,transcriber's ,note ,italic text is enclosed in underscores2 subscripts are enclosed in curly brackets4 ,additional notes will be found near the end of this ebook4 ,,the ,,manufacture ,,of ,,earth ,,colours ,,the ,,manufacture ,,of ,,earth ,,colours ,,by ,,dr4 ,,josef ,,bersch ,,translated ,,from ,,the ,,third ,,german ,,edition 7,,as ,,revised ,,by ,,prof4 ,,dr4 ,,wilhelm ,,bersch7 ,,by ,,charles ,,salter ,,with ,,thirty-,,one ,,illustrations ,,london ,,scott1 ,,greenwood ,,son #h ,,broadway1 ,,ludgate1 ,e4,c4#d #aiba ,the sole rights of translation in ,english remain with ,scott1 ,greenwood ,son4 ,,printed ,,in ,,great ,,britain ,,by ,,richard ,,clay ,,sons1 ,,limited1 ,,paris ,,garden1 ,,stamford ,,st41 ,s4,e4 #a1 ,,and ,,bungay1 ,,suffolk4 ,,preface ,originally issued as a volume of the series on pigments and colouring matters by the present author's father1 the necessity for a new edition afforded a welcome opportunity of revising 8,earth ,colours40 ,although1 in the nature of things1 little progress has been made in this subject itself1 there was a good deal to add in connection with the mechanical appliances for treating the colour earths and manufacturing them into pigments4 ,in other respects1 too1 the work has been carefully gone through and brought up to date1 with new and additional illustrations4 ,the author desires to express his thanks to the various firms who have afforded him assistance in his task by furnishing illustrations and descriptions of new machinery1 together with other information4 ,it is hoped that this third edition will meet the approval of those interested in the subject2 and the author will be glad to receive supplementary information to render the work more complete in the event of a future edition being found advisable4 ,,prof4 ,,dr4 ,,wilhelm ,,bersch4 #aiah4 ,,contents ,,chapter ,i ,,page ,,introductory #a ,,chapter ,,ii ,,the ,,raw ,,materials ,,for ,,earth ,,colours #h 7,a7 ,white ,raw ,materials and ,pigmentary ,earths #aa ,limestone 7,calcite1 ,limestone1 ,chalk7 #aa ,gypsum 7,alabaster7 #ah ,barytes1 or ,heavy ,spar #ai ,talc1 ,soapstone1 ,steatite #bj ,clay #ba 7,b7 ,yellow ,earths #bc ,brown ,ironstone #bc ,ochre #be ,yellow ,earth #bf ,terra di ,siena #bg 7,c7 ,the ,red ,earths #bg ,red ,ironstone #bh ,bole #ca ,alum ,sludge #cb ,mine ,sludge #cb 7,d7 ,blue ,earths #cc ,azurite1 or ,ultramarine #cc ,vivianite #cc 7,e7 ,green ,earth ,pigments #cd ,green ,earth #cd ,malachite #ce 7,f7 ,brown ,earth ,pigments #cf ,umber #cf ,asphaltum #cg 7,g7 ,black ,earth #ch ,black ,schist #ch ,graphite #ch ,,chapter ,,iii ,,the ,,preparation ,,of ,,the ,,colour ,,earths #dj ,crushing ,machinery #dc ,crushing and ,sifting #gg ,calcining #ha ,mixing and ,improving #ha ,moulding #he ,,chapter ,,iv ,,white ,,earth ,,colours #hg ,caustic ,lime #hg ,pearl ,white #id ,vienna ,white #ie ,chalk #ih ,precipitated ,chalk #ajg ,calcareous ,marl #aaj ,gypsum #aaa ,kaolin1 ,pipeclay #aab ,barytes1 or ,heavy ,spar #aai ,carbonate of ,magnesia #abc ,talc #abd ,steatite or ,soapstone #abe ,,chapter ,v ,,yellow ,,earth ,,colours #abg ,the ,ochres #abh ,calcining 7,burning7 ,ochre #acb ,ochres from ,various ,deposits #acf ,artificial ,ochres #ach ,ochres as ,by-products #adf ,,chapter ,,vi ,,red ,,earth ,,colours #aea ,bole #aeb ,native ,ferric ,oxide as a ,pigment #aed ,iron ,glance #aed ,hematite #aee ,raddle #aee ,burnt ,ferric ,oxide and ,ochres #aeh 7a7 ,burning in the ,muffle #aeh 7b7 ,caput ,mortuum1 ,colcothar #afj 7c7 ,calcining ,ferric ,oxide #afa ,ferric ,oxide ,pigments from ,alum ,sludge #afd ,,chapter ,,vii ,,brown ,,earth ,,colours #afh ,terra di ,siena #afh ,true ,umber #agj ,cologne ,earth 7,cologne ,umber7 #agc ,asphaltum ,brown 7,bitumen7 #agd ,,chapter ,,viii ,,green ,,earth ,,colours #agf ,green ,earth1 or ,celadon ,green #agf ,artificial ,green ,earth 7,green ,ochre7 #ahj ,malachite ,green #aha ,,chapter ,,ix ,,blue ,,earth ,,colours #ahc ,malachite ,blue 7,lazulite7 #ahc ,vivianite or ,blue ,ochre #ahd ,,chapter ,x ,,black ,,earth ,,colours #ahe ,graphite #ahe ,black ,chalk #aid ,,chapter ,,xi ,,the ,,commercial ,,nomenclature ,,of ,,the ,,earth ,,colours #aig ,white ,earth ,colours #aih ,yellow ,earth ,colours #bjj ,red ,earth ,colours #bjj ,brown ,earth ,colours #bjj ,green ,earth ,colours #bja ,blue ,earth ,colours #bjb ,grey ,earth ,colours #bjb ,black ,earth ,colours #bjb ,,index #bjc ,,earth ,,colours ,,chapter ,i ,,introductory ,both from the chemical and practical standpoint it is necessary to divide pigments into clearly defined groups1 the following classification being adopted on the basis and natural history of the substances concerned3-- 7#a7 ,pigments occurring native in a finished condition1 and only requiring mechanical preparation to fit them for use as painters' colours4 7#b7 ,pigments which are not ready formed in ,nature1 but contain some metallic compound as pigmentary material1 which requires certain chemical treatment for its full development4 7#c7 ,pigments which1 in contrast to these two groups1 contain only organic1 and no inorganic1 constituents4 ,this last class comprises all the natural vegetable pigments1 together with the large group of colours obtained artificially from tar products1 fresh groups of which are being continually introduced4 ,nowadays1 there is no longer any strict line of demarcation between the natural and artificial organic colouring matters1 it being possible to produce even those of the vegetable series1 such as madder and indigo1 by artificial means4 ,whilst this group of colours exhibits the greatest variety1 and is constantly being enriched and increased by the progress of colour chemistry1 the case is different with the first group1 the natural earth pigments4 ,here we have chiefly to do with the preparation of materials occurring in ,nature1 or with bringing about certain chemical results1 so that1 consequently1 the range of variety is far more restricted1 and there is little or no possibility of increasing the number of these colours by the manufacture of really new products4 ,the earth colours nevertheless have a high technical and economic importance1 on account of their extremely valuable properties1 coupled1 for the most part1 with low cost4 ,if the term 8earth colours0 were strictly adhered to1 the present work would have to be confined to a description of the physical and chemical properties of the various pigments1 and of the various means by which they can be brought into suitable condition for use in paints4 ,however1 of late1 the term has found wider application than formerly1 since it has been found practicable to modify 7shade7 certain of the earth colours by simple operations1 and thus considerably increase the range of tones of the substances known as earth colours4 ,the progress of chemical industry has also largely increased the number of the so-called earth colours1 certain methods of chemical treatment having enabled substances that are of little use for other purposes1 to be employed1 in large quantities1 as pigments4 ,the application of these--usually cheap--by-products is still further facilitated by the fact that they can be transformed1 by a simple chemical treatment1 into pigments which are distinguished by their beauty of colour and at the same time possess the great advantages of durability and cheapness4 ,as an example of this1 mention may be made of iron oxide1 which occurs in ,nature in the form of various minerals which can be made into pigments by mechanical treatment4 ,in many cases1 this treatment has already been carried out by ,nature1 and deposits of iron oxide are found in which the material has only to be incorporated with a vehicle to make it fit for immediate use as a painters' colour4 ,moreover1 the same oxide is obtained1 in large quantities1 as a by-product of the treatment of other minerals4 ,from the point of view of chemical composition1 this by-product is of very low value1 by reason of the large supplies of native oxide available4 ,by means of a very simple chemical treatment1 however1 this by-product oxide can be considerably improved in commercial value1 being1 in many cases1 convertible1 by merely heating it to certain temperatures1 into a variety of colours which sell at remunerative prices4 ,consequently1 in view of the present condition of the chemical industry1 the term 8earth colours0 can be enlarged to include a number of waste products which fetch good prices as colours1 though otherwise practically valueless in themselves4 ,the number of earth pigments is very large1 and comprises representatives of all the principal colours4 ,for painting purposes1 few pigments beyond the earth colours were known to the ancients2 and most of the colours in the paintings which have come down to us from antiquity are pure earth pigments1 thus affording proof of their great durability1 having retained their freshness unimpaired for hundreds--and some for thousands--of years4 ,the earth colours might be divided into such as occur ready-formed in ,nature1 and require only mechanical preparation1 and which either require special treatment 7e4 g4 calcining71 or are artificial products 7like the iron oxide mentioned above74 ,since1 however1 such a classification would not advantage our knowledge of the nature of this class of colours1 it appears useless and superfluous1 and we will therefore simply confine ourselves to arranging the earth pigments according to their colour--white1 yellow1 red1 etc4 ,adopting this classification1 the following minerals and chemical products may be considered as earth colours3-- ,white4--,these include the varieties of calcium carbonate1 such as chalk1 marble1 precipitated chalk1 calcium phosphate1 calcium sulphate 7in the form of gypsum1 alabaster1 muriacite and the precipitated gypsum produced as a by-product in many chemical works71 heavy spar1 the different varieties of clay1 and magnesia4 ,yellow4--,this group comprises ferric hydroxide 7hydrated oxide of iron7 in the form of the various minerals known as ochre2 all the preparations chiefly composed of this hydroxide1 and all those prepared by artificial means4 ,a very important member of this group is orpiment2 the other arsenical compounds frequently met with native1 being however1 on account of their poisonous properties1 no longer used as pigments4 ,red4--,chief among the red earth colours are those consisting of ferric oxide 7iron oxide71 under various names4 ,the only other member of the group is the far rarer vermilion4 ,blue4--,the blue earth colours are few in number and of no particular beauty2 but they are of importance on account of their cheapness and because all the artificial blue pigments are rather expensive4 ,two products in particular merit attention in this connection1 namely1 ultramarine1 and the mineral known as blue ochre or blue ironstone4 ,the latter1 as a matter of fact1 cannot be used for anything else than a painters' colour1 and can be obtained at a low price2 whereas ultramarine also forms a valuable raw material for the recovery of copper1 and is therefore dearer4 ,green4--,this group1 again1 contains only two members1 viz4 malachite green 7chrysocolla71 and the green earths 7seladonite71 known as ,verona1 etc41 green4 ,these occur fairly often in ,nature1 and the green earths in particular find a wide industrial application by reason of their low price4 ,malachite green is very similar1 in chemical constitution1 to ultramarine2 and both form sources of copper and are consequently expensive4 ,it should be mentioned that both ultramarine and malachite green can only be profitably made into pigments where the minerals can be obtained cheaply1 since both of them can be manufactured where artificial pigments are produced1 and are put on the market under the same names as the native articles4 ,the very low price of the green earths makes them highly popular as colouring matters in certain branches of industry1 and they are very largely used by wall-paper manufacturers4 ,brown4--,this is a large group1 and the pigments composing it are specially distinguished for their beauty and depth of colour1 on which account they are used in the finest paintings4 ,here1 again1 it is ferric oxide1 in combination with water--and therefore ferric hydroxide--that furnishes a large number of the members of the group4 ,like the renowned ,siena earth1 the artists' colours known as ,vandyck brown1 bole1 ,lemnos earth1 umber1 etc41 mainly consist of more or less pure ferric hydroxide4 ,these minerals are1 moreover1 specially important to the colour manufacturer1 inasmuch as most of them enable a large number of different shades to be obtained by a simple method of treatment consisting merely of the application of heat in a suitable manner2 and these colours are among the most excellent we possess1 by reason of their beauty and permanence4 ,amongst this series must also be classed native manganese brown1 which chiefly consists of a mixture of manganese oxide and the hydrated peroxide of the same metal4 ,black4--,there is really only one member of this class1 which1 however1 is frequently used1 viz4 that form of carbon occurring as hexagonal crystals and known as graphite4 ,another natural black natural product1 occasionally used as a painters' colour is the so-called black chalk4 ,however1 since black pigments can be produced very cheaply by artificial means1 the natural colours find only a limited application2 and only in one instance is graphite used alone1 viz4 for making blacklead pencils4 ,as already mentioned1 certain chemical industries furnish by-products which are of very little value in themselves1 and many of them1 indeed1 may be classed as worthless1 since chemical manufacturers naturally endeavour to get everything possible out of their materials in the course of manufacture4 ,some of these by-products1 however1 can advantageously be used as pigments1 a good example of this being afforded by the iron oxide formed as a by-product in the manufacture of fuming sulphuric acid 7,nordhausen oil of vitriol71 by the old process1 from green vitriol 7ferrous sulphate74 ,in itself1 this oxide is practically valueless1 but1 by very simple treatment1 it can be converted into very valuable pigments which have a market value far in excess of the original material4 ,although it has hitherto been the custom to confine the term earth colours to such as occur ready-formed in ,nature and only require simple mechanical treatment to make them ready for immediate use as pigments1 the author is nevertheless of opinion that a book dealing exhaustively with earth colours should also make some mention of all the mineral colouring matters which can be easily made into pigments by simple processes1 such as calcination or bringing into association with other substances4 ,in accordance with this view1 the present work will describe all the pigments that are obtainable in this manner4 ,most of the earth colours consist of decomposition products of certain minerals2 and this applies particularly to such of them as contain iron oxide4 ,according as the decomposition of the original mineral has been more or less extensive1 the natural product exhibits different properties2 and the manufacturer must consequently endeavour to treat them in such a manner as to ensure that the pigment obtained will be as uniform as possible in shade and permanence4 ,in order to accomplish this it is essential to have an accurate knowledge of the origin of the raw material under treatment1 and of its chemical and physical properties4 ,in view of this1 the author considers it necessary to deal more fully with the pigmentary earths forming the raw materials of the earth colours1 before passing on to the preparation of the colours themselves4 ,,chapter ,,ii ,,the ,,raw ,,materials ,,for ,,earth ,,colours ,the minerals constituting the raw materials for the preparation of the earth colours occur under very divergent conditions in ,nature4 ,some of them1 such as chalk1 form immense deposits1 even whole mountains1 whilst in other cases1 e4 g4 the blue ferruginous earths1 the occurrence is connected with certain local conditions1 and many are found only in isolated deposits1 as pockets or beds4 ,this last is the case1 for instance1 with the handsome brown iron pigments2 and indeed the names by which they are known indicate that they are only found in well-defined localities1 or that they are met with of special quality there4 ,the brown earth colour known to all painters as ,terra di ,siena1 is found at many other places as well as near ,siena1 but the product from that city acquired aforetime a special reputation for beauty1 and therefore all similar earths1 provided they are equal to that from ,siena1 also bear the same name in commerce4 ,a number of raw materials for the preparation of earth colours are found1 it is true1 in many deposits1 but their utilisation depends1 in turn1 on local conditions4 ,for example1 many copper mines contain1 in addition to the other cupriferous minerals1 those used1 in the powdered state1 as ultramarine or ultramarine green1 and not infrequently lumps of mineral are found containing both blue and green together4 ,however1 it is only when these minerals occur in sufficient quantity to make the necessary sorting profitable that their manufacture into pigments can be regarded as practicable4 ,before commencing to work a deposit it is essential to make sure whether the raw material1 or pigmentary earth1 is actually suitable for the manufacture of earth colour4 ,even the general character of the material is important1 those of soft1 earthy consistency being much easier to treat1 and the cost of preparation smaller1 than if the raw material be hard1 tough and crystalline4 ,the extent and thickness of the deposit1 and the ease with which it can be worked1 also play an important1 and even decisive part1 since1 other conditions being equal1 it will not pay to erect a colour works unless the raw material is available in sufficient quantity and is cheap4 ,generally1 the deposit is not homogeneous throughout1 the mineral being purer in some places and more contaminated with gangue in others4 ,the percentage of moisture also varies1 and in short1 a number of circumstances must be taken into consideration in forming a conclusion as to whether a deposit is workable or not4 ,in order to arrive at a reliable opinion on all these conditions1 sampling is indispensable4 ,if the samples are of uniform character1 they can be mixed together to make an average sample4 ,but if they differ considerably in appearance1 general character1 proportion of gangue1 etc41 it is preferable to examine them separately1 more especially when the area which each represents is large4 ,the examination should extend1 on the one hand1 to the natural percentage of moisture1 and1 on the other1 to the purity of the material4 ,the water content is determined by thoroughly drying a weighed sample1 bearing1 however1 in mind the fact that pigmentary earths of a clayey nature vary in water content according to the time of year1 besides changing in accordance with the weather when the won material is stored in the open4 ,the purity can only be ascertained by an examination in which a sample of the soft1 clayey material is crushed and passed through a narrow-mesh gauze sieve1 the amount of the coarse particles--sand1 small stones1 etc4--remaining on the sieve being determined4 ,a more accurate method1 of course1 is to separate the true pigmentary earth from the gangue by levigation4 ,for this purpose1 a weighed quantity of the crushed1 air-dry sample is placed in a relatively narrow glass vessel and thoroughly mixed with water1 the turbid supernatant liquid being poured off after a short interval4 ,the residue is repeatedly treated in the same way1 until no more fine particles remain in suspension1 the residue then consisting of impurities1 or gangue4 ,of course1 the washings can be collected1 the suspended matter allowed to settle1 and finally weighed in an air-dry condition4 ,by this means an approximate idea of the yield of earth colour can be obtained at the same time4 ,raw materials which are not amorphous1 soft and clayey must first be crushed1 an operation facilitated by heating to redness and quenching in cold water4 ,oftentimes the heating causes a change of colour and improves the covering power--a point to which reference will be made later on4 ,in the following description of the various raw materials1 the chemical composition of the pure minerals will be given1 together with an enumeration of the most common impurities4 7,a7 ,,white ,,raw ,,materials ,,and ,,pigmentary ,,earths ,limestone 7,calcite1 ,limestone1 ,chalk7 ,the number of materials furnishing white earth colours is comparatively large1 and these colours are particularly important1 because1 not only are they extensively used by themselves1 but they also serve as adjuncts to other colours and for the production of special shades4 ,the chief raw material for the preparation of white earth colours is the mineral calcite in its numerous modifications4 ,calcite1 or calc spar1 occurs very frequently in ,nature1 and is one of the most highly diversified minerals known4 ,in its purest state it appears as 8double spar0 7calcite71 in the form of water-white crystals1 which are very remarkable for certain optical properties4 ,white marble is also a very pure variety of calcite1 in which the individual crystals are very small4 ,the various coloured marbles owe their appearance to certain admixtures of extraneous substances1 chiefly metallic oxides4 ,no sharp line of demarcation separates marble from ordinary limestone1 the difference between them really consisting only in the degree of fineness of grain2 and all limestones which grind and polish well may be classed as marble4 ,as is the case with marble1 there are also limestones of various colours1 grey being1 however1 the most common4 ,this grey limestone forms huge mountain masses which1 in ,europe1 follow for example1 the ,alpine chain on its northern and southern edges4 ,a few other examples of calcite may be mentioned which occur in certain localities and1 in part1 are still in course of formation4 ,to these belong the stalactites and stalagmites1 which sometimes consist of extremely pure calcite4 ,they are formed by the action of water1 containing carbonic acid in solution1 which trickles through cracks and cavities in limestone rock and dissolves out calcium carbonate from the adjacent stone4 ,on prolonged exposure to the air such water gives off its free carbonic acid again2 and as the calcium carbonate is insoluble in pure water1 it separates out in crystalline form4 ,the masses formed in this way usually resemble icicles in shape1 and the finest examples are to be found in the well-known stalactite grottoes at ,krain1 whilst the grotto at ,adelsberg is renowned for its beautiful stalactites4 ,occasionally1 stalactites have an opaque yellow or brownish tinge1 which they owe to the presence of iron oxide4 ,a formation similar in its origin to stalactites is the so-called calc sinter and calcareous tuff4 ,the former often occurs in cavities as irregular masses which1 in some places1 enclose large quantities of fossil animal bones1 in which case they form 8bone breccia0 7crag breccia74 ,calcareous tuff is deposited from numerous springs1 occasionally in very large quantities1 enveloping plants and sometimes forming thick deposits in which the structure of the plants can be clearly recognised4 ,in some places a more or less pure white1 extremely friable variety of calcite is met with under the name 8mountain milk0 or 8mountain chalk0 7earthy calcite71 which seems to be a decomposition product1 and consists of a mixture of arragonite and chalk4 ,arragonite--which will be referred to later--is completely identical1 chemically1 with calcite--both being composed of calcium carbonate--the sole difference being their crystalline form4 ,the most important for the colour-maker1 however1 is the variety known as chalk4 ,this is really a fossil product1 i4 e4 it consists of the microscopic shells of marine animals united into solid masses4 ,despite the smallness of these animals1 their epoch lasted long enough for their shells to form entire mountains which are encountered all over the world4 ,a large part of the coast of ,england1 the island of ,rgen1 and many other localities1 consist entirely of chalk4 ,in many cases1 chalk is found interspersed with nodular masses of flint1 and in some places it also contains great quantities of the remains of other marine animals1 such as sea urchins1 the spines of which occur in such numbers in certain kinds of chalk as to unfit them entirely for use as a pigment4 ,the foregoing varieties of calc spar are the most important1 and also occur in large quantities2 but1 to complete the tale1 it is necessary to mention also a few others which1 however1 are only found in small amounts4 ,to these belong1 for example1 anthracolite1 a limestone stained quite black by coal2 the oolithic limestones or roe stones1 which are composed of granules resembling fish roe2 muschelkalk1 which is also of fossil character and is almost entirely composed of mussel shells cemented together with lime2 the marls1 which consist of calc spar mixed with varying quantities of clay and consequently often bear a great resemblance to loam in their properties4 ,a few of these varieties find extensive employment for certain purposes1 some marls for instance being used for making hydraulic lime1 whilst all modifications of calc spar that are sufficiently pure can be burned for quick lime4 ,it has already been stated that the mineral arragonite is identical1 chemically1 with calc spar1 since both consist of calcium carbonate1 but differ in their crystalline habit4 ,thus1 whereas the crystals of calc spar belong to the rhombohedral or hexagonal system1 those of arragonite are always rhombic4 ,this occurrence of one and the same substance in two different crystalline forms is known as dimorphism1 and calcium carbonate is therefore dimorphous4 ,whether calcium carbonate assumes the form of calcite or arragonite depends entirely on physical causes4 ,when the deposition of the carbonate takes place from a cold solution the shape of the crystals is always one belonging to the hexagonal or rhombohedral system2 but when it is from hot solution1 rhombic crystals are invariably formed1 calc spar resulting in the former case and arragonite in the latter4 ,these different methods of formation which can be carried out in the laboratory by producing the requisite conditions1 occur on the large scale in many parts of the world4 ,wherever a hot spring comes to the surface1 containing considerable amounts of lime in solution1 this separates out in the form of arragonite1 which received its name from the circumstance that specially handsome crystals of this mineral are found in ,arragon4 ,one of the best-known places where the formation of arragonite can be observed at the present time is ,carlsbad in ,bohemia4 ,the hot springs there deposit a very large amount of lime1 which is stained more or less yellow or red by the presence of varying quantities of iron oxide1 and1 under the name of 8sprudelstein0 is used for producing various works of art4 ,when the hot springs bring up particles of sand1 the lime substance incrusts these sand grains1 forming globular masses resembling peas1 and consequently named pisolite4 ,in chemical composition1 calcite and arragonite consist of a combination of calcium oxide 7lime7 and carbonic acid1 the formula being expressed by ,ca,c,o#c4 ,calcium carbonate is insoluble in pure water1 but dissolves somewhat freely in water charged with free carbonic acid4 ,it is assumed that a compound is formed1 which is known as calcium bi- 7or acid7 carbonate1 is very unstable and can only exist in a state of solution4 ,when a solution of calcium bicarbonate--which can be prepared by passing carbonic acid gas through water containing finely divided calcium carbonate in suspension--is exposed for some time to the air1 it soon becomes cloudy1 and a deposit of calcium carbonate settles down at the bottom of the vessel1 because1 in the air the dissolved calcium bicarbonate is decomposed into free carbonic acid gas and calcium carbonate1 which latter1 as has been mentioned1 is quite insoluble in water4 ,it has already been stated that this phenomenon goes on in ,nature in the formation of stalactites1 lime sinter and calcareous tuff4 ,calcium carbonate is readily soluble in acids1 the contained carbonic acid being liberated 7as carbon dioxide7 with effervescence4 ,when such acids are employed for solution as form readily soluble salts with lime1 such as hydrochloric1 nitric1 acetic1 etc4 acids1 a perfectly clear solution is obtained2 but if sulphuric acid is used1 a white pulpy mass is formed1 consisting of calcium sulphate1 or gypsum1 which1 owing to its low solubility1 separates out as small crystals4 ,any sandy residue left when calcium carbonate is dissolved1 mostly consists of quartz sand4 ,in dissolving dark-coloured limestones1 grey1 or even black1 flakes are left1 which consist of organic material very high in carbon4 ,on limestone being subjected to fairly strong calcination1 all the carbonic acid is expelled1 leaving behind the so-called quick or burnt lime1 which is1 chemically1 calcium oxide3-- ,ca,c,o#c ,ca,o ,,co#b ,calcium carbonate ,quick lime ,carbon dioxide ,if burnt lime be left exposed to the air for some time1 it again gradually absorbs carbon dioxide and is reconverted into calcium carbonate4 ,when burnt lime is sprinkled with water it takes up the latter avidly1 becoming very hot and finally crumbling down to a very friable white powder1 consisting of slaked or hydrated lime 7calcium hydroxide1 ,ca7,,oh7#b74 ,the considerable rise of temperature in quenching the lime is due to the chemical combination of the calcium oxide and water4 ,both quick and slaked lime dissolve to a certain extent in water1 and impart strongly alkaline properties thereto1 lime being one of the strongest of bases4 ,on exposure to the air1 the solution of quick lime in water 7lime-water7 quickly forms an opalescent superficial film of calcium carbonate1 and in a short time no more lime is present in solution1 the whole having been transformed into calcium carbonate1 which settles down to the bottom of the vessel as a very fine powder4 ,limestone that consists entirely of calcium oxide and carbon dioxide is of rare occurrence in ,nature1 foreign substances being nearly always present4 ,since the nature of these admixtures is of the greatest importance to the colour-maker1 owing to the considerable influence they exert on the suitability of the minerals for his purposes1 it is necessary that these extraneous substances occurring in limestone should be more closely described4 ,nearly all varieties of limestone contain certain proportions of ferrous and ferric oxides4 ,the presence of ferrous oxide1 when the relative amount is but small1 cannot be detected by mere inspection2 and even many limestones containing really appreciable quantities of ferrous oxide are pure white in colour so long as they are in large lumps4 ,if1 however1 such a limestone be reduced to powder and exposed to the air for a short time1 it gradually assumes a yellow tinge1 the depth of which increases with the length of exposure4 ,the cause of this change is due to the fact that ferrous oxide has a great affinity for oxygen1 by absorbing which it changes into ferric oxide4 7,ferrous oxide consists of ,fe,o1 ferric oxide of ,fe#b,o#c47 ,ferrous oxide and its compounds are of a pale green colour which is not very noticeable1 whereas ferric oxide has a very powerful yellow colour1 and consequently the limestone1 when its superficial area has been greatly increased by reduction to powder1 assumes the yellow tinge due to ferric oxide4 ,a limestone exhibiting this property can evidently not be used for making white earth colours1 but is1 at best1 only suitable for mixing with other colours4 ,occasionally1 limestone contains varying quantities of magnesia1 and when this oxide is present in large amount1 changes into another mineral known as dolomite4 ,in many places this dolomite forms large masses of rock1 which1 however1 is not employed for making colours1 owing to the yellow shade imparted by the fairly large amount of ferric oxide present4 ,gypsum 7,alabaster7 ,this mineral occurs native in many places1 and is frequently worked for a number of purposes4 ,gypsum occurs in ,nature in a great variety of forms4 ,the purest kind is met with either as water-clear crystals1 which cleave readily in two directions1 or as transparent tabular masses 7selenite7 which also cleave easily4 ,micro-crystalline fine-grained gypsum is milk-white in colour1 highly translucent and is largely used1 under the name of alabaster1 in sculpture4 ,owing to its low hardness1 alabaster can be readily cut with a knife1 and on this account is frequently shaped by planing or lathe-turning4 ,gypsum is generally met with in dense masses1 which may be of any colour1 grey1 blue and reddish shades being the most common1 whilst pure white is rarer4 ,the dark-coloured varieties can only be used for manurial purposes2 but the white finds a twofold application as a pigment1 and1 in the calcined state1 for making plaster casts4 ,in point of chemical composition1 gypsum consists of sulphate of lime1 or calcium sulphate 7,ca,s,o#d #b;,h#b,o74 ,it is soluble in water1 but only in such small quantity that over #djj parts of the latter are needed to dissolve one part of gypsum4 ,on being heated to between #abj and #acj ,c41 gypsum parts with its two molecules of combined water and becomes anhydrous calcium sulphate or burnt gypsum4 ,when this latter is stirred with water to a pulp1 it takes up the water again1 with considerable evolution of heat1 swelling up considerably and setting quickly to a solid mass4 ,the number of substances exhibiting this property being small1 burnt gypsum is very frequently used for making casts of statuary1 and for stucco work in building4 ,finely ground white gypsum can also be used as a pigment1 but is inferior to calcium carbonate in covering power1 and is therefore seldom employed for this purpose1 though frequently added to other colours4 ,the mineral known as muriacite or anhydrite consists of anhydrous calcium sulphate2 and is therefore similar in composition to burnt gypsum2 but it lacks the property of combining with water when brought into contact therewith4 ,barytes1 or ,heavy ,spar ,the mineral known as heavy spar occurs in very large quantities and in numerous localities4 ,it forms rhombic crystals1 which are very often extremely well developed and form flat plates of considerable size4 ,a remarkable peculiarity of this mineral is its high specific gravity1 which is due to the barium content4 ,it is found native in all colours1 white being the most common4 ,chemically1 heavy spar is barium sulphate1 ,ba,s,o#d4 ,it can be used as a pigment per se1 but only when prepared artificially1 the trade name for the product being permanent white1 or blanc fixe4 ,powdered native heavy spar1 even when ground ever so fine1 has not enough covering power1 this property being peculiar to the artificial product4 ,when it is desired to mix other pigments with a white substance1 to lighten the shade1 permanent white can be specially recommended1 since it is quite insensitive to atmospheric influences and has no chemical action on the colour1 so that it can be used with even the most delicate colours without risk4 ,in this way1 not only can the colours be considerably cheapened1 but over-dark colours can be shaded to the desired extent4 ,another advantage of such mixtures is that a smaller quantity of oil or varnish is required1 barytes only needing about #h of its own weight of vehicle to form a workable mixture1 whilst other pigments take five times as much1 or even more4 ,in many cases the low covering power of barytes enables large quantities to be added1 and this reacts favourably on the consumption of varnish4 ,another barium mineral is witherite1 or barium carbonate4 ,this is not used direct as a pigment1 but--in contrast to heavy spar--is readily soluble in hydrochloric acid1 and therefore serves as raw material for the preparation of artificial barytes and other barium compounds1 the first-named being obtained by treating a solution of barium chloride with sulphuric acid1 insoluble barium sulphate being precipitated4 ,talc1 ,soapstone1 ,steatite ,talc occurs in ,nature either as a pure white mass1 of greasy lustre1 or occasionally as yellow1 green or grey masses1 all distinguished by a peculiar greasy appearance and a soapy feel4 ,this appearance is common to all the minerals of the steatite group1 and is the cause of their generic name1 soapstone4 ,although the steatites have a very low degree of hardness--most of them can be scratched by the finger-nail--some difficulty is encountered in reducing them to fine powder4 ,calcination usually increases the hardness considerably1 so that1 in some cases1 the calcined mineral gives off sparks when struck with a steel instrument4 ,soapstone is composed of magnesium silicates1 containing varying proportions of magnesia and silica1 together with a small quantity of water1 apparently in a state of chemical combination1 a very high temperature1 approaching white heat1 being required to effect its complete expulsion1 the residue then attaining the aforesaid high degree of hardness4 ,the composition of talc can be expressed by the symbol ,h#b,mg#b7,si,o#c7d1 corresponding to #fceb of silica1 #cagb of magnesia1 and #dgf of water4 ,in some varieties of talc1 a portion 7#a-e7 of the magnesia is replaced by ferrous oxide4 ,talc is quite unaffected by the action of dilute acids1 boiling concentrated sulphuric acid being required to decompose it1 with separation of silica4 ,owing to its low specific gravity and chemical indifference1 talc is suitable for lightening the shade of certain lake pigments4 ,it can also be used as a pigment by itself1 and also as a gloss on wall-paper1 for mixing with paper pulp1 and for various other purposes4 ,clay ,the mineral known as clay is1 in all cases1 a product of the decomposition of other minerals1 mainly felspar4 ,this substance is a double silicate of alumina and potash1 ,k#b,o4,al#b,o#c47,si,o#b7f4 ,pure kaolin is ,al#b,o#c7,si,o#b7b #b;,h#b,o1 or #dfej silica1 #cief alumina1 #aci water4 ,clay may be supposed to have been formed by the conversion of felspar1 under the action of air and water1 into silicate of alumina1 the silicate of potash being dissolved out4 ,being insoluble1 the silicate of alumina would be transported by the water1 in a very fine state of division1 and finally deposited as a sediment1 which in course of time became a solid mass4 ,this1 when again brought into contact with water1 forms a very plastic pulp which1 when dried and baked1 forms a solid mass1 brick1 which is no longer affected by water4 ,perfectly pure clay forms a white mass1 which1 under the name of ,china clay or kaolin1 is used for making porcelain1 and is only occasionally met with in large quantities4 ,pure kaolin is characterised by its great chemical indifference1 being decomposed only by strong alkalis and sulphuric acid4 ,at the high temperature of the pottery kiln1 kaolin sinters to a very compact mass1 but cannot be fused1 except when small quantities are subjected to the intense heat of the oxyhydrogen flame1 whereupon it fuses to a colourless glass of great hardness4 ,in an impure state1 silicate of alumina occurs frequently in ,nature1 and then forms the minerals known under the generic names of clay1 loam1 marl1 etc4 ,these impure clays contain varying proportions of extraneous minerals which produce changes in the physical and chemical properties4 ,they are grey1 blue or yellow in colour1 the grey and blue varieties mostly containing appreciable quantities of ferrous oxide1 whilst the yellow kinds contain ferric oxide4 ,when fired1 all of them become yellow or red1 the ferrous oxide being transformed into ferric oxide by the heat4 ,some fairly white clays are high in lime1 which makes them fusible at high temperatures4 ,in some very impure kinds1 even the comparatively low heat of the brick-kiln is sufficient to cause partial fusion4 ,for colour-making1 the white clays1 especially kaolin and pipeclay1 form a highly important material1 being procurable at very low prices and fairly easy to prepare4 ,the white clays are either used as pigments by themselves1 or for mixing with other colours of low specific gravity4 7,b7 ,,yellow ,,earths ,the number of yellow earths is large1 but most of them exhibit a certain similarity in chemical composition1 the pigmentary principle in the majority being either ferric oxide or ferric hydroxide4 ,the former is yellow1 the latter brown1 and the colour of the minerals resembles that of the preponderating iron compound4 ,brown ,ironstone ,the mineral known as brown ironstone consists of ferric hydroxide1 and usually forms compact masses1 no decided crystals having1 so far1 been observed4 ,the lumps have an irregular or earthy fracture1 a hardness of #e-ee1 and a sp4 gr4 between #cdj and #cie4 ,the colour ranges1 in the different varieties1 from yellowish 7rusty7 brown1 through cinnamon to blackish-brown4 ,the chemical composition of the pure lumps may be expressed by the symbol #b;,fe#b,o#c #c;,h#b,o2 but a little manganese oxide and silica is generally present even in the pure kinds4 ,the chief varieties of this mineral are3-- 7a7 ,fibrous brown iron ore1 or brown hematite1 mostly forming reniform or stalactitic masses4 7b7 ,compact brown ironstone1 usually in dense masses1 and not infrequently also appearing in pseudo-morphs of other minerals4 7c7 ,ochreous brown ironstone4 ,this variety is the most important to the colour-maker1 for whose purposes it is preferably used4 ,it nearly always forms very loose1 earthy masses1 yellow or brown in colour4 7d7 ,clay ironstone4 ,this consists of a mixture of the above-mentioned varieties with variable proportions of other minerals1 clay being the most common ingredient4 ,nodular iron ore1 olitic1 bog and siliceous ore belong to this class1 as also the minette ores that are found in great abundance in ,alsace-,lorraine1 ,belgium and ,luxemburg1 and are classed with the olitic brown ironstones4 ,in most cases1 the varieties enumerated are found together1 and are used for the production of iron4 ,the ochre constituting the most interesting member to the colour-maker often occurs as deposits embedded in dense masses of brown ironstone1 though in many places it is found by itself4 ,,chemical ,,composition ,,of ,,various ,,brown ,,ironstones ,the following analyses of brown ironstone from different deposits will give an idea of the composition of these minerals4 ,ordinary ,brown ,ironstone ---------------------------------------- ----------------------- #a4 #b4 #c4 #d4 #e4 #f4 #g4 #h4 #i4 #aj4 ---------------------------------------- ----------------------- ,ferric oxide #gfgfgcgeggedghejghdbdhbe -- -- -- -- ,manganese oxide #afefajej #bgj #aie #acjbdgc -- -- -- -- ,iron -- -- -- -- -- -- #cci #cghhedhjeejd ,manganese -- -- -- -- -- -- #jae #jag #jeg #jbj ,alumina -- -- -- -- #aac #bccajjc #jhh #aae #bej ,lime #jfj #bge #jdh #ejh #cee #bhe #jda #jcb #jej #jcd ,magnesia #fdd -- #abe #dej #jah #jij #jfg -- #jjb #jch ,silica -- -- #cee #jhe #edhaacebhbiccch #jjb #jch ,,so#c -- -- -- -- -- #jji -- -- -- -- ,p#b,o#e -- -- -- -- #jji #jjh -- -- -- -- ,sulphur -- -- -- -- -- -- #jcc #jjf #jjd,trace ,phosphorus -- -- -- -- -- -- #jjd #jef #jjb #jjf ,loss on incineration #efeadjjadea #iab #iaj #ihj #ihh #gggajeeajga ---------------------------------------- ----------------------- ,deposits3 7#a7 ,hamm2 7#b7 ,schmalkalden2 7#c7 ,httenberg 7,carynthia72 7#d7 ,styria2 7#e7 and 7#i7 ,bilbao2 7#f7 ,algeria2 7#g7 ,schwelm 7,westphalia72 7#h7 ,elbingerode 7,harz72 7#aj7 ,pennsylvania4 ,argillaceous ,brown ,ironstone ---------------------------------------- ----------------------- a4 b4 c4 d4 e4 f4 g4 h4 i4 k4 ---------------------------------------- ----------------------- ,ferric oxide #hjgfaid #eeciffccegcbebejciejgefg -- -- ,iron -- -- -- -- -- -- -- -- #djijbafi ,manganese oxide -- #hb -- #fdb -- #edi #fab #jgb -- -- ,manganese -- -- -- -- -- -- -- -- -- -- ,zinc oxide #jib #af -- -- #jdg -- -- -- -- -- ,alumina #bcfaaj #abhj #ggd #afh #ebc #ihi #caj #die #chh ,lime -- #bf ,trace #jda #jac #ccfbjcd #eja #eeibabe ,magnesia -- #jb -- #jcg -- #jcf -- -- #jdi #jcj ,silica #deh #dhfabbgcabigcjfd #hfd #ebb #hgjaffcadga ,p#b,o#e -- -- -- -- #jcb #chf #bai #cfh -- -- ,phosphorus -- -- -- #jjb -- -- -- -- #aac #jdh ,,so#c -- -- -- #jjc,trace -- -- -- -- -- ,sulphur -- -- -- -- -- -- -- -- #jaj #jje ,loss on incineration#abga #ia #hejaaggabgjbjeebegd -- #afjdbhgj ---------------------------------------- ----------------------- 7a7 ,olitic 7pea7 ore from ,elligserbrick 7,brunswick72 7b7 from ,durlach 7,baden72 7c7 and 7d7 ,ore from ,esslingen2 7e7 ,olitic ore from ,siptingen 7,baden72 7f7 from ,adenstedt1 nr4 ,pirna 7argillaceous72 7g7 ,ibid4 7calcareous72 7h7 ,minette from ,esch2 7i7 ,red minette from ,dolvaux2 7k7 ,brown minette from ,redange4 ,limonite 7,bog ,iron ,ore7 ---------------------------------------- ------ #a4 #b4 #c4 #d4 #e4 #f4 ---------------------------------------- ------ ,ferric oxide #fajjfgdffefffgeigjjefbbj ,manganese oxide #gjj #cai #chg #ade #agh #gfj ,p#b,o#e #bjj #jfg #aac #jah #jcd #afj ,,so#c -- #cjg,trace #jba,trace,trace ,silica #fjj #gjj #gae #ghi #hjcaffj ,alumina -- -- #eji #dah #aej #bbj ,lime -- #jij #jhb #jdg #bca #afj ,magnesia -- -- #jae #jbc #jab #cgc ,water and organic acids #aijjagjj #fbbaghaaehgaiij ---------------------------------------- ------ 7#a7 ,limonite from ,lausitz2 7#b7 ,limonite from ,auer1 nr4 ,morizburg2 7#c to #f7 ,swedish limonite4 ,ochre ,ochre1 or yellow ,terra di ,siena1 forms earthy-looking masses1 fawn1 reddish-yellow to brownish-red in colour4 ,whilst not infrequent in ,nature1 ochre is only found in small quantities1 as pockets1 and not as extensive deposits4 ,the discovery of a bed of good coloured ochre is1 however1 always a very valuable find1 bright natural ochres being somewhat rare1 and most kinds requiring special preparation before they can be used as painters' colours4 ,owing to the comparative scarcity of good coloured ochres1 they are often called after the place of origin1 such as ,thuringian1 ,italian 7,siena71 ,english1 etc41 ochre4 ,in nearly every case1 ochre is a decomposition product of various ferruginous minerals1 which has been transported by water1 often in admixture with other minerals1 and finally deposited in the places where it is now found4 ,most ochres consist of varying mixtures of clay1 ferric hydroxide and lime2 and1 as a rule1 the higher the proportion of ferric hydroxide1 the deeper the colour4 ,thus1 for example1 the ferric hydroxide may amount1 in the dark grades1 to #be of the entire mass1 whilst in the lighter kinds it may be as low as #c4 ,it is very rare that ochre is put on the market in its native condition1 being mostly subjected to chemical treatment enabling a definite shade of colour to be obtained4 ,this will be gone into more fully later4 ,yellow ,earth ,yellow earth is found in many places as compact masses1 and less frequently as schistous deposits4 ,it has a fine earthy fracture1 and is mostly devoid of lustre1 except for a faint shimmer on the surface of fracture2 slightly greasy feel2 and a tendency to crumble1 in water1 to a non-plastic powder4 ,it contains silica1 ferric oxide and water in varying proportions1 and the yellow earths from different deposits always vary slightly in percentage composition4 ,these differences are clearly shown in the following analyses of two varieties from the vicinity of ,amberg 7,bavaria73-- ,i4 ,,ii4 ,silica #ccbc #ceaj ,alumina #adba #addj ,magnesia #ach -- ,ferric oxide #cggf #cfhj ,water #acbd #acfj ,when heated1 the colour changes gradually to red1 and the earth becomes extremely hard4 ,there are several recognised commercial grades1 the price of which varies mainly in accordance with the colour and fineness4 ,the ,amberg variety is specially esteemed1 the ,hungarian and ,moravian kinds being less valuable4 ,the colour not being particularly good1 this earth is never used for fine work1 but is largely employed as a yellow wash for houses and as ordinary distemper4 ,it may also be used as an oil paint4 ,red ,ochre is a less important1 cheap variety of ochre1 chiefly used in cheap paints and for low-priced wall-papers4 ,it occurs in the deposits as clayey masses4 ,terra di ,siena ,terra di ,siena is a very pure form of ferric hydroxide4 ,when ground1 the light to dark brown lumps furnish a pale to dark yellow powder1 which can be transformed into a number of gradations by burning4 ,in spite of its handsome colour1 this pigment is deficient in covering power1 in addition to which it darkens when mixed with varnish1 and dries slowly4 7,c7 ,,the ,,red ,,earths ,apart from the small quantities of native vermilion handsome enough for direct use as painters' colours when reduced to powder1 the red earths1 with practically no exception1 consist of ferruginous minerals1 and it is only within a recent period that red painters' colours have been prepared from certain chemical waste products from manufacturing processes4 ,in all cases1 however1 compounds of iron and oxygen constitute the bulk of the red earths4 ,in addition to ferric oxide1 which is the chief material used for making the important red colours1 are compounds of ferric oxide and water1 i4 e4 ferric hydroxides4 ,the ferric oxide pigments are among the most important in the entire series of earth colours1 being on the one hand very cheap1 and on the other so handsome in colour that ferric oxide can be used for the finest paintings4 ,ferric oxide can also be shaded very extensively by a fairly simple treatment1 so as to furnish a whole range of very handsome shades4 ,in nature1 ferric oxide occurs in numerous varieties of one and the same mineral1 red iron ore1 which is also known as hematite1 blood stone1 raddle1 etc4 ,red ,ironstone ,red hematite occurs native as rhombohedral crystals1 which mostly consist solely of ferric oxide1 and may be considered as pure oxide for the purposes of the colour-maker4 ,the difference between the several varieties is due1 not to any chemical variation1 but entirely to changes in physical structure4 ,the varieties with a radial1 fibrous structure are known as red hematite1 the colour of which ranges from blood red to dark brown and is frequently accompanied by metallic lustre4 ,the scaly modification of this mineral forms micaceous iron ore1 and is usually a deep iron black4 ,in the neighbourhood of volcanoes it is frequently found as particularly handsome crystals4 ,iron cream 7frosty hematite7 is the name given to a beautiful cherry red variety1 which easily rubs off1 has a greasy feel and is composed of extremely fine scales4 ,the so-called raddle occurs in ,nature as a readily pulverulent earthy mass of ferric oxide contaminated more or less with extraneous substances4 ,on account of its abundance and low market price1 it is largely used in painting4 ,although mixed with numerous foreign substances1 certain clay ironstones1 olitic ironstones and siliceous ironstones may be regarded as ferric oxide in the sense understood by the colour-maker1 all these minerals having a deep red to deep brown colour and being capable of finding advantageous employment as pigments4 ,ferric oxide is distinguished by two properties which render it specially valuable to the colour-maker4 ,when combined with water1 its colour is no longer red1 but a handsome brown2 and1 on the other hand1 when heated1 the colour passes through brown into a permanent dark violet4 ,by suitable treatment of such minerals as consist mainly of ferric hydroxide1 mixtures can be obtained which contain the oxide and hydroxide in variable proportions and give a whole range of shades between brown and red4 ,the preparation of these colours is easy when very pure red ironstone is available4 ,the somewhat expensive pigment1 ,indian red1 is--when pure--really nothing but a very pure ferric oxide of ,indian origin4 ,ferric oxide1 however1 often contains impurities which considerably influence the colour of the product4 ,owing to the fact that large quantities of ferric oxide are formed as by-products in certain chemical processes which are carried out on a very extensive scale1 this oxide1 which is very pure1 can be advantageously used for making iron pigments1 especially as its application for other purposes is very restricted1 and it can therefore be had at a very low price4 ,the following analyses show the composition of a number of red ironstones1 ,nos4 #a1 #b and #c being hematite from ,froment1 or ,wetzlar1 ,no4 #d from ,wetzlar1 ,nos4 #e and #f hematite from ,whitehaven1 ,no4 #g from ,thuringia1 ,no4 #h from ,bohemia1 ,no4 #i from ,spain1 ,no4 #aj from ,n4 ,america1 and ,no4 #aa from ,england4 ---------------------------------------- ------------------------- ,ferric ,manganese ,alumina1 ,no4 oxide4 oxide4 ,silica4 ,p#b,o#e4 lime and ,water4 magnesia4 ---------------------------------------- ------------------------- #a #idjj ,trace #bjj -- ,trace #bjj #b #hjie -- #afgd #jea #jig #jhc #c #gcgg -- #bcaf #jde #ada #aba #d #ibde -- #efc #jai #jfe #ajh #e #ifbg -- #dbj -- #jei #ddj #f #fcje #ebi #bbgf -- #jdi #ddj #g #hejj #afja #ccjd #jdeg #hgie #jfcc ---------------------------------------- ------------------------- ---------------------------------------- ---------------------- ,man- ,alu- ,mag- ,phos- ,loss on ,no4,iron4 ganese4mina4,lime4nesia4,silica4,sulphur 4phorus4calcina- tion4 ---------------------------------------- ---------------------- #h #ccfd #jaj #geh #haj #jhb #aghj ,trace #jai #ihb #i #cach #jai #jjfbiie #jce #jhg -- #jji #bcfh #aj #fbed #aic #aga -- #jej #chj #jjb #jjd #bbc #aa #fbia ,trace #aci #jgj #jdb #ehi #jje #jaa -- ---------------------------------------- ---------------------- ,there are certain other minerals closely allied1 both chemically and mineralogically1 to red ironstone1 namely1 the brown hematites or ironstones used in the manufacture of iron4 ,brown hematite consists of ferric hydroxide1 ,fe#b,o#c;,h#b,o1 and occurs in a variety of forms in ,nature1 the most frequent being pea 7olitic7 ore1 which owes its name to the spherical shape of the grains4 ,some brown hematites are decomposition products of other minerals1 and contain sulphur and phosphorus in addition to ferric hydroxide4 ,like the pure hydroxide1 they are brown in colour1 but differ therefrom considerably in their chemical behaviour when heated4 ,this is particularly the case with the so-called bog ore1 which is mostly found1 as spongy yellow-brown to black masses1 in swamps1 and owes its origin to the decomposition of various ferruginous minerals4 ,it varies greatly in chemical composition and occasionally contains up to about #ej of sand4 ,the amount of ferric oxide in bog ore varies between #bj and #fj1 and it also contains #g-cj of water1 up to #d of ,p#b,o#e1 small quantities of ferrous oxide and manganese hydroxide1 together with1 in most cases1 mechanically admixed organic residues4 ,the phosphorus content makes bog iron a very inferior material for smelting1 the resulting iron being of low quality4 ,nevertheless1 it can sometimes be advantageously used in making earth colours1 though the products cannot lay much claim to beauty of colour4 ,bole ,the native earth pigments known by this name form masses of the colour of leather to dark brown1 with a conchoidal fracture and an earthy appearance4 ,bole chiefly consists of iron silicate combined with water1 some varieties containing small quantities of alumina4 ,the composition fluctuates very considerably1 most varieties containing #da-db of silica1 #bj-be of alumina1 and #bd-be of water1 the remainder consisting of ferric oxide4 ,some kinds1 such as ,oravicza and ,sinope bole1 contain only #ca-cb of silica and #ag-ba of water4 ,bole is used as a paint for walls1 clapboards1 etc41 and is only mentioned here because of its relationship to the ferric oxide pigments4 ,alum ,sludge ,large quantities of clarification sludge are produced1 in alum works1 as the sediment from the red liquors4 ,this sludge consists mainly of ferric oxide1 with small quantities of other oxides and sulphuric acid 7basic ferric sulphate71 and would be an entirely worthless by-product except for the fact that it can be manufactured into pigments1 some of them of great beauty4 ,all alum makers should treat this residue and convert it into pigments1 which they could put on the market at a low rate1 the cost of preparation being small4 ,since the material is chiefly composed of ferric oxide1 the resulting colours are very similar to those obtained from iron ores2 and all shades1 from yellow-brown1 through red1 to the darkest brown1 are represented4 ,mine ,sludge ,the water frequently present in iron mines sometimes contains large quantities of sediment1 which consist mainly of iron ochre and can be advantageously worked up into pigments4 ,there is scarcely any need to mention that all substances containing ferric oxide can be used for making any of the pigments obtainable from the oxide itself1 the only difference between the various raw materials being their degree of purity1 so that it is not always so easy to obtain a certain desired shade from a given material in such beauty as is furnished by another material1 the small quantities of impurities associated with the ferric oxide having1 in many instances1 an important influence on the colour4 7,d7 ,,blue ,,earths ,only two minerals are known which are capable of direct use as blue pigments1 viz4 vivianite 7native ,prussian blue7 and copper carbonate 7azurite1 ultramarine71 and as neither of them is particularly handsome1 they are only used for unimportant work4 ,lapis lazuli is no longer employed4 ,azurite1 or ,ultramarine ,this mineral1 which is of frequent occurrence with malachite and other cupriferous minerals1 forms small crystals of a beautiful deep azure blue consisting of cupric oxide in combination with carbon dioxide and water1 expressed by the formula #b;,cu,c,o#c1 ,cu7,,oh7#b1 or ,cu#c7,,oh7#b7;,,co#c7b1 and containing #fiai of cupric oxide1 #beeh of ,,co#b and #ebc of water4 ,the colour of the powdered mineral is much paler than that of the crystals4 ,the pigment1 which is used for cheap paints1 is not particularly stable1 and loses much of its beauty when applied to plaster4 ,vivianite ,this mineral occurs in many places as crystalline masses1 but also forms earthy deposits1 some of which1 especially in certain bogs1 attain considerable thickness4 ,the colour is between indigo and blackish blue2 and the freshly won mineral often has an unsightly whitish appearance1 which1 however1 soon changes into the pure blue4 ,the cause of this peculiarity is due to the fact that vivianite originally consisted of hydrated ferrous phosphate1 which is white1 this compound being transformed1 under the influence of the air1 into the blue ferric phosphate4 ,vivianite contains ferric oxide1 phosphoric acid and water1 but in variable proportions4 ,the original composition1 expressed by ,fe#b7,,po#d7b #h;,h#b,o#b1 corresponds to #dcjc of ferrous oxide1 #bhbi of ,p#b,o#e and #bhfh of water2 but1 in the air1 part of the ferrous phosphate is oxidised to basic ferric phosphate1 so that the content of ferrous oxide may range from #ige to #dbga1 and that of ferric oxide between #aab and #chbj4 ,vivianite is also sold as blue ochre1 and is now seldom used as a painters' colour1 owing to the introduction of a large number of artificially prepared blues1 which are superior to vivianite in colour and are cheaply made4 ,however1 it can still find application in localities where it is obtainable in quantity4 7,e7 ,,green ,,earth ,,pigments ,the green earth pigments comprise green earth 7,verona green7 and malachite4 ,like the blue earths1 they cannot lay any particular claim to beauty1 but they are very cheap1 and consequently are largely used where low price is the chief consideration4 ,green ,earth ,in ,nature1 green occurs as an entirely non-crystalline earthy mass1 which is probably a decomposition product of augite4 ,it has a close1 earthy fracture1 a colour between seladon and olive green1 and a slightly greasy appearance4 ,in point of chemical composition it consists of silica1 alumina1 magnesia1 sodium1 potassium1 ferrous oxide and water1 the usual representative formula being ,,ros#a,o#b ,h#b,o1 in which ,,ro symbolises a metallic oxide4 ,the colour is due to ferrous oxide2 and if left exposed to the air for a long time1 or subjected to powerful calcination1 the great affinity of ferrous oxide for oxygen causes the colour to turn red and red-brown4 ,green earth is found in many localities1 e4 g4 ,bohemia1 ,hungary1 the ,tyrol and ,cyprus1 the finest1 however1 occurring near ,verona1 on which account it is known as ,veronese earth4 ,malachite ,the commercial pigment consists of powdered malachite1 a mineral which usually occurs in compact masses of a handsome emerald green colour1 though isolated lumps exhibit considerable variation in shade1 some of them being dark green and others very pale4 ,in chemical composition1 malachite is closely allied to azurite1 consisting of cupric oxide1 carbon dioxide and water1 and the difference is entirely one of percentage proportions4 ,the formula is ,cu,co#c1 ,cu7,,oh7#b1 or ,cu#b7,,oh7#b;,,co#c1 corresponding to #gaij of cupric oxide1 #aiid of carbon dioxide and #haf of water4 ,powdered malachite 7even the dark green varieties7 is always rather light in colour1 and for this reason is not much used4 ,furthermore1 the mineral is rather hard 7#ce71 and is consequently difficult to grind2 in addition to which the mineral is fairly expensive1 on account of its employment as a source of copper1 particularly fine pieces being also used as ornaments or for making works of art4 ,moreover1 like all copper compounds1 it is very sensitive to the action of sulphuretted hydrogen1 and liable to discoloration in course of time4 7,f7 ,,brown ,,earth ,,pigments ,numerous minerals are adapted for the manufacture of brown pigments4 ,on the basis of chemical composition1 they may be classed in two groups2 those consisting of ferric hydroxide1 and those in which the brown colour is due to organic substances4 ,the first group comprises the minerals which have already been mentioned in connection with the red earth pigments1 bole and brown ochre 7umber71 ,terra di ,siena1 ,cologne earth and a number of other earths rich in ferric hydroxide belonging to this category4 ,the second1 or organic group1 includes compounds that are very rich in carbon and are therefore of a very dark colour1 the shades ranging from light brown to black1 e4 g4 the true umbers and asphaltum4 ,umber ,as already mentioned1 the term 8umber0 was formerly applied to brown varieties of ochre1 whereas at present it is extended to certain masses of brown-coal character1 often interspersed with iron ochre and sometimes containing manganese4 ,umber generally consists of fairly dense1 earthy masses1 which are dried and ground--after crushing and levigation1 if necessary4 ,valuable varieties are ,cappagh brown and ,caledonian brown1 both with a reddish tinge4 ,it is thus evident that 8umber0 now implies two different kinds of materials1 organic masses and iron-manganese compounds1 which can also be used as oil paints4 ,these umbers can also be extensively shaded by burning1 the final colour being particularly influenced by the amount of manganese compounds present4 ,the carbonaceous umbers 7,cassel brown1 ,carbon brown7 are combustible1 and mostly leave behind a merely small residue of ash4 ,an important property of these umbers is their partial solubility in alkalis1 a peculiarity which is utilised for the preparation of brown wood stains4 ,asphaltum ,asphaltum forms very friable dark brown to black masses1 which1 in contact with a light1 easily ignite and burn with a bright1 but very smoky1 flame1 disengaging a peculiar1 8bituminous0 smell1 and leaving only a very small quantity of ash4 ,extensive deposits of asphaltum are found at the ,dead ,sea1 the ,pitch ,lake on the island of ,trinidad1 in ,dalmatia1 and many other places1 where1 however1 it is in an impure condition and frequently contains large quantities of sand4 ,in many localities the rock is impregnated with asphaltum1 which makes it dark brown to black in colour and gives rise to a bituminous odour when rubbed4 ,peat beds sometimes contain pockets of a mass with a handsome brown colour and consisting of a mixture of humic acids and other organic substances which may be ranked with the humin bodies that are always formed when organic matter decomposes in presence of an insufficient supply of oxygen4 ,these bodies are dark coloured1 mostly deep brown1 rich in carbon1 and1 to some extent1 similar to brown coal or peat in chemical composition4 ,their high carbon content renders these substances very inert towards chemical reagents1 and therefore particularly adapted for the preparation of painters' colours4 ,genuine ,vandyke brown1 which is the handsomest brown known1 is an earth rich in humin compounds2 and ,cassel brown also belongs to this group4 7,g7 ,,black ,,earth ,the colour of these earths is entirely due to carbon1 and pure carbon1 a certain form of which occurs native1 is itself used as a pigment4 ,actually1 there are only two minerals that require to be mentioned in this connection3 black schist and graphite4 ,black ,schist ,in most cases this is a clay shale1 so rich in carbon as to appear deep black4 ,in commerce1 this mineral is also erroneously called 8black chalk02 but at present it is seldom used as a pigment or drawing-material1 black chalks being produced far more cheaply than the expense of preparing the natural article4 ,grey clay shales are used for making grey earth pigments 7stone grey1 and mineral grey74 ,graphite ,this mineral is found1 in a very pure state1 in many localities1 celebrated deposits occurring in ,england1 ,siberia1 ,bohemia and ,bavaria1 whilst ,north ,american graphite has lately come into prominence4 ,graphite is a modification of pure carbon1 and is met with in the form of hexagonal 7rhombohedral7 crystals1 usually occurring as hexagonal plates with a lustrous1 iron-black colour4 ,it rubs off easily1 and readily burns away1 leaving a very small amount of ash1 when subjected to a very high temperature in presence of air4 ,the principal uses of graphite are as an anticorrosive paint for iron1 and for making lead pencils4 ,as already mentioned1 the term 8earth colours0 has been considerably broadened of late4 ,whereas1 formerly1 it was restricted to colours prepared exclusively from minerals by a simple treatment1 limited to crushing1 levigation or calcination1 it now includes the pigments obtainable from large by-products of certain chemical processes4 ,this latter class is especially important as affording an opportunity of utilising products formerly considered worthless and whose removal often entailed heavy expense4 ,by drawing on these materials the industry of the earth colours has greatly enlarged its scope4 ,at present1 many colours of this kind are on the market1 and it is to the interest of many manufacturers to endeavour to utilise certain waste products in the same direction4 ,the advantage of such a course hardly needs emphasising2 but1 to give only a single example1 it may be mentioned that the manufacture of fuming sulphuric acid from green vitriol1 by the old process1 produces residues which were formerly looked upon as quite worthless1 and sold at very low prices1 but are now worked up1 in a number of factories1 into very handsome and durable pigments4 ,,chapter ,,iii ,,the ,,preparation ,,of ,,the ,,colour ,,earths ,the preparation of the raw materials for the purpose of making earth colours is a very important matter1 because many minerals or pigmentary earths merely require mechanical treatment to render them at once fit for use4 ,the mechanical preparation differs considerably1 in accordance with the raw material under treatment1 substances that are found native in a finely powdered condition only needing1 for the most part1 to be levigated4 ,it rarely happens1 however1 that the raw material occurs in condition for use direct1 an example of this kind being afforded by the finest clays or ochres4 ,whilst these are found in a state of extremely fine powder1 they nearly always contain certain quantities of sandy ingredients or even large lumps of foreign minerals1 and therefore require levigating4 ,sometimes they need crushing as well1 the small particles cohering so strongly that mere treatment with water 7levigation7 is unable to separate them4 ,mechanical force is therefore necessary1 a passage through grooved rollers being generally sufficient to crush the lumps2 but in some cases stamps have to be used4 ,when solid materials have to be treated1 mechanical appliances must always be used1 their selection depending on the materials in question4 ,thus1 gypsum1 for example1 can be crushed with ordinary rolls or mill stones1 its degree of hardness being so very low 7#b7 that it can be scratched with the finger-nail4 ,if1 however1 the material to be reduced is limestone1 which belongs to the third degree of the scale of hardness 7can only be scratched with an iron nail71 or heavy spar 7hardness #c-ce71 very powerful stamps or edge-runners must be employed to break it down into small lumps1 which can then be further reduced1 without any special difficulty1 in an ordinary mill4 ,it is thus evident that a great variety of mechanical appliances are used in the manufacture of earth colours4 ,before going into their construction it is necessary to point out that1 whatever the mechanical treatment employed1 a considerable expenditure of mechanical force is entailed2 and more power is needed when mixtures have to be prepared4 ,it is therefore essential1 in planning a factory for making earth colours on a large scale1 to make provision for ample motive power4 ,this power may be supplied by a steam engine2 but it must not be forgotten that the prime cost and running expenses of such an engine are considerable1 and form an important item in view of the low value of most earth colours4 ,consequently1 it is highly important to be able to generate motive power as cheaply as possible4 ,now1 the cheapest and most uniform source of power is water2 and therefore1 wherever the conditions allow of the erection of the colour works near a stream or river1 which can supply the power to run the various machinery1 the most favourable circumstances will have been secured1 the power being obtained at minimum cost1 whilst the upkeep of the motor cannot be very great4 ,if there is sufficient head for the water to be run through a trough over the top of the levigation tanks1 the conditions will be ideally favourable4 ,wind power costs nothing1 once the motor has been installed2 but unfortunately1 one is dependent on the weather1 and sometimes there is not enough wind1 for days together1 to drive the sails at all1 and therefore all the operations have to be stopped1 including levigation1 the water for which has to be raised by a windmill pump4 ,in districts where the winters are severe1 water power may also fail and work have to be stopped2 and consequently1 even when water power is the prime source of energy1 a steam engine must be installed as a stand-by1 being1 of course1 only used when the main source of power gives out or proves insufficient4 ,the machines employed for preparing the raw materials in the manufacture of earth colours may be divided into the following groups3-- ,machines operating entirely by pressure3 crushers2 machines acting by impact3 stamps2 those acting by impact and pressure3 vertical mills 7edge-runners71 ball mills1 centrifugal mills2 and1 finally1 machines with a frictional action3 grinding mills4 ,then there are the levigating machines1 which do not reduce the material but separate the coarser particles from the finer4 ,the construction of the foregoing machines is a matter for the machinery manufacturer rather than the maker of earth colours2 but as the business of the latter is dependent on them1 a short description is considered necessary4 ,the selection depends1 on the one hand1 on the nature of the materials to be treated1 and1 on the other1 on the size of the works1 since a manufacturer who has to deal with large quantities of a given raw material will require different machines from those used on a small scale4 ,the sole purpose of the following description is to indicate to the colour maker the way in which the reduction of the raw material can be accomplished4 ,,crushing ,,machinery ,crushers and ,breakers4--,crushers usually consist of grooved iron rollers revolving on horizontal axes4 ,one of the rollers is fixed1 the other being adjustable by screws1 in order that lumps of different sizes may be treated in one and the same machine1 which may be employed either to turn out a roughly crushed product1 or to reduce it to a certain degree of fineness4 ,if several pairs of crushing rollers be mounted in series1 and each set a little closer than its predecessor1 the material can be reduced progressively from large lumps to a fairly fine powder4 ,each pair of rollers is geared together by pinions1 and is turned in such a way as to draw the material in between4 ,if the gear pinions have the same number of teeth1 the two rollers will revolve at the same speed and will then merely crush the material into lumps of a size depending on the distance at which the rollers are set apart4 ,nevertheless1 by simply altering the gear ratio of the pinions1 the crushing action of the rollers can be supplemented by a grinding action1 a much finer powder being then obtainable than otherwise1 the one roller running at a higher speed than the other4 ,these crushers differ in strength of construction1 very strongly built machines being required for dealing with large lumps of hard material1 whereas substances of low crushing strength1 such as clay or other earthy materials1 can be treated in much lighter machines4 ,in any case1 however1 it is advisable to have the machine stronger than is absolutely necessary for the work in view2 for1 although the prime cost is thus increased1 the outlay on repairs will be reduced1 and the machines can1 if necessary1 be used on harder material as well4 ,the framework supporting the rollers should always consist of a strong iron casting2 and the machine should be set up as close as possible to the engine or motor1 to minimise the loss of power in transmission through long shafting1 etc4 ,illustration3 ,,fig4 #a4 ,fig4 #a represents a breaker 7made by the ,badische ,maschinenfabrik1 ,durlach71 suitable for the rough crushing of clayey materials supplied in large lumps4 ,it can1 however1 also crush shale1 lime1 chalk1 as well as hard1 sticky masses which would clog up a stone-breaker4 ,the material fed into this breaker is gripped at once by the powerful projecting teeth1 which are connected together by sharp-edged ridges1 and is crushed in such a way that it can be easily reduced still further by a succeeding pair of smooth rollers4 ,illustration3 ,,fig4 #b4 ,the granulator 7,fig4 #b71 made by the same firm1 is an example of a machine for crushing harder materials4 ,it is similar in construction to a stone-breaker1 but differs in the movement of the jaws1 and combines the properties of breaker and grinder1 inasmuch as it tears the material as well as crushes it4 ,the figure shows the machine adapted for direct electric drive4 ,if necessary1 these granulators can be fitted with classifying jig screens4 ,stamps4--,stamps or stamping-mills have been used from prehistoric times1 and were probably employed for reducing hard materials long before the introduction of grinding-mills4 ,the underlying principle of the stamping-mill is very simple4 ,the material to be reduced is placed in a trough or mortar1 and the ram or head1 which is of considerable weight1 is raised by a mechanical device and then allowed to fall freely1 from a certain height1 on to the material underneath1 which it crushes4 ,the heavier the head and the greater the height of fall1 the greater the effect produced4 ,as a rule1 a large number of stamps are mounted together1 and in such a way that half of them are being lifted while the other half are falling4 ,either a separate mortar or trough is arranged under each stamp1 or else the whole drop into a common trough charged with the material under treatment4 ,sometimes a lateral movement is imparted to the material in the trough1 so as to bring it under the action of all the stamps in succession4 ,although the construction of stamping-mills in general appears simple1 various modifications are employed for different purposes4 ,as a rule1 a single passage through a stamping-mill is not sufficient to reduce the material completely to the desired fineness1 the first product always containing large and coarse fragments of various sizes1 as well as fine powder4 ,if the latter were left in with the larger pieces for the second stamping it would impede the work1 and the stamping-mill should therefore be provided with means for classifying the material discharged from the trough1 to separate the fine from the coarse and grade the latter into sizes4 ,this is usually effected by means of a grading-screen4 ,stamping-mills are chiefly used for reducing brittle materials4 ,a number of stamps arranged in a row are alternately lifted1 by means of cams mounted on a common shaft1 and then let fall on to the material lying on a solid plate1 or else on a grating through which the crushings fall4 ,fig4 #c is a stamping-mill constructed by ,h4 ,f4 ,stollberg1 ,offenbach4 ,illustration3 ,,fig4 #c4 ,these mills are very strongly built1 as independent units1 the frame being of cast-iron and the rams of best wrought-iron with interchangeable chill-cast heads4 ,in some mills the stamps are rotated during the up-stroke1 in order to equalise the wear on the heads1 and also to economise power4 ,the grating or trough holding the material is perforated with holes1 the diameter of which varies with the material under treatment and the desired degree of fineness in the product4 ,to increase the efficiency of the mill1 the grating or trough is adapted to move while the mill is running1 in order to clean itself automatically4 ,these mills are made in different sizes1 with #b1 #d1 #f1 or #h heads4 ,edge-runners4--,this type of crusher is highly suitable for reducing earth colours in large works4 ,the special feature of the type is that both stones are mounted vertically and turn on a common shaft in the same way that a cart wheel does on its axle4 ,these runners are particularly useful for reducing clay1 chalk and other earth colours1 which have to be dealt with in large quantities4 ,they will also crush fairly large lumps1 and they can therefore be used for the further reduction of materials roughly crushed in a breaker1 etc4 ,the material may be treated in either the wet or dry state1 only slight alteration being needed to change from one method to the other4 ,there are numerous different patterns of edge-runner1 but all of them can be divided into two groups1 viz43 mills with stationary troughs1 whilst the shaft carrying the runners rotates2 and those in which the trough revolves1 and the stones merely turn on the stationary horizontal shaft4 ,illustration3 ,,fig4 #d4 ,comparison of the efficiency of the two types has shown that the revolving-trough type is the better1 giving a larger output per unit time with a reduced consumption of power4 ,figs4 #d and #e show a vertical section and plan respectively of this type of edge-runner4 ,the trough ,g is turned by means of a toothed crown gearing with the bevel pinion ,o mounted on an overhead shaft ,c driven by a belt pulley ,n4 ,illustration3 ,,fig4 #e4 ,the bearings of the vertical shaft ,j of the trough are situated at ,l and ,m4 ,the runners ,h are loosely mounted on the fixed horizontal shaft ,e and revolve in consequence of the friction between them and the material in the trough4 ,as the latter revolves1 the material is continuously pushed aside by the runners1 and is again brought under them by the action of scrapers4 ,the great advantages afforded by edge-runners1 in consequence of their simplicity1 easy management and low wear in comparison with other grinding appliances1 have led to their reintroduction on a large scale4 ,it should1 however1 be borne in mind that the edge-runner mill must be of a pattern suitable to the materials it will have to treat4 ,the method of drive usually depends on local conditions4 ,the revolving-trough type is chiefly useful for mixing1 on account of the ease with which the materials can be charged4 ,the capacity of edge-runner mills depends on the nature of the material1 the diameter and weight of the runners1 the speed at which they are run1 and also on the rate at which the reduced material is discharged in order to give place to fresh portions of the charge4 ,this is effected by means of two sets of scrapers1 the individual members of which can be adjusted in any direction4 ,their ploughing action also greatly assists the mixing effect4 ,illustration3 ,,fig4 #f4 ,fig4 #f illustrates an edge-runner mill with revolving trough and overhead drive2 and ,fig4 #g one with stationary trough and bottom drive2 both made by the ,badische ,maschinenfabrik1 ,durlach4 ,the runners are of grey cast-iron1 chill-castings or cast-steel being used for crushing hard materials4 ,the trough in all cases is lined with detachable chill-cast plates4 ,special attention is bestowed on the lubrication of all the moving parts1 and all the lubricators are easily accessible4 ,illustration3 ,,fig4 #g4 ,the main shafts of the fixed-trough machines have forged cranks1 and the metal crank bearings are provided with dust caps4 ,all the shaft journals run in detachable metal bushes4 ,a special advantage attaching to this type is the automatic screening device and the returning of the screen residue4 ,in some cases1 complicated appliances are employed to return the coarse residue from the screen1 bucket elevators1 worm conveyors1 etc41 all entailing increased motive power1 not inconsiderable wear1 and a higher prime cost2 but in this instance the object is achieved1 without extra power or wear1 by very simple means4 ,the dust-proof shell enclosing the runners and screen is provided with large doors and charging hoppers4 ,the motive power required to drive edge-runner mills depends on the dimensions of the mill and on the class of material to be treated2 the larger the mill and the coarser the material1 the more power needed to drive it4 ,this type is the more suitable for raw materials that are of an earthy character1 so that all that is necessary is to destroy the cohesion of the particles1 as is the case1 for example1 with clay and all earthy minerals4 ,illustration3 ,,fig4 #h4 ,the wet method of crushing with edge runners is particularly suitable as a preliminary to levigation4 ,a machine arranged for this purpose is shown in ,fig4 #h4 ,it consists of two sets of edge runners1 one with fixed1 and the other with revolving trough4 ,the material is introduced by hand1 or by suitable charging mechanism1 into the upper1 fixed-trough machine1 where it is continuously sprinkled with water and kneaded by the one runner1 and is passed thence to the second roller which forces it through the slotted bed into the bed of the lower set4 ,the slotted beds of the upper and lower set are offset2 and the chief function of the lower set1 with rotating bed1 is to secure intimate admixture of the material which1 in most cases1 is already sufficiently reduced4 ,illustration3 ,,fig4 #i4 ,ball ,mills4--,ball mills are generally used for crushing dry materials to fine powder4 ,the mill shown in ,fig4 #i is a typical form of grinding drum enclosed in a dust-proof casing1 the latter being provided1 at the top1 with an opening connected to the dust exhaust pipe4 ,the discharge outlet at the bottom can be closed by a slide4 ,illustration3 ,,fig4 #aj4 ,the drum is provided with two strong lateral shields or cheeks 7,fig4 #aj71 one of which carries the interchangeable cross-arm and the charging hopper4 ,both cheeks are lined with detachable chill-cast plates1 to take up the wear4 ,the bed is formed of heavy steel bars 7which can be turned round71 between which are arranged adjustable slits for the discharge of the reduced material4 ,guard sieves are mounted all round1 and close to1 the bed1 and interchangeable fine screens surround these in turn4 ,the mesh of the fine screens determines the fineness of the product1 and the residue falls down on to a plate which returns it to the interior of the drum4 ,the reduction of the charge is effected by a number of very hard1 forged steel balls of various sizes4 ,the mill must be run in the direction marked by the arrow on the outer shell1 so that the residue on the screens can be returned to the drum by the plate provided for that purpose2 and the prescribed working speed must be maintained4 ,the mill must not be overloaded4 ,the impact of the balls should be mild1 but distinctly audible4 ,overloading reduces the output4 ,idle running causes the most wear1 since the balls then roll directly on the bed1 which1 of course1 should be prevented as far as possible4 ,the feed is continuous2 and1 of course1 only dry material should be introduced4 ,when the balls have lost size and weight through wear1 they must be replaced by a fresh set4 ,pulverisers4--,pulverisers are the best form of crusher for tough and not over-hard materials4 ,they are simple and strong in construction1 of high capacity with comparatively small consumption of power1 and furnish a good1 uniform product1 the size of which ranges from fine powder to coarse granules1 according to the screens used and the class of material treated4 ,illustration3 ,,fig4 #aa4 ,the crushing is effected by a cross-arm beater1 composed of four to six radial steel arms on a divided1 cast-steel hub1 keyed on to the horizontal shaft4 ,the arms are hardened1 and are adjustably and detachably mounted on the hub4 ,the beating action of the arms1 which run at high speed1 forces the material against the studded surface of the hardened cheeks of the machine and also against the hardened square steel bars forming the periphery1 the repeated impact of the material on itself1 as well as against the arms and bars1 progressively reducing it until small enough to fall through the screen on the under half of the casing1 into a closed receptacle below4 ,the screen mesh varies according to the degree of fineness required4 ,the peripheral bars are mounted in a very simple manner1 and in such a way that when one edge of the bars is worn1 a quarter turn brings a fresh1 sharp edge into operation1 so that all four edges of each bar can be utilised4 ,to prevent the escape of dust1 the machine is provided with an air-circulation chamber1 which maintains the flow of air in continuous circulation1 the resulting strong draught also drawing the fine material through the screen and keeping the meshes open4 ,by this means the capacity of the pulveriser is considerably increased4 ,the interchange of the crushing organs and screens1 and also the cleaning of the machine1 can be effected without difficulty or loss of time4 ,the charge is introduced through a feed hopper at the side1 and may vary1 according to the size of the machine1 from nut size to lumps twice as large as a man's fist4 ,if necessary1 suitable mechanical feed devices can be applied4 ,illustration3 ,,fig4 #ab4 ,disintegrators 7,figs4 #ab and #ac74--,this type of machine is used for reducing medium-hard or soft materials1 especially where it is desired to obtain a comparatively large output of a gritty product4 ,in the patterns shown1 the main shaft is of steel1 with dust- and dirt-proof red-brass bearings with pad or ring lubrication4 ,the spindle case draws out to facilitate cleaning4 ,mechanical feeding attachments can be provided4 ,according to local conditions1 the disintegrator can be mounted either on a brick foundation1 with lateral discharge outlet into a storage bin1 or on a raised grating of iron joists4 ,if the product is to be conveyed to a distance1 it is advisable to have a hopper-shaped collector leading directly to a worm conveyor or bucket elevator4 ,illustration3 ,,fig4 #ac4 ,the arrangement shown in ,fig4 #ac1 in which the disintegrator is mounted on a dust-proof cast-iron collector1 has been found very suitable for colour works of various kinds 7aniline1 lead1 mineral and other colours71 particularly on account of the suppression of dust2 whilst the automatic charging worm greatly increases the capacity as compared with charging by hand4 ,,levigation ,the effect of levigation is based on the circumstance that bodies of greater density than water remain longer in suspension in that medium in proportion as the fineness of their particles increases4 ,this treatment consequently enables the finer portions of a substance to be mechanically separated from the coarser4 ,levigation is extensively practised in colour works because it furnishes powder of finer grain than can be obtained by even the most careful grinding4 ,the appliances used for levigation may be of a very simple character1 consisting only of several tubs or tanks1 mounted in such a way that the liquid contained in one can be run off into the one next below4 ,with this primitive plant1 the material to be levigated is stirred up in the water in the uppermost tub and left to settle until the coarsest particles may be assumed to have settled down1 whereupon the turbid water is drawn off into another tub1 in which it is left to settle completely4 ,when the clear liquid has been carefully drawn off1 a fine sludge is left in the bottom of the tub1 consisting of the fine particles of material mixed with water4 ,when a particularly fine powder is required1 a single levigation does not always suffice1 but the liquid in the second tub must be left to settle for a short time only1 and then run into a third for complete subsidence4 ,illustration3 ,,fig4 #ad4 ,a well-designed levigator for treating large quantities of powder is illustrated in ,fig4 #ad4 ,a stirrer ,r1 driven by cone gearing1 is arranged in a wooden or stone vat ,g4 ,the levigating water enters close to the bottom of the vat1 through the pipe ,w4 ,when ,g is half full of water1 the stirrer is set running1 and the substance to be levigated is added4 ,after a while1 the water laden with the levigated powder begins to run off at ,a into the long narrow trough ,t#a provided1 at the opposite end from ,a1 with a number of perforations through which the water runs into the trough ,t#b4 ,from this it escapes through the perforations into the trough ,t#c and thence successively into ,t#d and ,t#e1 finally discharging into the large tank ,s4 ,the coarsest and heaviest of the water-borne particles deposit in the trough ,t#a finer particles settling down in ,t#b1 and so on in succession1 until the water reaching the tank ,s contains only the very finest of all in suspension1 these taking a long time to settle down to the bottom4 ,the deposit in the upper troughs can be returned to the vat1 whilst that in the lower ones will be fine enough to dry as it is4 ,the residue in the vat is discharged through ,z when the operation is finished4 ,it will be evident that the fineness of the product depends on the number and length of the troughs ,t1 the larger these factors the more delicate will be the particles remaining in prolonged suspension in the liquid4 ,many earth colours require no treatment beyond levigation to fit them for use in paints4 ,this is the case with1 e4 g41 the white clays2 and certain grades of ferric oxide1 which occur native in the state of fine powder1 may also be included in this category4 ,in many cases1 however1 if large quantities of a finely pulverulent mineral be stirred up with water and left to stand1 the deposited solid matter forms such a highly coherent mass that it can only be distributed in water with difficulty1 the fine particles adhering so firmly together that it is hardly possible to stir them up again completely in the liquid by means of a paddle4 ,nevertheless1 this can be easily effected by using a special appliance of the kind employed by starch manufacturers for a similar purpose1 viz4 the levigation of starch4 ,this apparatus is designed in such a way that the pulpy charge of material is gradually and completely disseminated in the introduced liquid4 ,illustration3 ,,fig4 #ae4 ,fig4 #ae shows a device of this kind1 consisting of a circular vessel provided with a step bearing for a vertical shaft driven by cone pinions4 ,the lower part of the shaft is provided with a thread1 on which a nut is adapted to travel up and down4 ,by means of rods1 this nut is connected to a wooden cross-bar provided with stiff bristles on its lower face4 ,a horizontal handle is attached to the nut4 ,the water is admitted through the pipe on the right4 ,in working the apparatus1 the shaft is rotated and the handle held firmly1 thus causing the nut and attached cross-bar to rise to the limit of its travel4 ,the levigating liquid1 mixed with the material under treatment1 is then admitted1 until the vessel is full1 and when the solids have completely subsided1 the clear liquid is drawn off1 and the operation is repeated until a thick layer of sediment has accumulated on the bottom of the vessel4 ,to levigate this1 the cross-arm carrying the bristles is lowered until it just touches the surface of the deposit1 and a continuous stream of water is admitted through the pipe at the side4 ,the bristles gradually disseminate the upper layers of the sediment in the water1 which becomes turbid and is then drawn off into another vessel1 cement-lined pits being used in the case of large quantities4 ,when the brushes no longer encounter any of the sludge1 the cross-arm is lowered sufficiently to stir up another layer2 and in this way1 large quantities of solid matter can be distributed in water4 ,if the cross-arm is rotated at low enough speed1 the coarser particles of material keep on settling down again1 and the collecting vessels will receive only the finest particles4 ,in addition to the mechanical separation of coarse and fine particles1 levigation accomplishes another purpose1 namely that the prolonged contact of the treated material with water dissolves out any admixed soluble constituents which might affect the quality of the colour1 the latter being left in a purified condition4 ,for successful levigation it is essential that the charge should be in a sufficiently fine condition at the outset4 ,clayey raw materials require no preliminary treatment other1 perhaps1 than passing them through a disintegrator1 whereas hard1 crystalline substances must first be ground in a wet mill1 such as an edge-runner mill with stationary bed1 into which the materials are fed with an admixture of water1 provision being made for keeping the charge under the runners all the time4 ,the crushed material is screened previous to levigation4 ,in the levigation process a few vessels of large size are preferable to a number of small ones4 ,the nature of the material will determine whether any stirrers are required or not1 these being unnecessary in the case of the pigmentary earths1 which naturally remain a long time in suspension and therefore do not require stirring up4 ,the pulpy levigated material is taken out of the tubs1 etc41 drained 7if necessary7 and dried4 ,the draining may be effected in bags1 or--in large plants--filter presses or hydro-extractors4 ,in these latter instances1 pumps will be provided for feeding the sludge direct to the presses1 and conveyors for delivering the pressed material to the drying-plant4 ,,draining ,,and ,,drying ,the levigated colour earths form a stiff pulp containing a large quantity of water1 which can be eliminated in various ways4 ,usually1 the mass is dried by spreading it out thinly on boards and leaving it exposed to the air until it has become solid2 or else it is only left long enough to acquire the consistence of a thick paste1 which is then shaped into cones or blocks1 which are allowed to dry completely in an airy place4 ,if the colours are to be sold in the form of powder1 the dried lumps are crushed4 ,to accelerate drying1 the pulp may be put through a hydro-extractor1 or dried in hot-air stoves or rooms4 ,as1 however1 this last method entails special appliances and also expenditure1 this acceleration is only resorted to when rendered necessary by special conditions4 ,the ,hydro-extractor4--,when a substance is set in rapid rotation1 it tends to fly away from the centre at which the rotational force is applied4 ,the centrifugal force thus coming into action increases with the velocity of rotation and with the distance of the substance from the axis of rotation4 ,the centrifugal hydro-extractor consists1 therefore1 of a vessel in rapid rotation2 and if a liquid be introduced into such vessel1 it is projected with considerable force against the peripheral walls4 ,if the peripheral surface be perforated1 the liquid portion of a charge consisting of liquid and solid matters will be ejected through the perforations1 while the solid matter remains inside4 ,as a rule1 a few minutes' treatment in a hydro-extractor is sufficient to separate the water from a thin pulp so completely that the solid residue is in an almost completely dry state4 ,a hydro-extractor which1 though of an old pattern1 is well adapted for the purposes of the colour-maker1 is shown in ,fig4 #af4 ,illustration3 ,,fig4 #af4 ,the drum ,a1 which revolves easily on a vertical axis1 is of metal1 and is provided with a large number of fine perforations on its peripheral surface4 ,it can be rotated at high speed by means of the crank f and pinions d1 e1 or by the fast-and-loose pulley a b connected with a source of power4 ,to prevent any of the charge from being projected over the rim of the drum1 the upper edge is turned over so as to leave only a comparatively small opening at the top4 ,the lower end of the drum shaft carries a strong steel spindle1 which must be carefully machined and enable the drum to revolve as easily as possible4 ,this is essential1 because even small machines require a comparatively large amount of motive power--which is not surprising in view of the high speed at which the drum has to revolve in order to perform its functions4 ,the drum is enclosed in a casing of somewhat larger diameter1 which may be of any convenient material4 ,the bottom of the casing is preferably tapered slightly downward1 and is covered1 at its lowest part--below the bearing of the drum--with a sieve communicating with a pipe through which the ejected liquid is drained off4 ,when a liquid1 containing solid matter1 is fed into the drum1 which is already running at high speed1 the liquid is thrown1 by the centrifugal force1 against the peripheral surface of the drum and escapes through the perforations1 leaving the solid matter behind4 ,where large crystals are in question1 as for instance in sugar factories1 the centrifugal machine can be employed without any additional precautions1 the liquid being expelled and the crystals being practically dried by keeping the machine running a short time longer4 ,in the case of the pulp obtained by levigating colours1 however1 this procedure would result in failure1 because the fine solid particles would be ejected along with the liquid and the drum would be left quite empty4 ,in this case it is therefore necessary to provide means for retaining the solid matter in the drum1 and allow only the water to escape1 with which object the drum is lined with a bag of closely woven fabric1 open at the top and fitting snugly against the inner surface of the drum4 ,when the drum is first started1 the ejected liquid is milky1 no fabric being sufficiently close to retain all the extremely fine solid particles present4 ,in a very short time1 however1 the liquid will begin to run away perfectly clear1 this occurring as soon as the pores in the fabric have become so far obstructed by the projected solids as to allow water alone to pass through4 ,the milky water is then returned to the feed tank and run slowly into the machine4 ,the water is very quickly expelled1 and the colour remains in the drum as a stiff paste1 of sufficient consistence to be moulded into lumps of any desired shape4 ,the use of the hydro-extractor may be particularly recommended when ample motive power is available and accelerated draining is desirable4 ,illustration3 ,,fig4 #ag4 ,fig4 #ag illustrates a modern type of hydro-extractor with bottom discharge and suspended drum1 the shaft of which is coupled directly to an electro-motor4 ,filter-presses4--,whereas the hydro-extractor is only used in particular cases for the purpose of the earth-colour manufacturer1 the filter-press enjoys more extensive application4 ,every filter-press is composed of a number of closely fitting press frames1 held together by the pressure of a screw4 ,these frames1 when assembled1 form chambers provided with inlet and outlet openings4 ,suitably shaped and stitched filter-cloths are secured inside the chambers1 and the sludge to be filtered is run into the press from a high-level tank4 ,the water passes through the filter-cloths and runs off1 whilst the colour earth gradually fills the chambers4 ,when draining is completed1 the press is taken apart and emptied4 ,in this way the earths are obtained in the form of more or less dry cakes1 which are then put through further treatment or dried4 ,illustration3 ,,fig4 #ah4 ,fig4 #ah shows a ,dehne filter-press suitable for the earth-colour manufacturer4 ,wood internal fittings are often used1 because wood does not affect the shade of the colours2 but1 wherever the nature of the materials admits1 iron presses are to be preferred on account of their greater durability and the certainty of the joints continuing tight4 ,the finer the grain of the levigated colour1 the more difficult the expulsion of the water2 but as a rule1 a pressure of #aae-aie inches1 water-gauge1 will be sufficient4 ,if the sludge be run into the press from a tank at sufficient height1 two charges can be worked in a day1 but the cakes will not be as firm as butter of medium hardness4 ,it is better to pump the charge into the press by means of a special diaphragm pump4 ,the drainage is then incomparably quicker1 the cakes will be formed in about an hour and will also be drier4 ,a good deal1 however1 depends1 naturally1 on the nature of the earth colour4 ,if the colour contains acid1 alkali or salts1 the filter-cloths can be washed by flushing the press with water under pressure4 ,the cloths are made of specially fine cotton fabric4 ,the press-runnings1 which are never quite clear1 are collected in a clarifying tank1 where they are treated with lime and kieserite1 whereby gypsum is formed1 and the mass is put through a filter-press1 which retains the solids and leaves the effluent clear4 ,illustration3 ,,fig4 #ai4 ,filter-cloths which have become choked by use are spread on a table and scrubbed with water1 or else washed in a special machine 7,fig4 #ai71 consisting of a rotary drum1 with belt drive1 the rotation circulating the water in the interior trough and enabling it to extract the dirt from the cloths4 ,the flow and discharge of the water are controlled by valves1 and the water may be warmed by admitting steam into the machine4 ,the size of the washer depends on that of the filter-cloths4 ,from the press1 the cakes of colour are conveyed to the drying-plant1 usually by the aid of automatic machinery4 ,drying ,appliances4--,the stiff paste or cakes from the hydro-extractor or filter-press can be shaped1 but require to be dried before they are put on the market4 ,drying is a wearisome operation1 the finely divided material taking a very long time to dry completely1 even during the summer months1 whilst in winter it is almost impossible to get certain colours--such as ferric oxide colours and levigated clay--quite dry in the air1 the inside of the lumps remaining soft and pasty after lying for months4 ,the only way in which this troublesome delay in the completion of the operation can be overcome is by artificial drying2 but as the employment of artificial heat entails expense1 it is necessary to carry on the process with the smallest possible outlay1 in view of the low commercial value of most earth colours4 ,long experience has convinced the author that the arrangement of the drying-rooms in many colour works is based on entirely wrong principles1 and that a great portion of the heat furnished by the fuel is wasted4 ,for this reason the description of a properly arranged drying-room will be welcomed by a number of readers4 ,it is a well-known fact that hot air is lighter than cold4 ,consequently1 when a room is artificially heated1 the highest temperature will be found just under the roof or ceiling1 and articles placed in that part of a heated room will dry much faster than those near the floor4 ,if the drying-room is heated by an ordinary stove1 articles placed on a fairly low level will only dry very slowly1 because the hot air flowing from the stove tends to ascend4 ,in order1 therefore1 to utilise the entire space of the drying-room1 it is necessary to place the heating apparatus in such a position that the whole of the room will be warmed as uniformly as possible4 ,the stove should therefore be situated in a chamber underneath the drying-room proper4 ,illustration3 ,,fig4 #bj4 ,because air that is already saturated with moisture cannot take up any further quantity1 care must be taken to remove the damp air continuously from the drying-room1 and to replace it by dry air4 ,this may be effected by suitably designed ventilation1 on the lines shown in ,fig4 #bj1 which represents a drying-room arranged in such a way as to provide for all the above-mentioned contingencies1 and ensure continuous drying4 ,the heating apparatus is located in the cellar1 and consists preferably of a slow-combustion stove comprising a cast-iron cylinder1 with an air inlet ,a 7with sliding regulator ,t71 for the air of combustion1 and a shoot ,f at the top1 through which the stove is fed with fuel--preferably coke1 on account of its great heating power4 ,the stove is surrounded by an iron or brick shell ,m1 having two flues ,r and ,r#a leading to the chambers ,i and ,,ii1 where they terminate in register cowls ,k1 which can be adjusted1 by turning the handles h1 so that when the slots o in ,k coincide with corresponding slots in the end of the pipe1 the maximum amount of hot air from the stove is delivered into the drying-chambers2 and1 by suitably adjusting the cowls and the draught through the fire-door ,t1 it is possible to regulate the temperature of the chambers to within one degree of the thermometer scale4 ,when only one of the drying-chambers is required to be heated1 the register in the other is closed1 and the whole of the hot air is delivered to the first one4 ,with this arrangement none of the heat is wasted1 and the contents of one chamber can be dried while those of the other are being removed and replaced4 ,the moisture-laden air from the drying-chambers can be led direct into the stove chimney4 ,when coke is used1 the flue gases consist almost entirely of carbon dioxide4 ,if the vent pipes are led from the top of the drying-chambers into the chimney1 the hot gases ascending the latter induce a strong draught in the chambers and carry off the moist air into the open4 ,these pipes1 also1 are fitted with registers1 which1 when suitably adjusted1 assist in the maintenance of a uniform drying temperature4 ,the colours to be dried are spread on trays laid on suitable racks in the drying-chambers2 and1 by carefully planning out the available space1 a very large quantity of colour can be quickly and completely dried in a comparatively small plant4 ,the cost of the fuel is so small as to be more than counterbalanced by the saving of time4 ,the heating arrangements in drying-rooms are capable of improvement in many respects1 especially where steam is at disposal2 and in such cases1 it is better to substitute steam heating for a fire4 ,it will then be necessary to put in a good fan1 or other device1 to ensure the removal of the moist air4 ,an excessive room temperature--above1 say1 #ej ,c4 7#abb ,f47--is not only superfluous1 but in many cases injurious1 because1 apart from the fact that some colours change in shade when over-warmed1 an unduly high temperature causes the surface layers to dry very quickly and form a crust which prevents the escape of water vapour from the interior of the material4 ,another form of drying-plant for earth colours is the drying-floor1 a large room with a rammed concrete or stone floor1 intersected with brick flues 7about one foot square71 covered with iron or concrete slabs and conveying hot flue gases from a furnace4 ,these floors are particularly suitable where there is a possibility of utilising an existing supply of hot flue gases4 ,drying-tunnels are specially adapted where large amounts of material have to be dried4 ,the tunnels are built of brick and provided with a rail track on which the trucks carrying a series of trays laden with colour are run4 ,as the trucks move slowly forward1 they are met by a current of hot air which dries the charge4 ,the tunnel is kept filled with laden trucks1 each fresh one introduced pushing a finished one out at the further end4 ,in many cases1 drying troughs are also useful4 ,these are long1 semicircular1 jacketed troughs of boiler plate1 hot air or steam being passed through the jacket space4 ,a worm conveyor keeps the contents moved forward1 turned over and mixed to facilitate drying4 ,mention may finally be made of vacuum drying-cupboards1 which are heated1 air-tight chambers1 for the material1 in which the air is partially exhausted1 thus increasing the rate of evaporation of the water and causing the materials to dry quickly at a much lower temperature than otherwise4 ,,crushing ,,and ,,sifting ,the distributing and covering power of the earth colours depends--apart from their special properties--on the fineness of their particles4 ,for this reason1 all the means adopted for the purpose of pulverisation are of particular interest4 ,the most important crushing and powdering devices have already been described1 and may be referred to1 all that needs mention in addition being the fact that stone mills also are used for fine grinding4 ,the ground products1 however1 are not entirely homogeneous1 always containing1 in addition to the very finest particles1 those of a coarser nature which must be removed by sifting4 ,sifting machines are essentially sieves through which the colour is passed4 ,the sieves are made of wire gauze or bolting-cloth1 stretched on prismatic frames which are rotated 7centrifugal sieves71 or superposed on the flat and reciprocated4 ,in centrifugal sieves1 the material is projected against the sieve1 and the whole apparatus is in a state of vibration1 or else beaters are provided to keep the fine orifices in the sieve from choking up4 ,nowadays there are numerous types of sifting devices1 none of which1 however1 can be considered as the best for all purposes1 since each type of earth colour behaves differently and requires special treatment4 ,the proportion of moisture in the material1 also1 has an important influence on the method of treatment required4 ,illustration3 ,,fig4 #ba4 ,a typical flat sifting-machine1 with eccentric jig motion1 is illustrated in ,fig4 #ba4 ,the machine is fed through a hopper provided with feed rollers1 the rate of feed being adjustable4 ,the screened product is discharged through a shoot at one side of the machine1 and the residue at the opposite side1 into boxes1 etc41 placed underneath4 ,for materials that give off a large amount of dust1 the machine can be enclosed in a dust-proof casing1 in which event the product and residue are delivered into drawers4 ,the machine is easily cleaned and the sieves quickly changed1 and is well adapted for dealing with a succession of different materials4 ,the hopper can be fitted with a pair of adjustable crushing rollers4 ,illustration3 ,,fig4 #bb4 ,fig4 #bb is a drum sifter1 which is fed by means of a hopper and worm2 and the drum can be covered with wire or silk gauze4 ,the sifted product falls into a worm conveyor in the bottom of the casing and is discharged at the side4 ,this may be replaced by a series of mouths for discharging direct into bags1 or the machine can be adapted to deliver into an elevator1 worm conveyor or other means of transport to a distance4 ,the screenings are discharged through a shoot at the back of the machine1 and can be handled in various ways4 ,a beater is provided to clear the drum and increase the output4 ,illustration3 ,,fig4 #bc4 ,fig4 #bc illustrates a centrifugal sifting-machine for producing very fine powder in large quantities without any escape of dust4 ,it contains a screening drum1 the frames of which are detachable and facilitate changing the sieves4 ,a beater revolving inside the drum projects the powder against the sieves1 such portions as pass through being taken up and discharged by a worm conveyor2 this1 however1 can be replaced by a bagging device1 etc4 ,,calcining ,colour earths are sometimes calcined at a high temperature in order to modify their structure and shade1 the operation being accompanied1 in some cases1 by the destruction of organic admixtures and the expulsion of volatile constituents4 ,an important feature of calcining is that it improves the covering power of many colours1 especially heavy spar and certain ferric oxide pigments4 ,this alteration is probably due to the heat causing the finest particles to cohere1 and also to the expulsion of chemically-combined water1 etc4 ,the change of shade1 which is often dependent on the degree and duration of the heating1 is probably also connected with cohesion2 but in many instances it is attributable to chemical modifications produced by the treatment2 ferric hydroxide1 for example1 losing its water of hydration when heated and becoming transformed into ferric oxide4 ,the details of the calcination process vary with the nature of the material1 and will therefore be described1 together with the appliances used1 when we deal with the colours which require to be put through this treatment4 ,,mixing ,,and ,,improving ,it is very important that the maker of earth colours should always be able to turn out his products uniform in shade1 and since the raw materials are liable to vary in character1 and the composition of the earths from one and the same deposit is not invariable1 the desired shade has to be obtained by mixing4 ,for this purpose1 standard samples must be prepared1 for comparison in matching4 ,illustration3 ,,fig4 #bd4 ,mixing is a highly important operation1 on the proper performance of which oftentimes depends the sale of certain colours and the reputation of the maker4 ,it may be effected in various ways1 such as shovelling the ingredients together or by combining the work with grinding in edge-runner mills1 ball mills1 etc4 ,another method is the mixing barrel shown in ,fig4 #bd1 a strong cask mounted on an axial shaft driven by a motor1 etc4 ,the barrel is filled about two-thirds full of the materials to be mixed1 and1 after closing the feed door1 is slowly rotated1 since1 if run at excessive speed1 the contents are merely projected against the sides of the barrel by centrifugal force1 and it can then be turned for hours without result4 ,the mixing effect can be considerably increased by mounting the barrel so that the shaft is offset from the longitudinal axis of the barrel by an angle of about #cj1 the contents being then moved from side to side at each revolution and thus more intimately intermixed by the twofold motion4 ,illustration3 ,,fig4 #be4 ,in addition to such home-made appliances1 there are mixing-machines of the type illustrated in ,fig4 #be1 the body of which is fitted with a distributing worm at the top1 and a pair of rollers at the bottom4 ,below the rollers1 which are covered by plates that can be adjusted at a convenient angle1 is a worm conveyor delivering into an elevator1 outside the machine casing1 which connects the two worms4 ,one or more discharging-doors1 according to the size of the machine1 are provided under the worm conveyor at the end next the elevator4 ,the feed hopper can be arranged on the elevator or on top of the machine1 according to local conditions4 ,in working this machine1 the elevator and distributing worm are started and the full charge is fed into the hopper4 ,when it has all passed through the distributor and is lodged on the sloping plates and bottom rollers1 the latter and the worm conveyor are set in motion1 the material being then carried through by the rotation of the rollers and dropping on to the conveyor1 which delivers it to the elevator1 to be returned to the distributor4 ,in this way the charge is kept in continuous circulation1 and the finely divided particles are repeatedly intermingled1 a uniform mixture being obtained4 ,the effect is heightened by the grinding action of the rollers as the material passes between them4 ,the serial order of the various ingredients1 their physical condition 7granular or powder71 and their density1 are all immaterial1 the mixing being effected so intimately that when1 for example1 a colour is shaded with aniline dyes1 the ingredients are so completely blended in less than an hour that even the smallest sample then taken will perfectly represent the bulk4 ,these machines are made in various sizes1 are entirely automatic1 both in charging1 discharging and mixing1 and are quite dust-proof1 the consumption of power being also small4 ,if necessary1 they can be combined with a crusher or sifter feeding direct into the hopper4 ,a simple means of ascertaining whether the mixing is completed1 and one that can also be employed for judging the character of ground materials1 consists in placing a sample of the product on a sheet of white paper and spreading it out1 under gentle pressure1 with a steel or horn spatula4 ,no irregularities1 streaks1 spots or granules should then be discernible either by the unaided eye or under a magnifier4 ,improving1 which consists in staining earth colours with other 7usually organic7 colouring agents1 to improve the shade1 is an operation which is generally resorted to only in case of need1 because it means extra expense1 and is of no value unless light-proof colours are used4 ,no permanent effect can be obtained by merely mixing-in coal-tar dyes at random4 ,in addition to certain organic dyestuffs1 artificially prepared mineral colours and colour lakes--artificial preparations of an organic dyestuff with an inorganic substratum--are also used for improving4 ,another way of improving earth colours is by precipitating certain coal-tar dyes on them1 in presence of a fixing agent4 ,of course the dyes used must not only be fast to light1 but also inert towards the substratum and to any other ingredient1 such as lime1 that is subsequently added to the earth colours4 ,the following dyestuffs 7,hchst7 are suitable for direct precipitation on siliceous colours 7green earths1 clay1 ochres1 etc474 ,auramine1 conc4 ,o1 ,i1 ,,ii2 new phosphine extra2 chrysoidine ,a cryst41 ,b cryst41 ,c extra2 ,vesuvine 7all marks72 cachou brown ,d1 ,g2 dark brown ,m1 ,,mb2 safranine ,g1 ,,gs conc41 ,b conc42 rhodamine ,o extra1 ,b1 ,b extra2 fuchsine 7all marks72 fuchsine acetate2 cerise ,g1 ,r2 grenadine ,o1 ,r1 ,,rr2 maroon ,o extra2 new fuchsine ,o1 ,p2 methylene violet 7all marks72 peacock blue ,p2 ,victoria blue ,b1 ,r2 thionine blue ,,go2 methylene blue 7all marks72 malachite green 7all marks72 brilliant green 7all marks72 coal black ,o1 ,i1 ,,ii4 ,,moulding ,the colour pulp can be made into tablets by moulding it in dry boxes divided into a number of compartments4 ,the colour shrinks in drying1 and the tablets will then easily fall out of the moulds4 ,cones are obtained by placing the pulp in a box1 the bottom of which is perforated with numerous holes of uniform size1 the box being then tapped against the surface of a stone table4 ,at each stroke1 a certain amount of colour is forced1 in the shape of small cones1 through the perforations1 on to a sheet of paper underneath4 ,the cones are then dried4 ,some colours are moulded into blocks by forcing the partly dried paste into suitable moulds--preferably of metal1 so that they may be engraved with the maker's name1 or other imprint--and left to dry slowly and without cracking4 ,the cakes may be prevented from crumbling by incorporating a small quantity of adhesive1 such as a weak solution of dextrin1 with the water in which the colour is suspended4 ,,chapter ,,iv ,,white ,,earth ,,colours ,the white earth colours are important for the purposes of the colour-maker1 because not only are they used by themselves as paints1 but also serve in the production of light shades of other colours4 ,the white colours containing clay or lime are the most abundant and important of all1 and will therefore be described first4 ,the lime colours comprise caustic lime1 carbonate of lime 7chalk or powdered limestone71 gypsum and bone ash4 ,,caustic ,,lime ,though this product is not used direct as a painters' colour1 it is employed in the preparation of compounds that are so used4 ,it is made on a large scale for the preparation of mortar1 and there is therefore no need for the colour-maker to manufacture it himself1 since it can always be bought from a lime-burner4 ,it must be borne in mind1 however1 that lime for the colour-maker's purposes must possess certain properties1 failing which it is of no use to him4 ,what these properties are and how the product is made will now be briefly described4 ,when carbonate of lime1 i4 e4 native limestone1 is exposed to strong heat it parts with carbon dioxide and is transformed into burnt or caustic lime4 ,ca,c,o#c ,ca,o ,,co#b ,carbonate of lime4 ,caustic lime4 ,carbon dioxide4 ,the limestone is burned either in kilns of very simple construction1 or else in more complicated furnaces in which a continuous process is maintained4 ,the ordinary limekiln1 which can be found in many parts of the country1 consists merely of four walls1 with a door in the front one for the introduction of the fuel4 ,kilns of this kind are usually set up in the vicinity of the limestone deposits1 and are abandoned when they get worn out4 ,the limestone is broken to lumps of fairly even size1 about as large as a man's head1 and these are piled up in a domed heap in the kiln1 sufficient space being left between the lumps for the passage of the flame4 ,a fire is then lighted under the pile1 pine wood being mostly used for this purpose on account of its high content of resin1 which gives a very strong flame4 ,the fire is kept up until the top of the pile has become white hot1 and only a blue1 smokeless flame is visible4 ,the appearance of this denotes that the burning is ended1 the fire being then allowed to die out and the lumps left until cool enough to be taken out of the kiln4 ,this operation is performed with great care1 particular importance being attached to preserving the lumps as intact as possible and preventing the formation of dust1 which is of little value4 ,the lime made in this way is endowed with properties that render it valuable for the purposes of the colour-manufacturer2 but1 on the other hand1 possesses certain disadvantages4 ,owing to the use of wood as fuel1 the caustic lime obtained in this way is usually a very pure white1 because the burning is continued until the whole mass is glowing and the firewood has been completely consumed4 ,if this is not the case1 the burnt lime is greyish in colour1 from the finely divided particles of carbon1 which1 of course1 spoils the lime for colour-making4 ,the defects existing in lime burned in the above type of kiln originate in the irregular character of the product4 ,it will be evident that the limestone lumps that are nearest the fire will be far more strongly heated than those in the upper part of the dome2 and when calcined lime is kept incandescent for a long time1 it becomes so compact in texture that it quenches with great difficulty when brought in contact with water4 ,this condition is known as 8dead burnt10 and such lime is of little value4 ,the lumps at the top of the pile are least exposed to the heat1 and very often still contain carbonate1 as is shown by the effervescence produced on treatment with an acid4 ,such lime is imperfectly burnt1 and the lumps frequently still exhibit the crystalline structure of limestone when broken4 ,they quench rapidly1 but when mixed with a little extra water1 the mass is no longer of the buttery consistency typical of caustic lime1 but contains gritty portions consisting of unaltered limestone4 ,owing to the defects of dead burning on the one hand and insufficient calcining on the other1 colour-makers now prefer lime that has been burned in continuous kilns1 because1 when properly made1 such lime is very uniform in character1 and is also cheaper than that burned with such an expensive fuel as wood4 ,in consequence of the greater capacity of the continuous kiln1 and the more uniform character of the product1 the old-fashioned kilns are more and more falling into disuse4 ,the arrangement of the continuous kiln is very simple4 ,the kiln consists of a fairly high shaft1 open at the top1 and provided at the bottom with a small hole for the removal of the burnt lime4 ,a coal fire is lighted1 and as soon as the kiln is heated up1 alternate layers of limestone and sufficient coal for burning it are introduced4 ,the burnt lime sinks to the bottom of the shaft and is pulled out1 with iron hooks1 from time to time4 ,given the right proportions of coal and limestone1 the lime made in these kilns is burnt to just the right degree1 and is excellent for builders' use4 ,in many cases1 however1 it is less valuable to the colour-maker1 and in some quite useless4 ,for example1 when the coal is not completely consumed1 carbon1 even though only a very small quantity1 is deposited on the lime1 and the burnt lime1 instead of being a brilliant white1 as it should be1 is grey2 and colour made therefrom is also greyish white and will spoil the shade of other colours with which it is mixed4 ,the chemical composition of the original limestone also has an influence on the character of the burnt lime4 ,limestone consisting entirely of carbon dioxide and lime is so rare that sufficient is never available for making burnt lime on a large scale4 ,even the purest limestone found native in large quantities--namely marble--is not pure carbonate of lime1 but contains a certain proportion of extraneous substances4 ,at the same time it is too expensive to use for technical purposes4 ,the ordinary impurities present in limestone are ferrous oxide1 ferric oxide1 magnesia and organic matter4 ,the presence of ferrous oxide can usually be detected by the greenish tinge of the raw limestone1 and the reddish cast of the burnt product4 ,ferric oxide is revealed by its reddish colour1 in both the limestone and burnt lime4 ,magnesia1 which is present1 for example1 in dolomitic limestone1 cannot be detected by the colour1 either before or after burning1 this oxide being itself perfectly white2 but its presence is a drawback because if in large quantity it makes the lime very difficult to quench1 and such lime is never of a fatty character4 ,organic matter betrays itself by the colour1 the lime being dark tinted1 varying from grey to black4 ,black limestones usually contain carbon in an extremely fine state of division1 and are quite useless to the colour-maker owing to the impossibility of completely burning off this contained carbon1 which always imparts a greyish tinge to the burnt lime4 ,the behaviour of limestones in this respect varies1 however1 considerably1 and can only be ascertained with certainty by a trial burning4 ,many that are rather dark in colour will1 nevertheless1 burn perfectly white1 whereas others1 much lighter in shade1 always give a product that is not quite pure in tone4 ,this divergent behaviour seems to have some connection with the chemical composition of the organic matter in question4 ,if it consists of coal1 or substances analogous thereto1 no really pure white lime can be obtained from a light grey limestone1 it being impossible to burn off the finely divided carbon completely4 ,in addition to making a trial burning with a fairly large sample of material1 the behaviour of a limestone towards hydrochloric acid will afford some information as to the nature of the grey colouring matter4 ,if the limestone dissolves completely when suffused with the acid1 the indications are favourable for its usefulness to the colour-maker4 ,if1 on the contrary1 a black residue is left1 the coloration is due to finely divided carbon1 and there is then little prospect of the material furnishing a suitable product4 ,in any event1 a trial burning is the most reliable guide4 ,in addition to carbon1 the presence of any large proportion of ferric or ferrous oxide is objectionable1 since1 in either case1 the product will be tinged red with ferric oxide1 into which the ferrous oxide is transformed at calcination temperature4 ,in addition to comparing the colour of the product with a standard sample1 the suitability of a burnt lime for colour-making can be tested by quenching4 ,if a lump about the size of the fist be placed in a large porcelain basin and suffused with a small quantity of water1 preferably poured in a thin stream1 the lime1 if properly burned1 will continue to absorb the water for a considerable time1 like a sponge1 and will very soon give evidence of a brisk reaction by increasing in bulk and generating such an amount of heat as to cause the immediate evaporation of a few drops of water allowed to fall on the surface of the mass4 ,finally1 the entire lump will crumble down to a very delicate1 voluminous powder1 consisting of slaked lime 7calcium hydroxide74 ,this chemical reaction is expressed by the equation3-- ,ca,o ,h#b,o ,ca7,,oh7#b ,lime ,water ,calcium hydroxide4 ,when the amount of water added to burnt lime is no more than sufficient to effect its transformation into hydroxide1 this latter1 as already stated1 forms a delicate white powder4 ,the addition of more water results in the formation of a homogeneous pulp1 of a peculiar fatty character4 ,since this fatty appearance is only possessed by pure lime1 it is a criterion of high quality in burnt lime1 and contrasts strongly with that of the less valued poor 7or lean7 lime4 ,calcium hydroxide acts as an extremely powerful base1 and therefore must not be mixed with colours that are sensitive to the action of strong bases4 ,as a matter of fact1 its direct use in painting is very small4 ,of course1 a thin milk of lime is used for whitewashing walls1 etc42 and if any colouring ingredients are added they must be such--e4 g4 ochres--as are not affected by the lime4 ,nevertheless1 quick and slaked lime are very important in colour-making1 as forming the originating material for the preparation of a number of colours4 ,when slaked lime is mixed with sufficient water to form a stiff pulp1 and is left exposed to the air for some time1 a change will be observed to take place1 the mass solidifying gradually 7commencing on the outside7 and finally crumbling to a soft white powder4 ,this change is due to chemical action1 the lime having a great affinity for carbon dioxide1 which it readily takes up from the atmosphere--a fact which explains the solidification mentioned4 ,it would be erroneous to assume that the lime is again completely converted into calcium carbonate in this way2 for1 though such conversion does ultimately take place1 it requires a very long time for completion4 ,the resulting compound is1 actually1 a double compound of calcium oxide and carbonate4 ,although this compound has fairly strong basic properties1 they are1 nevertheless1 far weaker than those of caustic lime1 being partly neutralised by the carbon dioxide absorbed4 ,if the superficial area of the slaked lime be increased by spreading it out thinly1 so as to offer greater opportunity for the action of carbon dioxide1 the formation of the double compound in question will be greatly accelerated4 ,this double compound is prepared artificially in special works1 and the resulting colours are put on the market under various names4 ,they1 too1 must not be mixed with colours that are sensitive to alkali1 and on this account they cannot be used in fine paints4 ,if applied as a white priming to the walls of rooms1 care must be taken to cover the coating with some substance that will protect the topping colour from the action of the lime4 ,for this purpose1 painters use a wash of milk1 soap and water1 etc4 ,an important property of lime is its behaviour towards casein1 the substance forming the curd of milk4 ,with this body it combines to form a mass which sets hard and is highly resistant1 viz4 calcium caseate1 and is formed when limewash is stirred up with milk or freshly precipitated casein4 ,weatherproof distempers for outside use are prepared in this manner4 ,,pearl ,,white ,the preparation frequently met with in commerce under this name is nothing more than a burnt lime of great purity4 ,it is prepared in the coastal districts by burning oyster shells1 the resulting burnt lime being easily transformed into a fine powder1 the pure white colour of which is due to the absence of iron4 ,it is used in the same way as pure burnt lime1 and is mainly of interest in seaside towns where oyster shells are often accumulated4 ,it may be pointed out that the name pearl white is often applied also to pure white grades of white lead4 ,,vienna ,,white ,this colour is prepared from any kind of burnt lime that is sufficiently pure2 that is1 free from ferric oxide4 ,the method of preparation is simple1 requiring no special apparatus1 and can therefore be carried out wherever suitable lime is available4 ,operations are commenced by carefully slaking well-burnt lime with water1 a sufficient excess of which is added to produce a fairly thick pulp4 ,to accelerate the absorption of carbon dioxide1 the mass is exposed to the air in thin layers1 by spreading it out on boards1 so as to present a large surface to the air4 ,as soon as the pulpy character has disappeared1 the mass is detached from the boards1 and is pressed and kneaded1 with wooden paddles1 into prismatic cakes which are left exposed to the air--being1 of course1 protected from the wet--until the absorption of carbon dioxide is complete--a condition that can be recognised by the earthy character of the product4 ,the cakes are then dried1 an operation entailing great care1 since lightness is a sign of good quality1 whereas a damp product is very heavy4 ,in forming the cakes they must not be touched by the bare hands1 because the lime is so caustic that it would soon destroy the skin4 ,the foregoing method of manufacture is capable of many improvements1 which can be introduced without adding much to the cost of production4 ,if the lime is formed into large blocks1 it will evidently take a long time for the mass to acquire1 all through1 the earthy character indicating combination with carbon dioxide4 ,this drawback can be easily remedied by forming the mass into small cakes1 which will become ripe1 owing to their larger surface1 much sooner than the bigger blocks4 ,a very good plan to adopt in moulding is to form the burnt lime into a stiff paste with water1 preferably by adding enough water to make a viscous mass1 and leaving this in a lime-pit for several weeks1 the prolonged storage enabling the lime to acquire the already mentioned fatty character1 and at the same time to become highly plastic4 ,lime treated in this way can be forced through a nozzle1 forming a cylindrical rope1 which can be cut by a knife into convenient lengths and left on boards for a few days until they have become firm enough to stand up without breaking4 ,cylinders made in this manner1 with a length of about four inches and a diameter of two inches1 will absorb carbon dioxide very quickly4 ,the absorption can be still further accelerated by setting up the cylinders in an atmosphere highly charged with the gas1 for instance in the vicinity of a manure pit1 as they will then avidly take up the carbon dioxide abundantly liberated from the rotting manure4 ,similar acceleration will take place if the boards carrying the cylinders are placed in a stable1 or in a room where wash for making spirits is fermenting1 because large quantities of carbon dioxide are liberated in both places4 ,working the caustic mass by hand is accompanied by so many inconveniences that it seems highly desirable to employ some mechanical moulding device which will render contact with the wet lime entirely superfluous4 ,it may be pointed out that such a device can also be advantageously used for moulding all earth colours in paste or pulp form1 and in particular for shaping ferric oxide colours into rods or small cylinders4 ,illustration3 ,,fig4 #bf4 ,such a machine 7,fig4 #bf7 is composed of a rectangular box with semi-cylindrical bottom1 a detachable shaft carrying a sheet-metal worm being arranged in the box so that the worm is in contact with the rounded bottom and is continued into the cylindrical extension of the box4 ,this extension terminates in a hollow cone1 to the mouth of which nozzles of varying aperture 7square1 rectangular or round7 can be attached4 ,a knife1 operated by hand or mechanical means1 enables the extruded soft mass to be cut into convenient lengths1 which drop on to a series of easy running rollers in front of the nozzle1 and are thereby delivered to an endless-belt conveyor from which they can be transferred to the drying-boards4 ,when the box has been charged with the lime pulp and the worm is rotated1 the latter forces the soft mass into the cone and extrudes it through the nozzle1 so that1 as long as there is any material in the box1 it is discharged as a continuous rope1 of square1 rectangular or cylindrical section1 on to the guide-rollers1 where it can be cut off into lengths by the knife4 ,a fundamental condition for the preparation of a good ,vienna white is the employment of pure raw material1 which must be free from ferric oxide or earthy impurities1 and fully burned4 ,an excellent material for this purpose is calcined mussel shells1 which furnish a loose1 and at the same time very pure1 lime1 and are very largely used for lime-burning in places such as ,holland1 where they are available in large quantities4 ,vienna white is not much used as a paint colour1 owing to its powerful alkaline properties which have a destructive effect on many colours4 ,it is1 however1 largely employed as a polishing agent1 for which purpose it is powdered and is put on the market--mostly in bottles--as ,vienna lime4 ,its very handsome white colour and low price render it particularly suitable for coarse painting1 for example as a prime coating for painted interior walls4 ,to guard against the danger of the painted decoration being destroyed by the alkaline nature of the white1 it is advisable to coat the dried ground with alum solution1 the alumina of which combines with the lime to form an insoluble compound to which organic colours adhere well4 ,the sulphuric acid also enters into combination with the lime1 the resulting gypsum having no effect on the paints subsequently applied4 ,,chalk ,the name chalk is used for a number of commercial substances which differ considerably in both the mineralogical and chemical sense4 ,french chalk1 for instance1 is a mineral belonging to the steatite group and1 apart from its name1 has nothing in common with true chalk1 except the white colour1 and even this differs altogether from that of chalk properly so called4 ,it is therefore necessary1 in the interests of proper nomenclature1 to differentiate the various kinds of chalk1 commencing with the mineral known by that name to the chemist and mineralogist4 ,in chemical composition1 true chalk is calcium carbonate1 but of a fossil character1 for if chalk dust be examined under a high-power microscope1 it will be seen to consist of the shells of minute animals1 and is therefore to be regarded as fossil4 ,the organic matter of the animals has long disappeared1 leaving the inorganic material1 a very pure calcium carbonate1 behind4 ,illustration3 ,,fig4 #bg4 ,such progress has been made that the zoological status of the animals which inhabited the shells--many thousands of which are present in a lump of chalk--has been identified2 and it is known that these animals were of marine type4 ,fig4 #bg shows the appearance of the animal remains in ,meudon chalk when highly magnified1 the upper half being viewed by transmitted light and the lower by reflected light4 ,notwithstanding the extremely minute dimensions of the chalk animalcul1 their remains form rocks of great thickness in all parts of the world4 ,in ,europe we find1 for example1 extensive chalk formations in ,england1 whose ,latin name ,albion was bestowed on account of the white chalk cliffs occupying long stretches of the coast4 ,the hills of ,champagne consist almost entirely of chalk2 and ,rgen1 together with many other islands1 is nearly all chalk cliffs4 ,it is only in very rare cases1 however1 that chalk occurs in sufficient purity to be immediately suitable for use as a pigment or writing-material4 ,for the most part it contains other minerals1 or large fossils1 from which it has to be separated by mechanical treatment4 ,nodular flints are often met with in chalk1 and many deposits contain such large numbers of the petrified shells of the sea urchin that the chalk really cannot be used as a pigment at all1 by reason of the high cost of purification4 ,the only places where chalk can be advantageously worked for the preparation of pigment is where the mineral is in a high state of purity1 and also contains only very few sandy particles4 ,such chalk deposits are worked on a mining scale1 and1 as a rule1 in the state in which the chalk comes from the quarry2 it is in the form of a soft mass1 easily scratched with the finger-nail and of fairly high density1 owing to the considerable quantity of water with which it is ordinarily impregnated4 ,in order to convert this crude chalk into a product that can be used as a pigment1 it is first left to dry until the lumps can be easily broken1 and then crushed into small pieces1 from which all the extraneous minerals1 which occur as large lumps1 are sorted out and removed4 ,this picking process is important1 especially when the chalk contains flints1 because these latter are very hard and would injure the millstones in the subsequent grinding4 ,the lumps of chalk are reduced by mechanical means1 such as a stamp-mill1 or1 more frequently1 in a mill of the same type as for grinding flour1 since it is impossible to get the lumps so dry as to produce the degree of brittleness necessary for a thorough reduction in a stamp-mill4 ,the millstones are enclosed in a wooden casing1 and the chalk is ground in admixture with water1 the ground mass escaping1 through an opening in the casing1 as a thick pulp which is stored for a considerable time in large tanks4 ,experience has shown that this method of prolonged storage in contact with water greatly improves the colour4 ,the only explanation of this fact is that the chalk still contains a very small amount of organic matter1 which gradually decomposes in presence of water4 ,the evidence in favour of this is the peculiar smell given off during storage4 ,even with the most careful grinding1 chalk cannot be transformed into such a fine powder that is directly fit for all purposes2 and the only way to obtain the requisite fineness is by levigation4 ,owing to the large quantities that are usually handled in this process1 the milky liquid coming from the mill is mostly run into large brick tanks1 where it is left to settle until all the chalk has deposited and the supernatant water is perfectly clear4 ,tapping-off being usually impracticable1 the water is generally drawn off by careful syphoning1 so as not to disturb the fine sludge at the bottom of the tank4 ,the deposit in the settling-tanks is shovelled into wooden boxes1 perforated at the sides to enable the water to drain away1 the chalk being prevented from escaping by lining the boxes with linen cloths4 ,the pulp soon loses its liquid character and shrinks considerably1 the boxes being then filled up with more sludge1 and so on until the contents have ceased to shrink4 ,when the mass is so far dry that it will no longer run when lifted1 the boxes are covered with boards and inverted1 discharging the contents on to the boards1 on which the mass is left to become quite dry4 ,filter-presses are also used4 ,large prismatic masses of chalk never dry so uniformly as to prevent the formation of cracks1 and if the chalk is to be sold in this form the cracks are plastered up with thick pulp2 this operation1 however1 being superfluous when the chalk is to be sold as powder4 ,in order to obtain a more compact product and accelerate the drying of the moulded lumps1 some makers use presses1 in which the fairly dry chalk is subjected to progressive heavy pressure4 ,owing to the fineness of the component particles of chalk1 they adhere so firmly together1 without any bind1 that a fair amount of force is necessary to break down a piece of perfectly dry levigated chalk4 ,sometimes1 however1 chalk exhibits the unpleasant property of losing its cohesion almost completely when dry1 and in such cases it can only be shaped into prisms with great trouble4 ,this peculiarity is specially accentuated when the chalk contains magnesia2 and in order to mould chalk of this kind into blocks1 a binding agent1 such as ordinary glue1 must be added to the water used in grinding1 care being taken not to use too much1 or the chalk will become too hard1 when dry1 for certain purposes1 e4 g4 as drawing or writing chalk4 ,for some purposes1 chalk is sold in powder form1 and very high purity is not then essential1 an admixture of magnesia or clay being harmless4 ,gilders1 for instance1 use large quantities of chalk for priming picture frames1 and stir the chalk up with a certain amount of bind 7mostly size71 to give the particles the desired cohesion4 ,the chief requirement exacted of a good quality chalk is a handsome white colour2 and this depends entirely on the quality of the raw material1 not on the method of preparation4 ,it is known that a substance quite devoid of colour will furnish a perfectly white powder1 because the colourless particles reflect the light in all directions without breaking it up into its constituent yellow1 red and blue rays4 ,chalk1 too1 is in reality a colourless substance1 and reflects light with greater uniformity in proportion as the fineness of the particles increases4 ,consequently1 when one has a chalk that is not perfectly white1 it can1 nevertheless1 be made to furnish a very handsome product by bestowing great care on grinding and levigation4 ,properly prepared chalk should be as fine as the finest flour4 ,when the colour of the best grades of chalk are compared with what may be termed pure white--such as that of white lead1 zinc white1 permanent white--a skilled eye will always detect a greyish or yellowish tinge in the former1 even if obtained from the whitest ,carrara marble4 ,the grey tinge is due to the presence of organic matter1 which cannot be eliminated by any known means1 but which can be shown to exist by the fact that when such chalk is heated to incandescence in the air for a short time1 the resulting burnt lime is pure white1 the organic matter having been burned off4 ,a yellow tinge is caused by minute traces of ferric oxide1 which--as also ferrous oxide--almost invariably accompanies calcium carbonate2 and limestone free from determinable quantities of these oxides is of rare occurrence4 ,ferrous oxide does not reveal its presence in limestone unless in large proportion1 its pale green colour being of low tinctorial power1 whereas ferric oxide1 which is a very strong colouring agent1 can be more readily detected4 ,to those who are engaged in the manufacture of white earth colours1 however1 it is quite immaterial whether a limestone or chalk contains ferrous oxide1 because that oxide quickly changes into ferric oxide in the finely divided product1 and a chalk which was originally pure white will become decidedly yellow in a short time4 ,fortunately1 such a yellow-tinged product can be rendered perfectly white by simple means and at small cost1 all that is necessary being to add a suitable quantity of a blue colouring matter4 ,when this has been done1 the chalk will seem pure white to even the most skilled eye4 ,this result of adding a blue pigment is based on the well-known physical fact that certain kinds of coloured light produce white light when combined1 the colours that give this effect being termed 8complementary40 ,a pure blue is complementary to a yellow with a reddish cast--e4 g4 ferric oxide--and therefore a chalk that is tinged yellow by a small quantity of ferric oxide can be changed into a seemingly pure white substance by the addition of a blue pigment4 ,the only pigments of use in this connection to the colour-maker are such as have very intensive colouring power and at the same time are low enough in price4 ,such substances are ultramarine1 smalt and coal-tar dyes4 ,smalt is the best because its colour is unalterable4 ,in point of chemical composition1 this substance is a very hard glass coloured blue by cobaltous oxide4 ,for improving the colour of chalk or any other white1 the smalt must be in an extreme state of fine division1 and levigated to an impalpable powder4 ,ultramarine can be used for the same purpose1 but is not so permanent4 ,to ascertain the correct proportion of blue pigment1 it is advisable to make a systematic experiment1 which is easily performed4 ,exactly #ij parts of the chalk in question are triturated with #aj parts of blue pigment in a mortar until the entire mass has become a perfectly uniform pale blue powder1 which contains #aj of the blue ingredient4 ,several samples1 each representing one hundred parts of the white pigment to be corrected are carefully weighed out1 #a part of the blue powder being added to the first sample1 #b parts to the second1 #c to the third1 and so on1 and the mixtures are compared with a standard white substance1 such as best white lead or zinc white1 to see which most nearly approaches the standard colour4 ,it is then easy to calculate how much of the blue requires to be added to #ajj or #ajjj lb4 of the material to be corrected4 ,the correction can be effected in several ways2 for instance1 by grinding the blue pigment directly with the bulk1 by adding it at the levigation stage1 or mixing it with the dry1 finished product4 ,the first two methods are attended with certain drawbacks which render it difficult to obtain a perfectly uniform product1 owing to the specific gravity of the blue pigments being higher than that of the whites4 ,consequently1 when the two are mixed in presence of water--as is always the case in grinding and levigation--the heavier blue pigment settles down more quickly1 and several strata can be clearly distinguished in the sediment4 ,the upper layers will still have a decided yellow tinge--the proportion of blue being too small for proper correction--whilst the next in order will be pure white--accurately corrected--and those at the very bottom will be decidedly blue1 because they contain the largest proportion of the blue substance4 ,the most satisfactory results are obtained by dry mixing2 and this can be successfully practised when the colour-maker has a cheap source of power 7such as water power7 available4 ,where1 however1 costly power plant has to be provided1 only the finest grades of white pigments can be improved in this way1 the expense of labour being too high for cheap materials4 ,as a pigment1 chalk possesses many valuable properties4 ,the organic structure of chalk gives it high covering power as a wash1 a thin layer applied to a surface sufficing to mask the colour of the underlying ground completely4 ,the lime in chalk being combined with carbonic acid1 its basic properties are so extensively weakened that chalk can be mixed with even the most delicate colours without fear of their shade being affected4 ,a coating of pure chalk paint on any surface will never change colour in the air2 and on this account1 chalk is extensively used both as an indoor wash and by wall-paper manufacturers4 ,,precipitated ,,chalk ,many chemical processes furnish soluble salts of lime that constitute a by-product of little value4 ,these salts1 however1 can be advantageously utilised for the preparation of an artificial chalk which is preferable to the native article in many respects4 ,for instance1 where large quantities of calcium chloride solution are available1 and soda can be purchased at a sufficiently cheap rate1 they can be converted into artificial chalk1 because these two substances react on each other1 forming1 on the one hand1 calcium carbonate1 which is precipitated as a very delicate1 insoluble powder1 and on the other1 sodium chloride1 or common salt1 which remains in solution1 according to the equation3-- ,ca,cl#b ,na#b;,,co#c ,ca,c,o#c ,na,cl4 ,if1 however1 these solutions were mixed together in a crude state1 the resulting product would be of only low value as a pigment1 being of a yellow tinge and never pure white4 ,this is due to the fact that the impure lime salts1 being waste products from chemical works1 frequently contain fairly large amounts of ferric oxide1 and the soda also is often so high in that impurity that the colour of the precipitated chalk is considerably impaired4 ,fortunately1 there is no difficulty in eliminating this ferric oxide by chemical means1 and obtaining a product of superior colour to the best native chalk4 ,this is effected by treating the perfectly neutral lime-salt solution with calcium carbonate1 which causes the precipitation of the iron1 a corresponding amount of lime passing into solution4 ,in order to eliminate the ferric oxide from the lime-salt solution so completely that not even the most delicate chemical test known will be able to reveal any trace remaining1 the solution is placed in a vat and stirred up with finely powdered chalk4 ,if the solution contains any free acid1 effervescence1 due to the liberation of carbon dioxide1 will take place2 and in such event the addition of chalk is continued until the free acid is all neutralised1 and the added chalk sinks to the bottom undissolved4 ,the chalk should be in slight excess1 so that a decided sediment is visible at the bottom of the liquid when at rest4 ,this deposit is stirred up again at intervals with the liquid for several days4 ,when ferric oxide is present1 the colour of the deposit will gradually change to a yellowish brown1 through the precipitation of ferric hydroxide by the chalk2 and in this way the final traces of iron can be removed4 ,the liquid is then carefully drawn off1 without disturbing the sediment1 and the soda solution is run in so long as a precipitate of calcium carbonate continues to form4 ,the completion of the reaction can be ascertained by pouring a small quantity of the liquid into a tall1 narrow glass1 leaving it to clarify1 adding a little more soda solution and observing whether any further precipitate is produced4 ,on the other hand1 it may be that an excess of soda has already been added in the precipitating tank2 and this can be determined by testing a sample with turmeric paper--blotting-paper soaked in a solution of the colouring-matter of turmeric root--which is turned brown by alkaline reagents4 ,even in very dilute solution1 soda will give this colour change1 and the test is therefore very accurate4 ,the complete precipitation of the lime in the solution can be ascertained by passing a small quantity through blotting-paper and treating it with a little acid potassium oxalate solution1 which1 if lime be present1 will at once produce a strong crystalline precipitate of calcium oxalate1 which is only very sparingly soluble in water4 ,if the oxalate gives merely a slight turbidity1 the residual amount of lime is so small that the process may be regarded as complete4 ,since carbonate of soda is usually much dearer than the lime-salt liquor1 it is preferable to leave a small quantity of the lime unprecipitated4 ,given sufficient care in effecting the precipitation1 and especially when fairly strong solutions are used1 a brilliant white precipitate of calcium carbonate is obtained1 which is in such a finely divided state that the minute constituent crystals can only be detected under a high magnifying power4 ,this precipitated chalk being already in an extremely fine condition needs no further preparation1 and1 when washed1 is ready for immediate use1 forming a handsome pigment with excellent covering power4 ,when precipitation is ended1 the deposit is allowed to settle down1 and the clear supernatant liquid is carefully drawn off so as not to disturb the delicate sediment1 which is then stirred up thoroughly with clean water1 left to subside1 washed again1 and then spread out to dry on cloths which are suspended by the four sides4 ,the surplus water drains away and the residue gradually assumes the consistency of paste1 in which condition it can easily be moulded to any desired shape4 ,if left long enough to dry completely1 it forms a very delicate powder1 furnishing a pigment of excellent quality4 ,if this precipitated chalk be moulded into prisms for sale1 the blocks are laid on one of their broad sides until firm enough to turn over on to one of the narrow faces1 slabs of gypsum being used as the supporting material1 in order to ensure uniform drying4 ,the gypsum absorbs water with avidity and thus dries the prisms evenly4 ,a defect of these prisms is their great fragility2 but their strength may be improved by mixing a little very weak solution of dextrin to the mass after the last washing-water has been completely removed4 ,in drying1 the dextrin binds the material of the prisms sufficiently to keep them from breaking except under the influence of a fair degree of force4 ,,calcareous ,,marl ,as already mentioned1 calcium carbonate rarely occurs in a perfectly pure condition in ,nature2 and chalk1 also1 is frequently contaminated by other minerals4 ,a variety of limestone occurring as extensive deposits in many places is that in which calcium carbonate is associated with clay4 ,sometimes the clay predominates1 and the mineral is then known as marl1 being really a clay contaminated with chalk4 ,if1 on the other hand1 the chalk forms the chief constituent1 the mineral is termed calcareous marl4 ,calcareous marls are used in much the same way as limestone1 some modification1 however1 being necessitated by the presence of the clay4 ,although limestone containing a certain amount of clay can be burned in the kiln1 it yields an inferior lime that is of little use to the builder owing to its low binding power4 ,marl of a certain composition finds an important application in the manufacture of hydraulic lime or cement4 ,the only kind of marl suitable for pigment is that containing clay with very little colour2 and this is of somewhat rare occurrence1 because most marls contain sufficient ferric oxide to give them a yellow shade4 ,marl that is fairly free from ferric oxide1 however1 can very well be used as pigment2 and many white pigments sold as 8chalk0 are really finely ground marl4 ,in accordance with the general practice1 in the colour industry1 of giving colours a great variety of names1 and suppressing the real names1 which1 so far as the artificially prepared colours are concerned1 should bear some reference to their chemical composition1 numerous white earth colours bear fancy names1 though really consisting of chalk1 lime 7generally marl71 or white clay4 ,in ,france1 where both chalk and clay are of frequent occurrence--the soil of ,champagne1 for instance1 being all chalky--the manufacture of the white earth colours is extensively practised1 and a large number are put on the market1 usually named after the place of origin1 and consisting of either calcium carbonate or marl4 ,the trade names of the white earth colours include ,cologne chalk1 ,bologna chalk1 ,brianon chalk1 ,champagne chalk1 ,blanc de ,bougival1 ,blanc de ,meudon1 ,spanish white1 ,blanc d',orleans1 ,blanc de ,troyes1 etc4 ,all are either more or less pure chalk1 marl1 or a fairly white clay1 pipeclay--which is also used for making clay pipes and for removing grease spots4 ,,gypsum ,the mineral known as gypsum1 or alabaster1 consists of calcium sulphate1 or sulphate of lime1 its composition being expressed by ,ca,s,o#d #b;,h#b,o4 ,in gypsum the crystalline structure is just discernible1 whilst other varieties1 such as the so-called 8marine glass10 occur in considerable quantities as large1 perfectly transparent masses4 8,russian glass0 consists of large1 transparent lumps possessing the specific property of gypsum1 viz4 that of cleaving in two directions1 in a high degree4 ,alabaster is composed of finely granular masses1 which are either quite white1 or else yellowish1 or traversed by grey veins4 ,this variety of gypsum is very abundant in central ,italy1 and the best blocks are employed for the production of works of art4 ,ordinary gypsum1 which frequently occurs in the vicinity of dolomitic limestones1 is found in a great variety of colours1 bluish-grey1 yellowish or reddish tints being the most common4 ,pure white lumps1 which are plentiful in some deposits1 can be used as white pigment1 the method of preparation being simple1 viz4 merely reducing the mass to powder4 ,this is easily effected1 the specific hardness of gypsum being only #b2 and in many cases it is soft enough to scratch with the finger-nail4 ,if the original gypsum is white1 the powder forms a dazzling white flour which1 notwithstanding1 is of comparatively little value as a pigment1 on account of its low covering power4 ,for this reason1 powdered gypsum is chiefly used for making plaster of ,paris 7calcined gypsum7 for plaster casts and stucco4 ,gypsum may also be employed to advantage for lightening various colours1 since it is inert towards even the most delicate4 ,,kaolin1 ,,pipeclay ,large areas of the earth's surface are covered with clay1 which often attains a considerable thickness4 ,nevertheless1 the kind of clay that is suitable for use as pigment is comparatively scarce4 ,the principal requirement for this purpose is a pure white colour1 but by far the great majority of clays are either yellow or of a shade between blue and grey 7for example the clay of the ,vienna basin74 ,the character of clay is just as varied as its colour4 ,in some places1 large deposits of extremely fine clay are found1 the material1 when mixed with water1 forming a highly plastic mass which1 when dried and subjected to slight pressure1 furnishes a very soft powder4 ,on the other hand1 some clays are so interspersed with large quantities of sand1 large stones and the debris of mussels1 that they cannot be used until they have been put through very careful mechanical treatment4 ,this great divergence in the physical character of clays is due to their method of formation4 ,clay originated in the weathering of felspar1 which chiefly consists of a double salt1 a compound of the silicates of alumina and potash4 ,under the influence of air and water1 this compound is decomposed1 the potassium silicate passing into solution1 whilst the aluminium silicate1 being insoluble in water1 is carried away by that medium4 ,when the water can no longer carry the particles of aluminium silicate in suspension--for example when it reaches a sea or lake--the silicate settles down to the bottom1 and a deposit of clay is formed4 ,if the original felspar was very pure1 and in particular very low in iron1 the resulting clay will be of a handsome white colour4 ,an example of this is afforded by kaolin1 or porcelain earth1 which is preferably used for making china4 ,if1 however1 the felspar contained a considerable proportion of ferric oxide1 the resulting clay is yellow2 and if stones or mussel shells became incorporated with the clay prior to deposition1 these bodies will be found as inclusions in the deposit1 and such clay will require much troublesome preparation--grinding and levigation--before it is fit for use4 ,for the purposes of the colour-maker1 the most suitable clay is one that is pure white1 free from inclusions1 and does not change colour when exposed1 in a finely divided state1 to the action of the air4 ,many clays that were originally white gradually assume a yellow tinge on prolonged exposure to air and moisture1 because the clay contained ferrous oxide1 which changes1 in the air1 to the stronger pigment1 ferric oxide4 ,many kinds of clay merely require a simple levigation to fit them for use as pigment4 ,the lumps of freshly dug clay are placed in large tanks1 etc41 filled with water and stirred up continuously in order that1 instead of forming a plastic mass which is very difficult to distribute in water1 the particles detached from the lumps may pass at once into suspension4 ,this turbid water is then transferred to another tank1 etc41 where the minute particles of clay are allowed to settle down1 and the water becomes quite clear4 ,where this work is carried on on a large scale1 it is advisable to put the freshly won clay into large pits close to the clay deposit1 and to leave it there1 covered with water1 during the winter season4 ,the freezing of the water breaks down the larger lumps of clay1 by the resulting expansion1 and this facilitates the subsequent levigation1 the cohesion between the particles being destroyed4 ,if the clay contains larger proportions of lime or magnesia1 a little experience will enable their presence to be detected at once by the way the clay behaves on being placed in contact with water4 ,pure clay quickly forms a fatty and extremely plastic paste1 and sticks closely to the tongue when applied in the dry state4 ,on the other hand1 clay containing much lime or magnesia is far less plastic when mixed with water1 and the dry clay hardly adheres to the tongue at all4 ,these latter clays are classed as poor or lean1 in contrast to the fat1 plastic kinds4 ,for certain purposes for which clay is used as pigment1 these admixtures are not harmful2 whereas others1 especially quartz sand and mica1 not infrequently present in white clays1 constitute a serious drawback4 ,as already mentioned1 clay is formed by the weathering of felspar1 which is a constituent of granite and gneiss1 both rocks composed of quartz1 mica and felspar4 ,when the clay has been derived from the weathering of such rocks1 it is easy to understand that it may contain admixtures of quartz and mica1 which are frequently visible to the naked eye1 or at any rate under the microscope4 ,whereas clay forms a white1 amorphous mass1 the grains of quartz sand are decidedly crystalline1 transparent and of vitreous lustre2 the scales of mica1 on the other hand1 appearing as thin tabular crystals1 mostly of a green or brown colour and exhibiting1 when viewed at certain angles1 a brilliant metallic sheen4 ,quartz sand can be eliminated from clay without any special difficulty1 quartz being of higher specific gravity and therefore settling down quickly1 leaving the delicate particles of clay in suspension in the liquid4 ,the scales of mica are harder to get rid of1 their tabular form retarding deposition from the suspending liquid2 and on this account1 several washings are often required to separate them completely4 ,in all cases where clay is to be used as a white distemper1 the presence or absence of lime is immaterial2 but where it is to be employed for removing grease1 lime is a drawback4 ,this is also sometimes the case when the clay is wanted for the purposes of the colour manufacturer4 ,the author has found1 by experience1 that perfectly pure1 white clay forms a good paint1 in a vehicle of oil or varnish--a purpose to which it has1 so far1 been seldom applied1 if at all4 ,such paint is of good covering power1 and possesses the valuable property of remaining quite unaffected by atmospheric influences4 ,if1 however1 the clay contains even but a small quantity of lime1 it cannot possibly be used as an oil or varnish paint1 for though the freshly made paint has a very good appearance1 its character soon changes1 turning viscous and suffering a considerable diminution of covering power4 ,thinning with turps or boiled oil results in the formation of small lumps1 so that it is quite impossible to obtain a uniform coating on even a small surface4 ,this behaviour is apparently due to the presence of the lime1 the explanation being that the fatty acids always present in the oils and varnishes used for the paint combine with the lime to form compounds which1 from the standpoint of the chemist1 must be regarded as soaps4 ,the small lumps already mentioned really consist of lime soap1 and the formation of these colourless compounds accounts for the lessened covering power4 ,given a fine white clay1 otherwise capable of forming a valuable pigment1 it is sometimes possible1 by simple means1 to eliminate accompanying lime1 provided the amount of the latter is not too great1 and also provided that very cheap hydrochloric or acetic acid is available4 ,the acid need not be pure1 and the impure but very strong pyroligneous acid1 which is very cheap on account of its empyreumatic smell1 may be used4 ,to eliminate lime from the clay1 the still moist levigated mass is introduced1 in small quantities1 into a vat containing the requisite quantity 7see later7 of hydrochloric or acetic acid1 the addition being continued until the liquid gives only a faintly acid reaction with blue litmus paper4 ,when the clay is run in1 effervescence is produced by the liberation of the carbon dioxide displaced by the stronger acid employed4 ,the amount of lime present in a clay may be determined by very simple means4 ,a small sample of the clay is dried by artificial heat1 until of constant weight1 and exactly #ajj parts by weight of the dry mass are placed in a glass and suffused with hydrochloric acid1 sufficient of the latter being used to make the liquid still strongly acid after effervescence has ceased4 ,the contents of the glass are transferred to a filter1 and washed with pure water so long as the washings continue to redden blue litmus paper4 ,the residue is then dried until of constant weight1 and the difference between the initial and final weights will give the percentage of substances soluble in hydrochloric acid4 ,after performing this simple test on a clay1 it is easy to calculate the quantity of acid needed to extract all the soluble constituents from a given weight of the material4 ,all that is necessary is to measure the volume of acid required to extract a small quantity of the clay completely4 ,thus1 if one pint of the acid at disposal is sufficient to treat one pound of the clay1 the amount needed for a given quantity of clay is a simple matter of calculation4 ,since1 on account of the cost of pure hydrochloric acid1 crude acid will always be used1 it will be necessary to remember that this crude acid always contains ferric oxide in solution--this being the cause of its yellow colour4 ,if the amount of acid taken is barely sufficient to combine the whole of the lime1 leaving the latter slightly in excess1 the ferric oxide--which would otherwise tinge the clay yellow--will be precipitated4 ,if1 on the other hand1 the acid is in excess1 the clay is obtained free from all constituents soluble in the acid4 ,the purified clay must then be freed from the calcium chloride1 formed by dissolving the lime1 by a thorough washing1 since the clay would otherwise always remain moist on account of the hygroscopic properties of the chloride in question4 ,moreover1 any small residuum of free acid would constitute a drawback on the clay being mixed with other colours4 ,calcium chloride is very soluble in water1 and therefore can be completely removed from the clay by washing4 ,the purified clay is left to settle down as completely as possible1 and after drawing the liquid off from the sediment1 the latter is suffused with pure water and left to settle once more4 ,as a rule1 two such washings will cleanse the clay of calcium chloride and free acid sufficiently to render the product suitable for any purpose4 ,when large quantities of clay have to be treated in this manner1 considerable amounts of calcium chloride solution will be obtained1 which can be advantageously utilised for the production of precipitated chalk1 all that is necessary being to collect the liquor in a large tank and treat it with a small quantity of slaked lime1 to transform the surplus free acid into calcium chloride and precipitate the ferric oxide present in solution4 ,at the end of a few days the liquor in the tank will consist of a very pure solution of calcium chloride which will furnish an excellent precipitated chalk when treated in the manner already described under that heading4 ,,barytes1 ,,or ,,heavy ,,spar ,this mineral--chemically1 barium sulphate1 ,ba,s,o#d--occurs native1 as extensive deposits1 in many places--,england1 ,bohemia1 ,saxony1 ,styria1 etc4 ,it sometimes forms handsome tabular crystals1 but more frequently compact masses1 which may be pure white1 grey yellow1 etc41 in colour1 and are distinguished by high specific gravity 7usually #dc-dg71 to which the mineral owes its name4 ,this high density also limits the application of the mineral1 and it cannot be used as a pigment1 in the true sense of the term1 being only suitable as an adjunct to artificially prepared colours4 ,the employment of barytes in the colour industry is often regarded as adulteration1 which1 however1 it is not when the case is considered from the right point of view4 ,for instance1 the only preparation which can properly be termed white lead consists of basic lead carbonate4 ,this1 when pure1 is a rather expensive pigment1 whereas1 for certain purposes1 the consumer requires a product that can be obtained at a low price4 ,in order to satisfy this demand1 the only course open to the colour-maker is to mix the white lead with a cheap white substance1 which enables him to turn out different grades of white lead1 which1 although low in price1 are far inferior to the pure article in covering power4 ,pure white lead being itself a very heavy substance1 the only bodies suitable as adjuncts are such as are also of high specific gravity2 and of all the cheap pigments known1 heavy spar is the only one endowed with this property4 ,consequently1 this substance is extensively used in making the cheaper grades of white lead and the pale kinds of chrome yellow4 ,the only cases in which the addition of heavy spar to a colour can be regarded as an intentional fraud on the consumer is when he is sold1 as pure white lead1 chrome yellow1 etc41 a product really composed of a mixture of such colour and barytes4 ,moreover1 the presence of barytes in white lead can be easily detected by a simple examination1 pure white lead readily dissolving1 with considerable effervescence1 in strong nitric or acetic acid1 whereas barytes is insoluble in all acids1 and therefore remains1 as a heavy white powder1 at the bottom of the vessel4 ,in this way both the presence and amount of barytes contained in a sample of white lead or chrome yellow can easily be ascertained4 ,the preparation of barytes for the purposes of the colour-maker is entirely a mechanical operation4 ,the barytes1 which though fairly hard is easily reduced1 is crushed with stamps1 ground in a mill and finally levigated1 it being impossible to obtain a sufficiently fine powder even by repeated grinding4 ,native barytes must not be confounded with the artificial barium sulphate sold as permanent white or blanc fixe1 which is an extremely finely divided barium sulphate obtained by precipitating a solution of a barium salt with sulphuric acid or a soluble sulphate1 and is a painters' colour that is highly prized for certain purposes4 ,both the native sulphate and the artificial variety have the property of remaining completely unaltered by exposure to air1 and they can therefore be mixed with any kind of pigment without fear of the colour deteriorating4 ,as a rule1 barytes is first roughly crushed in edge-runner mills or stamps1 and then ground to the extreme degree of fineness obtainable in ordinary mills4 ,even with the greatest care1 however1 it is impossible by this means to obtain sufficient fineness of division for mixing with fine colours1 the only way in which this can be accomplished being by levigation4 ,given a fairly pure white barytes to begin with1 levigation furnishes a handsome white pigment that can be mixed with colours of any kind2 but when used by itself in association with oil or varnish1 its covering power is very low and the colour never perfectly white4 ,native barytes is therefore unsuitable1 as such1 for paint4 ,varieties that are not pure white are sometimes corrected with ultramarine1 added in the grinding-mill4 ,if the yellow tinge is due to iron compounds1 this can often be remedied by treating the finely ground material with hydrochloric acid1 which dissolves them out1 this treatment being followed by a thorough washing with pure water4 ,as already mentioned1 white lead is most frequently mixed with barytes1 this being usually added when the white lead is being ground1 by feeding the two materials to the mill and grinding them together4 ,the crudeness of mechanical methods of reduction is clearly exemplified by comparing the most carefully ground and levigated barytes with that obtained by artificial means4 ,the permanent white largely used in the production of wall-paper1 and quite unalterable in air1 is1 chemically speaking1 identical with native barytes1 viz4 barium sulphate4 ,the two also seem to be identical in crystalline habit1 as is usual in the case of one and the same mineral1 whether native or prepared by artificial means4 ,artificial barytes is obtained by treating a soluble salt of barium with sulphuric acid1 or a solution of sodium sulphate 7,glauber salt71 so long as a precipitate continues to form4 ,this precipitate is barium sulphate1 which subsides completely on account of its extreme insolubility1 this being greater than that of any other salt known4 ,the rapid rate of deposition results in the formation of extremely small crystals1 which1 being colourless and reflecting the light completely1 appear to be perfectly white4 ,even when permanent white is applied in very thin layers to any surface1 its covering power is very considerable1 by reason of the extremely fine subdivision of the material4 ,this behaviour of artificial barytes in comparison with that of the natural product1 affords an important hint in connection with the preparation of earth colours1 namely1 that in order to obtain products of specially good quality1 the endeavour should be to reduce the raw materials to the finest condition possible4 ,this result is accomplished most securely by bestowing the greatest care on grinding and levigation2 and it is therefore highly important that the manufacturer should select1 from the various apparatus used in reducing the materials1 those that are best adapted for the purpose4 ,,carbonate ,,of ,,magnesia ,although carbonate of magnesia is seldom used alone as a pigment1 it can be advantageously employed as such when circumstances permit4 ,it is met with not infrequently1 in ,nature1 in a crystalline form1 as magnesite or bitter spar1 the latter name arising from the fact that the soluble salts of magnesia have a bitter taste4 ,still more frequently1 magnesia occurs in association with calcium carbonate1 in the mineral dolomite1 which contains up to #bj of magnesia4 ,a less abundant native mineral is hydromagnesite1 which consists of basic magnesium hydrocarbonate4 ,hydromagnesite is a very light1 chalk-white mass1 with a non-greasy feel1 which1 when reduced to a soft powder1 forms an excellent material for paint4 ,it is highly inert1 in a chemical sense1 and can therefore be mixed with the most delicate colours1 having no other effect thereon than to render them lighter in shade4 ,this product can also be prepared artificially1 by treating a dissolved magnesium salt with a solution of carbonate of soda1 the result being the formation of a pure white precipitate1 which is very brilliant when dry1 and is characterised by unusually low specific gravity4 ,in some places1 conditions are such that this preparation can be made on a large scale at very low cost4 ,for instance1 there is a spring at ,bilin1 in ,bohemia1 the water of which contains large quantities of alkali carbonates in solution2 whilst in the vicinity of ,saidschtz is a spring fairly rich in magnesia salts4 ,the waters from these two springs are concentrated by evaporation1 and mixed in large tanks2 and when a sufficient deposit of the resulting basic carbonate of magnesia has accumulated1 it is taken out of the tanks1 placed on linen filters and washed with water4 ,the residue is dried slowly1 without the employment of a high temperature1 and then forms a white powder1 which is very light and can be used for a number of purposes1 chiefly medicinal1 though it is also well adapted as a material for paint4 ,for this latter purpose it is1 however1 far too expensive2 but since the conditions obtaining at ,bilin are certain to occur elsewhere1 we have included carbonate of magnesia among the earth colours4 ,on account of its specific lightness1 carbonate of magnesia is specially adapted for making pale shades of certain delicate lake colours1 which1 if toned with even perfectly pure chalk1 would undergo alteration in course of time4 ,carmine1 for instance1 can be graded1 by the addition of carbonate of magnesia1 into every possible variety of shades between the pure red of carmine itself and the palest pink2 and the resulting colours are quite permanent whether mixed with gum solution or any other vehicle4 ,,talc ,although this mineral is not used as a pigment by itself1 it must be mentioned here because it is not infrequently employed for mixing with other colours1 and is also used in the wall-paper industry4 ,it also serves to distribute certain pigments in a state of fine division1 the 8rouge vgtal0 of the perfumer1 for example1 usually consisting of talc and a small quantity of very fine carmine4 ,in commerce the name talc is sometimes applied to two separate minerals1 true talc and steatite or soapstone4 ,the former is rarely met with native as well-defined crystals1 mostly occurring as scaly masses in primitive rocks4 ,thin pieces exhibit a certain degree of flexibility4 ,the hardness of this mineral is so small that it can be scratched with the finger-nail2 and its sp4 gr4 is #bi-bh4 ,talc is easily scraped1 and the powder remains sticking to the knife1 a property which renders the substance difficult to reduce to powder1 because it balls together and takes a very long time to convert into a fine flour4 ,the process is facilitated by calcining the talc and quenching it in cold water1 this treatment increasing the hardness and at the same time making it more brittle1 and thus more easy to pulverise4 ,a characteristic feature of all the talc minerals is their peculiar greasy appearance and feel4 ,the colour varies1 white pieces alone being of any use to the colour manufacturer4 ,the yellow- or green-tinged varieties owe their shade to the presence of ferric and ferrous oxides4 ,in chemical composition1 talc consists of a combination of magnesium silicate with hydrated silica1 the supposed formula being3 #d,mg,o 4 ,si,o#b ,h#b,o 4 ,si,o#b1 and the percentage composition3 silica1 #fbf2 magnesia1 #cbi2 water1 #di4 ,,steatite ,,or ,,soapstone ,steatite so closely resembles talc in most of its properties1 that the two minerals were long regarded as identical4 ,whereas1 however1 talc is scarcely acted upon at all by the strongest acids1 steatite is completely decomposed by prolonged boiling therewith1 although both minerals have exactly the same composition4 ,as a pigment1 steatite is far more important than talc1 and1 as ,french chalk1 is largely used for drawing or writing4 ,to prepare it for this purpose pure white steatite requires no preliminary treatment1 beyond cutting the large lumps up into quadrangular prisms1 which are mounted in wood1 like lead pencil1 and used for writing on the blackboard4 ,the powder produced in the cutting process is made up into pastel crayons4 ,with this object1 the powder is mixed with a sufficient quantity of some mineral pigment to produce a mass of the desired shade1 and is kneaded to a stiff paste with water containing an adhesive such as gum1 glue or tragacanth mucilage4 ,the mass is shaped into prisms1 which1 when dry1 are cut into pencils and mounted in wood4 ,steatite being like talc1 without action on even the most delicate colours1 can be used as a diluent in the preparation of light shades4 ,,chapter ,v ,,yellow ,,earth ,,colours ,all the yellow earth colours1 without exception1 have ferric oxide as their colouring principle1 the differences in shade being entirely due to the varying proportion in which that oxide is present4 ,the various names under which they are known date back to a period when the chemical nature of these colours was still unknown1 and have been mostly derived from the locality of origin4 ,the yellow earths can therefore be divided into two groups1 according to their chemical character4 ,the first group1 in which the ferric oxide is present as hydroxide1 comprises all the ochres1 ,siena earth1 and a number of others which are obtained from native ochre by special treatment4 ,in the colours of the second group1 ferric oxide is still the colouring principle1 but is combined with other substances in place of water4 ,it is1 as a matter of fact1 incorrect to rank the ochres in general as yellow earths1 because they can be made to yield nearly every variety of colour from the palest yellow to the deepest red1 brown and violet4 ,these colours merit the particular attention of the colour-maker and the painter1 being distinguished by very low cost of production1 unusual permanence and beauty of tone4 ,in the interests of that highly important matter to the artist1 namely the production of colours of unlimited permanence1 it is desirable that colour manufacturers should bestow greater care on the manufacture of these colours than has hitherto been the case4 ,an extremely favourable point about nearly all these pigments is that they can be very cheaply prepared by artificial means1 so that the manufacturer is in a position to turn out a large number of the handsomest and most durable colours with a small amount of expense and labour4 ,,the ,,ochres ,ochres are found in many localities1 most frequently in stratified rock and rubble4 ,the deposits are rarely extensive1 mostly occurring in pockets or beds4 ,wherever found1 ochre may be termed a secondary product1 that is to say1 one that has been formed through the destruction of other minerals4 ,the analysis of ochres from different deposits shows great divergence in composition2 and some consist almost entirely of pure ferric hydroxide1 that has already undergone natural levigation and can be used as a pigment as soon as dug4 ,such a form is1 however1 rare1 and most ochres are intermixed with smaller or larger amounts of extraneous minerals1 the contamination being sometimes so great as to preclude the use of the ochre as pigment by reason of the high outlay required for extracting the colouring constituents4 ,occasionally1 the ferric hydroxide is associated with a certain proportion of clay1 and as this increases1 the ochre passes over into ferruginous clay4 ,this class can also be used as pigment1 in certain circumstances1 that is to say when it is sufficiently rich in ferric oxide to furnish a deep red mass on calcination4 ,when1 however1 the proportion of ferric oxide is low1 its pigmentary power is no longer sufficient1 and the clay has not the requisite beauty of colour4 ,the ordinary earth used for making tiles is an example of this class1 its colour in the raw state being an ugly brownish-yellow1 but turning a dull 8brick0 red when fired4 ,in some deposits the ferric oxide is accompanied by lime4 ,unless the latter exceeds a certain proportion1 such ochres1 too1 are suitable as pigments1 the lime being easily removed by simple levigation2 but when the amount of lime is high1 it is difficult to obtain certain highly coloured shades of ochre from such material4 ,these shades entail the calcination of the ochre1 and the temperature required is oftentimes insufficient to transform the lime into the caustic state4 ,moreover1 the presence of caustic lime would be a drawback in some cases1 it being then impossible to mix the ochre with other colours without endangering the shade through the action of the lime on these latter4 ,the following analyses will show the percentage composition of ochres from various deposits3 ,ochre from-- ---------------------------------------- ------ ,comoal ,vierzen4 ,st4 ,georges4 7,savoy74 ---------------------------------------- ------ ,ferric oxide #ai #bce #be ,lime #b -- -- ,alumina #bj #fie #gj ,magnesia #a #fie #gj ,silica #dd #fie #gj ,water #g #g #e ---------------------------------------- ------ ,in the majority of cases the mineralogical characteristics of an ochre enable conclusions to be formed as to its suitability as pigment4 ,good ochre is more or less yellow to dark brown in colour1 and can easily be crushed between the fingers to a soft1 fine powder which feels like powdered steatite and does not produce a sensation of grittiness1 this latter indicating the presence of fine grains of sand in the ferric oxide4 ,the behaviour of the ochre in presence of water is specially important4 ,if it adheres firmly to the tongue1 and forms a fairly plastic paste when mixed with a little water1 the mineral contains a large percentage of ferric oxide1 and as a rule will yield ochre of good colour4 ,in general it may be said that the value of an ochre varies directly with its content of ferric hydroxide or oxide1 because when this is large the ochre will furnish a wide range of colours under suitable treatment4 ,a simple test for quality consists in weighing out an exact small quantity 7#aj grms471 and heating it to a temperature not exceeding #aaj ,c41 until the weight remains constant4 ,a simple calculation then gives the amount of uncombined water in the sample4 ,since the proportion of such water varies in different parts of one and the same deposit1 the test must be repeated1 in order to obtain accurate results1 on samples taken from different points1 or1 preferably1 on a properly prepared average sample4 ,even drying changes the colour of ochre considerably4 ,to ascertain the behaviour of an ochre on calcination1 a large sample is dried at #aaj ,c4 until the weight is constant1 and divided up into a number of small samples weighing1 say1 #aj grms4 each4 ,the samples are then heated to different temperatures1 one to the melting-point of lead1 another to that of zinc1 and so on4 ,the higher the temperature employed1 the more will the colour of the ochre approximate to red2 and specimens very rich in ferric oxide will give bright red colours4 ,beyond this range1 a further increase in temperature will give violet shades1 varying with the temperature and the duration of heating4 ,after this preliminary test1 it is desirable to make another on a larger scale1 with quantities up to about #a lb4 ,for this test1 the different kinds of ochre frequently found in the same deposit should be mixed together1 in order to obtain an idea of what the mean product1 obtained in working on the large scale1 will be like4 ,on the whole1 the results of this second test will be the same as in the first series1 the only object of the second test being to gain information which may be particularly valuable in practical work4 ,the bottles in which the calcined samples are stored should be marked with the temperature and length of heating1 so that1 when it is subsequently desired to obtain an ochre corresponding to a particular sample1 all that is necessary will be to heat it to the same degree from the same length of time4 ,the performance of this simple test will be of great assistance in standardising the work with a minimum loss of time4 ,when it is desired to ascertain the composition of an ochre superficially its behaviour towards hydrochloric acid may be noted4 ,a weighed quantity of the freshly dug 7undried7 ochre is treated with pure acid1 free from iron1 which will dissolve out the ferric oxide and lime1 leaving clay and quartz sand behind4 ,the presence of lime is indicated by effervescence on contact with the acid2 and if there is no effervescence1 lime is absent4 ,at the end of several hours the acid is carefully decanted from the undissolved residue which is then stirred up with water1 left to subside1 and weighed when dry4 ,this method will give the amount of substances1 other than ferric oxide and lime1 in the sample4 ,these substances usually consist of clay or sand4 ,for a quantitative determination1 a small quantity--usually #a grm4--is weighed out1 treated with a corresponding amount of hydrochloric acid1 and the solution filtered into a glass4 ,the residue on the filter is washed with distilled water1 the washings being united to the acid solution4 ,this solution is treated with ammonia so long as a precipitate of ferric hydroxide continues to form1 this being collected on a tared filter and dried at #aaj ,c4 ,the precipitate may be regarded as pure ferric hydroxide1 and its weight will indicate the proportion of hydroxide in the ochre with sufficient accuracy for technical purposes4 ,in reality1 however1 it is not pure ferric hydroxide1 but contains in addition all the oxides that are precipitable by ammonia1 lime being always carried down as well4 ,it is therefore desirable to dissolve the precipitate with a little hydrochloric acid1 and reprecipitate with ammonia4 ,,calcining 7,,burning7 ,,ochre ,in many places ochre is only put through a very simple mechanical preparation before being sold for pigment1 namely left to dry in the air so that most of the uncombined water evaporates4 ,no matter how this drying process is protracted1 however1 it is impossible to get rid of all the water in this way1 a certain proportion being retained by the hygroscopic action of the ferric hydroxide1 and to expel this the mass must be heated to above #ajj ,c4 ,drying is usually succeeded by pulverising and sifting the loose earthy mass1 which is then ready for sale4 ,when the ochre contains sand or stones1 this treatment is not sufficient1 and levigation is necessary4 ,no particular trouble is involved1 the mineral being fairly heavy as the result of its content of ferric hydroxide4 ,a simple method of treatment suffices to improve the value of the ochre considerably1 and enables a grade that is not particularly bright-coloured in its natural condition to be converted into products of very handsome tone and various shades4 ,this treatment consists in heating the raw ochre to a definite temperature1 during which process the colour changes progressively1 and any desired tone can be obtained by suddenly cooling the hot mass4 ,the reason for this phenomenon is that the higher the temperature1 the larger the amount of water driven off from the ferric hydroxide1 until finally1 when a very high temperature has been reached1 the whole of the water is expelled1 and the ferric hydroxide is transformed into ferric oxide4 ,the hydroxide is brown1 whereas the oxide1 provided the temperature has not been raised too high1 exhibits the characteristic colour known as 8iron red40 ,consequently1 the colour of moderately calcined ochre ranges through a whole scale from brown to red2 and the higher the temperature employed1 the redder the tone4 ,if the heating be protracted after all the hydroxide has become oxide1 the latter undergoes molecular change1 increasing considerably in density and altering in colour2 and after very prolonged heating1 the colour finally becomes violet4 ,the calcination1 or burning1 of ochre is ordinarily performed in a very crude manner4 ,the mineral is crushed to the size of peas1 and spread out on an iron plate which is made red-hot4 ,as soon as the ochre has reached the desired shade of colour1 it is dropped into a tub of water and then crushed to powder4 ,the calcination requires great experience on the part of the operator1 because so long as the product is hot1 it has quite a different colour from that assumed on complete cooling4 ,since only comparatively small quantities of ochre can be treated in this way1 and the operation unnecessarily increases the cost of the product1 owing to the large consumption of fuel1 it is highly desirable to employ a simple calcining apparatus capable of treating large quantities4 ,such an apparatus may consist of an iron drum1 mounted with a gentle slope inside a furnace1 from which it projects at both ends4 ,a shaft carrying a sheet metal worm is rotated inside the drum2 and the whole apparatus is very similar to an ,archimedean screw4 ,when the iron drum is raised to a strong red heat1 and small quantities of ochre are fed continuously into the upper end of the drum1 the rotation of the worm will push the material forward1 and contact with the glowing sides of the drum will produce the necessary calcination1 the degree of which can be modified by altering the speed at which the worm is turned4 ,the calcined product is discharged at the lower end of the drum1 either into a vessel of water1 or1 if only moderate heating has been applied1 direct into a collector4 ,illustration3 ,,fig4 #bh4 ,fig4 #bh represents an apparatus designed by ,halliday for the dry distillation of wood waste2 but1 with slight structural modifications1 it can also be used for calcining ochre4 ,the material to be heated is introduced1 in small pieces1 into the feed hopper ,b1 and is carried downward1 by the worm ,c1 into the red-hot drum ,a1 through which it is propelled by the worm ,d until it drops out1 at ,f1 into the tank ,g4 ,the length of time the material is subjected to calcination depends on the speed at which the worm ,d is run4 ,the pipe ,e carries off the water vapour expelled from the charge4 ,in order to obtain a uniform product when ochre is calcined in an apparatus constructed on this principle1 it is necessary that the material introduced should be fairly regular in size1 a condition which is easily fulfilled by squeezing the freshly dug ochre between fluted rollers1 and then passing it over a series of screens1 each grade being then calcined separately4 ,moreover1 the apparatus is only suitable for calcining at medium temperatures2 and when highly calcined products are in question1 the operation is best performed in fire-clay cylinders1 or in thick cast-iron drums1 similar to gas retorts1 built into a furnace4 ,other devices for calcining ochre will be described later4 ,,ochres ,,from ,,various ,,deposits ,as previously stated1 ochres are frequently met with in ,nature1 both in the immediate vicinity of iron ore1 and also at considerable distances from such deposits4 ,in the latter case1 the ochre must be assumed to be the decomposition products of ferruginous minerals and to have been carried off by water until the latter became stagnant and allowed the ochre to settle down4 ,in their method of deposition these ochres are therefore analogous to clay1 and they1 too1 often contain large quantities of extraneous minerals1 which have given rise to the diversified substances grouped under the name of ochre4 ,although ochres are so widespread in ,nature1 only certain kinds1 found in certain localities1 have acquired a high reputation4 ,for the most part1 these ochres are such as have already been prepared in a high degree1 by ,nature1 for the purpose for which they are employed4 ,thus1 we find that all the ochres which have acquired a high repute among painters for particular beauty of tone and permanence1 are distinguished by two properties3 a high content of ferric hydroxide and great purity4 ,the former of these properties imparts brightness of colour2 and such products will furnish1 on calcination1 a wide range of colour shades4 ,when1 as is the case with the finer qualities of ochre1 the mineral contains only a very small proportion of impurities1 there is no difficulty in bringing it1 by simple grinding or levigation1 into a condition in which it is at once fit for use as a pigment4 ,the ,italian ochres have1 for long ages1 enjoyed a high reputation for their beauty of colour and permanence4 ,this category includes1 for example1 the renowned ,siena earth1 ,roman earth1 ,italian umber1 and other ochre colours4 ,this high renown is probably due less to the inherent properties of the mineral than to the circumstance that the art of painting attained a high state of development at an early period1 and that the artists paid special attention to the use of bright and permanent colours for their work4 ,although1 at present1 many deposits of ochre are known that are quite able to compete1 on the score of beauty1 with the best ,italian products1 the good name of these latter has nevertheless been maintained4 ,it is true that the name of ,italian ochre is often merely borrowed1 for application to a product originating in some other country1 varieties of terra di ,siena1 for instance1 being put on the market that have actually been derived from deposits in ,germany4 ,as a result of this custom1 certain names1 such as terra di ,siena1 umbra di ,roma1 have become generic terms1 and their use denotes1 not an intention to suggest that the earth colours in question really come from ,siena or the vicinity of ,rome1 but that the properties of the article are equal to those of the old-established colours of ,siena or ,rome4 ,it would occupy too much space to go into an exhaustive description of all the native varieties of ochre1 and would inevitably lead to a good deal of repetition4 ,it will therefore be sufficient1 for our purpose1 to deal with only a few of them4 ,the best-known ochres are those of ,rome and ,siena1 the latter being frequently called1 in commerce1 by its ,italian name1 terra di ,siena4 ,roman ochre forms yellowish-brown masses1 of fairly fine texture and composed of ferric hydroxide and clay4 ,they are put on the market both in the raw and calcined state4 ,on calcination1 the colour soon changes to red1 and if carefully performed1 the resulting colours have a very warm1 fiery tone4 ,closely approaching ,roman earth is the ,english ochre1 which is worked more particularly in ,surrey1 and is not infrequently sold as ,roman4 ,in many deposits this ,english ochre occurs in such a high state of purity that the best pieces are picked out and sold without being even crushed or ground4 ,the pieces of lower quality are very carefully ground and levigated1 for the purpose of being calcined for the production of different shades1 and then furnish highly prized colours4 ,in point of chemical composition1 the ochre family also includes terra di ,siena1 bole1 umber and ,cassel brown4 ,these minerals1 however1 are not yellow like ochre1 but brown1 and will therefore be dealt with along with the brown earth colours4 ,,artificial ,,ochres ,products very similar1 both in chemical composition and colour1 to the native ochres can also be very simply and cheaply made by artificial means4 ,their preparation may be particularly recommended to colour-makers who desire to turn out a wider range of iron pigments1 but are not in a position to obtain natural ochres at a low price4 ,in the manufacture of artificial ochre1 an endeavour is made to imitate the natural processes which have led to the formation of ochre1 and1 of course1 to avoid anything likely to hinder the production of a suitable colour earth1 for example the presence of sand or a considerable admixture of extraneous minerals4 ,as already mentioned1 the chief impurities in natural ochres are clay and sand1 both of which can be easily excluded during the manufacture of artificial ochre1 or their amount controlled in such a manner that paler or darker products can be obtained at will1 and the tone varied1 in any desired manner1 by calcination1 as in the case of the native article4 ,the raw material for artificial ochre is always a ferrous salt1 which can be purchased in large quantities and at very low prices1 namely green vitriol1 which1 in the pure state1 consists of ferrous sulphate1 ,fe,s,o#d #g;,h#b,o4 ,this substance forms sea-green crystals1 which are readily soluble in water and impart an objectionable inky flavour thereto4 ,on exposure to the air1 green vitriol turns an ugly brown colour1 and is no longer completely soluble in water1 passing gradually into the condition of basic ferrous sulphate4 ,this is because ferrous oxide is a highly unstable substance1 which attracts oxidation and changes into ferric oxide4 ,this latter1 however1 requires for the production of soluble salts a larger quantity of acids than does ferrous oxide1 and therefore the oxidation of ferrous sulphate in the air leads only to the formation of salts that are imperfectly saturated with acid1 namely basic salts4 ,when a solution of green vitriol is left exposed to the air1 basic ferric sulphate is also formed1 which settles down to the bottom of the vessel as a rusty powder4 ,if1 however1 a corresponding quantity of sulphuric acid be added to the solution at the outset1 the resulting ferric sulphate remains in solution4 ,on treating the green vitriol solution with one of caustic potash1 caustic soda or quick lime1 the ferrous oxide is thrown down as the corresponding hydroxide1 forming a voluminous greyish-green precipitate4 ,this hydroxide still possesses a great affinity for oxygen1 and when the precipitate is brought into contact with air1 its colour rapidly changes to a rusty red1 through the transformation of the ferrous hydroxide into ferric oxide4 ,the ferrous hydroxide can also be precipitated by alkali carbonates1 the deposits behaving in exactly the same manner as that thrown down by the caustic alkalis4 ,various methods can be adopted in the preparation of artificial ochre1 the selection depending on the properties desired in the finished product4 ,to obtain an ochre with particularly good covering power1 the method must be different from that employed to furnish a cheap product1 in which low price is more important than covering power4 ,in the former case1 the ferrous hydroxide is mixed with substances which1 in themselves1 possess fairly high covering power1 such as chalk or white clay2 in the second1 gypsum1 which is of low covering power1 is used4 ,the preparation of the cheapest kinds of artificial ochre will be described first1 followed by that of the higher grades which belong to the most valued artists' colours4 ,for cheap artificial ochres1 the ferrous hydroxide is thrown down by caustic lime from a solution of green vitriol4 ,according as a lighter or darker shade is required1 two to three parts of ferrous sulphate are dissolved in water1 care being taken to select crystals of a pure green colour1 since those that have a rusty look are only imperfectly soluble1 because they contain basic ferric sulphate4 ,the solution will always be cloudy1 owing to the partial precipitation of the hydroxide by the lime in the water2 but this is immaterial4 ,for the precipitation1 a milk of lime is prepared by slaking one to two parts of quicklime 7according to the quantity of ferrous sulphate to be treated7 in water1 and stirring this up in enough water to make a thin milk4 ,care must be taken to exclude any large particles of lime1 since these would find their way into the finished product and make the colour uneven4 ,on this account1 the milk of lime should be carefully strained through a loosely woven cloth or fine sieve1 into the precipitation vessel4 ,the ferrous sulphate solution is then poured in1 the mixture being kept stirred1 and an ugly1 grey-green precipitate is produced1 consisting of a mixture of ferrous hydroxide and calcium sulphate1 the reaction being explained by the equation3-- ,fe,s,o#d ,ca7,,oh7#b ,fe7,,oh7#b ,ca,s,o#d4 ,the larger the amount of ferrous sulphate solution added to the milk of lime1 the darker the resulting ochre4 ,as soon as all the ferrous sulphate is in1 the stirring is suspended1 and the liquid is left until quite clear4 ,the water is drawn off through tapholes in the side of the vessel1 care being taken not to disturb the fine precipitate1 and fresh water is added1 in which the deposit is stirred up and again left to settle down4 ,this operation1 which is once or twice repeated1 is to wash the precipitate4 ,when this object has been sufficiently accomplished1 the mass is shovelled out of the vessel and spread thinly on boards1 where it is left until the desired shade of colour has been attained1 the colour changing quickly on exposure to air1 owing to the oxidation of the ferrous hydroxide into ferric hydroxide4 ,to ascertain whether oxidation is complete1 a large lump of the mass is broken across2 and if it is of a uniform yellow-brown colour throughout1 without being darker on the outside than in the middle1 all the ferrous hydroxide will have been transformed into the ferric state4 ,the product can now be dried at once1 and when ground will be ready for sale4 ,to obtain different varieties from the product1 it is carefully heated 7in a finely powdered condition7 in shallow pans2 but the operation needs caution1 or the water in the gypsum present will be expelled1 giving rise to drawbacks that are manifested when the colour is used4 ,for instance1 in mixing such a colour with water1 the gypsum would again absorb water and cause the whole mass to set as a useless solid lump4 ,since gypsum parts with its water at a comparatively low temperature1 it is better not to heat these cheap ochres at all1 but to obtain the various shades by modifying the proportion of ferrous sulphate employed4 ,another defect of the ochres prepared by this method resides in the excess of lime present1 it being impracticable to measure out the quantity of lime used with such accuracy that only just enough is taken to precipitate the ferrous hydroxide1 there being always a slight excess4 ,this lime is transformed into calcium carbonate on the mass being exposed to the air1 just as in the preparation of ,vienna white2 but as the saturation with carbon dioxide takes a considerable time1 some of the lime remains in the caustic state and is liable to affect other colours that may be mixed with the ochre4 ,an artificial ochre uniting in itself all the qualities of the natural product1 and also capable of being shaded by burning1 can be prepared in the following manner4 ,an accurately weighed quantity of pure crystallised ferrous sulphate is dissolved in a definite amount of water1 and the solution is treated with successive small portions of crude nitric acid1 until all the ferrous oxide has been changed into the ferric state4 ,the change can be detected by a very decisive test4 ,if a liquid containing ferric oxide in solution is brought into contact with a solution of red prussiate of potash 7potassium ferricyanide71 no precipitate is formed in the absence of ferrous oxide1 but only a brown coloration2 whereas1 if ferrous oxide is present1 a beautiful blue precipitate is formed at once1 the colour of which is so intense that very small quantities of ferrous oxide can be detected by this means4 ,for the purpose now under consideration1 the presence of small amounts of ferrous oxide in the solution is immaterial1 because they are soon changed into ferric oxide on exposure to the air4 ,it might1 therefore1 be asked1 why take the trouble to oxidise the ferrous oxide by means of an agent involving expense1 which could be saved by allowing the oxidation to take place in the air8 ,the advantage1 however1 of the direct employment of a solution of ferric oxide is that it gives at once a colour that can be dried straight away2 whilst at the same time the colour undergoes no change in drying1 whereas it does when ferrous oxide solution is used4 ,the method of producing ochres from this ferric solution varies according as the product is to be used without any further treatment than drying1 or is to be modified by firing4 ,in the former event1 caustic lime is again used as the precipitant1 but in only just sufficient quantity to throw down all the ferric oxide in the solution4 ,this amount can be calculated exactly1 #cfhd parts by weight of pure burnt lime being required for every #ajj parts of pure ferrous sulphate taken4 ,the actual quantity1 whether larger or smaller1 will depend on the relative purity of the sulphate and lime2 and this can readily be ascertained by a simple trial4 ,the lime is used in the form of milk of lime1 as already described4 ,if lime alone is employed1 the precipitate will consist of pure ferric hydroxide and the calcium sulphate thrown down at the same time4 ,the resulting colour1 when dried1 will be an intensely brown mass1 which can be used in place of the very dark natural ochres4 ,in order to obviate entirely the disadvantages resulting from the presence of a large amount of caustic lime in the precipitate1 fine levigated chalk or white clay is added in the preparation of the lighter shades of ochre1 the addition being made as soon as the two ingredients have been brought into contact2 and the mixture is thoroughly stirred1 to ensure uniform admixture with the ferric hydroxide4 ,the colour of the settled deposit will be lighter or darker in proportion to the amount of chalk or clay employed2 and in this way the whole range of shades from pale yellow to bright brown can be obtained without the application of heat4 ,ochre that has been made with chalk is unsuitable for toning by heat1 because this treatment would causticise the lime1 and the ochre could not be mixed with other colours1 since these would be affected by that substance4 ,on the other hand1 when white clay is used in preparing the ochre1 the latter can be more easily toned by firing1 provided care be exercised in the process4 ,the ochre must be dried completely in the air1 and either spread out in thin layers on iron plates1 for the burning process1 or else put into a drum1 of the kind already described1 in which the mass is moved onward by a worm4 ,the clay remains unaltered in firing1 but the gypsum parts with its water of crystallisation4 ,in order to restore the latter1 the ochre issuing from the drum is discharged direct into a vessel of water1 in which it can be kept in constant motion by a stirrer4 ,the water is soon warmed by the heat of the mass1 and absorption by the gypsum proceeds at a rapid rate4 ,when the whole charge has been fired and collected in the vessel of water1 the stirrer is stopped and the precipitate dried1 being then ready for use4 ,in certain circumstances1 ochre can be made by other methods4 ,in large towns1 ammonium salts are sometimes obtainable at a moderate price1 being manufactured in large quantities as a by-product in gasworks4 ,for our purpose1 crude gas liquor might be used1 since it contains ammonia for the precipitation of the ferric hydroxide4 ,in most cases1 however1 this gas liquor contains only very small quantities of ammonia1 and1 therefore1 in a works of any size1 very large vessels would be needed for the production of a comparatively small quantity of ochre4 ,on this account1 preference is given to crude carbonate of ammonia1 which is also obtainable at low prices4 ,on bringing a solution of this salt into contact with one of ferric oxide1 ferric hydroxide is precipitated1 and the sulphate of ammonia resulting from the reaction remains in solution4 ,by stirring white clay into the liquid at the same time1 the ochre can be correspondingly lightened in shade4 ,the precipitates obtained in this way can be dried at once1 and converted into any shade obtainable with natural ochre1 from brown to red1 by strong firing4 ,the sulphate of ammonia still remaining in the air-dried product is completely volatilised by the heat1 and the resulting ochres are even superior to the natural varieties in beauty and permanence4 ,,ochres ,,as ,,by-,,products ,in the manufacture of certain chemicals1 substances of divergent composition are obtained which are sold under the name of ochre and are used as painters' colours4 ,whereas ochre1 properly so-called1 consists of either ferric hydroxide or ferric oxide in association with clay1 lime1 etc41 the products now under consideration are basic ferric salts composed of varying quantities of ferric oxide in combination with certain proportions of sulphuric acid4 ,these ochres are obtained as by-products in the manufacture of green vitriol from pyrites1 and in alum manufacture2 and1 according to their origin1 they are classed as vitriol ochre1 so-called alum sludge1 and pit ochre4 ,all the basic ferric sulphates of which they are composed form fairly large crystals1 and1 therefore1 in most cases1 the covering power is small4 ,on this account the products are of low grade and are put on the market at low prices1 for which reason they are largely used in making cheap paints4 ,vitriol ,ochre4--,commercial green vitriol is1 for the most part1 manufactured from native sulphides of iron4 ,when many of these sulphides are piled in heaps and left to the action of the air1 oxygen is gradually absorbed and green vitriol is formed which is dissolved out by rain and is collected in large clarifying tanks4 ,in the case of pyrites1 however1 the mineral must first be roasted in a current of air1 since otherwise its conversion into green vitriol would only proceed in a very sluggish manner4 ,in any event1 the aqueous solution of ferrous sulphate has to be concentrated1 by evaporation1 to the point at which the green vitriol crystallises out4 ,both in the clarifying-tanks and--still more so--in the evaporating-pans1 a rusty-looking sediment forms at the bottom1 consisting of basic ferric sulphate4 ,this originates in the partial oxidation of the ferrous oxide 7first formed7 while the pyrites is exposed to the air1 and since the quantity of sulphuric acid present is insufficient to saturate all the ferric oxide1 basic salts are produced4 ,the yellow-brown sludge deposited in the pans during the concentration of crude green vitriol liquor1 constitutes the product termed vitriol ochre1 which contains varying amounts of ferric oxide1 sulphuric acid and water1 according to the quantity of ferric oxide resulting from the oxidation of the pyrites and the character of the latter1 e4 g43-- ,ferric oxide #fe-gj ,sulphuric acid #ad-af ,water #ac-af ,although the colour of these ochres is not particularly handsome1 they can be transformed1 by firing1 into colours of fairly good quality4 ,as this subject will be more thoroughly gone into when dealing with the preparation of the red iron pigments1 the applicability of these ochres will only be casually referred to here4 ,during the burning process1 these ochres1 of course1 part with the whole of their contained water2 and by protracted1 high calcination1 the whole of the sulphuric acid can also be expelled1 so that finally nothing but pure ferric oxide is left4 ,alum ,sludge4--,solutions of crude alum always contain a certain amount of ferric oxide which settles down at the bottom of the pans during concentration4 ,this sludge1 too1 consists of basic ferric sulphate1 but is inferior in covering power to vitriol ochre1 the crystals being of coarser grain4 ,on the other hand1 the ochreous sediment from the alum concentrating-pans has the valuable property of being readily transformable into red-brown to pure red tones by burning4 ,for this reason1 particular attention has been devoted to this sludge in a number of alum works4 ,since the products are only of value when burned1 and the shades thereby obtained are always red1 they will be dealt with more fully along with the red earth colours4 ,pit ,ochre4--,springs containing small quantities of ferrous sulphate and other salts are met with in many iron mines1 but1 in most cases1 the amounts are too small for their recovery by artificial concentration to be contemplated4 ,if1 however1 the conditions allow of the springs being easily diverted1 they may often be utilised for the preparation of low-grade ochre4 ,the chemical composition of these pit ochres varies considerably1 and depends on the geological character of the locality4 ,water can only dissolve such minerals as occur in the form of fairly readily soluble compounds2 and for this reason pit waters are always solutions of the metals which are found in the mine4 ,the variety of compounds that may be present in an ochre can be seen from the subjoined analyses of ochres deposited from pit waters at ,rammelsberg4 ,as elsewhere1 two distinct classes of ochre are met with1 having a conchoid and an earthy fracture respectively4 ,the latter usually contain rather more ferric oxide1 and1 in particular1 a higher content of foreign substances1 the most important of which is quartz sand4 ,in the ,table1 the ochres with conchoid fracture are marked ,a1 and those with an earthy fracture1 ,b4 ,a4 ,b4 ,ferric oxide #fhge #fche ,zinc oxide #abi #abc ,copper oxide #jej #jhh ,sulphuric acid #ihj #acei ,water #aeeb #ahde ,clay and ,quartz #dad #bjj ,the preparation of the ochre is a simple matter1 consisting in collecting the mass and sorting out the loose1 earthy portions of a pure yellow colour from the denser and darker parts4 ,the former are dealt with separately1 usually by a simple process of levigation1 for the sole purpose of getting rid of the earthy matter1 quartz sand in particular4 ,the denser varieties require much more work1 but yield a far superior product1 which1 by suitable treatment1 can be converted into the finest grades of ochre4 ,the first operation consists in a very careful crushing1 and as the pieces are often very hard1 they are treated in ordinary or stamp-mills1 edge-runners being also employed with advantage4 ,the product reduced by any of these means is passed through a number of sieves1 to separate the fine particles from the coarse2 and the finest dust is burnt4 ,this last treatment causes a considerable loss in weight1 both the accompanying water and most of the sulphuric acid being volatilised4 ,however1 since1 as already stated1 all varieties of ochre can be obtained1 the process is consequently very remunerative notwithstanding the loss in weight it involves4 ,yellow ,earth4--,from the particulars given in the general description of the earth colours1 yellow earth may also be regarded1 to some extent1 as an ochre1 but one containing a large proportion of foreign substances4 ,it might1 however1 be more accurately termed a clay contaminated with a considerable amount of quartz sand and a certain proportion of ferric oxide4 ,the method of preparation is on the same lines as for ochre1 but burning is never practised1 nor is the treatment so careful as for the better grades of ochre1 the low price of the colour making this unremunerative4 ,,chapter ,,vi ,,red ,,earth ,,colours ,the number of minerals that can be directly used as red earth pigments is comparatively small1 and by far the greater proportion consist of ferruginous colours1 a few of which are obtained by the mechanical treatment of native iron ores or clays coloured red by ferric oxide1 the majority1 however1 being formed by burning certain materials of another colour4 ,to these belong nearly all the materials mentioned in connection with the ochres and the brown iron colours1 together with a few by-products of the chemical industry4 ,in addition to the foregoing1 which have ferric oxide for their pigmentary principle1 is the native mercury sulphide1 occurring1 as scarlet1 crystalline masses1 under the name of cinnabar 7vermilion74 ,the only reason for including natural vermilion with the earth colours is to make the list complete1 the largest proportion of this pigment being prepared by artificial methods4 ,the product sold as 8,chinese0 vermilion may1 in former times1 have really been introduced from ,china into ,europe1 and prepared there by grinding and levigating the best-coloured lumps of the natural cinnabar2 but1 at the present time1 all the vermilion made--in ,europe at least--is from sulphur and mercury1 by artificial processes1 and the name ,chinese vermilion is merely retained to designate a particularly fine grade4 ,on the basis of occurrence and chemical properties1 the red earths can be classified into several groups4 ,the first comprises natural products requiring only mechanical preparation1 such as the minerals known as hematite1 micaceous iron ore1 ,elbaite1 etc41 and the special modification of red ironstone termed raddle4 ,all these minerals consist almost entirely of ferric oxide in a pure state4 ,the mineral1 bole 7red chalk1 terra sigillata1 ,lemnos earth71 is chemically allied to the ochres1 being1 like them1 composed of alumina1 frequently accompanied by lime and small quantities of magnesia1 but differing in that ferric oxide is always present in bole1 whereas the ochres always contain ferric hydroxide4 ,the second group consists of the artificial reds obtained by burning or calcining raw materials1 whose ferric hydroxide is more or less transformed by heat into ferric oxide1 such as vitriol ochre1 pit ochre and alum sludge4 ,of late years the artificial earth colours have attained a high degree of importance4 ,they are obtained in large quantities in the manufacture of sulphuric acid from green vitriol4 ,formerly1 it is true1 they were also used as pigments under the name of caput mortuum or colcothar1 but were not held in much esteem2 and it is only within recent times that it has been discovered that these inferior by-products can be converted into very handsome and brilliant colours1 which now form important articles of commerce4 ,,bole ,bole1 ,lemnos earth1 terra sigillata1 etc41 is1 for the most part1 a product of the decomposition of highly ferruginous minerals1 and occurs1 in the form of lumps1 having a conchoidal fracture1 in pockets or detritus4 ,the lumps have a sp4 gr4 of #bb-be1 are ,isabella brown to dark brown in colour1 and give a slightly greasy-looking streak4 ,there are two distinct varieties of bole3 the one adhering firmly to the tongue1 whilst the other lacks this property and1 when placed in water1 crumbles down to powder in emitting a peculiar noise4 ,the composition of the boles varies1 but all of them may be regarded as alumino ferric silicates combined with water4 ,most of the specimens examined from different deposits contain #bd-be of water1 #da-db of silica1 and #bj-be of alumina1 the remainder consisting of ferric oxide with small traces of manganese oxide4 ,some varieties1 however1 are exceptional and contain only #cj-ca of silica and #ag-ba of water1 e4 g4 those from ,orawitza and ,sinope4 ,lemnos earth1 the true terra sigillata1 is mostly silica 7#ff7 with #h of water1 and contains a smaller percentage of ferric oxide than the others4 ,it is also of a distinct colour1 lighter than the true boles and having a greyish or yellowish tinge4 ,the behaviour of the different kinds on burning is just as diverse as their chemical composition4 ,whilst some kinds are infusible at even the highest temperatures1 and merely change into hard1 red masses2 others1 again1 fuse at a moderate heat4 ,this difference is due to chemical composition1 those high in silica being generally less refractory than those in which alumina preponderates4 ,in order to render the boles suitable for painting1 they are put through a somewhat different treatment than the other earth colours4 ,the freshly dug material is first sorted1 the uniformly coloured lumps of fine texture being set apart and suffused with water1 with which they form a pasty mass of low plasticity1 which is kneaded by hand to make it homogeneous1 and is then stirred up with more water4 ,when the lumps have distributed in the water1 the latter is drawn off into a second tub1 and the residue is stirred up with fresh water1 the treatment being repeated until the effluent no longer shows any signs of colour4 ,the liquid in which the finely divided bole is suspended is left to settle1 and the bole subsides as a fine powder1 which is dried to the condition of paste1 pressed into moulds and dried completely4 ,owing to its low content of ferric oxide1 the colour of bole is not particularly bright1 but is very permanent--a property equally shared by all the other ferric oxide pigments4 ,,native ,,ferric ,,oxide ,,as ,a ,,pigment ,in nature1 ferric oxide forms extensive deposits1 which1 by reason of the light red colour characteristic of certain varieties of ferric oxide1 are largely employed in painting4 ,these colours may be classed among the oldest known to mankind1 ferric oxide pigments having been used frequently in the most ancient paintings4 ,the most important varieties of ferric oxide for our purpose are3 iron glance1 with its modifications1 micaceous iron ore and frothy hematite2 red hematite1 and raddle4 ,,iron ,,glance ,this substance forms handsome black crystals of very high lustre1 which1 when small and scaly1 constitute micaceous iron ore4 ,both1 when rubbed down1 furnish a dark red powder of no particular beauty4 ,micaceous iron ore forms the transition stage into frothy hematite1 or iron cream1 the sole difference being that the crystals of the latter are much smaller1 and the scales finer1 the iron-black colour passing gradually into cherry red4 ,at the same time1 the lustre1 though still high1 loses most of the metallic sheen exhibited by micaceous iron ore4 ,,hematite ,the variety known as hematite or bloodstone1 sometimes occurring as shiny nodules1 is distinguished by its handsome red colour4 ,some of the lumps are composed of long1 thin crystals grouped about a common centre so as to form a globular mass4 ,despite its bright colour1 the hardness of hematite 7between #c and #e7 prevents it from being used as a pigment1 the value of the product not being commensurate with the cost of reduction4 ,,raddle ,there are numerous deposits of red ironstone1 in the state of fine earth1 where the operations of grinding and levigation have1 to a considerable degree1 already been carried out by ,nature4 ,these deposits form the mineral which1 under the name of raddle1 is often used as a pigment for ordinary paints4 ,it may be considered to have originated in the transformation of red ironstone1 by the natural forces that can everywhere be seen disintegrating rocks1 namely water and frost1 into a fine powder1 which has been transported1 often over long distances1 by water1 and has finally settled down4 ,in places where the process has been carried out in this manner1 the raddle will be in a condition1 as regards fineness of division and beauty of colour1 that leaves nothing to be desired1 and the material itself is ready for use as a very valuable pigment4 ,large deposits of this kind1 however1 are of rare occurrence2 but there are plenty in which the ferric oxide is associated with varying quantities of clay1 sand1 and sometimes lime4 ,the conditions here are on all fours with those of clay1 which1 too1 has been formed in a similar way4 ,pure clay1 the so-called kaolin1 is a highly valuable material1 whereas ordinary loam--highly contaminated clay--is only of low value4 ,in judging the quality of raddle as a pigment1 the presence of impurities is of less account than their nature2 and in some cases a very highly contaminated raddle may be worth far more1 as a pigment1 than one containing only very small admixtures of extraneous substances4 ,as stated above1 the ordinary impurities in raddle are clay1 lime and quartz sand4 ,an admixture of clay1 even if fairly large1 is no great drawback1 since the material can be used in its natural state1 and also be toned by burning4 ,lime is less favourable1 for though a calcareous raddle can be used as it is1 the lime parts with its carbon dioxide on calcination1 becoming changed into caustic lime and imparting to the product qualities which preclude its employment for a number of purposes1 especially for mixing with delicate organic colours4 ,the presence of quartz sand is immaterial when the raddle is to be burned1 inasmuch as sand is unaltered by calcination4 ,but it constitutes a drawback because it makes the fine raddle gritty and unsuitable for fine paint work4 ,the only way to eliminate this impurity is by levigation--an expensive operation which should1 as far as possible1 be avoided for these native ferric oxides1 because they must be sold very cheaply1 and have to compete with the large quantities of oxide obtained as a by-product of the chemical industry4 ,the suitability of a given specimen of raddle for use as a pigment may be easily ascertained by weighing out exactly #ajj grams and heating to about #abj ,c4 ,the loss of weight will give the amount of water in mechanical retention4 ,the residue is suffused with strong vinegar1 and left for several days1 being stirred at frequent intervals4 ,the carbonates of lime and magnesia present will dissolve in the acid1 the ferric oxide remaining untouched4 ,the liquid is decanted1 and the residue washed several times with water and dried1 the diminution in weight being a measure of the carbonates in the sample4 ,if the vinegar has turned a yellow colour1 the presence of ferric hydroxide in the mineral is indicated1 this hydroxide being readily soluble in acetic acid4 ,if the residue feels gritty1 it contains quartz sand1 the amount of which can be found with sufficient accuracy by levigating the mass and weighing the sandy residue after drying4 ,deposits occur1 in many places1 of a mineral similar to raddle1 but formed under peculiar conditions4 ,thus1 there are found1 in the vicinity of brown-coal deposits that are rich in pyrites1 earthy masses which are occasionally of a handsome red colour and consist of a variety of minerals admixed with a considerable proportion of ferric oxide4 ,these masses probably originated in fires in the coal seams1 whereby the pyrites became transformed into ferric oxide and basic ferric sulphate2 and where the deposits are of sufficient size1 they may be advantageously utilised in the production of cheap reds4 ,in most cases1 however1 the minerals must be levigated1 owing to the frequency with which they contain large proportions of extraneous minerals in a gritty condition4 ,,burnt ,,ferric ,,oxide ,,and ,,ochres ,it has already been stated1 in dealing with the yellow ochres1 that these colours can be toned by burning1 part of the ferric hydroxide losing its water and changing into red ferric oxide4 ,the more severe the burning1 the larger the amount of ferric oxide formed and the nearer the colour of the product approximates to red4 ,according1 however1 as the original ochre was yellow or brown1 the tone of the burnt colour will lie between orange and brownish red4 ,if the heating be pushed so far as to transform all the ferric hydroxide into oxide1 the red will come more and more into prominence in proportion to the amount of hydroxide in the original material4 ,if the product consists entirely of ferric oxide1 as is the case with that obtained1 as a by-product1 in the manufacture of ,english sulphuric acid1 a pure red ferric oxide 7caput mortuum1 colcothar1 ,english red1 etc47 will be obtained4 ,if the heating be increased above a certain point1 the pure ferric oxide will change colour1 assuming a brown to violet tone according to the temperature employed4 7a7 ,burning in the ,muffle ,since1 as a rule1 the quantity of material treated in the preparation of these brown1 violet to black ferric oxide pigments for the purposes of the painter on porcelain is not large1 the same kind of muffle furnace 7,fig4 #bi7 as serves for making enamels can be used4 ,the fire-clay muffle ,m is inserted in a reverberatory furnace ,o1 with a good draught1 and is raised to a white heat4 ,the finely powdered material to be burned is spread out evenly on plates of sheet-iron or fire-clay1 and introduced into the white-hot muffle1 where it is left for a period corresponding to the colour desired4 ,to save time1 the plates may be pre-heated in a second muffle arranged above the first4 ,illustration3 ,,fig4 #bi4 ,by this means a large range of tones can be obtained from one and the same material1 by heating it to different temperatures2 and the colours so produced are distinguished1 not only by their warmth of tone1 but also by very high stability4 ,in fact1 they may be regarded as permanent1 because very strongly calcined ferric oxide only passes very slowly into solution even under prolonged boiling in the strongest acids4 ,owing to this excellent property1 which is equalled by very few other pigments1 and the low cost of preparation1 these colours deserve the most careful consideration by all manufacturers who are in a position to obtain suitable material in sufficient quantities4 7b7 ,caput ,mortuum1 ,colcothar ,previous to the ,english method of making sulphuric acid by the oxidation of sulphur dioxide with nitric acid1 this acid was manufactured by heating dehydrated ferrous sulphate 7green vitriol72 and even now1 fuming sulphuric acid--oil of vitriol1 or ,nordhausen sulphuric acid--is largely obtained by the same process4 ,when anhydrous ferrous sulphate1 ,fe,s,o#d1 is exposed to a very high temperature--strong white heat--it is decomposed into sulphur trioxide1 ,,so#c1 sulphur dioxide1 ,,so#b1 and a residue1 mainly composed of ferric oxide and a little basic ferric sulphate1 which remains behind in the heating-pan4 ,in fact1 even at the highest possible temperatures obtainable in the furnaces used for the distillation of the green vitriol1 it is impossible to recover the whole of the sulphuric acid1 a small portion being tenaciously retained by the iron4 ,this red residue is sold under various names--colcothar1 caput mortuum1 ,english red1 ,indian red1 etc4--and is used as a low-grade pigment1 and also as a polishing agent4 ,the name caput mortuum is a survival from the time of the alchemists1 and was probably applied to indicate a dead-burned product1 from which all the active ingredients had been removed4 ,although1 in former ages1 this substance was held in low estimation as a pigment1 attempts have been made in recent times to convert it1 by suitable treatment1 into a more valuable product2 and these attempts have been crowned with success1 affording another instance of how a high commercial value can be imparted to a waste product by proper manipulation4 7c7 ,calcining ,ferric ,oxide ,in order to obtain a series of tones of colcothar1 it is subjected to repeated calcination1 but not by itself1 since it would require an extremely large quantity of fuel to effect any change of tone in view of the very high temperature the material has already been exposed to in the sulphuric acid plant4 ,if1 however1 salt be added1 then a variety of tones can be obtained without recourse to any particularly high temperature4 ,it is frequently stated that the only effect of the presence of salt is to keep the calcining temperature uniform1 inasmuch as the salt volatilises at a strong red heat1 and when that temperature is reached1 the whole mass cannot get any hotter until the whole of the salt has passed off1 all the heat applied being consumed in transforming the salt into the state of vapour4 ,as a rule1 however1 the amount of salt added does not exceed #f of the weight of the charge to be calcined2 and this quantity does not seem to be sufficient to keep the temperature at a uniform level through the several hours required for the calcining process4 ,the author is therefore of opinion that the salt also has a chemical action on the material during the calcination4 ,as already mentioned1 colcothar is by no means pure ferric oxide1 but always contains basic ferric sulphate4 ,now1 it is feasible that some reaction may take place between the basic sulphate and the sodium chloride at calcination temperature1 with the formation of caustic soda1 which1 being a far more powerful base than ferric oxide1 deprives the latter of sulphuric acid1 sodium sulphate being formed4 ,the chlorine of the salt combines with the iron to form ferric chloride1 which volatilises at a glowing heat4 ,according to this hypothesis1 therefore1 the addition of common salt in the calcination of colcothar is less for the purpose of maintaining a uniform temperature within certain limits than for decomposing the basic ferric sulphate present and inducing the formation of a product consisting entirely of pure ferric oxide4 ,the various tones obtained are due to the varying length of exposure to the heat4 ,the following method is pursued in the conversion of colcothar into iron pigments on a manufacturing scale4 ,the crude colcothar from the sulphuric acid plant is ground1 as finely as possible1 in ordinary mills1 and the resulting soft powder is intimately mixed with salt1 #b1 #d or #f being the usual proportions added4 ,the calcination is ordinarily continued for six hours in the case of the mixture containing the largest amount of salt2 but only two hours1 or even one1 for the other mixtures4 ,the operation is carried on in earthenware pipes1 a large number of which 7up to sixty7 are built into a furnace4 ,the latter is fired very carefully1 the temperature being raised only very gradually1 since experience has shown that much better coloured products are obtained in this way than by raising the mass quickly to a high temperature4 ,when incandescent ferric oxide is allowed to cool down with unrestricted access of air1 the colour is not nearly so bright as when air is excluded during the cooling4 ,since air has no action on ferric oxide1 this remarkable phenomenon cannot be due to the presence of the air1 but probably to the influence exerted by the rapid change of temperature on the arrangement of the finest particles of the oxide4 ,nevertheless1 some manufacturers hold that rapid cooling1 with restricted access of air1 improves the colour4 ,to exclude air from the ferric oxide during calcination1 the open ends of the pipes are flanged and covered with close-fitting plates1 which are luted with clay4 ,the expansion of the internal air as it grows hot would burst the pipes unless a means of escape were provided1 which consists in leaving small vent holes in the cover plates4 ,as previously mentioned1 calcined ferric oxide is very inert1 chemically1 so that1 when the calcination has been strong1 prolonged boiling with the most powerful acids is needed to bring the oxide into solution4 ,if the heating has been continued up to the strongest white heat1 and the ferric oxide maintained in that condition for several hours1 even hot sulphuric acid will have only a slight effect on the oxide1 and the only way to make it more readily soluble is by fusion with potassium bisulphate4 ,now indifference to chemical action is just the property required of a pigment for fine work2 and in this respect1 the ferric oxide colours are superior to all others4 ,the gradations of tone that can be obtained from ferric oxide by varying the calcination are very numerous1 comprising all between iron red1 red-brown and pure violet4 ,the author has tried heating ferric oxide for a considerable time at a very high temperature1 equivalent to the strongest white heat1 and obtained a product which was no longer pure violet1 but had a decidedly blackish colour4 ,perhaps1 by greatly prolonging the heating1 it might be possible to get a pure black2 but1 even if this were so1 the matter would be of no special interest1 because black pigments for paints can be prepared in a much cheaper manner4 ,all that would be accomplished would be the proof that ferric oxide actually undergoes an extensive molecular modification when heated4 ,,ferric ,,oxide ,,pigments ,,from ,,alum ,,sludge ,alum is manufactured from alum shale and alum earth1 the former being a carbonaceous clay shale interspersed with pyrites1 and the latter a clay charged with pyrites and bitumen4 ,the raw materials are left in heaps for several years1 the pyrites being thereby oxidised with formation of free sulphuric acid and ferrous sulphate4 ,this free acid reacts further on the clay1 which it transforms into sulphate of alumina2 and by leaching the heaps with water1 a solution is obtained which contains the sulphate of alumina and the ferrous sulphate4 ,on the liquor being concentrated1 a basic ferric sulphate is deposited1 which is worked up into red pigment4 ,for this purpose it is first levigated in a special manner1 the sludge from the pans being placed in a large vat1 suffused with water1 and kept in slow circulation by stirrers1 which distribute the particles in the water1 forming a turbid liquid4 ,this liquid is conducted into a gently sloping shute1 the sides of which are perforated with openings at certain intervals1 to allow part of the liquid to run off into large collecting vessels underneath4 ,the heaviest of the suspended particles settle down first and are flushed out by the water escaping through the first opening4 ,the finer the particles1 the longer they remain in suspension1 so that the liquid escaping through the last holes carries off only a very fine powder4 ,the liquid collected in the different vessels is allowed to subside and is then drawn off from the firm deposit4 ,the operation is repeated with fresh quantities of sludge until sufficient sludge has been collected for further treatment4 ,the collecting vessel furthest away from the intake of the shute contains the finest levigated material1 and this is used for making the best ochres4 ,the levigated mass is dried in a very simple manner1 being usually spread out on boards1 which are exposed to the air in open sheds1 covered with a roof to keep out the rain4 ,here the sludge is left until it forms a pasty or earthy mass1 and is then calcined4 ,the best calcining furnace is of the type used for colcothar2 but the pipes must be connected to an exhaust pipe for carrying off the vapours disengaged during calcination4 ,illustration3 ,,fig4 #cj4 ,however1 since alum manufacturers do not usually go in for making the highest-grade pigments1 simpler calcining furnaces are used1 consisting of reverberatory furnaces in which the heating-gases are allowed to act directly on the materials of the charge4 ,a front elevation and section of such a furnace are shown in ,figs4 #cj and #ca4 ,the furnace is constructed with several arches1 one above another1 marked c1 k1 d4 ,the charge is introduced through the openings b and b'4 ,the furnace chamber is at a1 and the ashpit at g4 ,the gases of combustion flow over the charge on the hearths of the several arches and escape1 at the top1 into the stack1 along with the acid vapours liberated from the glowing mass4 ,illustration3 ,,fig4 #ca4 ,the further the hot gases get away from the fire1 the cooler they become1 and therefore the less strongly heated the charge on the upper hearths4 ,consequently1 the resulting product 7ferric oxide7 from the different stages of the furnace differs in colour2 and a number of gradations can be obtained by blending4 ,the ferric oxide pigments prepared in this way are not pure oxide1 but also contain small quantities of sulphuric acid and metallic oxides which were present in the original crude sludge4 ,however1 by reason of the simple process of preparation employed1 these pigments are usually sold at lower prices than those from colcothar2 and for less fine work they are excellent4 ,,chapter ,,vii ,,brown ,,earth ,,colours ,in point of chemical composition1 the majority of the brown earth colours are closely allied to the reds1 both kinds containing ferric oxide4 ,the main difference consists in that1 in the brown earths1 the ferric oxide is combined with water to form ferric hydroxide4 ,many of the brown earth colours1 however1 are of entirely different chemical composition1 and either consist mainly of organic matter derived from the decomposition of plants--and therefore very similar to brown-coal or peat--or else contain varying quantities of inorganic substances mixed with these dark-coloured organic decomposition products4 ,the brown earth colours form a highly important group1 some of the members of which are used in the finest paintings1 and1 for certain purposes1 cannot be replaced by other pigments4 ,those containing ferric hydroxide are found--though not very frequently--in natural deposits1 the most celebrated being the terra di ,siena1 occurring in the vicinity of that city4 ,,terra ,,di ,,siena ,this highly renowned pigmentary earth is found in deposits1 and1 in the crude state1 forms dark brown masses which are devoid of lustre1 crumble readily between the fingers1 have a smooth conchoidal fracture and absorb water with avidity1 in consequence of which property they adhere to the tongue4 ,their chief chemical constituent is ferric hydroxide1 with which1 however1 variable quantities of sand1 clay and ferric oxide are admixed4 ,these admixtures cause a considerable divergence in the colour of the earth1 ranging from pure brown to reddish-brown1 and1 in the case of very impure lumps1 to an unsightly yellow-brown4 ,mineralogically1 terra di ,siena is often regarded as a distinct species which1 according to the results of analysis1 must be considered1 not as ferric hydroxide1 but as ferric silicate combined with water4 ,sometimes1 a portion of the ferric oxide is replaced by alumina1 so that the percentage composition of the mineral becomes approximately3 ferric oxide1 #ff2 silica1 #aa2 alumina1 #aj2 and water1 #ac4 ,the hardness of this mineral is #be1 and the sp4 gr4 #cdf4 ,the method of formation of terra di ,siena was probably on the same lines as that already described in the case of ochre1 namely by the breaking down of minerals--in this case brown ironstone--and natural levigation1 the powder being deposited in places where the water containing the ferric hydroxide in suspension came to rest and allowed the solid particles to settle down4 ,the best lumps of terra di ,siena in point of purity and colour can be used as pigments without any preparation2 but in most cases the earth is lightly calcined1 in order to improve the colour4 ,this treatment enables a whole series of tones1 from pure brown to the brightest red1 to be obtained4 ,the stronger the heating1 the more water expelled from the hydroxide1 and consequently the closer the approximation of the colour to that of ferric oxide4 ,the pigments met with in commerce as terra di ,siena can also be prepared artificially1 by making ferric hydroxide and heating this1 when dried1 until the requisite tone is attained4 ,for this purpose1 ferrous oxide is precipitated from green vitriol and exposed to the air1 under which conditions it is rapidly transformed into ferric oxide1 and the greyish-green colour of the mass changes to brown4 ,lighter tones can be obtained by the addition of inert white substances2 and1 in other respects1 the method of preparation is the same as that of artificial ochre4 ,these pigments are sold under various names1 the dark shades1 between pure brown and red brown1 being usually called terra di ,siena or mahogany brown1 whilst the paler sorts are sold as satinober--more correctly satin ochre1 golden ochre1 etc4 ,other pigments1 chemically allied to the ferric oxide or ochre pigments1 are sometimes found on the market under various and entirely arbitrary names4 ,it may be pointed out that the greatest confusion exists in the nomenclature of pigments1 to such an extent that1 in many cases1 neither the chemist nor the manufacturer knows precisely what pigment is implied by a given name4 ,the confusion is still further increased by the use of names taken from different languages4 ,,true ,,umber ,umber1 properly so called--also known as ,turkish1 ,cyprian or ,sicilian umber1 from the country of origin--derives its name1 according to some authorities1 from the province of ,umbria 7,italy71 where a brown earth is found1 though others ascribe it to the ,latin 8umbra0 7shade7 because of the pigment being used for painting shadows4 ,true umber is an earthy mass of fine texture and liver-brown colour1 merging into chestnut in some of the lumps4 ,chemically1 it consists of a double silicate of iron and manganese combined with water1 a portion of these metals being usually replaced by alumina4 ,the greater hardness 7#ae7 and higher specific gravity 7#bb7 of true umber in comparison with ,cologne earth 7which is quite arbitrarily termed 8umber071 form a ready means of differentiation between the two4 ,according to ,viktor ,merz1 the umber found in ,cyprus consists of3 ferric oxide1 #eb2 manganese oxide1 #ade2 and alumina1 #c2 and is1 possibly1 merely a mixture of clay with hydroxide of iron or manganese4 ,an umber examined by ,klaproth contained #ac of silica1 #e of alumina1 #dh of ferric oxide1 #bj of manganese oxide and #ad of water4 ,the tone of umber can be modified1 in the direction of red1 by calcination1 but this process is seldom employed1 the dark brown shade of this colour being the one most appreciated4 ,in some parts of northern ,germany1 ,thuringia in particular1 the iron mines contain smaller or larger pockets of ferric hydroxide1 of a fine earthy texture1 from which umber is prepared1 by levigation and calcination4 ,the product is sold under various names3 chestnut brown1 wood brown1 mahogany brown1 bistre flea brown1 roe brown1 according to the shade of the calcined pigment4 ,a mineral 78siderosilicate10 according to ,von ,walterhausen7 composed of ferric silicate1 and approximating in this respect to terra di ,siena1 is found in the neighbourhood of ,passaro 7,sicily7 in deposits of tuff4 ,it forms masses which are transparent at the edges and are usually liver-brown to chestnut in colour4 ,the hardness of the mineral is #be1 the sp4 gr4 #bgac1 and the average chemical composition3 silica1 #cd2 ferric oxide1 #dhe2 alumina1 #ge2 and water1 #aj4 ,the foregoing are only a few examples of brown or red-brown earth colours4 ,in all these minerals the pigmentary principle is iron1 in combination either with oxygen alone 7ferric oxide71 with oxygen and water 7ferric hydroxide71 or silica compounds 7ferric silicate71 and always associated with certain quantities of other metallic oxides1 especially alumina and manganese oxide4 ,although but few of these minerals have gained any special reputation as pigments1 there is no doubt that similar minerals1 which are certain to occur in or near many deposits of iron ores1 could equally well be used for that purpose4 ,there is no need to emphasise that the discovery of such a mineral would be a very valuable find1 and that the products obtainable therefrom could be utilised to great advantage4 ,the testing of a mineral for its suitability as pigment is a very simple matter1 all that is required being to subject a small quantity to the same treatment that is applied to the earth colours on a large scale4 ,for this purpose a few pounds of the mineral are levigated1 and the residue is dried4 ,to ascertain the tones obtainable by calcination1 small samples--of about #ajj grms4--are placed in crucibles1 and gradually heated in a furnace4 ,when the masses have attained a sufficient temperature1 the samples are taken out of the furnace1 at intervals of ten minutes1 and left to cool4 ,it will then not be difficult to decide whether the mineral is at all suitable for the purposes of the colour-maker2 and if so1 these tests afford at once an indication of the temperature and time the mineral must be heated in order to obtain pigments of definite tones4 ,,cologne ,,earth 7,,cologne ,,umber7 ,the application of the term 8umber0 to this earth can only have been based on a certain similarity in colour to true umber4 ,in chemical composition1 however1 the two are quite different1 ,cologne earth really consisting of a mixture of humic substances4 ,it is well known that the rotted wood found in the interior of decaying trees is often a handsome brown colour2 and all woody matter1 after lying a very long time1 finally acquires this colour1 owing to the transformation of the wood into dark-coloured compounds richer in carbon4 ,this effect can be seen on the large scale1 in ,nature1 in the case of coal1 brown coal and peat4 ,now ,cologne earth consists of a brown-coal mould1 dark brown in colour1 of earthy character and of such low cohesive power that it crumbles with ease4 ,owing to this character1 ,cologne earth can be easily ignited by the flame of a candle1 and then burns with a strong1 smoky flame1 leaving very little ash and disseminating the peculiar bituminous smell given off when brown coal is burned4 ,the geological characteristics of ,cologne earth enable one to conclude that1 where similar conditions prevail1 materials of analogous nature may be discovered4 ,this earth is found embedded in a deposit of brown coal1 in which it forms pockets1 and occasionally large bodies4 ,now1 brown-coal deposits of enormous extent occur in very many localities1 as for instance in ,upper ,austria and in ,bohemia2 and many of these mines are sure to contain pockets of brown-coal mould1 which have perhaps been overlooked1 but might very well be utilised in the preparation of colours of very similar character to ,cologne earth4 ,the preparation of this material is very simple4 ,the earth coming from the deposits is put through a simple levigation treatment which leaves1 as residue1 lumps of semi-decomposed wood1 mineral admixtures1 sand1 etc4 ,the levigated earth is sold in the form of cubes4 ,cologne earth comes into the market under various other names1 such as3 umber1 ,cassel brown1 ,spanish brown1 etc4 ,the fiery brown which was so greatly preferred by the famous painter ,van ,dyck1 and named ,vandyke brown after him1 was of very similar composition to ,cologne earth1 and is said to have been obtained from a deep brown peat earth4 ,the ,vandyke brown of the present day1 however1 is almost invariably a ferric oxide pigment1 toned to the proper shade by suitable calcination4 ,,asphaltum ,,brown 7,,bitumen7 ,as a natural product1 which can be used as a painters' colour without any special preparation1 asphaltum 7bistre1 bitumen7 may also be classed among the earth colours4 ,chemically1 it is composed of hydrocarbons of various kinds1 and is thus similar to tar2 in fact1 asphaltum may also be regarded as a natural tar resulting from the decomposition of various organic substances4 ,many deposits of this mineral are known1 and two of them are particularly celebrated3 those of the ,dead ,sea1 in ,syria1 and the ,lake of ,asphalt1 in ,trinidad4 ,both deposits consist of craters filled with water on which the asphaltum floats in large cakes4 ,several kinds of asphaltum are met with in commerce1 ranging in colour from brown to black4 ,the preparation of the material as a pigment is confined to grinding the mass1 which is always of a low degree of hardness4 ,being readily soluble in oil of turpentine and then furnishing the most beautiful brown tones when laid on thinly1 the pigment is usually sold in this condition1 although it is also ground in oil for the same purpose4 ,finally1 it may be mentioned that various useless materials can be transformed1 by suitable treatment1 into brown pigments closely resembling ,cologne earth and applicable to the same uses4 ,such pigments can be prepared from brown-coal slack 7from inferior brown coal7 or bituminised wood--a variety of brown coal looking like charred wood--by treating these materials with a lye made from wood ashes and lime1 and washing and drying the residue4 ,,chapter ,,viii ,,green ,,earth ,,colours ,although the number of green-coloured minerals is large1 but few of them are suitable for painters' colours1 because they occur so rarely in ,nature that their employment for this purpose is out of the question1 more especially since a very large number of green pigments can be obtained by artificial means4 ,the most important of the earth colours in this category are ,celadon green1 or green earth1 and malachite green--the latter1 however1 less so1 because the substance of which it is composed can be prepared artificially4 ,,green ,,earth1 ,,or ,,celadon ,,green ,this mineral is of a peculiar green colour1 and the name 8,celadon green0 has been universally adopted in the nomenclature of colour shades4 ,green earth occurs native in many places1 being the decomposition product of an extensively distributed mineral1 augite1 crystals of which are found in many of the deposits4 ,the green earth of ,monte ,valdo1 on ,lake ,garda 7,upper ,italy7 has been used for a very long time as a pigment4 ,it is chiefly prepared in ,verona for distribution in commerce1 and from this circumstance has acquired the name 8,verona green10 or 8,verona earth40 ,the earth is also found in ,cyprus and ,bohemia1 where it frequently occurs as the decomposition product of basaltic tuff4 ,however1 whether obtained from ,monte ,valdo or elsewhere1 the product is always placed on the market as ,verona earth4 ,native green earth is always tough1 mostly occurring in amygdalous lumps1 but occasionally in the crystalline form of augite4 ,it has a fine-grained fracture1 a hardness between #a and #b1 and a sp4 gr4 between #bh and #bi4 ,the colour is not always quite uniform1 pure lumps having the characteristic ,celadon green appearance1 whilst impure lumps are olive green to blackish green4 ,in chemical composition it is chiefly ferrous silicate1 and this compound must be regarded as the actual pigmentary principle of green earth4 ,in addition1 it contains varying quantities of other compounds which influence the depth of shade of the product4 ,verona earth chiefly consists of ferrous oxide in combination with silica2 alumina1 magnesia1 potash1 soda and water being also present4 ,analysis shows it to contain3 ferrous oxide1 #ba2 silica1 #ea2 magnesia1 #f2 potash1 #f2 soda1 #b2 and water1 #g4 ,the green earths from ,gsen1 ,atschau and ,mnnelsdorf1 near ,kaaden 7,bohemia7 and the ,giant's ,causeway 7,ireland7 have the following composition3 ----------------------------------- ,kaaden4 ,giant's ,causeway4 ----------------------------------- ,silica #da #efd ,alumina #c #ba ,ferrous oxide #bc #ea ,ferric oxide -- #ada ,lime #h -- ,magnesia #b #ei ,potash #c #hh ,carbon dioxide #ai -- ,water -- #fh ----------------------------------- ,on account of the large quantity of mechanically associated water1 freshly dug green earth is greasy in character1 like wet clay4 ,in partial drying1 most of this water evaporates1 the mass becoming earthy and adherent to the tongue4 ,sometimes the colour is an ugly brownish-green1 owing to the presence of a considerable amount of ferric oxide formed as the result of changes set up by exposing the mineral to the air4 ,ferrous oxide is a very unstable compound1 having an energetic tendency to combine with more oxygen and thus undergo transformation into ferric oxide2 so that when green earth is left in the air for a long time1 a considerable proportion of its ferrous oxide is oxidised to ferric oxide1 the mass thereby assuming the brown tone in question4 ,such an unsightly product can1 however1 be converted1 by simple treatment1 into one of very bright and handsome appearance2 and it is this possibility that first enabled green earth to attain importance as a painters' colour4 ,formerly it was only used as a material for common work1 being added to whitewash or employed for indoor paints4 ,when the crude green earth is treated with very diluted hydrochloric acid1 the compound of ferrous oxide and silica is left intact1 but most of the extraneous admixtures are removed4 ,ferric oxide1 in particular1 passes into solution1 and the calcium carbonate largely present in some kinds of green earth is also dissolved4 ,after prolonged contact with the crude earth1 the acid liquor takes on a brownish coloration from the dissolved ferric oxide4 ,since the presence of iron salts has no influence on the purification of the green earth1 the most impure1 highly ferruginous hydrochloric acid can be used1 and the liquor can afterwards be employed in the preparation of artificial ochre by leaving it in prolonged contact with any strongly ferruginous mineral1 such as brown ironstone1 which neutralises the surplus acid4 ,this liquor is then precipitated by lime1 alkali1 etc41 the resulting deposit consisting mainly of ferric hydroxide1 the further treatment of which is conducted exactly as described in dealing with the preparation of artificial ochre4 ,the treatment of the crude earth is best carried on in the same vessels as are to be used in the subsequent levigation process4 ,after the acid liquor has been drawn off1 the earth is brought into contact with water1 stirred up well1 and the water run off1 by opening tapholes in the side of the vessel1 into settling-tanks1 where it is left until all the suspended matter has completely subsided4 ,the colour of green earth can also be toned by the addition of yellow ochre1 thus producing a range of greens with a yellowish tinge4 ,these lighter shades1 however1 are seldom met with in commerce1 the trade judging the quality of green earth more particularly on the depth of colour4 ,green earth is a valuable pigment for all kinds of painting1 on account of its extreme permanence4 ,it may be applied directly over lime without suffering any change1 whereas most of the cheap green colours are destroyed in like circumstances4 ,this behaviour renders green earth specially valuable in fresco work1 although it is also largely used as an oil colour4 ,augite is of frequent occurrence in volcanic districts2 and in such localities1 deposits of green earth are certain to be found4 ,the test for the suitability of a green earth consists mainly in treatment with dilute hydrochloric acid4 ,if the mineral assumes a handsome green tone1 it will generally form a useful pigment4 ,the test may be supplemented by applying the colour to a fresh coating of whitewash1 under which conditions it should remain unaltered4 ,,artificial ,,green ,,earth 7,,green ,,ochre7 ,a product sometimes put on the market as green earth or green ochre has nothing beyond its name in common with green earth properly so called1 except a certain similarity in colour4 ,this pigment is prepared by mixing yellow ochre to a thin pulp with water and adding about #b 7of the weight of ochre7 of hydrochloric acid4 ,after a few days1 a solution of #b parts of yellow prussiate of potash is added1 and if the liquor still gives a precipitate when tested with ferrous sulphate1 this last-named salt is added so long as such a precipitate continues to form4 ,the deposit is washed1 and dried in the ordinary way4 ,when the right proportions have been taken1 a pigment is obtained that coincides fairly in point of tone with true ,verona earth4 ,it is1 however1 inferior in point of permanence1 the ,berlin blue present being somewhat unstable and decomposing very quickly when brought into contact with lime4 ,the reaction taking place in the production of so-called 8artificial ,celadon green0 is that the hydrochloric acid used dissolves ferric oxide from the ochre1 the addition of the yellow prussiate of potash then forming a blue precipitate of ,berlin 7,paris7 blue which1 in conjunction with the yellow of the ochre1 gives a green-coloured mixture4 ,,malachite ,,green ,although the pigment sold under this name is nearly always an artificial product1 it cannot be omitted from a work dealing with the earth colours1 because1 in former times1 it was prepared exclusively from the mineral malachite4 ,owing to the fact that artificial malachite green is one of the cheapest of colours1 the troublesome work involved in the mechanical preparation of the native pigment has been almost entirely abandoned1 and the malachite itself is now utilised to greater advantage as a source of copper4 ,malachite green 7or mountain green7 is found in nearly every case where copper ores exist1 and is still--though very rarely indeed--prepared1 in a few places1 from the mineral1 the dark-coloured lumps being picked out because the lighter-coloured ones would furnish much too pale a colour4 ,the treatment of malachite for the preparation of pigment presents certain difficulties owing to the comparative hardness 7#ce-d7 of the mineral1 which is also rather heavy 7sp4 gr4 #cf-dj74 ,on the large scale1 the selected mineral is first put through a stamping-mill1 and then ground1 very hard stones being required for this purpose4 ,the fine product from this 7usually wet7 process is levigated and dried4 ,the pit water of some copper mines contains certain quantities of blue vitriol 7copper sulphate7 in solution2 and such pit water is generally treated for the recovery of a very pure form of copper1 the so-called cementation copper4 ,the liquor might also be worked up into malachite green1 by collecting it in large tanks and precipitating the dissolved copper oxide with milk of lime1 the bluish-green deposit separating in association with gypsum being transformed into a light malachite green by washing and drying4 ,a darker green1 free from gypsum1 could be prepared by using a solution of carbonate of soda as precipitant4 ,neither the native nor the artificial malachite green is particularly handsome in colour2 and both possess1 in addition1 the unpleasant property of gradually going off colour in the air1 all the copper compounds being quite as sensitive to sulphuretted hydrogen as those of lead1 and finally turning quite black under the influence of that gas4 ,,chapter ,,ix ,,blue ,,earth ,,colours ,only three minerals are known to be suitable as pigments2 and indeed1 at present1 only two1 the third1 lapis lazuli1 being now of merely historical interest4 ,nowadays1 no one would think of using this rare and expensive mineral as a pigment1 since ultramarine1 which has the same pigmentary properties1 is extremely cheap1 whereas the pigment from lapis lazuli was worth its weight in gold4 ,the only two blue earth colours of any interest at present are malachite 7copper7 blue1 and the blue iron earth ,vivianite2 and even these1 though by no means rare1 are little used1 since artificial blues are now made which are far superior in beauty and can be obtained so cheaply that the natural pigments are put out of competition4 ,,malachite ,,blue 7,,lazulite7 ,lazulite and malachite 7mountain blue7 are of frequent occurrence in copper mines1 and the former is distinguished by its beautiful azure blue colour1 which1 however1 suffers considerably when the crystals are reduced to powder4 ,both minerals are very similar in chemical composition1 and consist of cupric carbonate4 ,the formula of malachite is #b;,cu,o,c,o#b ,h#b,o1 that of lazulite being #c;,cu,o7,,co#b7b ,h#b,o1 so that the only difference between them is that of the relative proportions of the substances in combination4 ,lazulite is also rather hard 7#ce-dj71 but owing to the small size and brittle character of the crystals it is not very difficult to pulverise4 ,in the air1 malachite blue behaves in much the same way as malachite green1 turning black in presence of sulphuretted hydrogen4 ,malachite blue is chiefly used for indoor work1 and also as a water colour2 but it is always rather pale and dull4 ,,vivianite ,this mineral--also termed blue ochre--is a transformation product of various iron ores1 and occurs native as fairly extensive deposits in some places1 especially in peat bogs4 ,it forms ill-defined crystals1 which are of a low degree of hardness 7#bj7 and vary in specific gravity between #bf and #bg4 ,the colour of the freshly won mineral is whitish or pale blue1 but soon changes to a dark blue in the air1 owing to the oxidation of the ferrous phosphate1 originally present1 into ferric phosphate4 ,vivianite can be transformed into a pigment by a simple process of crushing and levigation2 but the product is never very handsome1 and1 at best1 is only suitable for quite common paint work1 though characterised by considerable stability4 ,,chapter ,x ,,black ,,earth ,,colours ,only two minerals are known that can be used as black earth colours1 namely black chalk or shale black1 and blacklead or graphite4 ,whereas the former of these is of merely subordinate importance1 most of the black chalks being prepared artificially1 graphite is all the more so because it is employed1 not only as the sole material for lead pencils1 but also for making graphite crucibles1 as blacklead stove polish1 as a lubricant1 etc4 ,one of its numerous applications is in connection with the electro deposition of metals1 its high electrical conductivity causing it to be used for coating the interior of the moulds in which this deposition is effected4 ,,graphite ,graphite1 also known as plumbago or blacklead1 consists of carbon4 ,it is usually spoken of as pure carbon1 but from a very large number of carefully conducted analyses1 it would appear that native graphite is never quite pure1 even the finest grades of the mineral containing #ifh of carbon at the most4 ,the accompanying substances--which in some cases form nearly #ej of the whole--are of divergent composition and consist of iron1 silica1 lime1 magnesia and alkalis4 ,even the combustible constituent of graphite is not pure carbon1 but always contains a certain--though small--proportion of volatile substances4 ,these slight traces of volatile matter are of considerable importance in connection with the hypothesis on the origin of the mineral4 ,contrary to the old idea1 it is now almost universally considered that1 instead of being of volcanic origin1 graphite consists of the remains of long-dead organisms1 and in this respect is closely related to coal4 ,this hypothesis1 however1 fails to explain one point1 namely the crystalline nature of graphite2 for even anthracites1 which form the oldest coals known to have had their origin in the decomposition of organic substances1 do not reveal the faintest traces of crystalline structure4 ,the upholders of the theory that graphite was formed by the action of plutonic forces adduce1 in support1 the fact that graphite can actually be produced1 in certain chemical processes1 at high temperature4 ,molten cast-iron in cooling causes the separation of carbon in the form of graphite2 and the same substance is also formed1 in large quantities1 in gas retorts1 through the decomposition of certain carbonaceous compounds when brought into contact with the glowing walls of the retorts4 ,recent investigations1 however1 have shown that the temperature necessary for the transformation of non-crystalline carbon into crystalline graphite is by no means so high as was formerly supposed2 and it is now known that the change takes place at as low as red heat4 ,possibly the two theories could be reconciled by the assumption of a very old coal--such as is found1 for instance1 as anthracite in many parts of the world--being so strongly heated1 by plutonic action1 as to change into graphite4 ,native graphite crystallises in the form of hexagons1 mostly tabular2 but really well-developed crystals are of extremely rare occurrence1 and by far the greatest quantities of this mineral are found in the condition of dense lumps1 in which only the crystalline structure1 and not any decided crystals1 can be discerned4 ,the hardness of the mineral fluctuates within fairly wide limits1 ranging from #je to #aj4 ,the sp4 gr4 averages #ahjah-ahdd1 but1 in the case of impure lumps may increase to #ai-bb4 ,the following analyses will give some idea of the considerable divergence existing between graphites from different deposits3-- ,,siberian ,,graphite #a #b ,carbon #idbh #djee ,ash #egb #efef ,water -- #bhj ,,portuguese ,,graphite ,carbon #dbfi ,water 7chemically combined7 #cif ,ash #ecce ,,bohemian ,,graphite #a #b ,carbon #faja #fijd ,alumina #ghj #fhf ,silica #agcd #adah ,magnesia #ajc #jec ,lime #bef #jhj ,ferric oxide #eed #djj ,potash #jhg #jia ,water and volatiles #cbd #bhi ,sulphur #jea #jfb ,,graphites ,,from ,,upper ,,styria #a #b #c ,carbon #hejj #hgaf #hbba ,ash #adhi #abff #agib #d #e #f ,carbon #hbdj #haaj #eeej ,silica #abch #aafa #bajj ,alumina #cij #efj #adef ,ferric oxide #jec ,manganese protoperoxide #jfb #bjj #dhd ,lime #jjb #bjj #dhd ,alkalis ,trace ,trace #jfb ,sulphur -- -- #jcj ,loss on incineration -- -- #bdc ,of these ,styrian specimens1 ,nos4 #a-d are crude kinds1 of sp4 gr4 #baddc2 ,no4 #e was levigated in the laboratory1 and ,no4 #f was levigated from an inferior quality at the mine4 ,according to the character of the crystalline structure1 the colour of graphite varies1 but is mostly deep black4 ,very pure specimens1 such as the beautiful graphite blocks 7from the renowned ,alibert graphite mines in ,siberia7 which1 as a rule1 are only to be seen in exhibitions and mineralogical collections1 have the appearance of unpolished steel or white pig iron 7spiegeleisen74 ,the most important property of native graphite is its low hardness and cohesion1 in consequence of which it leaves a streak when drawn over the surface of paper4 ,graphite seems to be of frequent occurrence all over the world1 though only few deposits are known which yield a product that is suitable for all the purposes to which graphite is applied4 ,in ,european countries1 ,austria is particularly rich in graphite2 and very large deposits of this mineral are found in ,bohemia4 ,considerable deposits also occur in ,bavaria1 where they have long been worked4 ,english graphite is celebrated for its excellent quality4 ,all these ,european deposits1 however1 are surpassed1 both in extent and in the quality of their products1 by those discovered in ,siberia1 the largest being that producing the aforesaid ,alibert graphite and situated1 near the ,chinese frontier1 in eastern ,siberia4 ,at one time1 ,america imported all her blacklead pencils from ,europe1 having1 at that period1 no known graphite deposits furnishing a suitable product4 ,at present1 however1 deposits of this kind have been found in ,california1 and there can be little doubt but that many others of this valuable mineral remain to be discovered in that enormous continent1 the geological investigation of which is still far from being complete4 ,the graphite of some deposits is so highly contaminated by extraneous minerals that it cannot be utilised1 since the cost of purification would exceed the value of the product4 ,on the other hand1 the purer kinds1 when suitably refined1 yield a graphite that is fully adapted to all requirements4 ,the refining process may be either chemical or mechanical1 the choice of methods depending entirely on the character of the associated minerals4 ,if these mainly consist of coarse1 stony fragments1 preference should be given to mechanical treatment2 but if they are of such a character that they cannot be eliminated in this way1 chemical methods must be employed4 ,sometimes the two systems are combined1 by first subjecting the graphite to a rough mechanical purification1 and then completing the operation with chemical reagents4 ,the mechanical treatment consists in first removing as many of the impurities as possible by hand-picking1 and grinding the remainder in edge-runner mills1 along with water4 ,the turbid liquid1 containing the powdered graphite and extraneous minerals in suspension1 is led through long launders1 the sides of which are notched at intervals to allow the water to overflow into large pits4 ,the graphite settling in the first of these pits contains numerous particles of the heavy associated minerals2 but that remaining suspended in the water and carried on to the further pits constitutes the bulk4 ,the water is left to clarify completely in the pits1 and is then drawn off1 the pasty residue being shaped into prisms1 which are compressed under heavy pressure1 to increase their density1 when partially dry4 ,although levigation will remove most of the accompanying extraneous minerals1 it cannot eliminate the ash constituents of the graphite4 ,experiments made in this direction have demonstrated that the ash content of the levigated graphite is exactly the same as that of the crude material4 ,whilst these ash constituents do not affect the quality of graphite for certain of its uses1 they nevertheless impair its beautiful black colour to a considerable degree4 ,the chemical treatment necessary to eliminate these constituents is attended with many difficulties1 the chief of which resides in the fact that the ferric oxide present is in a form that is not readily accessible to the action of chemicals4 ,for this reason1 attempts to purify graphite with crude hydrochloric acid are hardly likely to prove successful1 since both the ferric oxide and the accompanying silicates obstinately resist the action of this acid4 ,in order to obtain graphite of a high state of purity1 the attempt must be made to bring this ferric oxide and the silicates into a soluble condition4 ,this can be accomplished in various ways1 and the choice of the method will depend on the purpose for which the graphite is intended4 ,for example1 the operations may either be confined to purification1 or else include the attainment of a maximum condition of subdivision4 ,when foliaceous graphite has to be treated--and this kind of graphite cannot1 in its original condition1 be used for making lead pencils--it is preferable to employ a method which will produce both the above results4 ,the purification may consist in crushing the graphite to powder1 and fusing this with a mixture of sulphur and carbonate of soda1 whereby the silicates present are converted into soluble compounds1 and the ferric oxide into ferric sulphide4 ,on extracting the melt with water1 a portion of the contained salts pass into solution and is carried off4 ,the residue is then treated with dilute hydrochloric acid1 which dissolves out the ferric sulphide1 with liberation of sulphuretted hydrogen1 and leaves the graphite in a very pure condition after washing4 ,in order to render foliaceous graphite suitable for lead pencils1 a different method is pursued1 but should only be employed in special circumstances1 on account of the expense entailed4 ,according to the process recommended by ,brodie1 the graphite1 ground to coarse powder1 is mixed with about one-fourteenth of its own weight of chlorate of potash1 this mixture being heated1 with two parts by weight of sulphuric to each part of graphite1 in a water bath so long as fumes of hypochlorous acid continue to be disengaged4 ,the heating must be performed in stoneware or porcelain vessels1 those made of any other materials being strongly corroded by the chlorine compounds formed4 ,when the evolution of fumes ceases1 the mass is allowed to cool1 and is carefully washed with a large volume of water1 the residue being then dried and heated to redness4 ,during this calcination the graphite undergoes a peculiar change1 increasing considerably in bulk and forming an exceedingly soft powder which1 after another washing1 consists almost entirely of chemically pure carbon4 ,graphite purified in this way can be used for any purpose for which this material is employed1 and may be made into the finest lead pencils4 ,however1 as already mentioned1 this process is usually too expensive for general application4 ,the use of graphite for writing is more ancient than is usually supposed1 having been tentatively employed between #aedj and #aefj4 ,it was during this period that the graphite mines in ,cumberland were discovered2 and the extremely pure graphite found there soon began to be used as a writing material4 ,up to the close of the eighteenth century1 lead pencils were made by selecting pure lumps of graphite and sawing them into thin rods1 which were then encased in wooden sticks4 ,apart from their high price1 these pencils exhibited various defects1 one of the chief being that a stick of such pencil was seldom of uniform hardness throughout its length1 most of them being so soft in parts as to make a deep black1 smeary mark1 whilst other parts would hardly give any mark at all4 ,the defects inherent in native graphite are completely removed by the method now generally employed in making lead pencils2 and on this account the old process of sawing the lumps has been abandoned4 ,graphite with a fine earthy texture alone is suitable for lead pencils1 scaly varieties being useless for this purpose1 unless specially prepared1 since they will not give a solid black streak4 ,by means of the ,brodie process1 however1 even the most highly crystalline kinds can be rendered suitable for this purpose4 ,siberian graphite is distinguished by extremely high covering power1 and is specially preferred for the manufacture of pencils4 ,excellent varieties for this purpose are also found in many parts of ,europe2 and indeed1 a large proportion of all the lead pencils used throughout the world are made from ,bohemian1 ,styrian and ,bavarian graphite4 ,at present1 all pencils are made from ground graphite1 the extremely finely ground and levigated material being kneaded into a paste with clay4 ,this operation fulfils a twofold purpose1 the plasticity of the clay increasing the cohesion of the individual particles of graphite1 whilst the amount of clay used determines the hardness of the pencil4 ,the larger the proportion of clay1 the harder the pencil when baked1 and therefore the paler the mark the pencil will make on paper4 ,in the pencil factories1 the clay is incorporated in special machines2 and the operation requires extreme care1 since only a perfectly uniform mixture will give a composition of regular character in all cases4 ,the intimately mixed material is formed into thin rods1 which are dried and then baked1 the heat driving out the water in the clay and transforming it into a solid mass4 ,an addition to this main application of graphite1 the mineral is also used for making crucibles1 chiefly for melting the noble metals4 ,crucibles of this kind are largely manufactured near ,passau1 ,bavaria1 and similar crucibles are made in ,england from ,ceylon graphite4 ,another important use for graphite is as a coating for iron articles to protect them from rust4 ,for this purpose1 however1 only the inferior kinds are employed2 and these can also be made up into excellent cements capable1 in particular1 of offering considerable resistance to the action of heat and chemicals4 ,to complete the tale of the applications of graphite1 its employment as a lubricating agent for machinery1 especially for reducing friction in machines made of wood1 may be mentioned4 ,latterly also1 the finest levigated graphite has come into use1 in admixture with solid fats or mineral oils1 for lubricating large engines1 for which purpose it is excellently adapted4 ,,black ,,chalk ,black chalk1 slate black1 ,spanish chalk1 crayon1 etc41 is not a chalk at all1 in the mineralogical sense1 but consists of clay shale of varying colour4 ,some kinds of this shale are pure black1 almost velvet black1 and these are considered the best4 ,others have a more greyish or bluish tinge and are of low value as pigments4 ,the purer the black1 the finer the grain of the material1 and therefore the greater its value to the colour-maker4 ,the variety obtained from ,spain is generally admitted to be the best1 and for this reason the name of ,spanish chalk has been applied to all similar minerals4 ,in all cases the black colour of ,spanish chalk is due to carbon2 but the particular modification of carbon present has not yet been accurately identified4 ,according to some1 it is chiefly graphite1 whereas others ascribe the colour to amorphous carbon4 ,apparently1 the material found in different deposits contains either one or the other of these modifications of carbon4 ,deposits of black chalk are fairly plentiful1 but in many of them the material is so contaminated with extraneous minerals that a somewhat troublesome method of preparation is needed to fit them for the purpose of the draughtsman4 ,with this object1 the native product must be ground extremely fine1 and the powder levigated2 and owing to the expense of these processes1 they are now seldom used1 it being possible to obtain a good black chalk far more cheaply than by levigating the natural material4 ,this artificial black chalk is prepared by mixing ordinary white chalk1 or white clay1 with a black colouring matter1 shaping the mass into prisms1 and sawing these into suitable pieces when dry4 ,the white pigment may either be mixed with some very deep black substance1 such as lampblack1 or stained with an organic dyestuff1 which is1 in reality1 not black1 but either very dark blue or green4 ,the usual colouring matter used with white chalk is lampblack1 mixed to a uniform paste with thin glue1 a suitable amount of clay or chalk being incorporated with the mass4 ,the production of a perfectly homogeneous mixture entails subjecting the paste to a somewhat protracted mechanical treatment4 ,when the mass has become perfectly uniform throughout1 it is shaped into prisms1 which are exposed to the air to dry and are then cut up with a saw4 ,instead of prisms1 the mass can be shaped into thin sticks1 which dry more quickly4 ,a very handsome black chalk can be made1 with comparatively little trouble1 by treating chalk with a suitable quantity of logwood decoction previously mixed with sufficient green vitriol solution to render the liquid a deep black4 ,this liquid is added to the dry chalk1 intimately mixed therewith1 and the pasty mass shaped into sticks4 ,the colouring agent may be replaced by a solution of logwood extract blackened by the addition of a small quantity of chromate of potash2 or black dyestuffs may be used4 ,,chapter ,,xi ,,the ,,commercial ,,nomenclature ,,of ,,the ,,earth ,,colours ,mention has already been made of the great confusion prevailing in the nomenclature of pigments1 and that many of these are put on the market under a variety of names taken from different languages4 ,although the number of the earth colours is far smaller than that of the artificial colouring matters1 the nomenclature is in a no less confused condition4 ,most frequently1 earth colours are named after the localities where they are either discovered or prepared1 in combination with the word indicating the colour of the product--for example3 ,cologne white1 ,vienna white--or the term 8earth0 7,verona earth1 ,veronese green1 etc474 ,whilst these names give1 to some extent1 an indication of the nature of the pigment1 others have no reference to it at all2 such as colcothar1 bole1 umber1 etc4 ,finally1 a number of other names in use are calculated to produce the impression that the earth colours in question are of an entirely different nature to their real one4 ,as an example1 we may cite the name 8,french chalk10 which is not a chalk at all1 but consists of the mineral talc4 ,black chalk1 again1 is not chalk 7calcium carbonate71 but a black shale2 and graphite is often termed blacklead1 although it contains no lead at all1 and the name is merely a survival from the time when pencils of metallic lead were used for drawing4 ,in order to bring some kind of order into the various names which are applied to the earth colours1 a list of those in current use is appended4 ,many of these names1 it may be stated1 have been selected in a purely arbitrary manner1 some manufacturers1 for instance1 selling ordinary chalk under a variety of foreign names1 for the purpose of thereby obtaining higher prices4 ,these borrowed names would seem to be superfluous1 to say the least4 ,pure and properly levigated chalk is the same article everywhere1 whether prepared from ,english1 ,french or ,german limestone2 and in all cases the simple name1 8chalk10 with an explanatory 8single10 8double10 or 8triple0 levigated1 should be quite sufficient4 ,in the case of earth colours that are really obtained of special quality in certain localities1 such as terra di ,siena1 green earth from ,verona1 or the like1 the corresponding name might be retained1 even if the pigment did not originate from the locality in question1 as a generic term for a pigment possessing certain properties and of a certain composition4 ,in the following classification1 the names of the earth colours are given in accordance with their colour and chemical composition4 ,,white ,,earth ,,colours ,carbonate of ,lime3 ,chalk2 levigated chalk2 ,vienna white2 ,spanish white2 marble white2 artists' white2 ,bougival white2 ,champagne chalk2 ,paris chalk2 ,cologne chalk2 ,mountain chalk2 craie2 blanc minral2 ,blanc de ,champagne2 ,blanc de ,meudon2 ,blanc de ,bougival2 ,blanc de ,troyes2 ,blanc d',orleans2 ,blanc de ,rouen2 ,blanc de ,brianon4 ,basic ,carbonate of ,lime3 ,vienna white2 ,vienna lime2 pearl white2 whiting2 ,blanc de chaux2 ,blanc de ,vienne4 ,note4--,the calcareous marls1 consisting of carbonate of lime and clay1 are also frequently sold under the above names1 the same being the case with gypsum4 ,silicate of ,alumina3 ,white earth2 pipeclay2 ,dutch white2 ,cologne earth2 terre d',argile2 ,argile blanc2 ,terre blanche4 ,silicate of ,magnesia 7mineralogically1 talc and soapstone73 ,talc2 ,venetian earth2 ,french chalk2 ,venetian white2 glossy white2 feather white2 shale white2 face-powder white2 ,blanc de ,venise2 ,blanc d',espagne2 ,blanc de fard4 ,note4--,fine grades of white lead are also sold as ,venetian white1 ,spanish white and shale white2 but can easily be recognised by their weight4 ,the term 8prepared0 white1 frequently applied to earth colours in the trade1 usually indicates that the material in question has been either levigated1 ground or burnt--in short1 put through some kind of preparatory treatment--and is therefore in frequent use for all the colours4 ,barium sulphate3 ,heavy spar2 barytes2 heavy earth2 mineral white4 ,precipitated colours3 ,permanent white2 blanc fixe4 ,,yellow ,,earth ,,colours ,ferric hydroxide1 with admixtures of ferric oxide1 clay1 lime1 ferric silicate1 basic ferric sulphate1 etc4 ,ochre2 iron ochre2 golden ochre2 satin ochre 7satinober72 pit ochre2 vitriol ochre2 ,mars yellow2 ,chinese yellow2 ,imperial yellow2 permanent yellow2 terra di ,siena2 umber2 ,italian earth2 ,roman earth2 bronze ochre2 oxide yellow1 etc4 ,yellow ochre2 ,jaune de ,mars2 ,terre d',italie4 ,ferric ,silicate3 ,yellow earth2 ,argile jaune2 yellow wash4 ,,red ,,earth ,,colours ,ferric oxide 7with alumina and silica74 ,bolus2 bole2 ,terra sigillata2 ,lemnos earth2 red chalk2 raddle2 ,striegau earth4 ,ferric oxide3 ,colcothar2 ,english red2 angel red2 ,pompeii red2 ,persian red2 ,indian red2 ,berlin red2 ,naples red2 ,nuremberg red2 crocus2 chemical red2 ,crocus ,martis iron saffron2 caput mortuum2 raddle2 rouge de fer2 ,rouge de ,perse2 ,rouge des ,indes2 ,rouge de ,mars2 ,rouge d',angleterre4 ,,brown ,,earth ,,colours ,ferric oxide3 ,ferric hydroxide2 ,ferric silicate 7conf4 ,yellow ,earth ,colours1 which are often sold under the same names as the browns4 ,the paler kinds are usually called 8pale0 or 8golden10 such as pale ochre1 golden ochre1 etc474 ,terra di ,siena2 burnt ,siena2 satinober2 mahogany brown2 ,vandyke brown4 ,ferric silicate1 ,clay3 ,umber2 umber brown2 ,roman earth2 ,roman umber2 ,turkish brown2 ,sicilian brown2 ,cyprus earth2 chestnut brown2 burnt umber2 ombre2 ,terre d'ombre2 ,ombre brule4 ,organic decomposition products3 ,cologne umber2 ,cologne earth2 ,cassel brown2 ,spanish brown2 mahogany brown2 ,vandyke brown2 brown carmine2 ,terre brun de ,cologne2 ,brun de ,cologne2 ,brun d',espagne2 ,ombre de ,cologne2 ,brun de ,cassel2 ,terre d',ombre2 ,cologne brown4 ,asphaltum 7mineral rosin73 ,asphaltum brown2 bistre2 earth brown2 bitumen2 pitch brown2 ,asphalte2 ,brun de bitume2 ,bitume4 ,,green ,,earth ,,colours ,ferrous oxide with silica1 alumina1 lime1 etc43 ,green earth2 ,verona green2 ,celadon green2 ,verona earth2 ,italian green2 stone green2 ,bohemian earth2 ,cyprus earth2 ,tyrol green2 permanent green2 green ochre2 ,terre verte2 ,terre de ,vrone2 ,vert d',italie4 ,cupric carbonate3 ,malachite green2 mountain green2 ,hungarian green2 copper green2 mineral green2 ,tyrolese green2 shale green2 ,vert de montagne2 ,vert d',hongrie4 ,,blue ,,earth ,,colours ,cupric carbonate3 ,malachite blue2 mountain blue2 lazulite blue2 azure blue2 mineral blue2 copper blue2 ,hamburg blue2 ,english blue2 ,cendres bleues2 ,bleu d'azure2 ,bleu de cuivre2 ,vert-de-gris bleu2 blue verditer4 ,,grey ,,earth ,,colours ,grey clay shale3 ,mineral grey2 silver grey2 stone grey2 slate grey4 ,,black ,,earth ,,colours ,carbon3 ,graphite2 blacklead2 plumbago2 iron black4 ,clay shale3 ,black chalk2 slate black2 ,spanish black2 ,spanish chalk2 oil black2 ,schiste noir2 ,noir d',espagne4 ,,index ,alabaster4 ,see ,gypsum4 ,alumina1 silicate of1 #ba1 #bb ,aluminium-potassium silicate1 #ba ,alum sludge1 #cb ----1 artificial ochre from1 #adh ----1 ferric oxide pigments from1 #afd-afg ,ammonium salts1 artificial ochre from1 #ade1 #adf ,anhydrite1 #ai ,anthracolite1 #ac ,arragonite1 #ac ,asphaltum1 #cg1 #ch4 ,see also ,bitumen4 ----1 brown1 #agd1 #age ,augite1 #agi ,azurite1 #cc ,ball ,mills1 #ee-ef ,barium carbonate1 #bj ---- sulphate4 ,see ,barytes4 ,barytes1 #ai1 #bj1 #aai-abb ----1 artificial1 #acc ----1 correcting colour of1 #aba ----1 detecting1 in white lead1 #abj ----1 low covering power of1 #aba ,black chalk1 #ch ---- earth colours1 #ahe-aif ---- ----1 trade names of1 #bjb ---- earths1 #f1 #ch-ci ---- schist1 #ch ,bitumen1 #agd1 #age ,blanc fixe1 #ai ,blue earth colours1 #ahc-ahd ---- ----1 trade names of1 #bjb ---- earths1 #d1 #cc-cf ,bole1 #ca1 #cb1 #aeb-aed ,bone breccia1 #ac ,brown coal1 pigments from1 #age ---- earth colours1 #afh-age ---- ----1 trade names of1 #bjj ---- earths1 #e1 #cf-ch ,calcareous marl1 #aaj1 #aaa ---- tuff1 #ab ,calcining1 #ha ---- ,ferric oxide1 #afa-afd ---- furnaces4 ,see ,furnaces4 ---- lime1 #hh-ij ---- ochre1 #acb-acf ,calcite1 #aa1 #ab1 #ad1 #ae ,calcium carbonate1 #ab1 #ad1 #ae1 #af ---- ----1 action of acids on1 #ae ---- hydroxide1 #af ---- sulphate4 ,see ,gypsum4 ,calc sinter1 #ab ---- spar4 ,see ,calcite4 ,caledonian brown1 #cf ,cappagh brown1 #cf ,caput mortuum4 ,see ,colcothar4 ,carbon brown1 #cg ---- in limestone1 #af ,cassel brown1 #cg1 #ch1 #agd ,celadon green4 ,see ,green earth4 ,chalk1 #ac ----1 black1 #aid-aif ----1 colour of1 #ajc ----1 correcting colour of1 #ajd1 #aje1 #ajf ----1 covering power of1 #ajf ----1 grinding1 #aja ----1 impurities in1 #ajc1 #ajd ----1 precipitated1 #ajg-aji ----1 preparation and properties of1 #ih-ajf ,classification of earth colours1 #d-h ,clay1 #ba-bc ,clay1 formation of1 #aac ----1 impurities in1 #aad-aai ---- in ochre1 #abh ----1 levigating1 #aad-aag ,colcothar1 #afj1 #afa1 #afb ,cologne earth1 #agc1 #agd ,commercial nomenclature of earth colours1 #aig-bjb ,crushers and ,breakers1 #dc-de ,crushing1 #gg-hj ---- machinery1 #dc-fj ,disintegrators1 #eh-fj ,distemper1 weatherproof1 #id ,dolomite1 #ah ,draining and ,drying1 #ff-gg ,drying appliances1 #gc-gg ,dyestuffs for improving earth colours1 #he ,edge runners1 #dh-ee ,english red1 #afj ,ferric hydroxide in ochre1 #abh-acb ---- oxide1 artificial ochre from1 #adc-add ---- ---- as by-product1 #cj ---- ----1 burnt1 #aeh-afd ---- ----1 calcining1 #afa-afd ---- ---- in lime1 detection of1 #ia ---- ----1 native1 as pigment1 #aed ---- ---- pigments from alum sludge1 #afd-afg ---- ----1 range of colours1 #bi ---- ---- shading1 #bh ---- ----1 violet shades from1 #afd ,ferrous sulphate1 artificial ochre from1 #aci-adc1 #adf-adh ,filter-cloths1 cleaning1 #gb ,filter-presses1 #gj-gc ,furnaces1 calcining1 #aeh1 #afb1 #afc1 #aff ,granulator1 #dc ,graphite1 #ch1 #ci1 #ahe-aid ---- as a lubricant1 #aid ---- as anticorrosive1 #aid ,graphite in the manufacture of lead pencils1 #aia-aic ---- for crucibles1 #aic ----1 refining1 #ahi-aib ,green earth1 #agf-ahj ---- ----1 artificial1 #ahj ---- ----1 improving1 #agh ---- ---- colours1 #agf-ahd ---- ----1 trade names of1 #bja ---- earths1 #e ,grey earth colours1 trade names of1 #bjb ,grey earths1 #ch ,gypsum1 #ah1 #ai1 #aaa1 #aab ,heavy spar4 ,see ,barytes4 ,hematite1 #aee ----1 brown1 #bc1 #cj1 #ca ----1 red1 #bh1 #cj ,hydro-extractor1 #ff-gj ,improving earth colours1 #hd1 #he ,indian red1 #bi1 #afj ,iron cream1 #bi ---- glance1 #aed ---- in limestone1 #ag ---- ore1 bog1 #be1 #ca ---- ----1 micaceous1 #bh ,ironstone1 brown1 #bc1 #bd1 #be ----1 clay1 #bd ----1 red1 #bh-cj ,kaolin1 #ba1 #bb1 #aab-aai ,lazulite1 #ahc ,lemnos earth4 ,see ,bole4 ,levigation1 #fj-fe ,lime1 absorption of carbon dioxide by1 #ic ----1 action of1 on casein1 #id ----1 ----1 on colours1 #ic1 #ih ----1 calcining1 #hh-ij ----1 caustic1 preparation of1 #hg-id ----1 double compound of oxide and carbonate1 #ic ---- from mussel shells1 #ih ----1 impurities in1 #ia1 #ib ---- in clay1 #bb ---- ----1 eliminating1 #aag-aai ---- in ochre1 #abi ,lime in the preparation of artificial ochre1 #adj-add ----1 moulding1 #if-ih ----1 quick1 #af ----1 slaked1 #af ,limestone1 #aa-ah ----1 suitability of1 for colour-making1 #ib ,limonite1 #be ,magnesia1 carbonate of1 #abc1 #abd ---- in lime1 #ia ---- in limestone1 #ag ,magnesium silicate1 #ba ,malachite1 #ce ---- blue1 #ahc ,marble1 #aa1 #ad1 #ae ,minerals1 testing for suitability as pigments1 #agb ,mine sludge1 #cb ,mixing earth colours1 #ha-hd ,moulding1 #he1 #hf ,mountain chalk1 #ab ---- milk1 #ab ,muffle1 burning ochre in the1 #aeh-afj ,muriacite1 #ai ,muschelkalk1 #ac ,ochre1 #bd1 #be1 #bf ----1 blue4 ,see ,vivianite4 ----1 calcining1 #acb-acf ----1 ,english1 #ach ----1 green1 #ahj ----1 pit1 #adh-aej ----1 ,roman1 #acg1 #ach ----1 ,siena1 #acg1 #ach ----1 testing1 #acj-acb ----1 toning with chalk1 #add ----1 toning with clay1 #add ----1 vitriol1 #adf-adh ,ochres1 #abh-aej ----1 artificial1 #ach-adf ---- as by-products1 #adf-aej ----1 burnt1 #aeh-afd ---- from various deposits1 #acf-ach ----1 ,italian1 #acg1 #ach ,oolithic limestone1 #ac ,organic matter in lime1 #ia ,pastel crayons1 #abf ,pearl white1 #id ,permanent white1 #ai1 #abb ,pipeclay4 ,see ,kaolin4 ,preparation of colour earths1 #dj-hf ,pulverisers1 #ef-eh ,raddle1 #bi1 #aee-aeh ----1 impurities in1 #aef ----1 testing1 #aeg ,raw materials for earth colours1 #h-ci ,red earth colours1 #aea-afg ---- ----1 trade names of1 #bjj ,red earths1 #d1 #bg-cc ,sampling raw earths1 #i ,selenite1 #ah ,shading pigments with permanent white1 #ai ,siena1 ,terra di1 #be1 #bf1 #bg1 #afh-agj ----1 ----4 ,see also ,italian ochre4 ,siderosilicate1 #aga ,sifting1 #gg-hj ,soapstone1 #bj1 #ba4 ,see also ,steatite4 ,spanish brown1 #agd ,sprudelstein1 #ae ,steatite1 #bj1 #ba1 #abe1 #abf ,stamps1 #de-dh ,talc1 #bj1 #ba1 #abd1 #abe ,terra sigillata4 ,see ,bole4 ,testing purity of raw earths1 #aj ,trade names of earth colours1 #aig-bjb ,ultramarine1 #cc ,umber1 #cf1 #agj-agd ----1 ,cologne1 #agc1 #agd ----1 true1 #agj-agc ,vandyke ,brown1 #ch1 #agd ,vermilion1 #aea ,verona earth4 ,see ,green earth4 ,vienna white1 #ie-ih ,vivianite1 #cc1 #cd1 #ahd ,white earth colours1 #hg-abf ,white earth1 trade names of1 #aaa1 #aih1 #aii ,white earths1 #d ,white raw materials and pigmentary earths1 #aa-bc ,witherite1 #bj ,working earth colour deposits1 #i ,yellow earth colours1 #abg-aej ---- ----1 trade names of1 #ajj ,yellow earth1 #aej ,yellow earths1 #d1 #bc-bg ,,printed ,,in ,,great ,,britain ,,by ,,richard ,,clay ,,sons1 ,,limited1 ,,paris ,,garden1 ,,stamford ,,st41 ,s4,e41 ,,and ,,bungay1 ,,suffolk4 ,the ,manufacture of ,paint ,,the ,,practical ,,handbook ,,for ,,paint ,,manufacturers1 ,,merchants ,,and ,,painters ,,by ,j4 ,,cruickshank ,,smith1 ,b4,sc4 ,second ,edition--,revised and ,enlarged ,,demy #h,,vo4 #gc ,,illustrations4 #cjj ,,pages ,,contents ,,chap4 ,,part ,i ,i4--,,scope ,,of ,,subject ,,and ,,definition ,,of ,,terms4 ,,ii4--,,storing ,,and ,,handling ,,raw ,,material4 ,,iii4--,,testing ,,and ,,valuation ,,of ,,raw ,,material4 ,,part ,,ii ,,iv4--,,plant ,,and ,,machinery4 ,,part ,,iii ,v4--,,the ,,grinding ,,of ,,white ,,pigments4 ,,vi4--,,the ,,grinding ,,of ,,earth ,,pigments4 ,,vii4--,,the ,,oxide ,,of ,,iron ,,pigments4 ,,viii4--,,the ,,grinding ,,of ,,black ,,paints4 ,,ix4--,,the ,,grinding ,,of ,,chemical ,,colours4 ,x4--,,the ,,grinding ,,of ,,pigments ,,in ,,water4 ,,xi4--,,the ,,grinding ,,of ,,colours ,,in ,,turpentine1 ,,gold ,,size1 ,,and ,,special ,,mediums4 ,,part ,,iv ,,xii4--,,mixed ,,or ,,prepared ,,paints4 ,,xiii4--,,enamels ,,and ,,enamel ,,paints4 ,,part ,v ,,xiv4--,,modern ,,conditions ,,which ,,affect ,,the ,,selection ,,and ,,application ,,of ,,paint4 ,,xv4--,,the ,,designing1 ,,testing ,,and ,,matching ,,of ,,paints4 ,,xvi4--,,cost ,,charges--,,cost ,,of ,,handling--,,carriage ,,and ,,delivery ,,of ,,goods--,,cost ,,of ,,materials--,,machinery ,,as ,,affecting ,,manufacturing ,,cost--,,electricity ,,as ,,motive ,,power--,,manufacturing ,,oncost--,,prices--,,the ,,future ,,of ,,the ,,industry4 ,price #abs4 #f;d4 net 7,post ,free1 #acs4 #c;d4 ,home and ,abroad74 ,,published ,,by ,,scott1 ,,greenwood ,,son1 #h ,broadway1 ,ludgate1 ,london1 ,e4,c4 #d ,the ,chemistry of ,pigments ,,by ,,ernest ,j4 ,,parry1 ,b4,sc41 7,,lond471 ,f4,i4,c41 ,f4,c4,s4 ,,and ,,john ,h4 ,,coste1 ,f4,i4,c41 ,f4,c4,s4 ,demy #hvo4 #e ,illustrations4 #bhj ,pages ,,contents ,chapter ,i4--,introductory ,light--,white ,light--,the ,spectrum--,the ,invisible ,spectrum--,normal ,spectrum--,simple ,nature of ,pure ,spectral ,colour--,the ,recomposition of ,white ,light--,primary and ,complementary ,colours--,coloured ,bodies--,absorption ,spectra4 ,chapter ,,ii4--,the ,application of ,pigments ,uses of ,pigments3 ,artistic1 ,decorative1 ,protective--,methods of ,application of ,pigments3 ,pastels and ,crayons1 ,water ,colour1 ,tempera ,painting1 ,fresco1 ,encaustic ,painting1 ,oil-,colour ,painting1 ,ceramic ,art1 ,enamel1 ,stained and ,painted ,glass1 ,mosaic4 ,chapter ,,iii4--,inorganic ,pigments ,white ,lead--,zinc ,white--,enamel ,white--,whitening--,red ,lead--,litharge--,vermilion--,royal ,scarlet--,the ,chromium ,greens--,chromates of ,lead1 ,zinc1 ,silver and ,mercury--,brunswick ,green--,the ,ochres--,indian ,red--,venetian ,red--,siennas and ,umbers--,light ,red--,cappagh ,brown--,red ,oxides--,mars ,colours--,terre ,verte--,prussian ,brown--,cobalt ,colours--,cruleum--,smalt--,copper ,pigments--,malachite--,bremen ,green--,scheele's ,green--,emerald ,green--,verdigris--,brunswick ,green--,non-arsenical ,greens--,copper ,blues--,ultramarine--,carbon ,pigments--,ivory ,black--,lamp ,black--,bistre--,naples ,yellow--,arsenic ,sulphides3 ,orpiment1 ,realgar--,cadmium ,yellow--,vandyck ,brown4 ,chapter ,,iv4--,organic ,pigments ,prussian ,blue--,natural ,lakes--,cochineal--,carmine--,crimson-- ,lac ,dye--,scarlet--,madder--,alizarin--,cam peachy--,quercitron--,rhamnus--,brazil ,wood--,alkanet--,santal ,wood--,archil--,coal-tar ,lakes--,red ,lakes--,alizarin ,compounds--,orange and ,yellow ,lakes--,green and ,blue ,lakes--,indigo--,dragon's ,blood--,gamboge--,sepia--,indian ,yellow1 ,puree--,bitumen1 ,asphaltum1 ,mummy--,index4 ,price #abs4 #f;d4 net 7,post ,free1 #acs4 #c;d4 ,home and ,abroad74 ,,published ,,by ,,scott1 ,,greenwood ,,son1 #h ,broadway1 ,ludgate1 ,london1 ,e4,c4 #d ,transcriber's ,notes ,minor use of boldface in the advertisements is not shown in the ,plain ,text version of this book4 ,punctuation1 hyphenation1 and spelling were made consistent when a predominant preference was found in the original book2 otherwise they were not changed4 ,simple typographical errors were corrected2 unbalanced quotation marks were remedied when the change was obvious1 and otherwise left unbalanced4 ,illustrations in this e,book have been positioned between paragraphs and outside quotations4 ,the index was not checked for proper alphabetization or correct page references4