4 -- ,roman1 #df4 -- soda1 #dg4 ,alumina1 #di4 -- gold purple1 #aic4 ,aluminium compounds1 #db4 -- sulphate1 #dc4 ,alums1 #dd4 ,ammonia1 #bc4 -- cochineal1 #cfb4 ,ammonium chloride1 #be4 -- sulphide1 #be4 ,annaline1 #aca4 ,antimony blue1 #agi4 -- compounds1 #ei4 -- oxychloride1 #abi4 -- trioxide1 #abi4 -- vermilion1 #agh4 -- yellow1 #aea4 ,antwerp blue1 #bjc4 ,apparatus1 washing1 #abj4 ,appendix1 #dfi4 ,aqua regia1 #bi4 ,archil1 #cha4 ,arsenic compounds1 #ei4 ,asphaltum1 #dad4 ,aureolin1 #aef4 ,barium carbonate1 #db4 -- chloride1 #da4 -- compounds1 #da4 -- green1 ,bttger's1 #bga4 -- sulphate1 #aaf4 -- yellow1 #aeb4 ,barytes1 #aaf4 ,bismuth compounds1 #ei4 -- white1 #acj4 ,bistre1 #bhd4 ,black1 bone1 #bij4 -- charcoal1 #bhf4 -- chrome1 #cah4 -- chrome-copper1 #cah4 -- enamel1 #cbe4 -- ivory1 #bij4 -- lamp1 #cjg4 -- neutral tint1 #cah4 -- pigments1 #bhe1 #ddd4 -- pine1 #cab4 -- soot1 #bid1 #cac4 -- vine1 #bhh4 ,blowpipe1 #dcf4 ,blue1 antimony1 #agi4 -- ,antwerp1 #bjc4 -- ,bremen1 #bbf4 -- ,brunswick1 #bjj4 -- ,chinese1 #aif1 #bja4 -- chrome1 #bfg4 -- cobalt1 #bcj4 -- copper pigments1 #bbf4 -- ,egyptian1 #bej4 -- enamels1 #cbc4 -- lakes1 #cij1 #cig4 -- lime1 #bbh4 -- manganese1 #bgb4 -- mineral1 #bjj4 -- mineral pigments1 #aid4 -- molybdenum1 #bci4 -- ,neuberg1 #bbg4 -- oil1 #bbh4 -- ,payen's1 #bbh4 -- pigments1 examination of1 #dda4 -- ,prussian1 #aii4 -- ,soluble ,prussian1 #bjj4 -- ,tessi du ,motay's1 #bic4 -- tungsten1 #bch4 -- ,turnbull's1 #bjc4 -- ultramarine1 #bjd4 -- -- pale1 #bbc4 -- verdigris1 #beb4 ,bone black1 #bij4 ,bttger's barium green1 #bga4 ,brasilen1 #chd4 ,brasilin1 #chd4 ,brazil wood1 #chd4 ,bremen blue1 #bbf4 -- green1 #bbf4 ,brocade pigments1 #cda4 ,bronze1 electrolytic copper1 #ccg4 -- pigments1 #cbi4 -- pigments1 tungsten1 #cch4 ,brown1 chrome1 #bhj4 -- cobalt1 #bha4 -- copper1 #bhj4 -- decomposition products1 #bhc4 -- ,hachett's1 #bhj4 -- iron1 #bhj4 -- lead1 #bgi4 -- manganese1 #bgi4 -- mineral pigments1 #bgi4 -- organic pigments1 #dad4 -- pigments1 examination of1 #ddc4 -- ,prussian1 #bhj4 -- pyrolusite1 #bgi4 ,brunswick green1 #bdc4 ,cadmium compounds1 #ec4 -- yellow1 #aec4 ,cruleum1 #bca4 ,calcium carbonate1 #dj4 -- compounds1 #ci4 -- hydroxide1 #ci4 -- oxide1 #ci4 -- phosphate1 #dj4 -- sulphate1 #dj4 ,carajuru1 #cgi4 ,carbon1 #cj4 ,carmine1 #ced1 #ceg4 -- indigo1 #cid4 -- madder1 #cgf4 -- safflower1 #cfg4 ,carthamine red1 #cff4 ,casselmann's green1 #bdi4 ,cassel yellow1 #adh4 ,cassius1 purple of1 #aij4 ,caustic potash1 #cc4 ,caustic soda1 #cg4 ,charcoal blacks1 #bhf4 ,charvin's green1 #dab4 ,chica red1 #cgi4 ,chinese blue1 #aif1 #bja4 -- green1 #daa4 -- vermilion1 #agj4 ,chlorine1 #bj4 ,chlorophyll1 #dji4 ,chromaventurine1 #bff4 ,chrome alum1 #ce4 -- black1 #cah4 -- blue1 #bfg4 -- brown1 #bhj4 -- copper black1 #cah4 -- green1 #bfj1 #bgd4 -- -- ,elsner's1 #bgd4 -- -- lake1 #bfd4 -- red1 #ahf4 -- yellow1 #acd4 -- -- cadmium1 #aec4 -- -- calcium1 #aea4 -- -- pale1 #aci4 -- -- zinc1 #aeb4 ,chromic chloride1 #bgf4 ,chromium compounds1 #eh4 -- oxide1 #bfj4 -- stannate1 #ahi4 ,chrysean1 #afb4 ,cobalt arsenate1 #ahi4 -- blue1 #bcj4 -- brown1 #bhj4 -- compounds1 #ef4 -- green1 #bfh4 -- magnesia red1 #ahh4 -- red1 #ahh4 -- ultramarine1 #bcj4 -- zinc phosphate1 #bcb4 ,cochineal1 #ced4 ,colorimeter1 #dej4 ,colours1 simple and mixed1 #ga4 ,colour works1 design of1 #deg4 ,commercial names of pigments1 #dfj4 ,confectionery colours1 #dbg4 ,copper acetate1 #fe4 -- arsenite1 #bda4 -- borate1 #bej4 -- brown1 #bhj4 -- carbonate1 #bdj4 -- compounds1 #fe4 -- hydroxide1 #bbi4 -- nitrate1 #fe4 -- oxychloride1 #bdc4 -- silicate1 #bej4 -- stannate1 #bdh4 -- sulphate1 #fe4 -- violet1 #bgh4 ,covering power1 #aj4 ,crayons1 #dbc4 ,cream of tartar1 #cd4 ,cudbear1 #chb4 ,curucuru1 #cgi4 ,design of a colour works1 #deg4 ,dextrine1 #dbj4 ,drying oils1 #dbi4 -- stove1 #dei4 ,dutch pink1 #cdh4 ,dye-woods1 #ddi4 ,egyptian blue1 #bej4 ,elsner's chrome green1 #bgd4 -- green1 #bdi4 ,emerald green1 #bdd1 #bfd4 ,enamel colours1 #cai4 ,enamel white1 #aaf4 ,enamels1 black1 #cbe4 -- blue1 #cbc4 -- green1 #cbd4 -- red1 #cbb4 -- violet1 #cbd4 -- white1 #cbj4 -- yellow1 #cbb4 ,examination of pigments1 #dcd4 ,extracts1 #cih1 #djb4 ,fernambuco wood1 #chd1 #chf4 ,ferric oxide pigments1 #ahj4 ,ferrous chloride1 #ed4 -- sulphate1 #ed4 ,filter press1 #abd1 #abe4 ,florentine lake1 #cfa4 ,french purple1 #ch4 ,fustic lake1 #cea4 ,gamboge lake1 #cdi4 -- prepared1 #cej4 ,garanceux1 #cgb4 ,garancin1 #cga4 ,gardinia grandiflora1 colouring matter of1 #cec4 ,glucose1 #dbb4 ,gold1 compounds of1 #fi4 ,green1 ,arnaudan's1 #bfe4 -- ,bremen1 #bbf4 -- ,brunswick1 #bdc4 -- ,casselmann's1 #bdi4 -- ,charvin's1 #dab4 -- ,chinese1 #daa4 -- chrome1 #bfj1 #bgd4 -- cobalt1 #bfh4 -- ,elsner's1 #bdi4 -- emerald1 #bdd1 #bfd4 -- enamel1 #cbd4 -- ,guignet's1 #bfd4 -- ,kuhlmann's1 #bdi4 -- lakes1 #dji4 -- leaf1 #bfe4 -- lime1 #bej4 -- manganese1 #bgj4 -- mineral pigments1 #bdj4 -- natural1 #bge4 -- ,neuwied1 #bdc4 -- non-arsenical1 #bge4 -- patent1 #bej4 -- pigments1 compounded1 #bgc4 -- pigments1 examination of1 #ddb4 -- ,plessy's1 #bff4 -- ,rosenstiehl's1 #bgj4 -- sap1 #daj4 -- ,scheele's1 #bda4 -- ,schnitzer's1 #bff4 -- silk1 #bge4 -- ,turkish1 #bfe4 -- verditer1 #bdc4 -- ,vienna1 #bdh4 ,guignet's green1 #bfd4 ,gum ,arabic1 #dbj4 ,guyard's violet1 #bgh4 ,gypsum1 #dj4 ,hachett's brown1 #bhj4 ,hmaten1 #djf4 ,hmatoxylin1 #djf4 ,humins1 #bhc4 ,hydrometer1 #bd4 ,indian ink1 #caf4 -- madder1 #cgh4 -- red1 #ahe4 -- yellow1 #ceb4 ,indigo1 #cij4 -- carmine1 #cid4 ,introduction1 #a4 ,iron brown1 #bhj4 -- compounds1 #ed4 -- red1 #ahb4 ,ivory black1 #bij4 ,kuhlmann's green1 #bid4 ,lac1 #cfc4 -- dye1 #cfc4 ,lake1 blue1 #cij1 #cig4 -- ,florentine1 #cfa4 -- fustic1 #cea4 -- gamboge1 #cdi4 -- green1 #dji4 -- quercitron1 #cea4 -- weld1 #cdi4 ,lakes1 #f1 #i1 #cdc4 -- examination of1 #dde4 -- madder1 #cge4 -- red1 #ced4 -- yellow1 #cdh4 ,lamp black1 #cjg4 ,lead acetate1 #fb4 -- antimonate1 #aae4 -- antimonite1 #aae4 -- arsenite1 #aei4 -- brown1 #bgi4 -- chloride1 #fd4 -- chromate1 #acd4 -- compounds1 #fj4 -- iodide1 #aed4 -- monoxide1 #adc4 -- nitrate1 #fa4 -- orange1 #adf4 -- oxychloride1 #aac4 -- red1 #add4 -- sulphate1 #fa1 #aab4 -- sulphite1 #aad4 -- tungstate1 #abh4 -- white1 #gc1 #gd1 #ge1 #gg4 -- white1 hard and soft1 #aia4 ,leaf green1 #bfe4 ,lichens1 #chj4 ,lime1 #ci4 -- blue1 #bbh4 -- green1 #bej4 ,litharge1 #adc4 ,lithophone1 #aai4 ,litmus1 #chb4 ,logwood1 #cih4 ,lokao1 #dd4 ,madder1 #cgj4 -- carmine1 #cgf4 -- extract1 #cgb4 -- ,indian1 #cgh4 -- lakes1 #cge4 ,magnesia1 gold purple1 #aib4 -- white1 #acj4 ,magnesium carbonate1 #da4 ,manganese blue1 #bgb4 -- brown1 #bgi4 -- compounds1 #ei4 -- green1 #bgj4 -- sulphate1 #ef4 -- violet1 #bgh4 -- white1 #acj4 ,manganous oxide1 #bgb4 ,mangit1 #cgh4 ,mars yellow1 #aee4 ,massicot1 #adc4 ,mercuric ammonium chloride1 #age4 -- chloride1 #fh4 -- iodide1 #agf4 -- nitrate1 #fh4 -- sulphite1 #afc4 ,mercurous chloride1 #fh4 -- nitrate1 #fg4 ,mercury compounds1 #fg4 -- yellow1 #aeh4 ,metallic pigments1 #cbf4 ,metals1 heavy1 #ea4 ,mills1 paint1 #dcj4 -- white lead1 #hf4 ,mineral lake1 #bgh4 ,molybdenum blue1 #bci4 -- compounds1 #ei4 ,montpellier yellow1 #adh4 ,mosaic gold1 #afj4 ,naples yellow1 #adi4 ,natural green1 #bge4 ,neuberg blue1 #bbg4 ,neutral tint black1 #cah4 ,neuwied green1 #bdc4 ,nickel compounds1 #ef4 -- yellow1 #aeg4 ,non-arsenical green1 #bge4 ,oil blue1 #bbh4 ,orange lead1 #adf4 -- ,mars1 #aee4 ,orcen1 #cjj4 ,orcinol1 #chj4 ,orpiment1 #aei4 ,paint mills1 #dcj4 ,patent green1 #bej4 ,payen's mountain blue1 #bbh4 ,permanent yellow1 #aeb4 ,pigments1 artificial mineral1 #f4 -- commercial names of1 #dfj4 -- earth1 #f4 ,pine black1 #cab4 ,pink1 ,dutch1 #cdh4 ,plessy's green1 #bff4 ,poisonous pigments1 #ac4 ,potassium alum1 #de4 -- bichromate1 #ce4 -- bitartrate1 #cd4 -- carbonate1 #cb4 -- compounds1 #cb4 -- ferricyanide1 #ce4 -- ferrocyanide1 #ce4 -- hydroxide1 #cc4 -- nitrate1 #cd4 -- sodium chromate1 #ce4 ,precipitation1 #g4 ,preparation of pigments1 #dbi4 ,prepared gamboge1 #cej4 ,prussian blue1 #aii4 -- brown1 #bhj4 ,purple1 alumina gold1 #aic4 -- ,french1 #cha4 -- magnesia gold1 #aib4 -- of ,cassius1 #aij4 -- red1 #ahi4 ,purpurin1 #cgc4 ,purree1 #ceb4 ,pyrolusite brown1 #bhj4 ,quercitron lake1 #cea4 ,quicklime1 #ci4 ,realgar1 #aei4 ,red1 carthamine1 #cff4 -- chica1 #cgi4 -- chrome1 #ahf4 -- cobalt1 #ahh4 -- -- magnesia1 #ahh4 -- enamels1 #cbb4 -- hmatite1 #ahj4 -- ,indian1 #ahe4 -- iron1 #ahb4 -- lakes1 #ced4 -- lead1 #add4 -- ,mars1 #aee4 -- mineral pigments1 #afc4 -- pigments1 examination of1 #ddj4 -- purple1 #ahi4 ,red wood lakes1 #chd4 ,rosenstiehl's green1 #bgj4 ,safflower1 #cff4 -- carmine1 #cfg4 ,saffron1 #ceb4 ,sal ammoniac1 #be4 ,salt1 common1 #ch4 ,sandalwood1 #chh4 ,sap colours1 #daf4 -- green1 #daj4 ,scheele's green1 #bda4 ,schnitzer's green1 #bff4 ,sepia1 #dad4 ,shell-gold1 #cbf4 ,shell-silver1 #cbg4 ,siderin yellow1 #aef4 ,silk green1 #bge4 ,silver chromate1 #ahi4 -- compounds1 #fi4 -- imitation1 #cbh4 ,smalts1 #bcc4 ,sodium chloride1 #ch4 -- hydroxide1 #cg4 -- salts1 #cg4 -- thiosulphate1 #ch4 ,soluble ,prussian blue1 #bjj4 ,soot black1 #cac4 -- pigments1 #bid4 ,stannic chloride1 #ei4 ,stannous chloride1 #ei4 ,stove1 drying1 #dei4 ,sulphuretted hydrogen1 #bf4 ,swedish green1 #bda4 ,tessi du ,motay's blue1 #bci4 ,thallium pigments1 #aei4 ,thnard's blue1 #bcj4 ,tin compounds1 #ei4 -- violet1 #bgh4 -- white1 #acj4 ,tragacanth1 #dbj4 ,tungsten blue1 #bch4 -- bronze pigments1 #cch4 -- compounds1 #ei4 -- yellow1 #aeg4 ,turkish green1 #bfe4 ,turnbull's blue1 #bjc4 ,turner's yellow1 #adi4 ,turpeth mineral1 #aeh4 ,ultramarine1 #c1 #bjd1 #baa4 -- artificial1 #bjf4 -- cobalt1 #bcj4 -- natural1 #bje4 -- violet1 #bai4 -- yellow1 #aeb4 ,vanadium compounds1 #ei4 ,vegetable bronze pigments1 #cci4 ,verdigris1 #beb4 -- blue1 #beb4 -- distilled1 #bee4 -- ,german1 #beh4 ,verditer1 green1 #bdc4 ,vermilion1 #c1 #afc1 #aff4 -- antimony1 #agh4 -- ,chinese1 #agj4 -- chrome1 #ahf4 ,vienna green1 #bdh4 ,vine black1 #bhh4 ,violet copper1 #bgh4 -- enamel1 #cbd4 -- ,guyard's1 #bgh4 -- manganese1 #bgh4 -- mineral pigments1 #bgf4 -- ,nuremberg1 #bgh4 -- tin1 #bgh4 -- ultramarine1 #bai4 ,vitriol1 blue1 #fe4 -- green1 #ed4 -- oil of1 #bg4 ,washing apparatus1 #abj4 ,water1 #af4 -- colours1 #dai4 -- -- moist1 #dbb4 -- examination of1 #bj4 -- hard1 #ag4 -- iron in1 #ah4 -- organic matter in1 #ah4 ,weld lake1 #cdi4 ,white1 bismuth1 #acj4 -- enamel1 #aaf1 #aba1 #cbj4 -- lead1 #gc1 #gd1 #ge4 -- lead mills1 #hf4 -- magnesia1 #aca4 -- manganese1 #acj4 -- mineral pigments1 #gb4 -- patent1 #gc4 -- permanent1 #aaf1 #aba4 -- pigments1 examination of1 #dcg4 -- tin1 #acj4 -- tungsten1 #abh4 -- zinc1 #abf4 ,witherite1 #db1 #aag4 ,yellow1 antimony1 #aea4 -- barium1 #aeb4 -- cadmium chrome1 #aec4 -- calcium chrome1 #aea4 -- ,cassel1 #adh4 -- chrome1 #acd4 -- enamels1 #cbb4 -- ,english1 #adi4 -- ,indian1 #ceb4 -- lakes1 #cdh4 -- ,mars1 #aee4 -- ,mercury1 #aeh4 -- mineral pigments1 #acc4 -- ,montpellier1 #adh4 -- ,naples1 #adi4 -- nickel1 #aeg4 -- pale chrome1 #aci4 -- pigments1 examination of1 #dci4 -- ,siderin1 #aef4 -- tungsten1 #aeg4 -- ,turner's1 #adi4 -- zinc chrome1 #aeb4 ,zinc chrome yellow1 #aeb4 -- oxide1 #ec4 -- sulphate1 #ec4 -- sulphide1 #aai4 -- white1 #abf4 -- -- ,griffith's1 #abh4 ,,the ,,aberdeen ,,university ,,press ,,limited4