,transcriber's ,note3 ,minor typographical errors and inconsistencies have been corrected4 ,some words had inconsistent hyphenation throughout the book2 these have been made consistent4 ,in the mathematical and chemical expressions1 the caret character represents to the power of1 e4g4 e#b means e-squared4 ,curly braces are used to represent underscores1 e4g4 n#a means n with a subscript of #a4 ,equal signs are used to represent bold words1 and underscores are used to represent italics4 ,on page #aeb ,na,c,o#bc has been corrected to ,na#b;,,co#c4 ,on page #bab1 the variable n has been replaced with the correctly subscripted forms n#a and n#b4 ,the index entry for ,hemlock bark had no page number in the original text1 so the correct page number1 #cd1 has been supplied4 ,ions are shown as ,fe1 instead of using superscripts4 ,there is some inconsistency in the notation used in the original text for chemical formulae such as ,na#b;,cr#b,o#g7b;,h#b,o74 ,these have been regularized to use the modern mid-dot1 for example1 ,na#b;,cr#b,o#gb;,h#b,o4 ,greek letters in the original have been represented in this version by the name of the letter enclosed in square brackets1 e4g4 alpha4 ,,animal ,,proteins ,,by ,,hugh ,,garner ,,bennett1 ,m4,sc4 7,,leeds7 ,,member ,,of ,,the ,,society ,,of ,,leather ,,trades' ,,chemists2 ,,formerly ,,assistant ,,lecturer ,,and ,,demonstrator ,,at ,,the ,,leather ,,industries ,,department ,,of ,,the ,,university ,,of ,,leeds ,,author ,,of ,,the ,,manufacture ,,of ,,leather ,,london ,,bailli,,re1 ,,tindall ,,and ,,cox #h1 ,,henrietta ,,street1 ,,covent ,,garden #aiba 7,all rights reserved7 ,,general ,,preface ,the rapid development of ,applied ,chemistry in recent years has brought about a revolution in all branches of technology4 ,this growth has been accelerated during the war1 and the ,british ,empire has now an opportunity of increasing its industrial output by the application of this knowledge to the raw materials available in the different parts of the world4 ,the subject in this series of handbooks will be treated from the chemical rather than the engineering standpoint4 ,the industrial aspect will also be more prominent than that of the laboratory4 ,each volume will be complete in itself1 and will give a general survey of the industry1 showing how chemical principles have been applied and have affected manufacture4 ,the influence of new inventions on the development of the industry will be shown1 as also the effect of industrial requirements in stimulating invention4 ,historical notes will be a feature in dealing with the different branches of the subject1 but they will be kept within moderate limits4 ,present tendencies and possible future developments will have attention1 and some space will be devoted to a comparison of industrial methods and progress in the chief producing countries4 ,there will be a general bibliography1 and also a select bibliography to follow each section4 ,statistical information will only be introduced in so far as it serves to illustrate the line of argument4 ,each book will be divided into sections instead of chapters1 and the sections will deal with separate branches of the subject in the manner of a special article or monograph4 ,an attempt will1 in fact1 be made to get away from the orthodox textbook manner1 not only to make the treatment original1 but also to appeal to the very large class of readers already possessing good textbooks1 of which there are quite sufficient4 ,the books should also be found useful by men of affairs having no special technical knowledge1 but who may require from time to time to refer to technical matters in a book of moderate compass1 with references to the large standard works for fuller details on special points if required4 ,to the advanced student the books should be especially valuable4 ,his mind is often crammed with the hard facts and details of his subject which crowd out the power of realizing the industry as a whole4 ,these books are intended to remedy such a state of affairs4 ,while recapitulating the essential basic facts1 they will aim at presenting the reality of the living industry4 ,it has long been a drawback of our technical education that the college graduate1 on commencing his industrial career1 is positively handicapped by his academic knowledge because of his lack of information on current industrial conditions4 ,a book giving a comprehensive survey of the industry can be of very material assistance to the student as an adjunct to his ordinary textbooks1 and this is one of the chief objects of the present series4 ,those actually engaged in the industry who have specialized in rather narrow limits will probably find these books more readable than the larger textbooks when they wish to refresh their memories in regard to branches of the subject with which they are not immediately concerned4 ,the volume will also serve as a guide to the standard literature of the subject1 and prove of value to the consultant1 so that1 having obtained a comprehensive view of the whole industry1 he can go at once to the proper authorities for more elaborate information on special points1 and thus save a couple of days spent in hunting through the libraries of scientific societies4 ,as far as this country is concerned1 it is believed that the general scheme of this series of handbooks is unique1 and it is confidently hoped that it will supply mental munitions for the coming industrial war4 ,i have been fortunate in securing writers for the different volumes who are specially connected with the several departments of ,industrial ,chemistry1 and trust that the whole series will contribute to the further development of applied chemistry throughout the ,empire4 ,,samuel ,,rideal4 ,,author',s ,,preface ,it has been the author's chief concern that this volume should fulfil its own part in the programme set forth in ,dr4 ,rideal's ,general ,preface4 ,the leather1 glue1 and kindred trades have been for many years recognized as chemical industries1 but the great development of colloid chemistry in the last few years has given these trades a more definite status as such1 and they can now be placed in the category of applied physical chemistry4 ,the time is probably not far distant when some knowledge of pure physical chemistry will be a first essential to students1 chemists1 chemical engineers1 and to all engaged in these industries in supervision1 administration1 or control4 ,it is hoped that this volume will stimulate the study of these industries from that standpoint4 ,as the author has previously written upon one of the industries involved herein 7,the ,manufacture of ,leather3 ,constable ,co471 he has1 rather inevitably1 found it difficult to avoid altogether his own phraseology4 ,the changes of a decade1 however1 together with the wider field and newer view-point1 have made possible a radical difference of treatment4 ,the author desires to acknowledge the help he has received from the many books1 essays1 and researches which are mentioned in the references at the end of each section1 especially to ,procter's ,principles of ,leather ,manufacture1 and also to thank ,dr4 ,rideal for many useful suggestions4 ,the author would like also to acknowledge here his indebtedness 7as well as that of the trade generally7 to the work of ,dr4 ,j4 ,gordon ,parker1 who1 through his researches1 lectures1 and teaching work1 has done more than any other man to disseminate a knowledge of practical methods of tanning4 ,the author's thanks are also due to his brother1 ,mr4 ,w4 ,gordon ,bennett1 ,m4,sc41 ,a4,i4,c41 ,m4,c41 for assistance in proof revision1 and to his father1 ,rev4 ,john ,bennett1 for some literary criticism4 ,h4 ,,garner ,,bennett4 ,,beverly1 ,june1 #aiba4 ,,contents ,,general ,,preface ,,author',s ,,preface ,,contents ,,introduction 99 99 99 99 99 ,,part ,i4 ,,hides ,,for ,,heavy ,,leathers4 ,,section #a4 ,,the ,,raw ,,material ,,of ,,heavy ,,leathers #b4 ,,the ,,preparation ,,of ,,pelt #c4 ,,vegetable ,,tannage #d4 ,,finishing ,,process #e4 ,,sole ,,leather #f4 ,,belting ,,leather #g4 ,,harness ,,leather #h4 ,,upper ,,leathers #i4 ,,bag ,,leather #aj4 ,,picking ,,band ,,butts 99 99 99 99 99 ,,part ,,ii4 ,,skins ,,for ,,light ,,leathers4 #a4 ,,principles ,,and ,,general ,,methods ,,of ,,light ,,leather ,,manufacture #b4 ,,goatskins #c4 ,,sealskins #d4 ,,sheepskins #e4 ,,calfskins #f4 ,,japanned ,,and ,,enamelled ,,leathers 99 99 99 99 99 ,,part ,,iii4 ,,chrome ,,leathers4 #a4 ,,the ,,nature ,,of ,,chrome ,,leathers #b4 ,,general ,,methods ,,of ,,chrome ,,leather ,,manufacture #c4 ,,chrome ,,calf #d4 ,,chrome ,,goat ,,and ,,sheep #e4 ,,heavy ,,chrome ,,leathers 99 99 99 99 99 ,,part ,,iv4 ,,miscellaneous ,,tannages4 #a4 ,,alum ,,tannages #b4 ,,fat ,,tannages #c4 ,,oil ,,tannages #d4 ,,formaldehyde ,,tannage #e4 ,,synthetic ,,tanning ,,materials #f4 ,,combination ,,tannages #g4 ,,the ,,evolution ,,of ,,the ,,leather ,,industry 99 99 99 99 99 ,,part ,v4 ,,gelatine ,,and ,,glue4 #a4 ,,properties ,,of ,,gelatine ,,and ,,glue #b4 ,,raw ,,materials ,,and ,,preliminary ,,treatment #c4 ,,extraction #d4 ,,clarification ,,and ,,decolorization #e4 ,,bleaching #f4 ,,evaporation #g4 ,,cooling ,,and ,,drying #h4 ,,uses ,,of ,,gelatine ,,and ,,glue #i4 ,,the ,,evolution ,,of ,,the ,,gelatine ,,and ,,glue ,,industry 99 99 99 99 99 ,,part ,,vi4 ,,miscellaneous ,,proteins ,,and ,,bye-,,products4 #a4 ,,bye-,,products ,,of ,,the ,,leather ,,trades #b4 ,,bye-,,products ,,of ,,the ,,gelatine ,,and ,,glue ,,trades #c4 ,,food ,,proteins #d4 ,,miscellaneous ,,animal ,,proteins ,,index ,,animal ,,proteins ,,introduction ,proteins are organic compounds of natural origin1 being found in plants and in animals1 though much more plentifully in the latter4 ,they are compounds of great complexity of composition1 and of very high molecular weight4 ,the constitution of none of them is fully understood1 but although there are a great number of different individual proteids1 they present typical resemblances and divergences which serve to differentiate them from other groups of organic bodies1 and also from one another4 ,proteins resemble one another in both proximate and ultimate analysis4 ,they contain the usual elements in organic compounds1 but in proportions which do not vary over very wide limits4 ,this range of variation is given approximately below3-- ,element4 ,per cent4 ,carbon #di to #ee ,hydrogen #f4d to #g4c ,oxygen #ag to #bf ,nitrogen #ac to #ai ,sulphur #j4c to #c4j ,the most characteristic feature of the protein group is the amount of nitrogen usually present4 ,this is generally nearer the higher limit1 seldom falling below #ae per cent4 ,this range for the nitrogen content is determined largely by the nature of constituent groups which go to form the proteid molecule4 ,roughly speaking1 proteins consist of chains of amido-acids and acid amides with smaller proportions of aromatic groups1 carbohydrate groups and thio compounds attached4 ,in these chains an acid radical may combine with the amido group of another amido acid1 the acid group of the latter combining with an amido group of another amido acid1 and so on4 ,hydrogen may be substituted in these chains by alkyl or aromatic groups4 ,there is obviously infinite possibility of variation in constitution for compounds of this character1 the general nature of which varies very little4 ,practically all of the proteins are found in the colloid state1 and this makes them very difficult to purify and renders the ultimate analysis in many cases doubtful4 ,it is1 for example1 often difficult to ascertain their moisture content1 for many are easily hydrolyzed with water only1 and many part easily with the elements of water1 whilst on the other hand many are lyophile colloids and practically cannot be dehydrated or dried4 ,a few1 such as gelatin and some albumins1 have been crystallized4 ,the constituent groups have been investigated chiefly by hydrolytic methods4 ,the chains of amido acids are split up during hydrolysis1 and individual amido acids may thus be separated4 ,the hydrolysis may be assisted either by acids1 alkalies or ferments1 but follows a different course according to the nature of the assistant4 ,under approximately constant conditions of hydrolysis1 the products obtained are in approximately constant proportions1 and this fact has been utilized by ,van ,slyke in devising a method of proximate analysis4 ,it is not possible in this volume to enter deeply into the constitution of the different proteids4 ,reference must be made to works on pure chemistry1 especially to those on advanced organic chemistry4 ,it will be interesting1 however1 to mention some of the amido acids and groups commonly occurring in proteids4 ,these comprise ornithine 7#a3d diamido valeric acid71 lysine 7#a3e diamido-caproic acid71 arginine 7#a amido1 #d guanidine valeric acid71 histidine1 glycine 7amidoacetic acid71 alanine 7amido propionic acid71 amido-valeric acid 7amido-iso-caproic acid71 liacine1 pyrollidine carboxylic acid1 aspartic acid1 glutamic acid 7amido-glutaric acid71 phenyl-alanine1 serine 7hydroxy-amido propionic acid71 purine derivatives 7e4g4 guanine71 indol derivatives 7e4g4 tryptophane and skatol acetic acid71 cystine 7a thioserine anhydride71 glucosamine1 and urea4 ,there are a few general reactions which are typical of all proteins1 and which can usually be traced to definite groupings in the molecule4 ,amongst these is the biuret reaction3 a pink colour obtained by adding a trace of copper sulphate and an excess of caustic soda4 ,this is caused by the biuret1 ,,nh7,,conh#b7b radical or by similar diacidamide groups1 e4g4 malonamide1 oxamide1 glycine amide4 ,another general reaction is with ,millon's reagent1 a solution of mercuric nitrate containing nitrous fumes4 ,on warming the proteid with this reagent1 a curdy pink precipitate or a red colour is obtained4 ,this reaction is caused by the tyrosine group 7p4 oxy alpha amido phenyl-propionic acid74 ,another general reaction is to boil the protein with #a3b nitric acid for some days4 ,a yellow flocculent precipitate of xanthoproteic acid is obtained1 and this dissolves in ammonia and caustic alkalies with a brown or orange-red colour4 ,another characteristic of proteins is that on dry distillation they yield mixtures of pyridine ,c#e;,h#e,n1 pyrrol ,c#d;,h#e,n1 and their derivatives4 ,on the subdivision1 classification and nomenclature of the proteins much ink has been spilled1 and it is impossible in this volume to go into the various systems which have been suggested4 ,it should be noted1 however1 that some writers habitually use the terms proteid or albuminoid as synonyms for protein4 ,the classification of proteins adopted in this work is used because it is the most suitable for a volume on industrial chemistry and has the additional merits that it is simple and is already used in several standard works on industrial chemistry4 ,it is based upon the behaviour of the proteins towards water1 a matter of obvious moment in manufacturing processes4 ,on this basis proteins may be divided into albumins1 keratins and gelatins4 ,cold water dissolves the albumins1 does not affect the keratins1 and only swells the gelatins4 ,the behaviour in hot water confirms and elaborates the classification4 ,when heated in water1 the albumins coagulate at temperatures of #gj-ge ,c41 the gelatins 7if swollen7 dissolve readily1 whilst the keratins only dissolve at temperatures above #ajj ,c4 ,albumins and keratins may be distinguished also from gelatins by adding acetic acid and potassium ferrocyanide to their aqueous solutions4 ,albumins and keratins give a precipitate1 gelatins do not4 ,another distinguishing reaction is to boil with alcohol1 wash with ether1 and heat with hydrochloric acid 7,s4,g4 #a4b74 ,albumins give a violet colour1 keratins and gelatins do not4 ,albumins may be first discussed4 ,they are typified by the casein of milk and by white of egg4 ,their solutions in water are faintly alkaline1 optically active1 and lvorotatory4 ,they are coagulated by heat and also by mineral acids1 alcohol1 and by many poisons4 ,the temperature of coagulation 7usually about #gb ,c47 is affected by mineral salts1 the effect being in lyotrope order 7see ,part ,v41 ,section ,i474 ,the coagulated albumin behaves in most respects like a keratin4 ,some of the albumins 7globulins7 are1 strictly speaking1 not soluble in cold water1 but readily dissolve in weak solutions of salt4 ,the albumins are coagulated from these solutions1 as usual1 when heated4 ,into this special class fall myosin 7of the muscles71 fibrinogen 7of the blood7 and vitellin 7of egg yolk74 ,by a gentle or limited hydrolysis of the albumins with dilute acids in the cold1 a group of compounds called albuminates are obtained4 ,they dissolve in either acids or alkalies1 and are precipitated by exact neutralization4 ,they may also be salted out by adding sodium chloride or magnesium sulphate4 ,they are not coagulated by heat4 ,after further hydrolysis with either acids1 alkalies or ferments1 very soluble compounds are obtained called albumin peptones or albumoses4 ,these are soluble in alkalies1 acids and water1 and are readily hydrolyzed further into amido acids and acid amides4 ,they are very similar to the peptones obtained from keratins and gelatins4 ,they are not coagulated by heat4 ,keratins are typified by the hair of animals4 ,they soften somewhat in cold water and even more in hot water1 but are not dissolved until digested for some time at temperatures exceeding #ajj ,c4 ,with some keratins1 however1 the cystine group is to some extent easily split off by warm water1 and on boiling with water hydrogen sulphide is evolved4 ,the sulphur content of keratins is often greater than the average for proteids4 ,all keratins are dissolved with great readiness by solutions containing sulphydrates and hydrates1 e4g4 a solution of sodium sulphide4 ,in solutions of the hydrates of the alkali and alkaline earth metals1 keratins behave differently4 ,some dissolve with great ease1 some with difficulty1 some only on heating and some not even if digested with hot caustic soda4 ,they are dissolved 7with hydrolysis7 by heating with mineral acids1 yielding peptones and eventually amido acids1 acid amides1 etc4 ,many keratins have a comparatively low content of nitrogen4 ,gelatins are very difficult to distinguish from one another1 their behaviour being closely similar to reagents4 ,they are also very readily hydrolyzed even with water1 and the products of hydrolysis are even more similar4 ,the gelatins are known together1 commercially1 under the general name of gelatine4 ,gelatins of different origin1 however1 have undoubtedly a different composition1 the nitrogen content being variable4 ,if the gelatins are not bleached whilst they are being manufactured into commercial gelatine1 they are called glue4 ,gelatine is colourless1 transparent1 devoid of taste and smell4 ,it is usually brittle4 ,its ,s4,g4 is about #a4db1 and it melts at #adj ,c4 and decomposes4 ,it is insoluble in organic solvents4 ,when swelling in cold water it may absorb up to #ab times its own weight of water4 ,the swollen product is called a jelly4 ,jellies easily melt on heating and a colloidal solution of gelatine is obtained4 ,this sets again to a jelly on cooling1 even if only #a per cent4 gelatin 7or less7 be present4 ,the solution is optically active and lvorotatory1 but with very variable specific rotation4 ,some observers have thought that the different gelatins have different specific rotations and may so be distinguished4 ,gelatins are precipitated from solutions by many reagents1 such as alcohol1 formalin1 quinone1 metaphosphoric acid1 tannins1 and many salt solutions1 e4g4 those of aluminium1 chromium and iron1 and of mercuric chloride1 zinc sulphate1 ammonium sulphate1 potassium carbonate1 acidified brine4 ,many of these precipitations have analogies in leather manufacture 7see ,parts ,i4 to ,,iv474 ,the gelatin peptones or gelatoses are formed by hydrolysis with acids1 alkalies1 ferment or even by digestion with hot water only4 ,a more detailed description of the properties of gelatine is given in ,part ,v41 ,section ,i4 ,gelatine is sometimes called glutin and ossein4 ,animals are much the most important source of proteins1 especially of those which are of importance in industrial chemistry4 ,proteins occur in nearly every part of all animals1 and the protoplasm of the living cell is itself a protein4 ,the keratins include the horny tissues of animals3 the epidermis proper1 the hair1 horns1 hoofs1 nails1 claws1 the sebaceous and sudoriferous glands and ducts1 and also the elastic fibres4 ,the gelatins are obtained from the collagen of the skin fibres1 the bones1 tendons1 ligaments1 cartilages1 etc4 ,fish bladders yield a strong gelatin4 ,the albumins are obtained from the ova1 blood1 lymph1 muscles and other internal organs of animals4 ,the classification of proteins herein adopted fits in well with the scope and purpose of this volume4 ,the keratins are of little importance in chemical industry1 but are of immense importance in mechanical industry1 e4g4 the woollen trade1 which is based upon the keratin comprised by sheep wool4 ,the collagen of the hide and skin fibres is of vast importance to chemical industry1 and is the basis of the extensive leather trades discussed in ,parts ,i4 to ,,iv4 ,the waste pieces of these trades1 together with bones1 form the raw material of the manufacture of gelatin and glue1 as discussed in ,part ,v4 ,the proteids of animals' flesh and blood1 milk and eggs form the source of the food proteins discussed in ,part ,,vi4 ,the food proteins embrace chiefly albumins1 but gelatins and even keratins are involved to some extent4 ,,part ,i4--,,hides ,,for ,,heavy ,,leathers ,section ,i4--,,the ,,raw ,,material ,,of ,,heavy ,,leathers ,the term hide possesses several shades of meaning4 ,in its widest sense it applies to the external covering of all animals1 and is sometimes used derogatively for human skin4 ,in this wide sense1 it is almost synonymous with the term skin4 ,the term hide1 however1 has a narrower meaning1 in which it applies only to the outer covering of the larger animals1 and in this sense is used rather in contrast with the term skin4 ,thus we speak of horse hides1 cow hides1 camel hides1 and buffalo hides4 ,it is used in this sense in the title of ,part ,i4 of this volume4 ,as such hides are from large animals1 the leather which is manufactured therefrom is thick and in large pieces1 and is therefore commercially designated as heavy leather4 ,from the standpoint of chemical industry hides are amongst the most important of animal proteins1 and their transformation into leather for boots1 shoes1 belting1 straps1 harness1 and bags comprises the heavy leather trade1 which is one of the largest and most vital industries of the country4 ,the heavy leather trade predominates over other branches of leather manufacture1 not only because of the comparatively large weight and value of the material handled1 but also because the resulting products have a more essential utility4 ,there is also a still narrower use of the term hide1 in which it applies only to the domesticated cattle--the ox1 heifer1 bull and cow--which use arises from the fact that the hides of these are both the largest and most valuable portion of the raw material of the heavy leather industries4 ,in a very narrow sense the term is also sometimes applied only to ox hides1 which for most heavy leathers are the ideal raw material4 ,the ,home ,supply of hides forms a large important proportion of the total raw material4 ,its importance1 moreover1 is rapidly increasing1 for the excellence and abundance of the home supply determines the extent to which it is necessary for the industry to purchase its raw material abroad4 ,the position of our national finances makes this an increasingly serious matter1 for hides are comparatively a very expensive material4 ,the quality of our home supply of hides is very valuable1 being determined by the conditions of the animal's life1 its precise breed1 and by other factors such as age and sex4 ,the best hides are usually obtained from animals which have been most exposed to extremes of wind and cold1 as such conditions tend naturally to develop a thicker and more compact covering4 ,broadly speaking1 these include the hides from cattle of the northern and hilly districts4 ,the age of the animal when killed is also a dominating factor4 ,calf skins are very soft1 fine grained and compact1 the state of rapid growth favouring the existence of much interfibrillar substance4 ,the youngest animals supply suitable raw material for various light leathers 7see ,part ,,ii41 ,section ,v471 and are also very suitable for chrome work 7see ,part ,,iii41 ,section ,,iii474 ,bull and cow hides1 on the other hand1 are from animals whose growth is complete1 and show in consequence a lack of interfibrillar substance1 coarse fibres and a rough and often wrinkled grain4 ,the resulting leather tends consequently to be spongy1 thin1 empty and non-waterproof4 ,intermediate between these extremes are the hides of the ox and heifer1 large1 yet of good texture1 and well supplied with interfibrillar substance4 ,these hides are much the best for sole leather1 a firm1 smooth-grained and well-filled leather being needed4 ,the term kip is often applied to small hides and to hides from large calves4 ,in the trade1 however1 kip is sometimes used also for larger hides1 as a verbal enhancement of value2 just as a man with a few old fowls is said to keep chickens4 ,cow hides tend to be spready1 i4e4 to have a large area per unit weight1 and are therefore more suitable for dressing leather4 ,bull hides are thicker in the neck and belly1 and thinner in the back1 which characteristics reduce their commercial value4 ,market hides are sold by weight1 and are therefore classified chiefly by their weight1 which is marked on near the tail by a system of knife-cuts4 ,the animals are flayed after cutting the hide down the belly and on the inside of the legs4 ,of the various breeds1 ,shorthorns yield a large supply of useful hides4 ,the name1 however1 covers a variety of similar breeds1 and the hides therefrom are rather variable in texture and quality4 ,they tend to be greasy owing to high feeding4 ,the ,herefords1 obtained from ,midland markets1 are generally excellent hides for sole and harness leathers4 ,they give a good yield of butt pelt1 a stout and smooth shoulder1 and are not often greasy4 ,devons yield a good-textured and well-grown hide1 but are often badly warbled4 ,the ,sussex cross breeds yield somewhat larger hides4 ,suffolk ,red ,polls1 common in ,east ,anglia1 yield a good butt1 and the cow hides make good dressing leather4 ,channel ,island cattle yield very thin hides1 but with a fine undamaged grain4 ,scotch hides possess deservedly the very highest reputation4 ,the climatic conditions favour the production of a hardy race of cattle with thick well-grown hides1 yielding a large proportion of butt4 ,these hides are amongst the best obtainable for heavy leather1 and particularly for sole leather4 ,highlanders1 ,aberdeen ,angus1 ,galloways are typical breeds1 with short neck1 legs and straight backs4 ,cross breeds are also excellent 7e4g4 ,scotch ,shorthorns74 ,the natural value of these hides is further enhanced by the usual care in flaying4 ,ayrshires yield good milch cows and consequently yield often a more spready hide4 ,the ,welsh breeds for rather similar reasons also yield valuable hides4 ,the ,irish ,kerrys are small but stout1 and yield hides suitable for light sole leather4 ,irish cross-breeds1 ,shorthorns1 have a rather bad reputation1 and are often ill flayed4 ,all the varieties of the home supply are subject to various defects1 which influence seriously their commercial value4 ,one of these defects is warble holes or marks1 caused by the ,ox ,warble fly 7,hypoderma bovis74 ,this is a two-winged fly about half an inch long4 ,the larva of this fly1 the ,warble maggot1 lives and thrives in the skin of cattle1 and causes a sore and swelling4 ,the life-history of this insect is still in dispute1 but it is generally thought that the eggs are laid in the hair on the animal's back1 and the young larva eats its way through the hide until just below the dermis1 and there feeds until mature4 ,it then creeps out of this warble hole1 falls to the ground1 pupates for a month1 after which the imago or perfect insect emerges from the chrysalis4 ,hides which have been thus infected have1 in consequence1 often quite a number of holes through the most valuable part of the hide1 thereby rendering it unsuitable for many kinds of leather4 ,even old warbles which have more or less healed up are a weakness1 and warbled hides and leather fetch a decidedly lower price than undamaged4 ,another of these defects is bad flaying4 ,clearly the hide should be as little cut as possible1 but many of our market hides are abominably gashed and often cut right through4 ,this1 of course1 often reduces seriously the commercial value of the hide4 ,careless treatment after flaying also results in another common defect1 viz4 taint4 ,as the term implies1 the hide is partly putrefied1 sometimes only in patches1 but sometimes also so extensively as to render the hide quite rotten and quite incapable of being made into leather at all4 ,hides are of course putrescible1 and dirt1 blood1 dung and warm weather encourage rapid putrefaction4 ,as market hides are usually uncured1 this defect is constantly appearing1 and is a cause of considerable loss4 ,other defects are due to injuries to the animal before it is killed1 e4g4 brands1 scratches due to hedges and barbed wire1 old scabs1 goad and tar marks4 ,all these reduce the value of the hide4 ,all the defects in hides involve a very serious loss to the community1 and the time is rapidly approaching when their continuance is insufferable4 ,the loss is not usually very considerable to any individual1 though very large in the aggregate4 ,the hide is a minor part of the beast's value1 and a somewhat damaged hide does not involve a very serious loss to the farmer4 ,some with typical stupidity regard a few warbles as the sign of a healthy beast4 ,these defects involve practically no loss to the hide merchant1 tanner or currier1 as each pays less for damaged material4 ,the loss falls upon the community1 and the time is ripe for the community to insist upon the elimination of these defects4 ,the national resources will be for some years strained to their uttermost1 and preventable damage must be considered intolerable4 ,the principal defects in hides are preventable1 and ought to be prevented4 ,the warble fly could1 by a united effort1 be rendered before long practically extinct1 a task which is facilitated by the fact that it is not migrative4 ,bad flaying and careless treatment of hides resulting in putrefaction are still more easily remedied4 ,the communal slaughter-house is long overdue from the standpoint of public health1 and would1 under conditions of cleanliness and skilled workmanship and oversight1 also solve the problem of ill-flayed and tainted hides4 ,the question of the raw material is of first importance to the leather trades4 ,there was1 before the commencement of the ,european ,war1 a steadily increasing scarcity of hides1 causing a constant increase in their price4 ,this was due partly to the fact that cattle were increasing at a less rate than the population1 partly to the growth of civilization1 and more extensive use of leather in proportion to the world's population1 and partly to the constant discovery of new uses for leather1 e4g4 for motor cars1 aeronautics1 etc4 ,the question of raw material was under these conditions serious enough4 ,the terrific slaughter1 necessary at the same time to provide the belligerents with food and the army with leather1 is bound to result in a serious crisis for the leather industries2 and in conjunction with the country's financial condition1 will make it absolutely necessary that all care should be taken with the raw material of one of our most important industries4 ,the farmer who pays no heed to the warble fly1 the man who gashes the hide in flaying and who allows the hide to putrefy1 are equally criminal with the man who throws bread crusts into the dustbin4 ,it is impossible to foresee1 as yet1 anything in the nature of a satisfactory solution to the problem of raw material1 especially in respect to heavy leather production1 for the food question will rank first in the popular mind1 and the earlier slaughter enjoined for the more economical production of meat will scarcely tend to increase the proportion of heavy hides4 ,the ,foreign ,supply of hides is also of great importance and value4 ,in the case of imported hides precautions to prevent putrefaction are essential1 and some method of curing is always used4 ,salting the hides is one of the most satisfactory methods for temporary preservation4 ,the action of salt is hygroscopic1 and mildly antiseptic4 ,moisture is withdrawn from the hides1 which are then under conditions no longer favouring the growth of bacteria4 ,well-salted hides will keep for years1 especially if quite clean4 ,a light salting is also useful for a short preservation1 and is becoming common in hide markets and tanneries during the summer and autumn months4 ,salting is a method used extensively in the ,united ,states4 ,the packer hides of the stockyards are carefully and systematically salted with about #be per cent4 of salt and stored in cool cellars4 ,the hides are so piled up in heaps1 that brine easily drains away4 ,the great disadvantage of salting is the so-called salt stains4 ,these stains have been ascribed to the iron in the salt1 to the iron in the blood1 to calcium sulphate in the salt1 and also to chromogenic bacteria1 whose development is favoured by salting4 ,the relative importance of these factors is not yet satisfactorily determined1 but cleanliness and pure salt tend to eliminate the trouble4 ,drying the hides is a less satisfactory cure4 ,the principle is similar1 viz4 removal of moisture4 ,dried hides are1 however1 much drier than salted1 and are quite hard and horny1 hence the name flint hides4 ,the hides also lose much weight1 a considerable advantage in reducing freight4 ,tropical hides are often flint-dry1 and where preservatives are expensive or unprocurable1 it is often the only practicable method of cure4 ,nevertheless1 the method has many serious disadvantages1 and is difficult to execute4 ,if dried too slowly the hides putrefy partially2 if too quickly they dry on the outside1 and the interior is left to putrefy4 ,the fact that hides are of uneven thickness1 and the climate often hot1 increases the difficulty1 and often results in partial destruction of the fibrous structure of the hide4 ,when dried1 moreover1 the hides are still subject to the attacks of insect larv1 for the prevention of which the usual sprinkling of naphthalene or arsenic is only an imperfect remedy4 ,this method of cure is also a nuisance to the tanner1 who has to employ labour1 pits and time in attempting to restore the hides to their original condition1 and often loses up to ten per cent4 of the goods in so doing4 ,dried hides are also subject to the presence of anthrax4 ,dry ,salting the hides is an excellent method of curing4 ,as the name implies1 it combines methods of drying and salting which are used alternatively4 ,the method is used extensively in ,south ,america4 ,a modified form of it is also used for preserving the ,e4,i4 kips1 which are cured1 however1 not with common salt1 but with earth containing up to #gj per cent4 of sodium sulphate4 ,dry-salted hides are largely free from the defects of dried hides1 but of course are more trouble to the tanner in the process of soaking 7see ,section ,,ii47 than the wet-salted goods4 ,freezing the hides is now a commercial process4 ,on the whole the process is satisfactory1 but the expansion of water after freezing may tend to damage the hide fibres4 ,sterilizing the hides has been frequently suggested1 but no method has yet been advocated which does not interfere either with the tanning processes or with the quality of the finished leather4 ,hides from the ,european ,continent1 usually wet salted and well flayed1 exhibit much the same variable quality as the home supply1 those from highland districts tending to be thick1 yet even1 well grown1 tight textured and smooth grained1 whilst those from lowland regions are less satisfactory4 ,thus hides from the ,swiss ,alps and ,scandinavia have ranked high1 whilst the spready ,dutch cows are typical of a lowland hide4 ,in the hides which once came from ,germany the same features appear4 ,bavarian highland hides had an excellent reputation1 whilst those from ,berlin1 ,cologne1 etc41 tended to be long in shank and not well grown4 ,french hides are often ill flayed1 and ,spanish and ,portuguese are often subject to scratches4 ,italian hides have a very good name1 being small but stout in butt4 ,the ,american supply is important4 ,south ,america yields an excellent class of hide1 salted or dry-salted4 ,they are from an excellent breed of animals1 slaughtered and flayed with every care1 and efficiently cured4 ,a most serious defect in this class of hide is the brand1 which is both deep and large and in the most valuable part of the hide4 ,one side1 however1 is usually unbranded1 so that each hide yields one good bend4 ,these hides1 e4g4 ,frigorifics1 have recently been much more extensively tanned in ,britain because of the shortage in the home supply of market hides caused by the ,european ,war4 ,south ,america also yields good horse hides4 ,north ,american hides are usually wet-salted 7e4g4 packer hides74 ,they are usually good4 ,central ,america yields mostly dried hides exhibiting usual defects4 ,the ,asiatic supply comprises the frozen ,china hides1 which are clean but small1 with flaying of uncertain quality4 ,there are the buffalo hides from ,asia and ,east ,europe1 which are suitable for cheap and sole and strap leather1 and also the dry-salted ,e4,i4 kips1 obtained from a small breed of ,indian cattle1 and extensively made into upper leather4 ,the ,asiatic humped cattle also provide a limited supply4 ,the ,african supply is of increasing importance4 ,the tropical parts yield dried hides of uncertain quality1 but the more temperate parts of ,south ,africa yield a growing supply of good quality4 ,,references4 ,the ,manufacture of ,leather 7,bennett71 pp4 #bg-cg4 ,principles of ,leather ,manufacture 7,procter71 pp4 #cc-ef4 ,the ,ox ,warble or ,bot ,fly 7,e4 ,ormerod74 ,the ,making of ,leather 7,procter71 pp4 #b-bb4 ,section ,,ii4--,,the ,,preparation ,,of ,,pelt ,before hides are tanned it is necessary for them to pass through a series of preparatory processes4 ,the object of these processes is to obtain from the hide the true hide substance in a pure and suitable condition4 ,each class of leather has its own appropriate processes1 the adjustment of which largely determines the quality of the finished article4 ,so prominent is the influence of these preparatory methods that the paradox good leather is made before tanning is in trade circles almost a platitude4 ,these processes1 sometimes lumped together under the general name of ,wetwork1 comprise soaking1 liming1 beam house work and deliming4 ,these will be discussed in turn4 ,the term applied to the hide after these processes1 but before tannage1 is pelt4 ,soaking has for its object the cleansing and softening of the hides1 chiefly by means of water4 ,it aims at the removal of dirt1 blood1 dung1 and curing materials by washing4 ,the process is usually simple1 and is much the same for all classes of leather4 ,the ideal to be aimed at is to restore the hide to its condition when it left the animal's back4 ,cleanliness in leather manufacture is as essential at the commencement as anywhere1 for the hide is in its most putrescible state4 ,the soluble proteids 7blood1 lymph1 part of dung1 etc47 which always adhere to hides encourage the rapid growth of putrefactive bacteria1 and cannot be washed away too soon4 ,dung is often difficult to remove1 being caked on the butt end amongst the hair4 ,soaking only softens it1 and mechanical removal is usually necessary4 ,if such substances are not removed1 they go forward with the goods into the lime liquors1 causing stains1 loss of hide substance1 and counteracting plumping4 ,the detailed method and time of soaking are determined mainly by the nature of the cure4 ,one of the purposes of the soak liquors is to dissolve the salt used in curing hides and to rehydrate the hide and make it again soft and pliable4 ,as a #aj-per-cent4 salt solution exerts a solvent effect on hide substance1 it is necessary soon to change the first soak liquor of salted goods4 ,market hides1 which are uncured1 require the least soaking1 the cleansing effect being most needed4 ,the hides are inserted into pits 7water dykes7 of water for a few hours1 and the water changed once or twice4 ,the soaking should not be prolonged as the hides are so putrescible1 and where it is customary to leave the goods in a soak liquor overnight1 it is advantageous to add a little slaked lime to the water before inserting the goods4 ,this not only softens hard water1 but is mildly antiseptic and plumping1 and forms a suitable introduction to the liming proper4 ,each pit contains a pack of #cj-ej hides1 according to its capacity1 which varies in different tanneries from #ajjj to #bjjj gallons4 ,tainted goods1 which are indicated by a characteristic white colour on the flesh side and by loose hair1 need a preliminary washing either in a drum1 tumbler or in a paddle4 ,this ensures a rapid change of liquor and the removal of most of the putrefactive agencies4 ,bad cases may need the application of antiseptics1 such as immersion in #j4a per cent4 carbolic acid2 but if possible these should be avoided1 as they lengthen the time required for liming4 ,after drumming or paddling1 tainted goods should be placed directly into a lime liquor4 ,salted hides need very similar treatment to uncured hides1 but the soaking is longer1 because of the dehydration caused by salting4 ,hence they receive also a greater number of changes of water1 three or four usually1 but often more4 ,as much loose salt as possible should be shaken from the hides before insertion into any liquor4 ,the employment of drum or paddle before pit soaking is extremely useful to effect the rapid removal of superficial salt1 and is also useful after pit soaking to remove the last traces4 ,dried and dry-salted goods need a soaking still more prolonged1 up to one week if water alone be used4 ,with the assistance of caustic soda1 however1 the process can be shortened to about two days4 ,the first soak liquor should consist of a #j4a per cent4 solution of caustic soda1 and after the goods have been inserted twenty-four hours1 they will be materially improved by a few hours' drumming or paddling4 ,another caustic soda soak will complete the process4 ,sodium sulphide crystals may replace caustic soda1 but about three times the weight will be needed4 ,carbonate of soda and caustic lime also are a convenient commercial substitute for caustic soda4 ,for #aj lbs4 caustic soda1 use #cf lbs4 carbonate and #g lbs4 lime4 ,extra lime should be added in all cases when the water is hard4 ,acid liquors will also soften dried and dry-salted goods1 but such processes do not fit in so well with the subsequent liming4 ,the use of putrid soaks and stocks may be now considered out of date4 ,liming follows soaking1 and consists essentially in immersing the hides for #g-aj days in milk of lime4 ,the chief object in view is to loosen the hair and prepare for its mechanical removal4 ,liming takes place in pits1 the tops of which are level with the limeyard floor4 ,the lime is slaked completely and mixed well with water in the pit1 being particularly well plunged just before the insertion of a pack of goods4 ,saturated limewater is only a #j4ac-per-cent4 solution4 ,the goods are occasionally handled i4e4 hauled out of the pit and reinserted after plunging 7hauling and setting74 ,this is necessary to keep the liquor saturated with lime4 ,the hides are inserted one by one1 each being poked down to ensure its contact with the liquor4 ,the goods are invariably immersed first in a previously used lime liquor4 ,most tanneries now carry this out in a systematic way1 so as to ensure regularity in the process4 ,as the goods are large and heavy it is less laborious to carry out the whole process in one pit4 ,in this one-pit system the goods are inserted for 7say7 four days in an old used lime liquor1 with occasional handling2 this liquor is then run to the drain and a new liquor made up in the same pit1 into which the goods are inserted for 7say7 five days4 ,they are then hauled and sent to the unhairers4 ,each pack thus gets two liquors1 old and new4 ,a better method is the three-pit system4 ,in this case each pack receives three liquors and has 7say7 three days in each1 first an old lime1 then a medium lime1 and finally a new lime4 ,this system ensures a greater regularity of treatment1 and is deservedly the most popular method for liming hides for sole leather4 ,after being used once as a new lime1 a liquor then becomes a medium lime1 and after being thus used becomes the old lime which receives the green hides from the soaks4 ,the system involves the goods being shifted twice to another pit1 which is more laborious than reinsertion into the old pit1 but if the limeyard be arranged in sets or rounds of three pits1 the shift is usually only to the adjacent pit4 ,one special advantage of this system is that the top hides in one pit become the bottom hides in the next pit1 and vice vers4 ,rounds of more than three pits are sometimes used4 ,many factories have now adopted systems in which there is no handling at all4 ,the hides are suspended in lime liquors which are agitated by mechanical contrivances 7e4g4 ,tilston-,melbourne process71 or by jets of compressed air 7e4g4 ,forsare process74 ,the goods are soaked and limed mellow to fresh by changing the liquors by means of pumps1 air ejectors1 etc4 ,thus the hides need no labour from first being inserted until drawn for depilation4 ,in liming1 the whole of the epidermis as well as the hair is loosened1 and is subsequently removed in depilation4 ,the corium or true hide substance becomes much more swollen by imbibation of water1 and when taken out of the new lime is plumped to very firm jelly4 ,this plumping is a matter of prime importance to the tanner4 ,the coarser fibres are thereby split up into the finer constituent fibrils1 which fact assists very materially in obtaining a quick and complete tannage1 good weight1 and a firm leather4 ,during the liming1 the natural grease of the hide is saponified or emulsified1 which prepares for its removal in scudding4 ,liming is thus a complex process3 the hair is loosened1 the hide is plumped1 and the grease is killed4 ,all these results may be hastened by the use of other alkalies in addition1 and most heavy leather yards assist the liming by adding also sodium sulphide or caustic soda or both4 ,sodium sulphide is a powerful depilatant1 and will alone unhair hides easily in strong solutions even in a few hours4 ,as in solution it forms caustic soda by hydrolysis1 it possesses also the powerful plumping and saponifying powers characteristic of the latter4 ,the addition of arsenic sulphide 7,as#b,s#b7 7realgar7 to the lime when slaking causes the presence of calcium sulphydrate in the lime liquors thus made4 ,this is also a powerful depilatant1 but not much used for heavy leather4 ,the function of the lime in depilating is complex and has occasioned much discussion4 ,its main purpose1 however1 is that of a partial antiseptic4 ,when hides putrefy1 one of the first results is that the hair is loosened4 ,in ,america depilation by sweating is carried out commercially by such a mild putrefaction1 the lime liquor permits a similar fermentation at a slower rate1 and all tannery lime liquors are swarming with putrefactive bacteria4 ,liming is thus a safer method than sweating1 which may be easily carried too far4 ,various workers have isolated specific organisms--,wood a bacillus1 ,schmitz-,dumont a streptococcus--but it seems highly probable that the limeyard bacteria are just the common organisms of putrefaction sorted out or selected by the exact nature of the liquor and the method of working the limes4 ,many putrefactive bacteria are very adaptable and could easily accommodate themselves in this way4 ,it is known that the exact nature of the culture medium has a great influence on the rate of development of such organisms1 and which particular species thrive and obtain predominance in any limeyard will depend upon the amount and nature of the dissolved organic matter available as food1 and upon the exact alkalinity and the concentration of other apparently inert substances1 such as common salt and sodium1 calcium and arsenic salts4 ,hence no two lime liquors operate alike1 and approximate regularity is only assured by systematic method4 ,in handling and shifting1 the organisms are subjected to further selection1 and the most adaptable survive4 ,it is probable that different species may act symbiotically4 ,the depilating organisms of lime liquors are probably mostly anrobes1 but some may be anrobic by adaptation4 ,it is probable that robic ferments commence the depilation1 but this will be done before the goods are put into work1 or at any rate before they reach the limes4 ,more strictly1 it is the enzymes secreted by bacteria which are directly responsible for the hydrolytic work2 these enzymes are chiefly proteolytic 7proteid splitting71 but the lipolytic 7fat splitting7 enzymes have also a place4 ,the lime1 however1 not only limits and selects the course of the putrefaction1 but also affords more positive assistance4 ,lime plays its own hydrolytic part and assists the depilation by purely chemical action4 ,lime will unhair without the assistance of bacteria1 but its action is slow and forms a minor part of the operation in the average limeyard4 ,this action is due chiefly to its progressive formation of calcium sulphydrate from the cystine group of the softer keratins4 ,lime also plays an essential part in assisting the putrefactive fermentation4 ,it softens the keratins and thus assists the bacterial attack1 it hydrolyzes other proteids and provides the bacteria with food in solution1 the calcium ion increases the proteolytic action of certain enzymes1 and finally the apparently inert excess of undissolved lime has an accelerating effect on the bacterial activity4 ,in the average limeyard these various functions are inextricably mixed up1 and it is impossible to assign any definite proportion of the total depilatory effect to any of the factors at work4 ,lime alone will unhair1 bacteria alone will unhair1 and sulphides will also unhair without lime or bacteria1 but in the limeyard all three agencies are at work4 ,putrefactive fermentation1 however1 obtains a good start4 robic fermentation commences with the slaughter of the animal1 and the anrobic organisms soon commence their part1 and are at work in the hide house and soaks4 ,on entering the limes1 the purely chemical hydrolytic action of lime is added to that of the bacterial enzymes as well as the action of lime as bacterial assistant1 and the three continue to operate side by side4 ,each gives rise to the formation of calcium sulphydrate1 whose own special solvent effect is superadded4 ,if sulphydrates be deliberately added to the liquors there is yet another factor assisting4 ,speaking broadly1 the bacterial enzymes have their maximum activity in the old limes1 and the chemical action of sulphydrate formed from the keratin cystine is also at a maximum in these liquors4 ,the chemical action of added sulphide1 and the simple hydrolytic action of calcium hydrate have their maximum activity in the new limes4 ,most observers would agree that in practice the bacteria shoulder the greater part of the work4 ,from the limeyard is taken about the only waste bye-products of the tannery1 viz4 the residues from the soak and lime pits4 ,these consist mainly of lime and chalk1 with some hair and dung1 and possibly a little sulphide4 ,the sludge possesses some value as a manure1 especially if from the soak pits on account of the greater nitrogen content4 7,part ,,vi41 ,section ,i47 ,the ,beam ,house ,work consists in the mechanical removal of those parts of the hide not wanted for leather manufacture4 ,unhairing removes the hair and the epidermis made loose in liming4 ,the hides are placed over a sloping beam with a convex surface1 and the hair scraped off with a blunt concave and double-handled knife4 ,the hides are then thrown into a pit of water4 ,the hair is carefully collected1 washed well with water1 preferably centrifuged1 and then dried out by a current of warm air4 ,it forms a valuable bye-product4 ,white hair is usually kept separate and fetches a higher price4 ,fleshing is the next process4 ,the hides are again placed over a beam1 with the flesh side 7i4e4 the side nearest the flesh7 uppermost4 ,skilled workmen then cut off1 with a sharp convex knife1 the fat1 flesh and connective tissue left in flaying4 ,rounding is usually the next process4 ,the unhaired and fleshed hide is spread out flat and cut up into butt1 shoulder and a pair of bellies4 ,these parts have different commercial values1 and may afterwards be tanned by different methods for very different purposes--for dressing leather1 and sometimes even for sole leather4 ,scudding is the last piece of beam work4 ,the fleshed hides 7whether rounded or not7 are washed1 or at least rinsed1 with water1 and again placed on the beam grain side up4 ,they are then scraped with a rather sharp concave knife1 to remove scud1 which consists of hair roots and sheaths1 lime soaps1 fat1 pigment and other dirt4 ,short hair is shaved off by a very sharp hand knife4 ,the beam work demands a certain amount of skill from the workmen1 especially from the flesher1 whose sharp knife may prove very wasteful in incompetent hands4 ,hand labour was slowly but surely being replaced by machinery before the war1 and war-time conditions have greatly accelerated the rate of transition4 ,beam house machinery is rapidly becoming universal4 ,the machines are cumbrous and expensive in cost and in power1 but machine work is quicker1 less laborious1 and needs much fewer workmen4 ,many types of machine have been suggested1 but the most useful are those in which the hides pass over rollers and are simultaneously acted upon by a rapidly revolving cylindrical knife with spiral blades1 one half being a left-handed and the other a right-handed spiral1 so that the hide is scraped outwards as well as in the direction of motion4 ,the part of the hide being acted upon rests on a pneumatic roller4 ,by changing the type of spiral knife cylinder the machine will unhair1 flesh or scud4 ,deliming is a general name covering a number of similar operations whose primary object is the neutralization and removal of the caustic lime and soda in the plumped pelt1 or at any rate on the surface of the hide4 ,this is a preparation for the tan liquors4 ,all the tannins and many associated substances darken rapidly with oxidation when in alkaline solution1 so that to place the fully limed hide in a tan liquor would give a dark-coloured leather4 ,a short insertion in a bath of weak acid would secure the elimination of surface lime and the disappearance of this difficulty1 but there are other purposes in deliming4 ,the more completely lime is removed the more the plumped pelt falls into a soft1 pliable1 unswollen and relaxed condition1 and this change assists very materially in the production of a soft dressing leather1 suitable for boot uppers1 bags1 etc4 ,for such leathers1 therefore1 the deliming must be much more complete than for sole leather1 in which the object is to obtain a firm and plump leather4 ,in the case of the softer dressing leathers1 experience indicates the advisability of allowing some further bacterial action on the interfibrillar substance in order to produce the requisite pliability and softness4 ,this is secured by bating the hides4 ,this process consists in immersing the goods into a cold fermenting infusion of hen or pigeon dung4 ,the infusion is made in a special tub or pit with warm water and allowed to stand for a day or two until the fermentation has commenced1 and then run into the bating pit through a coarse filter such as sacking4 ,the hides are immersed for some days1 but are handled frequently to ensure an even effect4 ,the bate is always slightly alkaline4 ,the caustic alkalinity increases rapidly at first owing to the diffusion of caustic lime1 then at a slower rate1 afterwards slowly declining4 ,this is explained by the production of organic acids1 and their salts with weak bases from the dung infusion by the action of bacteria4 ,the total alkalinity of the bate liquor increases rapidly at first owing to the diffusion of lime and its liberation of organic bases1 then very slowly1 but towards the end of the operation the total alkalinity increases very rapidly indeed1 owing probably to the commencement of a violent anrobic fermentation which produces ammonia and other organic bases1 and which heralds the approach of a putrefactive action1 which if allowed to continue for even a short time will ruin the hides4 ,bating is consequently a risky process1 and needs experienced oversight4 ,for goods which need only a mild bating1 there is the alternative of giving a longer liming in older limes4 ,this of course involves more bacterial hydrolysis1 and perhaps does it in a safer1 more economical and certainly in a less offensive manner4 ,bating is often followed by a further deliming by acids4 ,boric1 lactic1 acetic1 formic and butyric acids are all used1 and with care even hydrochloric and sulphuric acids may be employed4 ,innumerable artificial bates have been put on the market1 but most are merely weak acids1 acid salts or salts of strong acids with weak bases4 ,an ,american bacterial bate consists of a lactic fermentation of glucose in the presence of glue4 ,closely similar to bating is puering1 investigated by ,wood4 ,drenching is another fermentive deliming process4 ,in this the goods are inserted into an infusion of bran4 ,this is made by scalding the bran with hot water1 and allowing it to stand until it is about #gj-ij ,f4 ,the infusion is then inoculated with a few gallons of old drench liquor1 and the goods are immersed4 ,this fermentation has been examined carefully by ,j4 ,t4 ,wood4 ,first the enzyme cerealin converts bran starch into glucose1 which is then fermented by the drench bacteria with the production of lactic acid1 some acetic acid and small amounts of formic and butyric acids4 ,the butyric fermentation is liable to become too violent4 ,these acids1 as they are formed1 neutralize the lime in the hides and plump the pelt slightly4 ,various gases 7carbon dioxide1 hydrogen1 nitrogen1 methane and sulphuretted hydrogen7 are involved1 and the proportion produced in the pelt itself has a peculiar opening effect on the hide fibres4 ,the activity of the drench can be decreased by dilution and by using a less starchy bran1 and can be increased by adding pea meal or rye meal4 ,drenching usually follows bating4 ,scudding sometimes follows deliming4 ,the theory of the volume and elasticity changes of pelt during preparation will be better understood after considering the behaviour of gelatine gels4 ,the determining factors are the nett charge of hydroxyl ions on the disperse phase1 resulting from ionic adsorptions1 and the lyotrope influence of dissolved substances on the continuous phase4 ,in softening dried hides the swelling may be due to either influence1 but the latter tends to loss of hide substance and the production of soft leather4 ,in liming1 the nett adsorption of hydroxyl ions is the principal factor1 but the lyotrope influence of the alkali cations and of the impurities is important4 ,plump pelts are those in which the contained water is in a relatively greater average state of compression4 ,few substances can assist plumping1 but many can hinder it4 ,in plumping all lyotrope influence is objectionable1 and sharp 7pure7 alkali solutions are required4 ,mellow limes reduce elasticity and plumpness by lyotrope influence4 ,in bating and puering the essential change is that before the process the swelling is due chiefly to adsorption of hydroxyl ions1 whereas afterwards it is due chiefly to a composite lyotrope influence4 ,,references4 ,principles of ,leather ,manufacture1 ,procter1 pp4 #ajh-ahd4 ,the ,manufacture of ,leather1 ,bennett1 pp4 #di-aac4 ,lyotrope ,influence and ,adsorption in the ,theory of ,wetwork1 ,bennett1 ,j4,s4,l4,t4,c41 #aibj1 pp4 #ge-hf4 ,analytical ,examination of ,bating1 ,bennett1 ,leather ,trades ,review1 #aiaa1 p4 #igb1 and #aiab1 p4 #bh4 ,the ,bating1 ,puering and ,drenching of ,skins1 by ,j4 ,t4 ,wood4 ,,section ,,iii4--,,vegetable ,,tannage ,all tannages have for their object the conversion of the readily putrescible hide tissue of the corium 7the pelt7 into an imputrescible1 insoluble and permanent material called leather which1 possessing considerable strength and pliability1 is capable of application to a variety of useful purposes4 ,the conditions necessary for this transformation have been clearly stated by ,procter4#a ,for the production of leather from pelt it is not only necessary to dry the fibres in a separate and non-adherent condition1 but so to coat them or alter their chemical character that they are no longer capable of being swelled or rendered sticky by water4 ,whatever substance will secure this permanent dehydration of the hide fibres in a separate condition is called a tanning material4 ,the change from pelt to leather is known as tannage1 the process is termed tanning1 and those who undertake it are tanners4 ,footnote #a3 ,principles of ,leather ,manufacture1 p4 #ahd4 ,in vegetable tannage the tanning materials are of vegetable origin1 and contain a group of organic compounds called tannins which are extracted by the infusion of these materials with water4 ,pelt1 when immersed in these infusions1 is converted into leather1 rather slowly2 but a gelatin solution gives an immediate precipitate of amorphous leather1 even if the tannin infusion be exceedingly dilute4 ,the tannins are aromatic compounds of phenolic character1 and contain carbon1 hydrogen and oxygen only1 but our knowledge of their chemical constitution is exceedingly small owing to their instability and colloid nature1 which make impossible their preparation in a pure state4 ,they are all1 however1 derived from either catechol or pyrogallol1 and yield these substances if carefully heated to about #bjj ,c4 ,the tannins are soluble in water1 alcohol1 acetone1 ethyl acetate and acetic acid1 but insoluble in benzene1 chloroform1 carbon disulphide1 petroleum ether1 dilute sulphuric acid and pure ethyl ether4 ,the aqueous infusions of the tannins are in reality colloidal solutions2 i4e4 heterogeneous systems of two phases4 ,the systems are lyophile1 or1 more particularly1 hydrophile1 i4e4 there is an affinity between the two phases4 ,as usual with lyophile systems the two phases may be considered as both liquid1 and an aqueous infusion of tannin forms an emulsoid sol1 which therefore is subject to the phenomenon of adsorption4 ,the tannins are all precipitated by solutions of basic lead acetate and copper acetate1 and many of them with varying completeness by solutions of many other metallic salts and hydroxides1 of basic dyestuffs and of alkaloids4 ,they give dark colorations with ferric salts4 ,the tannins are widely distributed in plant-life1 but only in a limited number of cases do the plants contain sufficient tannin to render them of commercial importance4 ,tannin is found in all parts of plants1 but usually in greatest amount in the bark or fruit4 ,the tannins are classified into pyrogallol tans and catechol tans1 according to the parent phenol4 ,this classification is confirmed by their chemical1 analytical and practical behaviour1 and the vegetable tanning materials may be classified into the same two groups1 for1 although even the same plant contains both pyrogallol and catechol tans1 it is usual to find in any one part of the plant that one group is predominant4 ,pyrogallol tans1 which are oftenest obtained from fruit or leaves1 contain usually about #eb per cent4 of carbon4 ,used alone they produce a rather soft and porous leather4 ,associated with them--in many cases probably as decomposition products--are certain other substances of well-known properties and constitution4 ,these substances are not only typical of the group1 but also form the most valuable clue to the chemical constitution of the group and the key to their chemical behaviour4 ,one of these substances is gallic acid 7#c3d3e trihydroxy-benzoic acid ,c#f;,h#b7,,oh7#c;,,cooh71 which possesses properties very similar to the tannins1 but does not precipitate gelatin and will not itself make leather4 ,another of these substances is ellagic acid ,c#ad;,h#f,o#h1 a double lactone of a hexa-hydroxy-diphenyldicarboxylic acid4 ,this is deposited as an insoluble yellow powder from infusions of many pyrogallol tans1 by boiling with dilute acids only1 allowing them to stand for a few days4 ,in practice the deposit is found as mud at the bottom of the tan pits1 and also upon the leather1 to which it strongly adheres4 ,it is technically known as bloom4 ,it is insoluble in acids and cold alcohol1 but soluble in alkalies4 ,it is a feeble dye-stuff4 ,the pyrogallol tans yield very different amounts of bloom4 ,other associated substances are the sugars4 ,in practice these sugars ferment to lactic1 acetic1 and other acids which cause sour liquors4 ,such liquors plump the hides and tend to give firm1 thick leather4 ,these acids also probably cause increase of adsorption of tannin by the hide and therefore assist in giving good weight4 ,solutions of pyrogallol tans all give a blue-black colour with a dilute solution of ferric alum4 ,if a solution of sodium arsenate be added to an infusion of pyrogallol tan diluted until no longer distinctly coloured1 and the mixture allowed to stand for about two hours1 a green colour develops at the surface of the liquid4 ,the reaction is due to gallic acid or a similar grouping1 and is1 in the author's experience1 the most satisfactory qualitative test for the group4 ,another test is to mix equal volumes of a #j4d per cent4 infusion of tan and a #aj per cent4 solution of sodium bisulphite2 a few drops of #aj per cent4 potassium chromate are added1 and either a transient blood-red colour or a more permanent deep purple is obtained4 ,the former colour is due to gallic acid4 ,if a tannin infusion be largely diluted with hard water and a little iodine solution added1 the pyrogallol tans yield either a purple-red or a dark blue colour1 the former being a reaction of gallic acid4 ,pyrogallol tans yield no precipitate with bromine water4 ,they yield a yellow or brown colour when one drop of infusion is added to concentrated sulphuric acid4 ,myrabolans is one of the most important of the pyrogallol tanning materials4 ,it is a name given to the dried fruit of ,terminalia chebula and other species of ,indian trees4 ,the nuts resemble an elongated walnut4 ,they are dried and exported from many parts of ,india to all parts of the world1 but largely to this country4 ,the varieties of commerce are named according to origin and quality3 thus we have ,j#a's1 i4e4 ,jubbelpore1 ,no4 #a quality1 ,r#a's 7,rajpore1 ,no4 #a71 ,b#a's 7,bhimley1 ,no4 #a71 etc4 ,the little difference in tannin strength 7about #cb per cent47 in these varieties is usually compensated by corresponding differences in price4 ,the quality of myrabolans cannot be safely judged by appearance4 ,much bloom is deposited by myrabolans liquors1 especially by ,j's4 ,myrabolans are amongst the most sugary of tanning materials1 containing up to #e-a_/b per cent4 ,it is therefore one of the best materials for giving a plump leather4 ,broadly speaking1 those varieties which yield most sugar yield least bloom1 and vice vers4 ,myrabolans tannin has a small affinity for hide substance and penetrates the hide very slowly4 ,it gives a mellow tannage1 but a bright1 good colour1 which characteristics are imparted to the leather when the material is blended with other materials containing dark or astringent tannins4 ,when used alone it yields a rather spongy leather1 and it is not considered a good weight-giving material1 though its acid-producing powers are very helpful to other more astringent tannins4 ,valonia has been the other staple tanning material of the heavy leather trade4 ,it is the acorn cup of oaks common in ,asia ,minor and ,greece1 chiefly the ,turkish oak 7,quercus gilops74 ,the fruit is gathered when ripe and dried in layers of about one foot deep until the acorn drops out1 ,smyrna is the great export centre4 ,greek valonia is obtained from many parts of the ,archipelago and mainland4 ,it is gathered in a more immature condition and includes the acorn4 ,it is considered slightly inferior in strength and colour to the ,smyrna valonia4 ,the exterior of the acorn cup is covered with rather scaly protuberances known as beard1 which contains usually about #dj per cent4 of tannin4 ,the cup alone contains usually about #be per cent4 tannin1 and the whole about #cj per cent4 ,the valonia tannin has been thought to contain two chemical individuals1 only one of which produces bloom4 ,parker and ,leach#b found that the tannin of the cup produces more bloom than that of the beard1 and that ,smyrna valonia yields more bloom than ,greek4 ,the more bloom is deposited1 the less acid will be produced4 ,under all conditions the yield of bloom is large1 and its deposition in and on the leather assists materially in giving the weight and water-resisting powers associated with sole leather which has been largely tanned with valonia4 ,the valonia tannins have only a moderate affinity for hide1 which1 like myrabolans1 they penetrate very slowly4 ,when used alone the leather is less yellow than that from myrabolans1 and is also duller4 ,after most of its bloom has been deposited valonia makes a very suitable tannage for dressing leather1 and in conjunction with gambier has been largely thus used4 ,since the outbreak of war the ,turkish product has1 of course1 not been available for importation4 ,footnote #b3 ,j4,s4,s4,i41 #aijc1 #aahd4 ,sumach#c is the other pyrogallol tan of commercial importance4 ,it consists of the leaves and small twigs of the ,sicilian sumach 7,rhus coriaria7 cultivated in ,italy extensively for export4 ,the leaves are hand picked1 dried and often ground to powder4 ,it contains #bf-bh per cent4 of a tannin which yields little or no bloom1 but much gallic acid4 ,it is an unstable tannin1 and its infusion rapidly ferments4 ,sumach is a very valuable tanning material1 and when used alone gives an exceedingly durable leather of excellent light colour4 ,it gives a soft mellow tannage1 and is therefore most suitable for light leather tanning1 and is extensively used for this purpose4 ,it is used1 nevertheless1 in large quantities by the heavy leather tanners for finishing purposes1 for it contains some organic reducing agent which exerts a powerful bleaching action on other tannages1 and which assists to brighten as well as lighten the rather dull appearance of leathers largely tanned with valonia4 ,it is rather an expensive tannin1 but most manufacturers find that its results are worth its cost4 ,footnote #c3 ,also spelt ,sumac and ,shumac1 and always pronounced like the latter4 ,other pyrogallol tans are also used to a limited extent4 ,algarobilla and divi-divi are the fruit pods of several species of ,american csalpina4 ,they are strong in tan 7#de per cent47 and yield a light-coloured and bright leather1 but are unstable tans1 yielding much bloom4 ,babla is a small pod yielding a mellow tannage and much gallic acid4 ,celavinia is another pod containing no colouring matter and giving an almost white leather4 ,the tannin is closely similar to that of oak galls4 ,these last were once extensively used for tanning in ,austria4 ,willow bark is used for tanning in ,russia and ,denmark4 ,valuable pyrogallol tannins are obtained from oak wood and chestnut wood1 but the woods are not used in tanning as the percentage of tan is so small4 ,catechol tans1 often obtained from barks1 contain usually about #fj per cent4 of carbon4 ,they are seldom used alone1 for they usually have little or no sugar associated1 and hence their liquors do not either sour or plump4 ,they can be used alone if artificially acidified1 but without acidifying or blending would give a rather flat leather1 though possibly firm4 ,they yield no bloom or gallic acid1 but have associated with this other characteristic substances4 ,of these the catechins are the most typical1 and have been considered as the parent substances of the catechol tans4 ,the catechins are white crystalline substances1 apparently isomers with the general formula ,c#ae;,h#ad,o#f4 ,they have different melting-points1 and varying amounts of water of crystallization1 but are otherwise exceedingly similar in properties4 ,they are sparingly soluble in cold water1 but freely in hot1 and in alcohol and ether4 ,they are precipitated by lead acetate1 mercuric chloride and albumin1 but not by gelatin1 tartar emetic or alkaloids4 ,in gambier liquors they are especially strong1 and sometimes crystallize on the side of the pits1 being thus known as whites4 ,the phlobaphenes or reds are also typical of catechol tans from which grow catechins2 they can be formed by boiling with dilute mineral acids4 ,they are considered to be anhydrides of the catechol tans4 ,they are difficultly soluble in cold water1 but freely in hot1 and in cold alcohol and dilute alkalies4 ,they are true tannins and alone are capable of making a red leather1 but in practice are often found as mud in the tan liquors owing to their limited solubility4 ,they naturally influence the colour of leather made with catechol tans1 which is usually distinctly redder than the leather made from pyrogallol tans4 ,infusions of catechol 7cp4 catechin7 give a green-black colour with iron alum4 ,the sodium arsenate test gives a red colour due to catechin4 ,the chromate and iodine tests mentioned for pyrogallol tans give negative results with the catechol tans1 but bromine water gives a precipitate1 and sulphuric acid a crimson colour4 ,mimosa bark is one of the most important catechol tans4 ,it is usually obtained in this country from ,natal 7,natal bark72 but the tree 7,sydney green wattle1 ,acacia mollissima7 is a native of ,australia4 ,it is being cultivated now extensively in ,south ,africa1 and forms a most valuable portion of the ,empire's stock of tanning material4 ,its more extensive use has been long recommended by the author1#d but its gradually increasing employment in ,british tanneries has been greatly accelerated by the war1 which has prevented its delivery in ,germany and has cut off ,turkish valonia from ,britain4 ,it yields about #cj per cent4 of a stable and excellent tannin1 and will produce a firm1 durable leather1 with a colour much less red than that obtained from many other catechol tans4 ,it is an astringent tan1 and if carelessly used yields a harsh or even drawn grain4 ,most of the tannin is easily extracted1 yielding a clear infusion which penetrates fairly quickly and gives good weight4 ,it contains less than #a per cent4 of sugar1 which unfortunately rapidly ferments to carbonic acid1 so that it is not a good plumping material4 ,it makes in all respects an excellent blend with myrabolans4 ,like all catechol tans1 the resulting leather darkens on exposure to sunlight4 ,footnote #d3 ,j4,s4,c4,i41 #aijh1 #aaic4 ,oak bark1 from ,quercus robur1 is the ancient tanning material of ,britain1 and is still used to a limited extent4 ,it contains about #ac per cent4 of tannin and is mainly a catechol tan1 but also contains a pyrogallol derivative4 ,it yields catechin1 and gives a red colour with the sodium arsenate test1 but also will yield some bloom and gallic acid1 and gives a blue-black with ferric salts4 ,the tannin itself is exceedingly similar to that of mimosa bark1 but the material contains about #b-a_/b per cent4 of sugar1 which makes it possible to employ oak bark alone for making sole leather4 ,it is noted for yielding a sound1 durable leather of good typical tan colour4 ,its tannin combines well with hide and penetrates quickly4 ,the fatal disadvantage of oak bark is its weakness in tannin strength compared with other materials4 ,this results in heavy freight and heavy cost per unit tannin1 bulky storage1 expensive handling in the factory1 comparatively large bulk of spent tan1 after relatively greater trouble in extracting1 and the impossibility of making the strong liquors so necessary in these days to produce good weight in a short time4 ,no satisfactory extract has yet been made from it4 ,pine bark1 from ,pinas abies1 is one of the staple materials of the ,continent4 ,it contains up to #ad per cent4 of a catechol tan1 and1 unlike most of this group1 contains a high proportion of sugar and will give good results alone4 ,hemlock bark has been the staple tanning material of ,north ,america4 ,it is obtained from the hemlock1 or ,pinus canadensis4 ,it contains up to #aa per cent4 of tan and much phlobaphene1 and yields a characteristic red leather of good quality1 but which rapidly darkens with sunlight4 ,it contains some sugar1 but is usually employed in conjunction with sulphuric acid or with sugary materials4 ,mallet bark yields another catechol tan similar to that of mimosa1 but somewhat less astringent and more yellow in colour4 ,quebracho wood and mangrove bark have been used1 but are now made into extracts4 ,leaching4--,whatever class of leather is being made1 and whatever blend of tanning materials is being employed1 the tannins must be efficiently extracted by water in order to make the tanning liquors4 ,this process is called leaching4 ,the tanning materials1 after being ground1 crushed or shredded1 are placed in large pits arranged in rounds1 sets1 or batteries of #f1 #h or #aj units1 through which water is percolated systematically1 so as to secure a continuous extraction4 ,water itself is added to only one of the pits of material4 ,the liquor produced is passed on to the next pit1 and then to the next1 and is continually gathering strength4 ,after passing thus through the series1 the liquor becomes the source of the strong extracted tan liquors which are used in the tannery proper4 ,with this system the stronger leach liquors are being acted upon by fresh material1 and the nearly spent material is being acted on by the weakest liquors1 and finally by water1 thus ensuring a complete extraction4 ,in the press leach system1 which is now practically universal1 the bottom of one pit communicates with the top of the next1 and the liquor presses round by gravity flow caused by a few inches fall4 ,liquor is thus constantly percolating downward through the material in each pit4 ,the head leach and tail leach are always adjacent in a double row of pits1 and when the material in the latter is quite spent1 it is cast1 and the pit is filled with fresh material4 ,the liquor is then pressed round into this pit by adding water to the tail leach4 ,hot water is used to secure better diffusion4 ,at least two such sets of leaches 7taps and spenders7 are necessary to spend the material of the average tannery and to obtain liquors of the necessary strength4 ,the ,manufacture of ,extracts4--,in addition to the use of the natural tanning materials described above1 modern leather manufacturers employ also a variety of tanning extracts1 i4e4 vegetable tanning materials in which the tannin has been already extracted1 and which are supplied in form of a solid or concentrated liquid4 ,such extracts only need to be dissolved in warm water in order to make a tan liquor1 and the cost and trouble of leaching is avoided4 ,they are a great convenience as making strong liquors of definite strength4 ,many vegetable tanning materials are too weak in tan for the tanner to leach1 and indeed to justify the cost of importation have been made available by manufacturing an extract at the source of the material4 ,with such weak materials the extract manufacturer has had to secure a much more complete extraction than in ordinary leaching1 and to concentrate his infusions by means of steam-heated vacuum pans4 ,with such experience he has naturally begun to make extracts also from the stronger materials1 such as myrabolans and mimosa bark1 and it is now possible to have a tannery without any leaches at all4 ,tanners also have begun to realize the advantages not only of more rapid and complete extraction1 but also of doing the work for themselves1 and extract factories are beginning to appear as an adjunct to the larger tanneries4 ,the more complete extraction of tan also involves a greater extraction of unwanted colouring matters1 hence decolorization is a feature of extract manufacture4 ,chestnut ,extract is from the wood of the ,spanish chestnut 7,castanea vesca71 which contains #c-f per cent4 of a valuable pyrogallol tan very similar to that of valonia4 ,its weight-giving and water-resisting powers are as good as valonia1 and its penetrating power is even better1 so that it forms an exceedingly suitable material for the modern short tannage1 and also for drum tannages4 ,the extract is manufactured extensively in ,france4 ,the wood is stripped of bark and usually piled for some months to dry and to allow the resins to become insoluble4 ,some factories1 however1 use the green wood direct4 ,there are two methods of extraction1 viz4 in open vats and in closed vats under pressure4 ,the two methods yield extracts which differ in composition and properties4 ,in either case the vats have a capacity of up to #c1jjj gallons1 and hold up to #f-a_/b tons of wood4 ,they are arranged in series1 as in leaching1 and the liquor passes in succession through all the vats over wood less and less spent4 ,the temperature is highest in the vat containing the fresh water and nearly spent wood4 ,in open vats of wood or copper the temperature is near boiling-point1 whilst in the closed autoclaves 7copper or bronze7 the pressure reaches about two atmospheres and the temperature about #acj ,c4 7#bff ,f474 ,the series may contain #e1 #g1 #i or even #ab vats1 and the liquor obtained has a strength of #c to #d-a_/b ,beaum 7#bb to #cc ,bkr474 ,after extraction the liquor is allowed to stand1 and much insoluble matter settles out--resins1 wood1 fibre1 etc4 ,the clarified and settled liquor is then passed through a cooler up to about #ee ,c41 and then run into the decolorizing plant1 a deep vat fitted with a copper steam coil and mechanical stirrer attached to power4 ,the best decolorizer is bullock's blood1 which is run into the vat and well mixed4 ,the temperature is next raised to about #gj ,c41 causing the blood albumin to coagulate4 ,it carries down with it a little tannin1 but much colouring matter4 ,after standing a few hours the settled liquor is run off direct to the evaporator4 ,a multiple-effect evaporator is usually employed1 and the concentrated liquor1 which has a strength of about #be ,beaum1 is run into suitable oak casks4 ,the extracts contain #bg-cb per cent4 tannin4 ,an extract made with open vats has about #g per cent4 soluble non-tanning matters1 whilst a pressure extract may contain up to #ab per cent4 of these non-tans4 ,pressure extracts obtain also a better yield of tannin1 which more than compensates for the slightly lower price4 ,open extraction yields1 however1 the purer product and an extract with better penetrating powers1 and is consequently the more suitable for drum tannages4 ,chestnut extract is extensively used by the heavy leather tanners4 ,oakwood ,extract is manufactured from the wood of the common oak 7,quercus robur74 ,the centre of the industry has been the oak forest of ,slavonia4 ,the wood contains #b-d per cent4 of a tannin very similar to that of chestnut wood1 but somewhat more astringent4 ,the manufacture is also similar to that of chestnut extract1 but decolorization is often omitted1 and greater care has to be taken and in other ways to keep the colour within limits4 ,one of these is to strip the wood more completely of bark4 ,another is to operate at as low a temperature as possible1 about #aaj ,c4 ,the extraction is made in large circular vats about #ad feet high and holding about two tons material4 ,a battery is composed of about eight vats or extractors4 ,open extraction is used1 and the liquor is passed forward after #b-c hours' boiling1 so that the material is spent in about #bd hours4 ,a liquor of about #e ,b 7#cf ,bkr47 is obtained1 and the strength of the material reduced from #d to #a_/d per cent4 of tannin4 ,getting rid of insoluble matter is a difficulty1 and is attained by settling1 by rapidly cooling1 and then passing through a filter press of wood4 ,for evaporation a double-effect vacuum pan is preferred1 which operates first at about #aac ,f41 and afterwards at #adj ,f4 with a higher vacuum4 ,the liquor is concentrated from #e to #be ,beaum 7s4g4 #a4jcf and #a4baj respectively74 ,the extract has a much higher colour than chestnut1 and is not used now as much as some years ago4 ,as the principal supply was ,german1 it has been unavailable4 ,quebracho ,extract is made from the wood of the ,south ,american tree ,loxopteryngium ,lorenzii1 which contains about #bj per cent4 of a typical catechol tan4 ,it is associated with a little catechin1 much phlobaphene1 but practically no sugar4 ,the tannin is very astringent1 penetrates quickly and gives a firm red leather which darkens on exposure to light4 ,it is not noted for weight-giving powers4 ,the wood itself1 as chips or shavings1 has been used in ,british tanneries1 to a limited extent1 but the great bulk of the material is made into extract chiefly in ,south ,america4 ,the crude extract1 made by evaporating aqueous infusions of the wood1 is largely exported for refinement in ,europe4 ,it is also refined on the spot to a large extent and converted into solid extract containing #fj per cent4 of tannin4 ,the great difficulty with quebracho has been the disposal of the phlobaphenes1 and a great variety of quebracho extracts are now available which deal with this problem in different ways4 ,in some the more soluble reds are simply left in the extract under the idea that they are really tannins and may be of some use in some part of the tanning process2 in others they have been removed by settling and filtration at appropriate temperatures and concentrations2 in most1 however1 they have been solubilized by treatment with alkalies1 in the presence of reducing agents1 notably by heating with sodium bisulphite in closed vats4 ,the base combines with the phlobaphenes1 which are made completely soluble and available for tanning4 ,sulphurous acid is evolved1 and its reducing powers assist materially in retaining and promoting a good colour in the product4 ,such sulphited extracts are now extensively manufactured in this country from the imported crude extract1 and sold as liquid extracts containing #cj1 #ce or #dj per cent4 of tan according to the requirements of the buyer2 mixed extracts which are solubilized quebracho blended with about #ae per cent4 of myrabolans1 are also used4 ,by solubilizing quebracho with excess of bisulphite an extract is obtained which possesses considerable bleaching powers1 and such extracts are also extensively manufactured for the vatting or bleaching of heavy leather after tannage4 ,the excess of sulphurous acid not only bleaches the leather1 but also swells it up and thus permits a further absorption of strong tan liquor1 which is conducive to good weight4 ,these bleaching extracts are usually of #cf-ch per cent4 strength in tan4 ,gambier is an extract of the leaves and twigs of the eastern shrub ,nauclea gambir4 ,it is a catechol tan of peculiarly mellow quality and great practical value4 ,it contains much catechin1 but little phlobaphene1 and yields a beautifully soft leather1 but without weight4 ,it is an exceedingly suitable material for the early stages of tanning1 and is much liked for tanning leathers that have to be curried1 and is widely used in the manufacture of upper leather4 ,it is1 however1 an exceedingly expensive tannin1 and the extract is made in a very crude way by ,chinese and ,malays without much supervision4 ,hence its strength in tan and general quality is extremely variable4 ,the plant is cultivated for the purpose of extract manufacture1 and prunings are taken in the plant's third year4 ,they are bruised and boiled with water in the open4 ,the infusion is strained1 concentrated1 and poured into cooling vessels in which it sets to a paste4 ,two varieties of gambier are well known1 cube gambier and block gambier4 ,in the latter the extract remains as a paste containing #be to #dj per cent4 of tannin4 ,it is sold in oblong blocks of #a or #b cwt41 either wrapped in cocoanut matting or in wooden boxes4 ,cube gambier is made by running the concentrated syrup into trays #b inches deep and drying in the sun4 ,when partly dry1 it is cut up into #a-a_/b-;in4 cubes and dried further on cocoanut matting4 ,the rough cubes as imported contain #dj-ej per cent4 of tannin4 ,myrabolans ,extract is now largely manufactured in this country4 ,a liquid extract of #be1 #cj or even #ce per cent4 strength is made for home consumption1 and a solid extract for export4 ,the light colour1 high strength and easy extraction of the natural material have all facilitated the task of the manufacturer4 ,the material is extracted in open vats or stills of copper1 which take one ton or more of nuts4 ,a battery of #d1 #f or #h of such stills is usually employed1 and the temperature is kept well below boiling-point except in the vats containing the nearly spent material4 ,the liquors move forward quickly1 and the material is quite spent in #bd hours4 ,the material when cast contains less than #a_/b per cent4 of tannin4 ,the liquor obtained is #dj-ej ,bkr4 7#f - #g-a_/b per cent4 tan71 and after settling is concentrated at #dj-ej ,f4 in a single effect vacuum pan1 which though more costly in steam is quicker than the multiple effects1 and gives the low temperature required4 ,for solid extract the more concentrated liquor is run direct into tarred bags1 in which it soon solidifies4 ,hemlock ,extract is manufactured from the ,north ,american pines and imported into this country to some extent4 ,it gives a very red colour4 ,mangrove ,extract is made from the bark of ,rhizophona ,mangle and other species of mangrove which grow freely in the tropical swamps of ,west ,africa1 ,borneo1 etc4 ,much solid and liquid extract has been made from this material1 but is not very popular on account of its harsh tannage and dark red colour4 ,pine ,bark ,extract 7,larch extract7 is made in ,sweden from the ,norway spruce 7,pinus abies74 ,it is slightly sulphited and gives a good colour4 ,it is a liquid extract of about #cj per cent4 strength1 and is sometimes used as a chestnut substitute4 ,it should not be confused with the so-called spruce or pine wood extract1 which is a paper trade bye-product and contains ligneous matters rather than tannin4 ,american ,chestnut ,extract1 made from the chestnut oak1 is either a liquid or a solid extract in powder form4 ,it gives a wretched brown-black colour1 which is quite unsuited to the usual ,british needs4 ,,theory ,,of ,,vegetable ,,tannage4 ,vegetable tannage is a phenomenon of colloid chemistry4 ,the old arguments as to whether tanning was a chemical or a physical process have been rendered obsolete by the advent of a new set of explanations1 which1 though shedding light on many obscure points1 have enormously increased the complexity of the problem4 ,in vegetable tannage an emulsoid gel 7pelt7 is immersed in a complex emulsoid sol 7tan liquor71 which immersion results1 not in simple reaction or change1 but in a series of changes4 ,one of these changes is adsorption4 ,pelt is a gel which possesses a great development of surface4 ,it not only exhibits like gelatine the phenomenon of imbibition and dehydration to a very marked extent1 but also possesses a very fine fibrous structure due to its organic origin2 thus pelt possesses an enormous specific surface1 further intensified by the preparation processes previously discussed1 which split up the hide fibres into smaller bundles and into much finer constituent fibrils4 ,tannins1 on the other hand1 are hydrophile colloids which in water form emulsoid sols1 and which may thus be expected to exhibit the phenomenon of adsorption4 ,a tan liquor usually contains several tannins in addition to other closely similar substances1 also in colloidal solution1 and is therefore a sol of considerable complexity4 ,the immersion of pelt into a tan liquor results in an adsorption1 which consists essentially in an inequality of concentration in the sol1 the greater concentration being at the interface4 ,this inequality between the surface concentration and the volume concentration of the sol1 is due primarily to considerations of surface tension and surface energy1 and exists before the immersion of the pelt4 ,the surface layer having excess over the volume concentration1 any considerable extension of surface in a fixed volume of sol must produce a very considerable decrease in the volume concentration4 ,this is what occurs when pelt is immersed in a tan liquor1 the immersion being the considerable extension of surface4 ,it should be especially remembered that the inequality of concentration is in the sol1 on the liquid side of the interface4 ,in adsorption1 the substance adsorbed1 i4e4 the excess at the surface1 is too frequently regarded as bound to the solid immersed4 ,this is because the excess is in the layer which wets the solid and remains wetting it when the solid is removed4 ,thus the immersion of pelt produces primarily only a change in the distribution of the tannins in the liquor4 ,it follows from this that the adsorption is an equilibrium1 and that if the sol be diluted1 the equilibrium will become the same as it would have been by immersing the pelt directly into the dilute solution4 ,thus1 if pelt be first immersed in one tan liquor and then into a weaker one it will yield tan to the latter solution4 ,the chief object in heavy leather tanning is to obtain the maximum possible adsorption in the minimum possible time1 or in other words1 to obtain good weight quickly4 ,the amount adsorbed is proportional to the actual extension of surface1 i4e4 the adsorption is a function of the specific surface of the adsorbent4 ,hence1 to obtain good weight it is necessary to develop in the pelt its maximum possible specific surface4 ,this is one of the objects of plumping1 which splits up the fibres4 ,it is attained also by the solution of interfibrillar substance in limes and bates4 ,the amount adsorbed is also a function of the volume concentration in the sol after equilibrium is reached4 ,hence the better weights are obtained with stronger liquors4 ,the adsorption law is y_/m ac7#a_/n7 where y is weight adsorbed by the weight m of adsorbent1 and c the volume concentration after adsorption2 a and n are numeral constants4 ,hence weight is determined by the strength of the liquor which the goods finally leave4 ,the commencement of tannage is necessarily in weak infusions1 in order to secure the maximum diffusion into interior of the fibres before they become heavily coated on the exterior4 ,as the equilibrium is being established in such liquors the volume concentration diminishes1 and thus makes it less likely that good weight will be attained2 hence it is necessary in practice to move the goods constantly into fresh liquors of gradually increasing strength1 and so maintain the rate of adsorption and save time4 ,a further consequence of the adsorption isotherm is that as y varies as c7#a_/n7 and n is #a1 y is increased appreciably only by a relatively large increase in c4 ,hence1 though stronger liquors give better weight1 there is a limit beyond which any further gain in weight is not justified by the enormous increase in the concentration necessary to attain it4 ,such great increase in c is impracticable not only on the ground of expense1 but also on account of the great viscosity of the sol4 ,the amount of adsorption depends also upon the exact nature of the sol4 ,it has been previously pointed out that the tannins differ largely in their penetrating and weight-giving powers4 ,some are readily adsorbable and are deposited in great concentration at the surface of the fibre1 but for good weight it is necessary to use also the less adsorbable and more diffusible tans1 which penetrate the fibre itself4 ,hence it is necessary for good weight to use a blend of materials1 and so supply many grades of liability to adsorption4 ,it is particularly advantageous to blend judiciously the two main types of material1 the pyrogallol and catechol tans4 ,it is also necessary for good weight to present to the pelt the more diffusible and less adsorbable tannins first1 in order to secure the maximum diffusion into the interior of the fibre before the exterior of the fibre is heavily coated with the heavily adsorbable and astringent tans4 ,the least adsorbable materials are therefore used in the early stages of tanning1 and the most adsorbable materials at the end of the tanning process4 ,thus gambier is added to the early liquors 7suspenders71 solubilized quebracho to the later liquors 7handlers71 and mimosa bark extract to the final liquors 7layers74 ,there is also another excellent way of ensuring this progressive astringency of the liquors2 this consists in leaching the required blend of materials together 7or mixing them in the case of extracts7 and presenting the mixed infusion to the nearly tanned goods1 which adsorb chiefly the more astringent tannins4 ,the liquor is then used for goods at a less advanced stage of tanning1 which again take the most adsorbable constituents4 ,this is repeated until the stage is reached when the fresh pelt is inserted into the nearly exhausted liquor1 which naturally contains only the least adsorbable substances4 ,this system is almost universal1 and in practice is known as working the liquors down the yard4 ,it has the additional advantage of being a systematic method of economically exhausting 7spending7 the tan liquors4 ,when free acid is present in the tan liquors1 it tends to distend the fibres composing the pelt by a strong and rapid adsorption4 ,thus distended or plumped the fibres present a still greater surface for adsorptive operation1 but the distension naturally leaves less space between the fibres for the diffusion of the sol4 ,hence acid or sour tan liquors give in the long run more weight1 but tan more slowly4 ,pelt tanned whilst thus plumped forms naturally a thicker and less pliable leather4 ,this occurs in tanning sole leather1 to a less extent with heavy dressing leather1 and to a very small extent in the case of softer dressing leathers4 ,in addition to adsorption1 there is another phenomenon of colloid chemistry in operation1 viz4 the mutual precipitation of the sols in the liquid by the gels in the hide4 ,in most sols the disperse phase is electrically charged4 ,the sol therefore possesses electric conductivity1 and migration occurs in the electric field to the cathode or anode according to the nature of the charge4 ,oppositely charged sols precipitate one another1 the precipitate containing both colloids4 ,the maximum precipitation occurs when the charge of one sol exactly equals and neutralizes the - charge of the other4 ,there is thus an electrical equivalence2 an amount of sol which is equivalent to a given amount of the other4 ,this is not a chemical equivalence1 however1 and the precipitate is not a chemical compound in spite of its fairly constant composition4 ,the composition of the precipitate1 indeed1 is not quite constant1 for the optimum precipitation may not correspond exactly with the electrical equivalence1 being influenced by the number of particles required1 their size 7dispersity71 the rate of mixture1 and the relative concentrations of the sols4 ,this mutual precipitation is exhibited by emulsoids as well as suspensoids1 but the charge 7 or -7 on an emulsoid is in many instances largely an accidental matter1 being determined by the medium in which it happens to be1 its normal condition being electrical neutrality4 ,gelatin and pelt are such emulsoids1 and a positively charged gelatin sol has been observed to precipitate a negatively charged gelatin sol4 ,it is thought1 however1 that gelatin is primarily a positive sol4 ,pelt 7whether delimed or not7 is rapidly acidified by the quickly penetrating and strongly adsorbed organic acids of the old tan liquors and becomes positively charged before the tannins are adsorbed4 ,the positive charge increases with the acidity of the liquor4 ,other emulsoids are not electrically neutral1 but are electrically charged and exhibit considerable conductivity4 ,into this class fall the tannins1 and in tanning it is thought that there is a mutual precipitation of the negative tannin sol with the positive hide gel1 the precipitation of the negative sol being favoured by the acid condition of the liquor4 ,the effect of increasing acidity soon falls off1 however1 as a saturation limit is soon reached4 ,this mutual precipitation of colloids in tanning is in reality but an extension of the adsorption theory1 which explains the predominant effect of ,h1 and ,,oh- on the electric charge by stating that these ions are more readily adsorbed than other ions1 and that as ,,oh- is more readily adsorbed than ,h most sols are negative to water4 ,in addition to the adsorption phenomena described1 there are in vegetable tannage secondary changes which are slow and irreversible4 ,these changes are obscure and are difficult to investigate4 ,oxidation1 dehydration and polymerization have all been suggested1 but there is little direct evidence4 ,certain it is1 however1 that time renders the tannage more permanent4 ,it perhaps should be pointed out that in the very strongest tan liquors the viscosity of the tannin sol is so great that adhesion would be a better term than adsorption4 ,there is no abrupt division between the two phenomena4 ,in the theory of vegetable tannage there is another factor the importance of which has been strongly emphasized by the author1 viz41 lyotrope influence4 ,this has been most conveniently discussed in connection with gelatin gels1 but its effect on hide gels is analogous4 ,it has also an effect upon the diffusion and gelation of the tannin and non-tannin sols4 ,mechanical ,operations4--,in the tanyard the liquors are almost invariably divided up into sections1 called rounds or sets1 in which the mechanical operations are different in aim and method4 ,in the first pits entered by the goods there is rapid adsorption in spite of the low concentration and small astringency1 and the great aim is to obtain evenness of action and a good level colour4 ,it is also necessary to maintain the rate of adsorption4 ,all the aims are attained by frequently moving the goods4 ,heavy leather is suspended vertically in the pits of tan liquor and handled up and down as well as forward from pit to pit4 ,such pits are termed suspenders4 ,in the earliest suspenders it is indeed advantageous to have the goods in constant motion4 ,this is done by suspending on wooden frames which are rocked gently by mechanical power2 such pits are termed rockers4 ,for dressing leather in which firmness and smooth grain are not so essential1 the goods may be paddled in the first liquors4 ,this is occasionally done with stronger liquors for the express purpose of working up the grain pattern4 ,the goods after passing through the suspenders are usually passed to handler rounds1 in which they are moved less frequently4 ,in these pits the goods are laid horizontally one above the other4 ,one advantage of handlers is that the goods flatten thoroughly and straighten one another by their own weight2 another is that more goods can be placed in one pit than in suspenders4 ,they are not so convenient to work1 however1 as suspenders1 and the goods do not feed so rapidly4 ,hence the tendency is now to tan more in suspension1 and to economize labour by an extension of the rockers4 ,the handling of the goods is also saved by pumping the liquors and by working rounds of suspenders or rockers like the press leach system1 with the difference that the stronger liquor is pumped in to the head pit1 and the liquor passes upwards through the goods4 ,finally the goods are placed in layers or layaways1 in which they remain undisturbed for a decidedly longer time4 ,these pits contain the strongest liquors of the yard1 and their principal function is to complete the tannage and give weight and firmness by the adsorption of bloom1 reds1 etc41 in the interior of the hide4 ,the goods are placed in horizontally1 and are dusted in between with fresh tanning material which maintains the local strength of the liquor and keeps the goods somewhat apart4 ,drum tanning attains a more rapid penetration of the pelt by giving constant motion in stronger infusions4 ,it is of course liable to result in an under-tannage of the interior of the fibre4 ,after the goods have been struck through in the ordinary way1 however1 drumming in extract is increasingly used as a substitute for much labour in handling1 and also to save the time spent in the early layers4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 pp4 #bbj-cej4 ,bennett1 ,manufacture of ,leather1 pp4 #aac-agi4 ,bennett1 ,celavima and ,babla1 ,l4,t4,r41 #aiad1 #abb4 ,dumesny and ,noyer1 ,manufacture of ,tanning ,extracts4 ,theory3-- ,meunier and ,seyewetz1 ,collegium1 #aijh1 #aie4 ,stiasny1 ,collegium1 #aijh1 #aag-aei1 #bhi1 #bid1 #ccg4 ,procter and ,wilson1 ,collegium 7,london71 #aiag1 #c4 ,wilson1 ,collegium 7,london71 #aiag1 #ig1 #ajj1 #aje4 ,moeller1 ,collegium 7,london71 #aiag1 #ac1 #ch1 #df1 #ajc2 and ,j4,s4,l4,t4,c41 #aiag1 #bb1 #ef1 #ib4 ,bennett1 ,j4,s4,l4,t4,c41 #aiag1 #acj-acc1 #afi-ahb2 #aiah1 #dj2 #aibj1 #ge-hf2 ,s4,l4,r41 #aiaf1 ,march4 ,,section ,,iv4--,,finishing ,,processes ,after the tannage is complete1 leather is hung up to dry4 ,in the case of heavy leather this drying must be very carefully carried out in order to obtain a product of satisfactory appearance and saleable qualities4 ,associated with the drying are many mechanical operations 7scouring and rolling7 which assist very materially in imparting the desired qualities4 ,after tanning1 however1 the quality of the final product is most strongly influenced by the amount of grease added in finishing4 ,some grease is always used in finishing1 partly because even sole leather requires some measure of pliability and partly because a coating of oil over the leather during drying prevents the loose tannin from being drawn to the surface of the leather by capillarity1 thereby causing dark and uneven patches and a cracky grain4 ,the added grease is also a contribution to the weight of the finished article--a primary consideration for heavy leather1 which is usually sold by weight4 ,the finishing processes1 indeed1 tend to be dominated by this consideration1 and become a series of efforts to retain as much tannin and add as much grease as are consistent with the requirements of the class of leather being manufactured4 ,sole leather does not contain more than about #b per cent4 grease1 or its firmness is impaired4 ,belting leather1 in which considerable pliability is needed1 may contain about #i per cent41 whilst harness leather1 which must be exceedingly tough and durable1 may contain up to #ac per cent4 of fatty matters4 ,upper leathers1 which need to be soft and pliable as well as waterproof and durable1 are very heavily stuffed and often contain up to #cj-dj per cent4 of grease4 ,sole leather is thus rather distinct from the rest1 which are called curried1 stuffed1 or dressed leathers4 ,the actual drying out before1 after and between the various mechanical operations1 each have an appropriate degree of wetness4 ,in this country the drying is usually under the prevailing atmospheric conditions and is known as weather drying4 ,the goods are suspended by hooks or strings or by laying over poles in special sheds fitted with louvre boards by which the rate of drying can be roughly controlled4 ,weather drying is cheap1 but exceedingly slow1 and in unfavourable weather is very unreliable4 ,the goods1 moreover1 need constant attention to obtain an even result4 ,steam pipes are usually laid along the shed floors1 and are used in winter and damp weather to accelerate the drying1 and also in the final shed stove to remove the last traces of moisture4 ,wet weather1 however1 will not stand a high temperature1 and steam drying is better avoided when possible4 ,air-dried leather still contains about #ad per cent4 of moisture4 ,many systems of shed ventilation have been suggested to hasten the drying and to secure a better control of the process4 ,in one system a screw fan is fitted at one end of a shed 7without louvre boards7 and sucks air through the goods from an inlet at the other end4 ,the air can be heated by a steam coil near the inlet4 ,in another system a centrifugal fan blows air through an arrangement of pipes which distributes it to the drying sheds1 and discharges it close to the floor by various branch pipes4 ,the outlets are near the roof4 ,a system of dampers permits hot air1 warm air and the used wet air to be blended in the desired proportions4 ,in ,america turret drying has been used4 ,the sheds are vertically above one another and have latticed floors4 ,heated air is admitted at the bottom and rises through the goods up the building just as in a chimney4 ,for many of the finishing operations it is important to obtain the leather in a uniformly half dry or sammed condition4 ,this may be done by careful drying1 and wetting back the parts that have become too dry with tepid water or weak sumac liquor1 and then leaving the goods in pile until of uniform humidity4 ,it may also be done by wetting back leather which has been completely dried out4 ,there are also samming machines which by means of rollers squeeze out the excess liquor4 ,sole leather is dried out and finished immediately after tanning1 but dressing leather is often rough dried out of tan liquors and wet back for finishing when required4 ,dressing leather is often treated in different factories2 tanners selling it as rough leather and curriers finishing it4 ,scouring is one of the first operations in finishing leather4 ,the grain side is wet and worked with brushes and stones until the bloom and loose tannin are removed4 ,this process aims at producing a good even colour and level surface1 but is liable to cause a loss of weight4 ,dressing leather is often scoured on both grain and flesh1 and weak soap or borax solutions are used to assist the process4 ,in this operation hand labour has been now quite superseded by machine work4 ,a great variety of machines have been devised4 ,the mechanical working of leather takes place in various parts of finishing4 ,these operations1 known as striking1 setting1 pinning1 jacking1 may be carried out often by the same machine as used for scouring1 but with a change of tool4 ,the object of these operations is to get rid of wrinkles and creases1 to produce softness1 pliability and area1 and to remove superfluous moisture1 grease1 dirt4 ,the tools are of steel1 brass1 slate or vulcanite4 ,scouring is often effected by putting the goods into rotating drums together with extract and sumach4 ,the bloom is removed by friction1 the colour is improved by the sumach1 whilst the extract keeps up the weight4 ,in finishing sole leather firmness is enhanced by rolling4 ,a brass roller passes to and fro over the goods with the exertion of considerable pressure4 ,the operation is carried out by machinery4 ,shaving is an important operation in the case of many dressing leathers4 ,its object is to produce a uniform thickness of the leather and an even surface on the flesh side4 ,the sammed goods are laid over suitable beams and shaved with special sharp knives which possess a turned edge4 ,this hand process1 which demanded considerable skill1 is fast becoming extinct1 and machine shaving is already almost universal on account of its greater speed4 ,the machines consist essentially of two rollers1 one of which is smooth1 whilst the other is a spiral knife-blade cylinder 7cp4 ,section ,,ii474 ,the sammed goods are held in the hands and placed over the smooth roller1 which is raised to the cutting roller by a foot treadle4 ,a number of similar operations 7flatting1 whitening1 buffing7 are carried out by a suitable change of tool4 ,in all these operations good samming is important4 ,splitting is another important operation on tanned leather4 ,in this process the leather is cut parallel to its grain surface1 thus yielding two pieces with the same area as the original1 the grain and the flesh split4 ,it is essentially a machine operation1 and is carried out by presenting the carefully sammed leather to a sharp knife-edge1 towards which it must be constantly pressed4 ,the band knife machine is the most popular arrangement4 ,the knife is an endless belt1 which continually revolves round two pulley wheels of equal size4 ,in between these the knife is horizontal1 and is then used for splitting4 ,the sammed leather is pushed towards the blade by two feed rollers1 and the grain passes above the knife on to a small platform1 whilst the flesh or split passes below and falls to the ground4 ,emery grinders and thick felt cleaners in the lower part of the machine keep the knife in good condition4 ,the adjustment of the machine is delicate and requires considerable experience4 ,with care splits may be obtained down to #a_/af thick1 and sometimes as many as #f or #g splits are obtained from one hide4 ,oiling is still usually done by hand1 and cod oil is still preferred for many classes of goods4 ,of recent years there has been a great extension of the use of sulphonated oils1 which have the valuable property of forming an emulsion with water or tan liquor4 ,with these materials it is easier to ensure the goods being completely covered with oil4 ,the penetration of the oil into the leather is also quicker and more complete4 ,these oils have often the disadvantage of leaving solid fats on the exterior of the leather1 which gives it an ugly smeared appearance4 ,stuffing the dressing leathers is carried out in a variety of ways and with a variety of materials4 ,the old process of hand stuffing employs a mixture of tallow and cod oil called dubbin4 ,this is made by melting the ingredients together and allowing them to cool with constant stirring to a nearly homogeneous salve4 ,the dubbin is brushed thickly on to the flesh side of the sammed leather1 which is then hung up to dry4 ,as the moisture dries out the oils and soft fats penetrate the leather and leave the more solid fats on the outside4 ,the proportions of tallow and oil are varied with the time of year and with the method of drying1 for if the dubbin be too soft it will run off the leather1 and if too hard will not penetrate it so well4 ,drum stuffing is a more modern development in which a higher temperature is employed1 about #adj ,f4 ,the drum is heated up by steam or by hot air1 and the sammed goods are then inserted and drummed for a few minutes until they are warmed4 ,the drum is fitted with a heated funnel containing the melted grease1 which is run in through the hollow axle4 ,after a half to three-quarters of an hour's drumming the grease is completely absorbed by the leather4 ,the drumming is continued for a while until the goods have cooled4 ,whilst still warm they are set out to remove creases and superfluous grease4 ,drum stuffing is not only quicker than hand stuffing1 but also makes it possible to use the hard fats1 and so make a leather which carries more grease without appearing greasy4 ,thus in drum stuffing1 paraffin wax and wool fat are used1 and their penetration assisted by small proportions of cod oil or dgras4 ,if the leather be too wet the grease is not absorbed1 whilst if it be drier than usual the leather will take more grease1 but the resulting colour is not so good4 ,there is also another method of stuffing which originates from the ,continent4 ,it is known as burning in and involves the use of still higher temperatures 7#aie to #bab ,f474 ,wet leather will1 of course1 not stand this temperature1 so that it is first necessary to make the leather absolutely dry4 ,this is effected by drying in stoves at temperatures up to #aaj-aae ,f4 ,there are two ways in which the grease is applied4 ,in one method the melted grease is poured by a ladle on to the flesh side and brushed over until evenly distributed4 ,a second application of grease is made to the thicker parts4 ,the hides are then put into warm water 7#abj ,f47 for about a quarter of an hour1 and then drummed for half an hour4 ,in the other method the goods are completely immersed in the melted fats for a few minutes in a steam-jacketer tank at a temperature of #aie ,f4 ,after softening in water at #abj ,f4 the goods are drummed4 ,burning in is used for the heavier dressing leathers such as belting and harness4 ,it does not give good colour1 but permits the employment of still more hard fats4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 pp4 #bbc1 #cgh4 ,bennett1 ,manufacture of ,leather1 pp4 #bea-cab4 ,bennett1 ,principles of ,leather ,stuffing1 ,leather ,trades ,review1 #aiaa1 #ahf4 ,,section ,v4--,,sole ,,leather ,leather for the soles of boots and shoes is a matter of essential interest to all1 and forms one of the best appreciated applications of animal proteids to useful purposes4 ,methods for its manufacture are as numerous as the factories producing it1 hence all that can be done is to describe broadly the general method which is typical of our time1 to classify the many varieties into types1 and to indicate the recent changes and present tendencies4 ,sole leather is mainly manufactured from butt pelt1 and the great aim is to produce a firm1 thick1 waterproof and smooth grained leather which will bend without cracking4 ,it must have a light tan colour to be saleable1 and contain as much weight as possible to be profitable4 ,the modern mixed tannage of sole butts or scoured bends generally utilizes ox-hides of the ,scotch and ,english markets1 though salted ,continentals and ,south ,americans are also employed4 ,after the usual soaking a short and sharp liming is given4 ,the special aim in liming sole hides is to obtain the maximum plumping effect with the minimum loss of hide substance4 ,both these achievements are necessary to obtain good weight4 ,the limes should be kept as clean as possible1 which is best obtained by putting clean hides into work4 ,this reduces bacterial activity and loss of hide substance4 ,the shortness of the process is attained by the use of sodium sulphide 7from #b to #af ozs4 per hide of sulphide crystals71 by which depilation may be accomplished easily in about nine days4 ,the amount of sulphide should be increased somewhat in the short-hair season and in cold weather4 ,some factories take up to about #ab days using less sulphide1 whilst others will lime in about a week by using the larger quantities4 ,the amount of lime used varies enormously1 and is invariably in great excess of the actual requirements4 ,probably #b-c per cent4 on the green weight of the hides is all that can be really utilized1 the remainder being wasted4#e ,this amounts to about #b-a_/b lbs4 lime per hide1 but in practice it is more frequent to find #g1 #h1 #i or even #aj lbs4 per hide being used4 ,the excess is innocuous1 owing to the limited solubility of lime4 ,some excess is desirable1 to replace in the liquor the lime adsorbed by the goods in plumping1 to assist bacterial activity1 and also because in sharp lime liquors the undissolved portions do not remain so long in suspension4 ,the use of sulphide and other alkalies does not make it possible to reduce the amount of lime used1 it merely renders the excess more superfluous4 ,the use of sulphide not only shortens the process1 but also sharpens it1 on account of the caustic soda produced by hydrolysis4 ,usually for sole leather1 however1 it hardly sharpens it sufficiently1 and it is very common to add also caustic soda 7or carbonate of soda7 to the limes4 ,about #b ozs4 caustic soda 7or its equivalent in carbonate7 is used per hide4 ,the hides are limed generally by the three-pit system1 giving about three days in each pit4 ,they should be handled each day in the first pit 7old lime7 and once in the other pits4 ,footnote #e3 ,procter1 ,principles of ,leather ,manufacture1 p4 #abi4 ,unhairing and fleshing by hand labour is still common1 in order to avoid great pressure on the plumped hide4 ,scudding should be very light1 and in some yards is entirely omitted4 ,only the lime on the surface of the hide should be removed by deliming1 and this immediately prior to the insertion of the butts into the tan liquor4 ,this is to ensure good colour and yet keep the butts plump4 ,boric acid is the best for this purpose1 using #aj-ae lbs4 per #ajj butts4 ,the goods are inserted 7and preferably rocked7 in a dilute solution for a few hours only4 ,about the same quantity of commercial lactic acid may be substituted for the boracic4 ,this deliming can also be accomplished by adding the acid to the worst suspender in the tanyard4 ,to obtain firmness and plumping it is necessary that the early liquors in tanning should be more acid than for other leathers4 ,with old methods of tanning one could trust to the natural sourness of the liquors to complete the deliming and replump the goods with acid4 ,in such cases any deliming was also unnecessary4 ,in the modern yard1 however1 we get sweet liquors coming down the yard1 partly on account of the greater proportion of extract used and partly because the liquors themselves are not so old4 ,hence it is now practically always necessary to acidify artificially the tan liquors4 ,this may be done by adding a few gallons of lactic1 acetic1 formic1 or butyric acid to the handlers and suspenders1 especially in the winter and spring4 ,it is now increasingly common to place sole butts in a special acid bath after they have been in tan liquor for about a week4 ,this bath is often made from sulphuric acid1 and may be #a or #b or even #d per cent4 in strength4 ,the actual tanning of sole butts lasts three to four months1 and just prior to the war the tannage consisted often of about one-third myrabs1 one-third valonia1 and one-third extract4 ,the myrabs and valonia were leached together1 and the extract added to the best leach to make layer liquors of the required strength4 ,some mimosa bark was generally used also1 and now it is extensively employed to replace the valonia4 ,the most widely preferred extract is chestnut1 but quebracho1 myrabs extract and mixtures have also a prominent place1 and mimosa bark extract an increasing importance4 ,it is recognized that this tannage is if anything too mellow1 and that if only a smooth grain and plump butt can be ensured in the first weeks of tanning1 it is much better for sole leather to employ the most astringent tans possible and the sharpest liquors 7i4e4 liquors with a small relative proportion of soluble non-tannin matters74 ,hence there is the tendency in sole-leather tanning to employ fresh clear liquors for the butts and use up the more mellow liquors on the offal 7shoulders and bellies74 ,four types of sole butt tannage will now be described1 all of which illustrate the methods employed in a modern mixed tannage4 #a4 ,the first type consists in a four-months tannage1 in which the liquors are worked down the yard4 ,the butts pass first through the suspenders 7#bj-dj ,bkr47 in about a week1 and are rocked in the first liquors4 ,they next enter the handlers 7#dj-ee7 rounds of eight pits1 six floaters and two dusters4 ,myrabs1 or a mixture with algarobilla is used as dusting material4 ,the goods remain in this set for two weeks1 and should then be struck through4 ,the suspender handlers 7#ee-fe7 are next entered1 in which they remain up to three weeks in suspension1 being shifted forward on alternate days4 ,the goods now enter the layers1 of which four are given3 first #gj for one week2 second #ge for two weeks2 third #hj for three weeks2 and fourth #ij for a month4 ,the goods thus take sixteen weeks to tan1 of which ten weeks 7#fb-a_/b per cent47 are in layers4 ,the system of working the liquors is expensive1 and is only possible if the butt liquors can be spent out by the offal4 ,the best or fourth layer1 #ij1 is made from the best leach liquor1 #fe1 and extract 7chestnut with some oakwood or mimosa bark74 ,after use it becomes the second layer1 #ge4 ,the third layer1 #hj1 is also made from fresh leach liquor and extract 7chestnut with some myrabs or mixed extract74 ,after being used thus it is used for the first layer1 #gj4 ,the used first and second layers are mixed together and used partly to form the belly layers1 and partly to make a sharp liquor for the handlers 7#ee-dj7 by diluting with #dj leach liquor and adding quebracho extract4 ,the old handler liquor is run to the suspenders 7#dj-bj71 and finally used for colouring off the offal in drum or paddle #ah4 ,the suspender handlers 7#fe-ee7 are made from fresh leach liquor and chestnut extract4 ,they are afterwards used to make shoulder layers4 ,the course of the liquors is shown in the diagram below4 ,it will be seen that fresh leach liquor and fresh material are used to each set except the suspenders1 which must have some mellowness to ensure plumping and smooth grain4 ,layer liquors are used twice only1 and then 7when only five weeks old7 pass to the handlers4 ,these are further sharpened by fresh leach liquor and fresh extract and dry materials4 ,the forward handlers are fresh liquors with fresh extract4 ,this tannage is fairly typical of high-class sole leather1 in which the liquors are worked down the yard1 but worked towards the offal1 which thus receives liquors with relatively greater proportions of mellow tans and soluble non-tans4 ----------,leach liquor------------------- _/ ,v #dth layer1 #ij ,v ,v #crd layer1 #hj #bnd layer1 #ge ,v #ast layer1 #gj _/ _/ ,v ,v 7mixture7--bellies _/ ,v ,v ,v ,suspender handlers--7#fe-ee77shoulders7 ,handlers1 #ee-dj ,v ,suspenders --offal #b4 ,the second type consists in a tannage of about four months1 in which the liquors are not worked down the butt yard4 ,in this method also there is an attempt to save much of the labour in handling1 first by shortening the time in the handlers by one week 7as compared with the above71 and second by fusing the two progressive handler sets into two sets of equal strength1 through which the goods pass more slowly and with less disturbance4 ,the goods go through the suspenders 7#aj-be7 in about a week1 rocking in the early liquors1 and then into large rounds of handlers 7#cj-de7 for one month4 ,the handlers consist of floaters and several dusters1 in which the butts are laid away with #a-c cwt4 myrabs4 ,the goods next enter the layers1 of the same strength as in ,type #a1 and in which they remain the same time4 ,the total tannage is thus #ae weeks1 of which #aj weeks 7nearly #fg per cent47 are in layers4 ,the best or fourth layer is made up from leach liquor and extract1 and is then used successively as a third1 second and first layer1 and then passes to the offal layers4 ,the handler liquor is made entirely from fresh leach liquor and quebracho extract1 and is a sharp liquor of greater strength than its ,bkr4 strength would indicate4 ,the old handler liquor is run to the butt suspenders4 ,the course is represented thus3-- ,leach liquor _/ _/ #dth layer1 #ij _/ _/ #crd layer1 #hj _/ _/ #bnd layer1 #ge _/ _/ #ast layer1 #gj--offal layers ,v ,handlers 7#de-cj7 ,v ,suspenders 7#be-aj7 #c4 ,the third type consists of a short three-month's tannage in which the liquors are worked straight down the yard4 ,to compensate for the short time it is necessary to have stronger layer liquors in which the goods spend a still greater proportion of their total time4 ,the stronger liquors involve a greater proportion of extract1 particularly of quebracho1 which fact causes the whole of the liquors to be sharper than their ,bkr4 strength indicates1 and justifies them being worked straight down the yard4 ,the goods go through suspenders 7#bj-dj7 as usual one week1 and then pass into suspender-handlers 7#dj-fj7 for two weeks1 and thence to the layers4 ,in the first two of these 7#fe and #gj7 they are actually in suspension1 a week in each liquor4 ,they are then dusted down for ten to eleven days1 first in #he and then in a #ie liquor1 and finally for a month in a liquor of #aaj4 ,the total tannage is thus twelve weeks1 of which nine weeks 7#ge per cent47 are in layers4 ,there is considerably less handling than in ,type #b1 and it is more convenient1 the goods being in suspension4 #d4 ,the fourth type is also a three-month's tannage4 ,in this it is attempted to obtain even greater weight with still less labour4 ,the layer liquors are kept much stronger by the more extensive use of extract1 and this makes it impracticable as well as too costly to run these liquors down the yard4 ,they are therefore repeatedly strengthened with extract and used again4 ,the goods go through suspenders 7#bj-dj7 as usual one week1 and then through a round of suspender-handlers 7#dj-ee7 consisting of fresh sharp liquor from the leaches together with quebracho extract4 ,they are in this set two weeks1 and then are laid away4 ,they receive three layers3 first1 #aje for #b weeks2 second1 #aaj for three weeks2 and finally1 #abj for a month4 ,of the twelve weeks1 therefore1 nine weeks 7#ge per cent47 are spent in layers4 ,in this method the goods are immersed in #c per cent4 sulphuric acid after passing through the suspenders4 ,there is possible1 of course1 a tremendous number of variants of the above types4 ,the number of handler rounds is determined by the number of butts being dealt with4 ,with a large number it is more easily possible to arrange for them to be in progressive strength as in ,type #a4 ,there are also many systems of working the layers1 of which the most notable is to make the second or third layer from fresh leach liquor and extract1 and strengthen it with extract for the succeeding layers4 ,it is then used as a first layer and worked down the yard4 ,the bellies and shoulders often go through separate sets of liquors1 but it is common to put them through suspenders1 and even handlers together4 ,they receive1 of course1 a distinctly shorter tannage1 and are often drummed with extract before laying away or after the first layer4 ,by way of illustration1 the course of the offal and their liquors may be given in the case of ,type #a4 ,the shoulders and bellies are coloured off in a paddle or drum with old butt suspender liquor1 which is then quite exhausted4 ,they then pass through suspenders 7#ah-dj7 together in #d-e days1 and go through a handler round 7#dj-ee7 for #c weeks1 including one duster4 ,the bellies are removed after #b weeks1 and given three layers 7#fj1 #gj1 #hj7 of a week each4 ,they receive1 therefore1 nearly #f weeks in all4 ,the shoulders also have three layers 7#fj1 #fe and #hj7 of #b1 #c and #d weeks respectively4 ,the course of the liquors is shown thus3-- ,butt layers ,butt suspender ,butt suspenders 7and extract7 ,handlers 7 extract7 ,v ,v ,belly layers ,shoulder layers 7#hj-fj7 7#hj-fj7 _/ ,v ,v ,offal handlers 7#ee-dj7 ,v ,v ,offal drums ,offal suspenders 7#dj-ah7 7#ah7 _/ _/ _/ _/ _/ _/ ,v ,v ,drain ,the tanned butts are piled for #b-c days1 sometimes rinsed to remove dusting material1 and then scoured either by machine or by drumming with sumac and extract4 ,this removes bloom1 but causes some loss of weight4 ,vatting or bleaching now follows1 in which it is attempted not only to bleach the colour of the leather1 but also to impart as much weight as possible4 ,the vat liquor is made several degrees stronger than the last layer by means of quebracho bleaching extract and good coloured chestnut or myrabs extract4 ,the liquor is kept warm by a steam coil1 at about #ajj ,f41 but not much more without risk4 ,the goods remain in the bleach liquor #b-c days and are then horsed or suspended to drain4 ,sumach is sometimes used in the vats4 ,a new vat liquor must be made up after some weeks' use4 ,the goods are sometimes rinsed in weak sumac liquor before vatting to get good penetration1 and sometimes after to ensure good colour4 ,the butts are next oiled and hung up in a dark shed and allowed to dry slowly and evenly to an india-rubbery consistency and rather slimy feel4 ,they are then struck out by machine1 wiped1 re-oiled and again hung up to dry1 preferably with sulphonated oil4 ,after a short drying to a suitable and even condition they are rolled on1 and1 possibly after further drying1 rolled off with greater pressure1 and then dried for a day or two with the help of a little steam4 ,finally they are machine-brushed and sent to the warehouse1 where they are weighed and classified4 ,the offal is often drum oiled4 ,it needs more striking and is more difficult to obtain in suitable condition for striking1 rolling4 ,it is treated similarly to butts1 but often also goes for dressing leather1 and may be split4 ,it is of some interest to compare the above processes with that once very popular manufacture of bloomed butts in the ,west of ,england from ,south ,american salted hides4 ,these receive a liming from #ab-ad days1 using #ab-af lbs4 of lime per hide4 ,they receive then a tannage of about #i months1 comprising #c weeks in suspenders 7#bj-dj7--very sour and mellow liquors--#d weeks in handlers 7#dj-ee71 #d weeks in dusters 7#fj71 #d weeks in round made from hemlock extract 7#fj71 and #bj weeks in six layers 7#fj-ij7 in which they were dusted heavily with valonia4 ,oakwood extract was used for the layers1 which took #eg per cent4 of the total time4 ,the butts were scoured in a much-dried condition1 so that only the loose and surface bloom was removed4 ,no bleaching was given in the modern sense4 ,in the old oak-bark tannage of sole leather up to #ab months were taken for tanning1 two-thirds to four-fifths of which time the goods were in layers4 ,the strongest liquor rarely exceeded #ej even where valonia and gambier were also used1 and rather more than #cj if not4 ,it will be understood from the above that the tendency for many years has been to shorten the time and the labour required for tanning4 ,drum tanning is obviously the next stage in shortening the time4 ,in one such process the butts are put through suspenders 7#be-dj7 for #b weeks1 drummed for #ab hours in an #hj extract liquor1 and finally in a neat extract #bjj for #cf hours4 ,drum tanned sole leather1 however1 is not as yet of good quality2 the grain is not smooth1 and the heavy weight finish 7striking and rolling7 needed to counteract this tendency is liable to cause poor substance4 ,the leather1 too1 readily wets and goes out of shape4 ,possibly some drumming may be adopted to save time in the early layers1 but the most serious rival to the #c months' tannage is the waterproof chrome sole leather 7,part ,,iii41 ,section ,v474 ,,references4 ,parker1 ,j4,s4,c4,i41 #aijb1 #hci4 ,procter1 ,principles of ,leather ,manufacture1 p4 #bbj4 ,bennett1 ,manufacture of ,leather1 pp4 #agi1 #bei4 ,bennett1 ,j4,s4,c4,i41 #aiji1 #aaic4 ,,section ,,vi4--,,belting ,,leather ,the manufacture of belting leather is well illustrated by the tanning and finishing of strap butts4 ,in general1 the tannage presents many points of great similarity with the tannage of sole leather2 indeed1 the resemblance is so close that in some factories there is little difference observed1 and the currying and finishing operations are relied on to produce the desired difference in final results4 ,nevertheless1 there is considerable difference in the type and ideal of the two leathers1 which may be expressed in trade parlance as a greater mellowness for the belting leather1 and in the best methods of manufacture this fact is in evidence throughout the whole process of manufacture4 ,in liming1 there need be little difference between sole and belting hides1 and a sharp treatment of #i-aj days1 by the three-pit system1 with a day or two extra in the coldest weather1 would meet ordinary needs4 ,for the conservation of hide substance and for the saving of time a shorter liming is sometimes given1 in which more sulphide is employed than is usual for sole leather4 ,even the very short processes of liming1 #a to #c days1 which involve the use of strong solutions of sodium sulphide1 have been successfully employed for belting leather4 ,the tendency to harsh grain with such processes is not so serious a defect with belting as with sole leather1 and can be minimized by careful deliming4 ,american and ,continental factories tend to favour the use of those quick processes which employ warm water in addition to sulphide4 ,the hides after a short liming in sulphide limes are immersed in warm water1 which greatly accelerates both the chemical and bacterial actions4 ,for example1 after about #c days' liming1 in which both old and new limes are used as usual1 the hides may be thrown into water from #ajj-aje ,f41 and will be ready for depilation in #g or #h hours4 ,even a stronger liming may be given1 especially if the soaking is unusually prolonged4 ,such processes undoubtedly save hide substance1 and the pelt is obtained more free from lime1 but they have the disadvantage that the natural grease of the hide is only imperfectly killed 7i4e4 saponified or emulsified71 and may interfere with the normal course of the tannage4 ,the plumping is also apt to be insufficient4 ,on the other hand1 liming processes are also used in which a mellower liming or a longer liming is preferred in order to produce the desired degree of softness and pliability in the finished leather4 ,belting must not be too soft1 of course1 and it will be clear that the required difference from sole leather can be produced either in liming or tanning or partly in both4 ,these considerations also decide whether bating is to be omitted or not4 ,a hard astringent tannage in sour liquors after a sharp liming might make bating essential1 but in these days it is usual to avoid it and produce the effect in other ways4 ,a light bating of a few hours is sometimes given1 but it is more unusual to delime the grain thoroughly with boric acid1 using up to #bj lbs4 per #ajj butts4 ,crackiness is a fatal defect in strap butts1 so that a sound grain must always be obtained4 ,generally speaking1 therefore1 strap butts receive more washing in water1 and rather more deliming than sole leather1 even when they are not bated4 ,it is also usual to scud much more thoroughly1 and to round a larger proportion of butt1 especially in length4 ,the tannage is usually carried out with a blend which includes a much greater proportion of the fruit tans1 and correspondingly less of extract4 ,distinctly more myrabs are used than in sole leather tannages1 in the dry material1 and amongst the extracts chestnut is preferred to quebracho1 and myrabs to mimosa bark1 though all these may be used in some degree4 ,in the past the most favoured extract has been undoubtedly gambier1 which gives a tannage which is easily curried and imparts the required mellowness to the uncurried leather4 ,the great expense of this material1 however1 together with the advent of drum stuffing and shorter tannages in stronger liquors1 have tended to cause a considerable reduction in the proportion used for strap butts1 and to limit its employment to the earlier stages of tanning4 ,the same tendencies for reducing the time taken to tan1 employing stronger liquors1 and securing economy of labour in handling1 have been evidenced in the tannage of strap butts as in sole butts4 ,it is nevertheless true that1 broadly speaking1 strap butts receive rather more handling and rather weaker liquors than sole butts4 ,a greater amount of mechanical assistance is also employed with early stages 7paddling1 drumming1 rocking74 ,this is less objectionable for curried leather than for sole butts4 ,the handling is more usually in suspension4 ,the liquors are usually worked straight down the yard as a greater mellowness is needed in the early liquors than for sole butts4 ,the offal is given a separate tannage and often used for different purposes1 e4g4 the shoulders for welting and the bellies for fancy goods4 ,plumping with sulphuric acid is generally considered inadmissible for strap butts4 ,it has been shown that leather containing sulphuric acid tends to perish after the lapse of a number of years4 ,sole leather will be worn up before this effect is observed1 but belting is an article which is intended to last much longer1 and the use of sulphuric acid is consequently inadvisable4 ,plumping must be obtained1 to a considerable extent1 but must be achieved by the organic acids 7lactic1 acetic1 formic and butyric acids74 ,a few gallons of such acids are consequently added to the handlers1 especially in the winter and spring4 ,less may be used in the autumn1 when the layer liquors which fermented in the summer months have worked down to the suspenders4 ,a mixture of these acids is usually better than any one alone1 for they not only differ very considerably in price1 but also have different powers of neutralizing lime and plumping the goods4 ,lactic acid 7,m4,w4 #ij71 ,acetic acid 7,m4,w4 #fj71 and formic acid 7,m4,w4 #df7 are each monobasic acids2 consequently #c lbs4 formic will neutralize as much lime as #d lbs4 acetic or #f lbs4 lactic4 ,their plumping powers are somewhat influenced by the anion4 ,in determining what quantities to take1 the commercial strength of the acids must also be considered4 ,formic is often #hj-ij per cent4 pure1 acetic #fj-hj per cent41 and lactic #dj-fj1 but may be as low as #be per cent4 ,the blend must be adjusted accordingly4 ,as strap butts do not need the firmness of sole leather1 less of these acids may be used than for sole butts4 ,the exact nature of the tannage and the strength of the liquors is largely influenced by commercial considerations4 ,if the manufacturer is both tanner and currier1 he need not go to such great expense in strong liquors and in time in layers1 for he can obtain some of this weight in currying4 ,if1 however1 the tanner sells the butts rough dried1 he must naturally aim at obtaining greater weight in tanning4 ,the actual details of the tanning processes are as usual very varied1 but may be classified according to type1 just as in the case of sole butts4 ,illustrations will now be given4 ,type #a1 which may be compared with ,type #a for sole butts1 is a tannage of about #e months4 ,the goods pass through suspenders 7#h-cj7 in #b-a_/b weeks1 and then pass to the handlers 7#cj-ej71 in which they remain a month2 they are then put into suspension again and pass through the suspender handlers 7#dj-ee71 which takes #b-a_/b weeks4 ,in this round much gambier is added1 and the goods are frequently handled4 ,four layers are usually given1 viz4 first layer #ee1 one week2 second layer #fj1 two weeks2 third layer #fe1 four weeks2 and fourth layer #ge1 four weeks4 ,the tannage is thus #bj weeks1 of which #aa weeks 7#ee per cent47 are in layers4 ,extra layers may be given to heavier goods1 using stronger liquors made up with extract4 ,all liquors work straight down the yard4 ,the tannage consists of #ce per cent4 myrabs1 #ce per cent4 valonia1 #aj per cent4 ,natal bark1 and #bj per cent4 extract1 chiefly gambier1 though some chestnut and quebracho are used4 ,type #b represents the modern tendency to use stronger liquors and a shorter time4 ,the strap butts pass through the suspenders 7#bb-ej7 in #a-a_/b weeks1 during about a third of which time they are rocked4 ,they next pass through two sets of suspender-handlers 7#ej-fg and #fg-hj71 which takes a month1 and thence to the layers4 ,three layers are given 7#he1 #ij and #ajj71 in which the goods remain one1 three and four weeks respectively4 ,the tannage is thus #ac-a_/b weeks1 of which #h weeks 7nearly #fj per cent47 are in layers4 ,the liquors work down the yard4 ,longer time may be given to heavier goods4 ,the tannage consists of #dj per cent4 myrabs1 #ce per cent4 valonia or ,natal bark1 and #be per cent4 extract1 chiefly chestnut1 though some gambier may be added to the suspenders4 ,however tanned1 strap butts are first dried out rough over poles4 ,this assists in making the tannage permanent1 on account of secondary changes discussed in ,section ,,iii4 ,they are next wet back for currying by soaking in water or sumach liquor for a few hours and piling to become soft and even4 ,the first operation is skiving1 which is a light shaving on the flesh side1 carried out by a sharp slicker with a turned edge4 ,the butts are next scoured thoroughly by machine on both flesh and grain1 and sumached in a vat for several hours at #ajj ,f41 after which they are slicked out and hung up in a cool shed to samm for stuffing4 ,hand stuffing is often still preferred1 with tallow and cod oil4 ,the butts are next set out1 and it is important that this should be thoroughly done4 ,machines are now generally used1 and the goods are often reset after further drying4 ,after drying out completely they are given a light coating of tallow and laid away till wanted for cutting up into straps1 which is now done by machinery4 ,a ,continental method for making belting leather is to give #f weeks in a suspender set 7#gj-bd7 of twelve pits arranged on the press system1 running two fresh liquors a week1 and to give them two layers 7#bd and #bh7 of #f and #h weeks4 ,the material is chiefly pine bark1 but some oak bark1 valonia1 myrabs and quebracho are also used4 ,the goods are stuffed by burning in1 molten fat being poured on the flesh side4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp #aid1 #bie4 ,,section ,,vii4--,,harness ,,leather ,when discussing the question of oak bark 7,section ,,iii471 reasons were advanced for its decreased use and popularity4 ,these were quickly appreciated in the sole leather trade1 but the obsolescence of oak bark in the dressing-leather section was much more prolonged1 partly because there was less pressing need to obtain good weight in the actual tanning1 and partly because in some branches of dressing leather1 such as belting and harness1 a leather was required of great durability and toughness1 for which qualities oak bark tannage had a deservedly high reputation4 ,hence harness leather manufacture affords a good illustration of the transition between the methods of the late nineteenth and those of the twentieth century4 ,with the use of oak bark lingered the old methods of liming1 bating and tanning in weak liquors for a long time with plenty of gambier4 ,hence in this section it will be necessary to observe a gradual transition of method1 both in wet work and tanning4 ,it should be pointed out that this transition has not been and is not going on in all factories at the same rate4 ,many factories remain in which the old methods are still preferred at some stages of the manufacture1 and some remain in which many of the changes indicated below have not taken place at all4 ,the leather trade has always been considered conservative in its methods1 but it should be realized that much of the prejudice in favour of old methods is due to the public1 and that after all tanners and curriers1 like other business men1 have to suit their customers4 ,the march of industry is not like a regiment in line2 it is rather more like nature1 a survival of the most adaptable4 ,hides for harness leather are limed in various ways1 of which the following are types4 #a4 ,a rather mellow liming of #aj-ae days 7longer than for sole leather71 in which nothing but lime is used1 and a certain amount of old liquor used in making up the new limes4 ,the liming was carried out by the one-pit system1 but the goods and liquors were kept clean by a good soaking process4 ,hence the loss of hide substances was not very great2 goods so treated were bated before tanning4 #b4 ,a shorter liming than the above by the three-pit system4 ,this saved time 7taking #i-aj days71 saved hide substance1 and ensured greater regularity of treatment4 ,the limes were about as mellow1 but a little sulphide 7#b-d ozs4 per hide7 was used to assist the depilation1 especially during the short-hair season4 ,these goods were also bated4 #c4 ,a distinctly longer liming1 #ae-af days1 in mellower limes4 ,this differed from ,type #a also in the respect that greater regularity was ensured by the three-pit system2 a foot or two of old liquor was used in making up the new lime4 ,more hide substance was lost than in either of the above processes1 but this was deliberate1 the object being to dispense with bating1 which is always light for harness hides4 ,thus a longer and mellower but systematic liming was used as a substitute for shorter liming and bating4 ,no sulphide was used in this process4 #d4 ,a short liming of #f-g days1 using up to #ab ozs4 of sulphide per hide4 ,the object here is to save time and hide substance4 ,the three-pit system is preferred4 ,bating again becomes necessary1 but the pigeon-dung bate is replaced by artificial bates1 less objectionable1 quicker1 and more scientific in management4 #e4 ,a still shorter process of about five days1 using still more sulphide 7about #af-bj ozs4 per hide71 together with some calcium chloride to reduce harshness4 ,in such a method there is a tendency to revert to the one-pit system1 which involves rather less labour4 ,the three-pit system shows to a great advantage in the longer processes of liming when the process is reduced to five days2 there is little difference between the two1 for a one-pit system is a two-liquor method4 ,hence again an artificial bate is used4 ,the various methods of liming1 together with analogous variations in tannage1 have resulted in great variety in bating4 ,sometimes up to three days' bating has been given at #gj ,f41 but more often the goods are merely immersed overnight1 and then delimed with boric acid1 but with sulphide processes it is an advantage to use some of the commercial bates of the ammonium chloride type1 and finish off with boric acid4 ,scudding is always more thorough than for sole or belting1 the hides are rounded into long butts which include most of the shoulder harness backs4 ,the goods are sometimes bate shaved4 ,a few tannages will now be outlined1 in order of historic type4 ,type #a may be taken to represent the so-called high-class process in which oak bark myrabs and valonia are the staple materials4 ,a good deal of gambier is also used1 and a little myrabs and chestnut extract are helpful in attaining the desired strength of liquor4 ,the backs go first through suspenders 7#h-cj71 which takes up to three weeks1 and then in to handlers 7#cj-dj7 for four weeks1 consisting of rounds of clear liquor4 ,they next go through a duster round1 in which they are put for a week with oak bark and myrabs into a liquor of #de4 ,four layers are given 7#ej1 #ee1 #fj and #fe71 in which the goods remain for two1 three1 four and five weeks respectively1 oak bark being the chief dusting material4 ,the tannage is thus for twenty weeks4 ,light backs receive less time in the layers 7only #aa weeks74 ,if the tanner is also the currier1 the fourth layers are omitted4 ,he then saves five weeks and gets the weight in the stuffing4 ,type #b is a tannage in which oak bark and valonia are replaced by myrabs1 mimosa bark and chestnut extract4 ,it is therefore considerably cheaper and probably no less durable4 ,expense is also curtailed in handling4 ,the harness backs go through suspenders 7#af-cj7 in two weeks1 handlers 7#cj-de7 in four weeks1 and then receive four layers of the same strength as in ,type #a1 but only one1 two1 three and four weeks respectively4 ,the last layer is omitted for light harness1 and an extra layer of #ge is given if the tanner is not the currier also4 ,thus the usual tannage is #af-bj weeks1 of which #aj-ad weeks 7#fc-gc per cent47 are in layers4 ,type #c is a tannage which may consist of myrabs 7#ee per cent471 valonia or mimosa bark #be per cent41 and extract 7#bf per cent474 ,the extract is chiefly quebracho1 though some chestnut may be used4 ,more valonia and less myrabs may be used if desired 7and when possible71 and myrabs extract will then replace quebracho and chestnut4 ,the goods are coloured off in drums or paddles1 and then pass through two sets of suspenders handlers 7#bj-ee and #ee-ge74 ,they are handled up and down very frequently in the first set and rapidly pass into stronger liquors4 ,the backs then receive three floaters at #hj1 in each of which they remain one week4 ,the tannage is completed by three layers3 first1 #he for one week2 second1 #ij for one week2 third1 #ie for two weeks4 ,the tannage is thus #aa weeks1 of which #g weeks involve little labour4 ,if the tanner is not the currier1 still stronger liquors may be used4 ,in all these tannages little or no acid is used for plumping1 as the natural acids of the liquors are sufficient to ensure what is necessary in this direction for this class of leather4 ,a little organic acid or even boric acid may be used in the earliest liquors for deliming purposes1 when necessary4 ,after tanning the goods are dried out and sorted in the rough state4 ,harness is a somewhat broad term1 and there is scope for considerable variety in classification4 ,the hides are sometimes not rounded until after tanning4 ,the finished article may be any grade between heavy harness for artillery and leather for ordinary bridles4 ,in currying heavy black harness1 the backs are soaked and sammed for shaving4 ,lighter goods may be machine-shaved1 but the heaviest are shaved lightly by hand over the beam or merely skived with the shaving slickers4 ,the neck needs most attention1 and it is often advisable to stone by machine and split4 ,the scouring should be thorough1 on flesh and grain4 ,this is done by machine1 and not only cleans the goods from bloom1 dirt and superfluous tan1 but also assists in setting out4 ,sumaching may be for several days1 merely overnight or even only for a few hours1 being stoned after wetting back to temper4 ,hand-stuffed goods get a coat of cod oil first1 and during the drying are often well set out4 ,drum-stuffed goods are well set out by machine1 and after some drying1 stoned and reset by hand4 ,it is now usual to buff the grain1 i4e4 remove the coarser parts by light shaving4 ,this prevents cracking in the finished article4 ,the goods are blacked with logwood1 iron and ammonia1 thinly dubbined again1 again well set out and tallowed4 ,setting out1 indeed1 may be done at any convenient opportunity4 ,the superfluous grease is removed by slicking1 scraping1 brushing with a stiff brush1 and finally with a soft brush4 ,for brown harness the goods are more carefully selected1 more thoroughly scoured and sumached1 and bleached frequently with oxalic acid4 ,they are hand stuffed1 stained twice1 and after the usual setting out1 glassing and brushing1 are finally rubbed with flannel4 ,for bridle leather the goods are carefully shaved but are not stuffed1 being merely oiled with cod oil on flesh and grain4 ,they are dried out before scouring1 and then sized1 set out1 stained and resized4 ,the goods are heavily glassed during the finishing4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp4 #aie1 #big4 ,section ,,viii4--,,upper ,,leathers ,the manufacture of leather for the uppers of boots and shoes embraces a bewildering variety of goods1 suitable for anything between a baby's shoe and a man's shooting boot4 ,almost all degrees of lightness1 softness1 and waterproofness are in demand4 ,a great variety of finish is also involved1 determined by the ingenuity of the currier and the ever-changing fancy of the public4 ,even greater is the variety of methods by which all these results are obtained by methods which superficially seem quite different2 the desired qualities being imparted in one case largely by the tannage and in another case almost entirely by the currying4 ,under such circumstances the selection of types becomes a problem4 ,the variety1 moreover1 commences from the earliest stages1 the selection of the raw material4 ,upper leather may be made from light calfskins1 heavy calfskins1 kips 7home and foreign71 light dressing hides and heavy dressing hides1 which last may replace any of the former after splitting to the required substance4 ,in this section it will be necessary to take kips as typical of the rest1 and to use it in a rather broad sense1 including heavy calf and light dressing hides4 ,speaking quite generally1 kips for upper leather receive usually a long and mellow liming1 a thorough bating and a sweet and very mellow tannage in weak liquors4 ,in currying they are well scoured and set out1 heavily stuffed and stained black1 being sometimes finished on the grain and sometimes on the flesh4 ,these outstanding features of upper-leather methods will be further illustrated by a brief account of the tanning of kips 7light hide and heavy calf71 and outlining the best known types of finish for butt1 shoulder and belly4 ,the goods receive usually a long and mellow liming of #ad-af days1 using only lime as a rule4 ,in some factories lime liquors are used repeatedly for successive packs to an almost indefinite extent4 ,dissolved hide substance1 ammonia1 mud and dust1 and bacteria accumulate for months and sometimes for years4 ,it is obvious that in such liquors putrefaction is a more correct term than liming for the depilation4 ,such methods have been used even in recent years1 but there has now been a tendency for some time to make the liming more methodical4 ,such old limes make a leather which is empty1 loose1 and dull grained1 but the defects are minimized by the system of stuffing heavily and finishing the flesh1 and hence the ancient lime remained with surprising tenacity4 ,even so late as #aijc we find that ,procter with characteristic caution could write1 ,probably no lime ought to be allowed to go for more than three months at the outside limit without at least a partial change of liquor4 ,it is within the writer's experience to find an upper leather factory with limes which had never been emptied for over three years4 ,in other factories1 however1 there has been a revulsion of feeling with regard to such processes1 and it has been found advantageous to adopt a more scientific routine1 in which the lime pits are cleaned out at regular intervals4 ,there is little doubt that a mellow liming is desirable1 but this can be secured by blending some old lime liquors with fresh lime liquor in a systematic manner4 ,similar considerations apply to the question of working the various packs through the limes4 ,it is clear that with a mellow liming a one-pit system is quite possibly satisfactory1 but the revulsion of feeling against a lack of method produced a method of liming more elaborate than usual1 and it is now not uncommon to find kips limed in a round of #f-h pits1 the goods passing through each pit4 ,they remain in one pit about two days1 and are shifted forward4 ,in the green or old limes the goods are handled up and down4 ,the old limes are1 of course1 mellower than the new and exert the desired softening effect4 ,the working is quite analogous to that of a round of handlers4 ,unhairing is sometimes assisted by the use of arsenic sulphide4 ,e4,i4 kips need a thorough soaking before any liming2 several days are usually needed4 ,the old methods involving putrid soaks and stocks may be considered out of date1 and it is usual to soften back in caustic soda or sulphide soaks with some assistance by drumming4 ,a little sulphide is sometimes added to the older limes to continue the treatment4 ,the goods are next thoroughly bated and delimed4 ,the hen or pigeon dung bate is still usual1 and probably gives the best results1 though closer approximations have been made of recent years on artificial lines4 ,some bating with solution of hide substance seems necessary for these goods4 ,the lighter goods are often drenched also to complete the deliming1 using #f per cent4 bran on the weight of pelt4 ,the heavier goods are more often treated with boric acid after bating1 which not only delimes completely and gives a soft relaxed felt1 but also acts as antiseptic and stops the action of the bate1 a matter of some importance 7see ,section ,,ii474 ,lactic acid may substitute boric1 in which case about #b per cent4 on the pelt weight of #ej per cent4 acid may be required4 ,it is important to avoid a strong solution and local excess1 hence lactic acid must be added gradually so that the liquor is never stronger than #j4b per cent4 ,drumming and paddling is an advantage in deliming4 ,the tannage is light in most cases1 partly because some of the finished goods are sold by area1 but partly also because even if sold by weight1 the weight is obtained quicker and more easily by stuffing1 which course is also often preferable to obtain the desired mellow feel1 waterproofness and durability4 ,hence it is seldom that strong liquors are employed4 ,the tannage is also mellow1 on account of the softness and pliability required2 no acids are consequently employed1 and no material which is liable to yield sour liquors4 ,gambier is easily the first favourite amongst the tanning materials1 whilst oak bark comes second4 ,it should be observed1 however1 that a hypothetical tannage of equal weights of cube gambier and oak bark is in reality a tannage by four-fifths gambier and one-fifth oak bark1 on account of the relatively greater strength of the former4 ,this observation is so apposite with respect to some tannages that it is nearly correct to say that the tannage is gambier and the oak bark an excuse for having leaches through which the gambier liquors may be run occasionally to clear and to sharpen slightly4 ,no serious theoretical objection to such a method is possible if the liquors are weak and the system of working the liquors is scientific and the process carefully regulated4 ,upper-leather tannages1 however1 have scarcely merited scientific praise4 ,it is often a case1 not of poor methods1 but of no method at all4 ,the same lack of system1 principle1 and regularity observed with regard to the limeyard has been equally obvious in the tanyard1 when perhaps the need was even greater4 ,even a mellow tannage has varying degrees of mellowness possible to it2 there still remains the question of the soluble non-tans4 ,however1 method in the upper-leather tanyard has often been conspicuously absent4 ,there has been many a factory where any one tan liquor was as good as any other in the yard4 ,in the writer's experience are two such cases3 in one the liquors were all #be ,bkr41 in the other they were all #j ,bkr4 ,in such cases1 handling the goods from pit to pit is somewhat futile1 and handling forward from set to set still more so4 ,hence it is possible to find dressing leather tanned by putting it slowly through one round of handlers1 adding a few buckets of gambier where it apparently is necessary4 ,it is1 from one point of view1 surprising to see what serviceable and excellent-looking upper leather can be manufactured by such happy-go-lucky processes4 ,it is1 however1 also possible to see how this may occur4 ,gambier is a stable tan1 and no souring and little decomposition take place in gambier liquors4 ,it is also extremely mild and non-astringent1 and is always used in weak liquors4 ,the hides1 moreover1 are completely delimed1 and there is little danger of bad or uneven colour4 ,tanning under these conditions is at its easiest2 it is almost more difficult to spoil the goods than make them right4 ,under such conditions tanning deteriorated rather than improved in method4 ,when neglecting it made little difference to the finished leather1 it was neglected4 ,this state of affairs1 however1 was embarrassing whenever a tanner wished to try any other tanning material4 ,the expense of gambier and oak bark made valonia and mimosa bark into obviously desirable alternatives and substitutes4 ,methods which would tan with gambier1 however1 would not work with ,natal bark or valonia1 and many a tanner has had to revise his method of tanning from end to end4 ,the use of myrabs also raised the problem of souring1 and it has become evident that working the liquors down the yard is as desirable a method for dressing leather as after all other tannages4 ,it will be clear from the above that types of upper-leather tannages are less typical than for other leathers1 but nevertheless the more progressive manufacturers have for some years now been working on sounder lines1 economically and scientifically4 ,in such cases it is now usual to pass the goods through at least two sets of handlers1 and through liquors of gradually increasing strength4 ,occasionally dusters or layers are given1 especially for the heavier goods4 ,the tannage is nearly always commenced now by paddling the goods in the oldest liquor4 ,this paddling may be anything from half an hour up to twenty-four hours4 ,it is sometimes desired to work up a grain1 and the old liquor is then often sharpened by the addition of fresh gambier or leach liquor4 ,the same tendency to save labour in handling is to be observed in upper leather tannages as in sole and other dressing leather factories4 ,there is also a tendency to obtain rather more weight in tanning by using stronger liquors1 and in the heavier goods to shorten somewhat the time taken4 ,the following methods may be taken to illustrate modern processes1 in order of evolution4 ,they all last about seven weeks4 ,type #a4--;,in this process the kips are first paddled in an old liquor 7#c71 and passed to the first handlers 7#c-cj7 for three weeks4 ,after working through this set they pass through the second handlers 7#bj-cj71 in which they are not handled quite so frequently4 ,they are in this set also three weeks4 ,heavy goods may then receive a floater 7#cj7 for another week4 ,type #b4--;,in this process the goods are paddled1 and then enter a large handler round 7#h-cj71 through which they pass in five weeks4 ,the goods are handled frequently in the early stages4 ,the tannage is completed by one layer of two weeks 7#cj74 ,the layer is made by the ancient method of putting the goods and dust alternately into an empty pit1 and then filling up with liquor from the best leach4 ,oak bark1 valonia and myrabs are used as dust1 though sumach and gambler have been used4 ,type #c4--;,in this process an attempt is made to save handling and obtain more complete tannage4 ,the goods are paddled for three to five hours in a rather sharp liquor of #aj1 and are then handled well for a week in the first handlers 7#e-bj74 ,the goods then go through the second handlers 7#bj-de7 in six weeks1 and heavy goods may then receive an extra floater 7#de7 for one week4 ,in type #a the leaching material is two-thirds oak bark and one-third valonia2 in type #b it is half oak bark and half mimosa bark2 in type #c it is one-third oak bark1 one-third valonia or ,natal bark1 and one-third myrabolans4 ,in all cases the strongest handler is obtained from the leaches1 and made up to the required with strong infusion of gambier4 ,when the liquor has passed through the forward handlers1 it is returned to the leaches to clear and sharpen1 and then run to the green handlers4 ,after passing through this round it is returned to the paddle1 from which it passes to the drain4 ,the rest of the paddle liquor may be from the forward handlers4 ,it is often customary to obtain the best liquor from the second leach1 and allow the best leach to stand for a few days4 ,this allows the bloom to deposit in the leaches4 ,the system secures the result desired1 but the deposition of bloom involves a loss of tannin1 which waste makes the system expensive4 ,heavier dressing hides are tanned by methods similar to the above1 but with floaters1 dusters and occasionally layers added after they have passed through two sets of handlers4 ,thus they may have first handlers 7#h-ah7 two weeks2 second handlers 7#dj-de7 for six weeks1 making twelve weeks in all4 ,lighter goods may receive two rounds1 being two weeks in each4 ,after tanning1 the kips are rounded usually into butts1 shoulders and bellies1 to which different finishes are given4 ,the currying may be illustrated by selecting types1 but it must be borne in mind that there is much elasticity in this matter4 ,thus kips may be made into waxed butts1 satin shoulders and lining bellies1 but also may be cut down the back in sides1 both of which are finished limings4 ,waxed kip butts are a type of many similar upper leathers 7waxed shoe butts1 waxed calf1 waxed splits1 etc474 ,the finish is on the flesh side4 ,the kip butts are soaked carefully1 and shaved by machine4 ,they are then drummed in sumach for an hour or two1 slicked out and sammed for stuffing4 ,the sumaching is also the scouring unless the goods be too heavily bloomed4 ,the samming is often done by machine4 ,drum stuffing follows1 wool fat and stearin being staple greases1 with varying amounts of degras and cod oil1 and of tallow and cod oil4 ,a little paraffin wax and resin are also used sometimes4 ,the goods are well slicked out and dried4 ,they may be now dubbined and laid away to mellow for whitening1 which consists of a careful shaving of the flesh by a turned-edge slicker or by machine4 ,the grain is stoned1 set out and starched1 and the butts grained by boarding the flesh4 ,in the waxing1 one of two courses may be adopted4 ,the butts may be blacked with lampblack and oil1 bottom sized with glue1 soap and logwood1 and then top sized with glue1 dubbin1 beeswax and turpentine2 or they may be given a soap-blacking of soap and logwood and lampblack1 applied by machine1 and sized once only4 ,dressing hide butts may also be given a grain finish1 such as the memel butts for heavy uppers4 ,the butts are soaked1 shaved or split1 sumached in drum1 and preferably thoroughly scoured on flesh and grain4 ,they are then sammed and heavily stuffed in the drum4 ,the grain is buffed and stained black with logwood1 ammonia and iron solution 7curriers' ink74 ,the butts are then dried1 set out1 thinly sized and slowly dried4 ,when dry on the face they are printed or embossed by machine to give the characteristic memel pattern and dried out completely4 ,they are then grained four ways4 ,the grain is finished by a coating of linseed oil containing resin1 and the flesh is whitened1 ,french chalked and glassed4 ,shoulders for satin receive a currying which strongly resembles the waxed finishes1 but the smooth finish is on the grain side4 ,the grain is buffed1 and blacked1 dubbined1 set and reset1 with intermediate drying1 and is sized and finished by compositions similar to those used for waxed leathers4 ,the flesh is whitened4 ,satin hide and satin calf are dressed similarly4 ,shoulders may also be finished for levant4 ,after soaking1 splitting1 and shaving to substance1 they are drum-sumached1 machine-sammed1 and oiled up to dry4 ,they are stained with logwood on the grain1 and at once printed with the typical levant grain1 blacked and dried out4 ,they are then softened by machine1 seasoned with logwood and albumen1 glazed1 grained and oiled lightly with mineral oil4 ,it will be observed that stuffing is omitted4 ,bellies may be dressed for linings4 ,after soaking and splitting to the required substance1 they are bleached in a weak and warm solution of oxalic acid1 and drum-sumached at #aaj ,f4 ,after slicking well out they are hand-stuffed on the grain with dubbin and water1 or merely oiled1 and hung up to samm4 ,they are then set-out flesh and grain4 ,if the grain be coarse1 it is buffed and reset4 ,after drying out the flesh is fluffed and the grain dusted with ,french chalk4 ,in this section may be conveniently discussed the manufacture of legging leather4 ,whilst in many respects a typical dressing leather there are some rather important differences from the average upper leather4 ,broadly speaking1 the differences are that legging leather needs a smooth grain1 greater firmness and more thorough tannage on account of the absence of stuffing4 ,the liming and bating are somewhat similar to dressing leather1 though a shorter liming with sulphides and a milder bating would be in order4 ,the tannage is mellow1 but not so much as is usual for upper leather4 ,thus gambier is used1 but more valonia and myrabs are employed1 and the liquors may be strengthened with chestnut and quebracho extracts4 ,the hides are rounded before tanning into long butts or backs1 and the tannage is commenced in suspenders 7#ah-dj71 which are kept acid by the addition of lactic or acetic acid1 in order to obtain the required firmness2 the goods are three weeks in these liquors4 ,the backs next go through rounds of dusters 7#dj-ej71 in which they are put down with oak bark and ,natal bark4 ,they are six weeks in this section1 and then pass to the layers4 ,three layers are given1 first #ej for one week2 second #ee for two weeks2 and third #fj for two weeks4 ,the tannage thus takes fourteen weeks4 ,in finishing1 the goods are soaked and split1 and then scoured flesh and grain4 ,they are heavily sumached1 slicked out thoroughly1 oiled up with linseed oil and dried out4 ,they are then next damped back1 stoned and flatted4 ,after further wetting and tempering they are dressed with ,irish moss and tallow on the flesh1 and with gum tragacanth on the grain4 ,they are glassed whilst drying out1 and then stained twice and glassed again4 ,they are again brushed1 seasoned and glassed by machine4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp4 #aig-bja and #cja-cjh4 ,,section ,,ix4--,,bag ,,leather ,hides to be tanned for bag leather receive a treatment which is little different in fundamental principle from that of dressing hides for upper leather1 except that the tannage is usually shorter4 ,hides for bags and portmanteaux represent a type of dressing leather in which the outstanding features are that the goods are split but not rounded4 ,the splitting is done at all stages1 according to the requirements of the tanner4 ,some tanners split green1 i4e4 split the pelt itself4 ,the advantage of this is that the fleshes may then be treated in quite a different way1 e4g4 pickled or given a much cheaper tannage4 ,other manufacturers split after tanning1 the advantage being that there is much less material to handle4 ,the general opinion1 however1 favours a middle course in which the hides are split after being in the tan liquors for a short time4 ,the advantage of this course is that the hides are easiest to split under these conditions--a great consideration--being coloured through with tan1 just a little plumped1 but not hard4 ,a smoother flesh is obtained together with more even substance4 ,here again1 however1 are differences2 some tanners prefer to split after two days1 others after two weeks in tan4 ,much depends upon the nature of the tan and the strength of the liquors4 ,for this class of work1 flat1 spready and evenly grown cowhides are obviously the most suitable material1 and are invariably used4 ,it is important1 however1 that the grain be good1 and free from scratches and similar defects4 ,the tannage must be sweet and mellow1 i4e4 contain no acid and little astringent tan4 ,hence myrabolans and gambier have always been the favourite tanning materials4 ,a soft and mellow tannage is the more important1 inasmuch as the leather is not heavily stuffed with grease in finishing4 ,these types of method for tanning split hides will now be outlined1 and the nature of the currying then indicated4 ,type #a4--;,in this a long mellow liming of #ae-af days is given1 much like that described for harness leather in ,section ,,iii41 ,type #c4 ,only lime is used1 but the liquors are not allowed to get dirty4 ,the three-pit system is much the best4 ,the hides are trimmed at the rounding tables1 and then bated in hen or pigeon dung for three days at #ge-he ,f4 ,the deliming is commenced by washing in tepid water before bating1 and is completed by a bath of boric acid1 using up to #cj lbs4 acid per #ajj hides as necessary4 ,in this and other processes for split hides it is essential to obtain all the lime out1 but to do no plumping with acid4 ,lactic acid may also be used1 but it is not so convenient to hit the neutral point with it4 ,the tannage consists of oak bark and myrabs together with gambier4 ,these may be partly replaced by ,natal bark1 valonia1 and quebracho respectively4 ,it is sometimes desired to have a smooth finish1 but sometimes to work up a grain4 ,in the latter case the hides are first put through colouring pits containing fresh leach liquor4 ,in these they are constantly handled for a few hours4 ,a little experience indicates which leach liquor will serve the purpose4 ,the hides then go through the green handlers 7#h-bj7 in two weeks4 ,the liquor is the old forward handler liquor made up with gambier4 ,the hides may be sammed and split up at this stage1 but the heavier goods may be tanned further4 ,these heavies and the grains of the split hides now go through the forward handlers 7#bj-dj7 for four weeks1 and the heaviest goods given two layers 7#dj7 of two weeks each1 and making ten in all4 ,type #b4--;,in this a shorter liming of #h-i days is given with the help of sulphide4 ,no dung bate is used1 but the goods are washed with water and bated with ammonium chloride and boric acid4 ,the tannage is chiefly of myrabs1 but some valonia or ,natal bark may be used together with chestnut extract and some quebracho4 ,gambier is used in the early liquors4 ,the goods are coloured off in drum or paddle and tanned in several sets of handlers1 viz4 green handlers 7#ae-ce7 three or four days2 second handlers 7#ce-fj7 two weeks2 forward handlers 7#fj-hj7 #a-a_/b weeks2 and floaters 7#hj-ij7 for three weeks4 ,the tannage is thus #f-a_/b weeks in all4 ,the arrangement of pits is a matter of local convenience1 and the number of sets of equal strength is determined by the number of hides being tanned4 ,the hides are split green or after passing through the green set4 ,after tanning they are oiled with cod oil and dried out4 ,type #c is illustrated by ,american methods4 ,the goods are tacked on laths or racks with copper nails in order to ensure smooth grain4 ,they are then suspended in tan liquors4 ,the tannage is largely with gambier and in weak liquors1 which also help to give smooth grain4 ,the tendency is to employ handler rounds involving a rather large number of pits1 and to work these on the press system4 ,handling is also saved by plumping the liquors instead of shifting the goods forward1 and by rocking the suspenders instead of handling up and down4 ,the hides are split after about a month1 and the heavier grains laid away in hemlock liquors4 ,type #d4--,this is a rapid process throughout4 ,the hides are limed in #f-g days with the help of sulphide1 and bated by washing in warm water and then in cold to which hydrochloric acid is gradually added1 finishing off again in tepid water4 ,the hides are now coloured off in paddles1 put through a small handler round 7#aa-bj7 for half a week1 and then split4 ,the grains are drum tanned in a mixture of chestnut and quebracho extract1 over a period of about three days in which the liquor is strengthened gradually from #cj to #ej4 ,the fleshes are drum tanned with the old grain liquors after strengthening with quebracho4 ,the split hide grains for bag work1 after tanning1 are drummed in sumach1 rinsed1 drained1 and oiled up to dry out1 with some setting out4 ,after wetting back they are shaved if necessary1 hand scoured1 and heavily sumached again to get a light even colour4 ,the goods are slicked out1 oiled up to samm1 reset and dried out4 ,they are next stained1 sammed1 printed by machine1 dubbined or tallowed1 grained 7see ,part ,,ii41 ,section ,i471 brushed and rubbed with flannel4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp4 #bjb1 #cjh4 ,,section ,x4--,,picking ,,band ,,butts ,it is the paradox of vegetable tannage that the less the pelt is tanned the stronger is the leather produced4 ,the manufacture of butts for picking bands affords a good illustration4 ,what is required is a leather of maximum toughness1 pliability and durability4 ,any factor reducing the tensile strength of the leather is fatal4 ,hence1 compared with most other tannages1 picking band butts are under-tanned4 ,to ensure the desired softness and pliability1 moreover1 it is necessary to have a mellow liming1 rather heavy bating1 and a soft mellow tannage in sweet and weak liquors4 ,the required durability and the necessity for weak liquors both point to oak bark as the most suitable tanning material1 assisted by some gambier in the early stages4 ,a good quality hide is chosen1 and given a long and mellow liming of about #ae-af days4 ,the one-pit system may be used1 and the hides are put into an old lime for about five days with frequent handling and then placed in a new lime which is made up in a pit containing about a foot depth of the old liquor4 ,after about twelve days another #a_/c cwt4 of lime may be added4 ,after unhairing and fleshing the goods are bated in pigeon dung for four days at a temperature of about #gh ,f41 handling twice on the first and last days4 ,the bating is stopped and the deliming completed by paddling with boric acid 7#ae lbs4 per #ajj butts74 ,the tannage is commenced by paddling in a spent handler liquor 7#d7 to which a little gambier has been added4 ,the butts then go through the first handlers 7#e-ae71 which are rounds of ten pits in which the goods are handled every day in the first week1 and alternate days in the second week1 and are shifted forward twice a week in the next pit4 ,the goods are therefore in this set for five weeks4 ,gambier is added to these liquors as needed4 ,the butts next pass to duster rounds of four pits1 in which they are dusted down in a liquor of #bj for four weeks with #a-b cwt4 of oak bark4 ,the liquor is obtained from the leaches1 and afterwards run alternately to the leaches and to the first handlers4 ,as many as six layers are now given of #bj-be strength1 in which the butts are dusted down with #b-c cwt4 oak bark for three weeks4 ,the layer liquors are received from and returned to the leaches1 which are made from the fishings from the layers4 ,the tannage lasts1 therefore1 #bg weeks1 of which #ah weeks 7two-thirds7 are in layers4 ,shorter tannages are now often given1 using stronger liquors1 much as in ordinary dressing leather4 ,the tanned butts are rough dried1 and then wet in for shaving4 ,they are thoroughly scoured1 flesh and grain4 ,they are next drummed for three-quarters of an hour in sumach1 struck out and hung up to samm4 ,hand stuffing is best1 to avoid any tendering owing to high temperature1 but drum stuffing is also used4 ,after setting out and stoning on the grain they are stuffed with warm cod oil and laid away in grease for several weeks1 re-oiling occasionally4 ,they may be stained before stuffing4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp4 #bjc1 #caj4 ,,part ,,ii4--,,skins ,,for ,,light ,,leathers ,,section ,i4--,,principles ,,and ,,general ,,methods ,,of ,,light ,,leather ,,manufacture ,the term skin1 like the term hide1 in its widest sense applies to the natural covering for the body of any animal1 but is generally used with a narrower meaning in which it applies only to the covering of the smaller animals4 ,thus we speak of sheep skins1 goat skins1 seal skins1 pig skins1 deer skins1 and porpoise skins4 ,it is in this sense that it will be used in this volume4 ,the treatment of such skins to fit them for useful purposes comprises the light leather trade4 ,whilst this branch of the leather industry is certainly utilitarian1 the artistic element is a great deal more prominent in it than in the heavy leather branch4 ,thus the light leathers are often dyed and artistically finished1 and their final purposes 7such as fancy goods1 upholstery1 bookbinding1 slippers1 etc47 have rather more of the element of luxury than of essential utility4 ,the total weight and value of the skins prepared1 and of the materials used in their preparation1 are naturally considerably smaller than those of the heavy leather trade4 ,in the latter1 moreover1 one has to consider the purpose in view from the very commencement of manufacture and vary the process accordingly1 but in light leather manufacture one aims rather1 in the factory1 at a type of leather such as morocco leather1 and only after manufacture is it fitted to such purposes as may be particularly suited to the actual result4 ,these results depend very largely upon the grain pattern which is natural to the skin of any one species of animals4 ,hence in ,part ,,ii4 of this volume it has been found most convenient to deal with the different classes of skins in different sections4 ,just as the hides of ox and heifer were much the most numerous and important of hides1 so also naturally are sheepskins the most prominent section of the raw material of the light leather trade4 ,this is the more true because the skin is valued for its wool as well as for its pelt2 indeed1 the wool is often considered of primary importance1 and receives first consideration in fellmongering4 ,unfortunately for the light leather trade1 sheepskins1 though most numerous1 do not give the best class of light leather1 the quality being easily surpassed in strength1 beauty and durability by the leather from goat or seal skins4 ,in the wet work for the preparation of skins for tannage much the same general principles and methods are embodied as in the case of hides1 but with appropriate modifications4 ,as soft leathers are chiefly wanted1 a mellow liming is quite the usual requirement for all skins4 ,it is also usual to have a long liming1 for some skins 7like those of sheep and seal7 have much natural fat which needs the saponifying influence of lime and lipolytic action of the enzymes of the lime liquors2 whilst other skins 7like those of goat and calf7 are very close textured and need the plumping action of the lime and a certain solution of interfibrillar substance4 ,in consequence of the long mellow liming1 sulphides are not usually necessary1 and indeed sodium sulphide is not usually desirable1 on account of its tendency to make the grain harsh4 ,it is used1 however1 for unwoolling sheepskins1 in such a manner that the grain is not touched4 ,similarly caustic soda is seldom required1 and the yield of pelt by weight is usually a small consideration4 ,systems of liming show some variety4 ,the one-pit system is very common1 and is less objectionable for a long mellow liming1 but rounds of several pits are also used1 and in some cases even more than one round4 ,this is obviously conducive to regularity of treatment1 and as the work involved in shifting the goods is much less laborious than in the case of heavy ox hides1 it would seem a preferable alternative4 ,the depilation of sheepskins involves very special methods of treatment 7sweating and painting7 on account of the importance and value of the wool1 the quality and value of which would be impaired by putting the skins through ordinary lime liquors4 ,the pelts1 however1 are limed after unwoolling4 ,in deliming light leathers the process of puering is widely used4 ,this consists in immersing the skins after depilation in a warm fermenting infusion of dog-dung4 ,in principle this disgusting process presents a close analogy with bating1 and indeed the two terms are both used somewhat loosely1 but there are nevertheless several points in which the two processes are radically different4 ,the dog-dung puer is a process carried out at a higher temperature than the fowl-dung bate2 it is also a much quicker process1 and the infusion employed is generally more concentrated4 ,whilst the fowl-dung bate is always slightly alkaline to phenolphthalein the dog-dung puer is always acid to this indicator1 and the course of the puering may be conveniently followed by testing the pelts with it4 ,the mechanism of the two processes is also probably somewhat different4 ,the mechanism of the dog-dung puer has been largely made clear by the researches of ,wood and others1 and been found due partly to a deliming action by the amine salts of weak organic acids and partly to the action of enzymes from a bacillus of the coli class1 which received the name of ,b4 erodiens1 and which effects a solvent action on the interfibrillar substance4 ,as we have noted 7,part ,i41 ,section ,,ii471 the fowl-dung bate involves two fermentations1 in each of which 7robic and anrobic7 several species of bacteria are probably active4 ,wood found the bacteria of the bate to be chiefly cocci1 and ascribed part of the difference in mechanism by the nature of the media1 which in the bate includes also the urinary products4 ,in the dog-dung puer1 also1 a lipolytic action is probably an essential part of the total effect4 ,the puer gives a much more complete deliming and a much softer and more relaxed pelt than the bate1 it is therefore particularly suited to the needs of light leather manufacture4 ,the puering action has been imitated fairly successfully by artificial methods4 ,erodin 7,wood1 ,popp and ,becker7 involves the use of ,b4 erodiens and a suitable culture medium including organic deliming salts3 ,oropon1 ,pancreol and others involve the use of ammonium chloride and trypsin1 together with some inert matter4 ,light-leather goods are usually drenched after puering4 ,they are also often split green after the wet work4 ,sheepskins thus yield skivers 7the grain split71 whilst the flesh split is often given an oil tannage 7see ,part ,,iv41 ,section ,,iii474 ,the greasy nature of sheep and seal skins necessitates the processes of degreasing4 ,in the case of sealskins this is done largely before liming1 but with sheepskins either after being struck through with tan1 or after tannage is complete4 ,sheepskins are often preserved in the pelt by pickling with sulphuric acid and salt1 which process forms a temporary leather4 ,the fibres of the pelt are dried in a separate condition1 but the adsorption is easily reversible and the pelts may be depickled by weak alkalies and afterwards given an ordinary vegetable tannage4 ,in the vegetable tannage of skins for light leathers1 the same theoretical considerations have force as in the heavy-leather section1 but the former has its own rather special requirements and aims4 ,generally speaking1 a softer and more flexible leather is required1 but these qualities must not be imparted by stuffing with grease as in the currying of dressing leather1 because a bright and grease-free result is usually required4 ,hence it is important that a sweet mellow tannage be given4 ,the durability of the leather is also a primary consideration for goods intended for bookbinding1 upholstery1 etc41 and the tannage must be arranged to impart this quality and avoid anything tending to cause the perishing of the fibre4 ,thus oak bark is a popular tanning material1 and sulphuric acid very definitely avoided4 ,the tannage must be fast1 and take the dyestuffs well1 and for the production of light shades of colour in dyeing must be a light-coloured tannage4 ,all these qualities are imparted by sumach1 which also fits in excellently with the other general requirements1 such as softness1 brightness and durability4 ,hence sumach is the principal light-leather tanning material1 but the tendency is to employ other materials--oak bark1 myrabs1 and chestnut extract--to do much of the intermediate tanning1 so that the expensive and useful sumach may be used for setting the colour and grain at the commencement1 and for brightening1 bleaching and mordanting the leather at the end of the tanning process4 ,weight is generally no consideration1 but area is often a definite aim1 partly because some goods are sold by area and partly because the striking out1 setting out and similar operations improve the quality of the leather by giving evenness of finish4 ,leather well struck out1 moreover1 is less liable to go out of shape4 ,as the grain pattern is so important in the finished leather1 appropriate care must be taken during tannage4 ,if a smooth or a fine grain finish is wanted1 for example1 the goods must not be allowed to get wrinkled1 creased1 doubled or unduly bent to and fro during the tanning4 ,for such goods1 suspension1 careful handling and even the bag tannage may be desirable1 whilst for coarser and larger grains paddles or drums may be more extensively used4 ,amongst the finishing processes dyeing holds an important position4 ,the nature of the process has many points of similarity with that of tanning4 ,the great specific surface of pelt is probably more enhanced than otherwise during tannage1 at any rate with light leathers1 owing to the isolation of fibres1 and consequently leather is as liable as pelt to exhibit adsorption4 ,the dyestuffs1 on the other hand1 are substances very easily adsorbed4 ,some 7like eosin and methylene blue7 are crystalloids1 some 7like fuchsin and methyl violet7 are semi-colloids1 whilst others 7like ,congo red and night blue7 are undoubted colloids forming sols 7usually emulsoid7 with water as dispersion medium4 ,the crystalloids and semi-colloids may also be obtained in colloidal solution1 sometimes being so changed on the mere addition of salts to the solution4 ,in addition1 the pelt has been mordanted with tannin4 ,if1 however1 leather has been kept long in the rough-tanned or crust state1 this may not be so effective1 owing probably to the secondary changes in tanning 7,part ,i41 ,section ,,iii471 but such leathers are usually retanned or prepared for dyeing by sumaching 7which process also incidentally bleaches74 ,the tannin mordant assists materially in the fixation of the dyes4 ,in the case of basic dyestuffs1 lakes also are formed1 i4e4 there is a mutual precipitation of oppositely charged colloids 7dye1 -tannin74 ,the dyeing of leather is thus a case of colloid reactions even more complicated than that of tanning4 ,another finishing operation typical of the light leathers is graining or boarding4 ,in this the skins after dyeing and drying are worked by a board which is covered by cork1 rubber1 perforated tin or other material1 and so grips or bites the leather4 ,the object of graining is to work up the grain pattern by pushing or pulling a fold on the skin with the board4 ,the nature of the grain varies with the thickness and the hardness of the skin1 with the amount of pressure applied1 with the nature of the board1 with the direction of the boarding and with the total number of directions boarded4 ,there is thus infinite scope for variety of finish1 and hence arise bold grain1 fine grain1 hard grain1 straight grain1 cross grain1 long grain1 etc4 ,the operation requires considerable skill and experience4 ,in the case of skins with little natural grain 7such as sheepskin7 embossing and printing machines impress the desired pattern4 ,in seasoning1 a dressing is applied containing essentially albumins and emulsified fats1 e4g4 egg albumin and milk4 ,colouring matters are also often added to intensify or modify the shade4 ,after seasoning the goods are usually glazed by a machine which rubs the seasoned grain with considerable pressure1 by a glass or hardwood tool1 and so produces a high gloss1 for which the seasoning is very largely a preparation4 ,light leathers are very lightly oiled with linseed or mineral oil4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 pp4 #bbj1 #cid4 ,bennett1 ,manufacture of ,leather1 pp4 #cf-da1 #ee1 #he-ij1 #ib-aab1 #cab1 #ccb4 ,wood1 ,puering1 ,bating and ,drenching of ,skins4 ,lamb1 ,leather ,dyeing and ,finishing4 ,,section ,,ii4--,,goatskins ,goatskins are amongst the most valued raw material for the manufacture of light leather4 ,the leather obtained from them is of the very finest quality in respect to durability and adaptability to the principal purposes in view4 ,the texture of the fibres in goatskin is exceedingly compact and very strong1 whilst the grain exhibits naturally a characteristic pattern which renders it most suitable for a grained finish4 ,hence for purposes like upholstery1 bookbinding1 slippers1 it forms almost an ideal material4 ,the tanning and finishing of goatskins into morocco leather may indeed be taken as a quite typical example of light leather manufacture4 ,the skins are obtained from all quarters of the globe where goats exist1 and the excellent quality of the leather produced has created a demand which is greater than the supply4 ,this is due not only to the demand for morocco leather1 but also to the popularity of the goatskin chrome upper leathers such as glac kid 7see ,part ,,iii41 ,section ,,iv474 ,the large ,american trade in the latter has produced the saying that wherever there is a goat there is an ,american waiting for it to die6 ,the ,european supply of skins is somewhat limited4 ,they are obtained from the ,balkans and ,bavaria1 in which case they are small1 fine-grained and plump skins4 ,the ,swiss goatskins are larger1 and have also a fine grain2 they are well grown and well flayed4 ,scandinavian skins have a poor reputation1 being very flat4 ,the ,african supply is important2 ,abyssinian skins are exceedingly compact and tough1 and are very suitable for bold grain finishes4 ,the ,cape skins are particularly large1 strong and thick1 but their quality is often impaired by the cure1 the skins being flint-dry1 and1 like hides so cured1 prone to unsoundness4 ,large quantities of goatskins also come from the ,east4 ,many of these are imported in a tanned state 7,e4,i4 ,goat74 ,these skins are tanned with turwar bark1 which contains a catechol tannin4 ,they are also heavily oiled with sesame oil1 and need degreasing4 ,the tannage is also stripped as far as practicable1 and the skins retanned with sumach before finishing4 ,they make good morocco leathers for many purposes1 but the primary catechol tannage renders them ineligible for finishing under the specifications of the ,committee of the ,society of ,arts4 ,the skins have a ,persian or ,indian origin4 ,india also supplies a large number of raw dried goatskins which are small and of variable quality4 ,these1 however1 are more extensively used for chrome uppers4 ,goatskins are imported in either a salted or a dried condition4 ,the great aim of soaking is to obtain the skins in a thoroughly soft condition4 ,hence the soaking is prolonged1 and some mechanical treatment is desirable in addition to various steepings in water4 ,to be certain of softness it is desirable to avoid the use of alkalies in the soak waters1 for although they cause hydration of the fibres by imbibition1 they also have a plumping effect which is not wanted at this stage4 ,salted goatskins are first immersed in water and left until the following day4 ,this dissolves the salt4 ,they are then stretched and given a fresh soak liquor of water only to soften further1 clean1 and remove the rest of the salt4 ,this second water lasts only a few hours1 and the goods are then drummed well in running water4 ,this not only cleans quickly1 but has an excellent softening effect4 ,they are again returned to a soak liquor1 then softened mechanically by working them over a beam4 ,this treatment must be repeated1 drumming again if necessary1 until the skins are perfectly relaxed and thoroughly softened4 ,if the treatment be very prolonged it becomes advisable to use antiseptics in the soak waters after the first drumming4 ,solubilized 7or emulsified7 cresols of the ,jeyes fluid type are the most suitable antiseptics1 but too much must not be used or the sterilization affects the liming1 in which bacterial action is needed4 ,flint-dry skins are left longer in the first soak1 which should be of water only4 ,they are then given a fresh soak liquor containing #j4b per cent4 of sodium sulphide4 ,sometimes a #a4j per cent4 solution of borax is used instead2 it softens excellently1 is antiseptic1 and avoids the plumping effect1 but is rather expensive4 ,the goods are next drummed well1 and resoaked and worked as for salted skins4 ,in either case the soaking takes about a week4 ,the liming of goatskins presents some points of contrast with the methods used for other skins4 ,these differences are due to the exceedingly tight and compact nature of the skin fibres4 ,this compactness of texture makes it quite necessary to dissolve the interfibrillar substance to a greater extent than usual1 and also to plump the fibres and split them into the constituent fibrils4 ,these effects are essential to obtain a rapid and complete tannage and a soft leather4 ,too much bacterial action should be avoided1 however1 or the brightness and soundness of the grain may be impaired1 which would be a fatal defect in such a leather4 ,hence the liming is long rather than mellow1 and sharp limes rather similar to those required for sole leather are often used4 ,another result of the tight texture of goatskin is that depilation is not easily effected4 ,this feature is rather intensified by the deepness of the hair-root4 ,hence it is usual to employ sulphides to assist the depilation4 ,in one method two rounds of five pits are used4 ,the skins are given about two days in each pit1 so that the liming lasts approximately three weeks4 ,in the first round1 which consists of rather mellow limes1 arsenic sulphide is used to assist depilation4 ,up to #f per cent4 on the weight of lime is added during slaking4 ,this is a comparatively large amount of arsenic sulphide1 and the depilation is considerably hastened2 the skins indeed are unhaired after passing through this round1 i4e4 after about #aj days' liming4 ,in the next round the object is plumping1 and caustic soda 7or carbonate7 is added to the lime liquors in quantities comparable to those suggested for sole leather 7,part ,i41 ,section ,v474 ,in this round the goods stay also for about #aj days4 ,an alternative to the above process is to hasten the earlier part of the liming by employing sodium sulphide instead of realgar4 ,more sulphydrate may be obtained in solution in this way1 and the unhairing may be in about half the time4 ,the sulphide of soda also commences the plumping action which follows in the next round1 but this alternative has the disadvantage that the skins are unhaired whilst the pelt is swollen with sulphide1 which renders the grain both harsh and tender and consequently more liable to damage by the unhairer's knife4 ,deliming is by puering and drenching1 and is often associated with a further mechanical working of the goods4 ,the skins are inserted into a puer liquor at #he ,f4 and thoroughly pulled down4 ,the caustic alkalies should be completely neutralized4 ,a slight cut into a thick part at the butt end should develop no pink colour with phenolphthalein4 ,the skins should be thoroughly relaxed1 and the swelling so much eliminated that they are quite soft1 weak and fallen4 ,the resilience and elasticity of the plumped skins should have quite disappeared1 and the impressions of hand or thumb should be readily retained by the pelt4 ,the grain should appear white and possess a soft and silky feel4 ,in this condition they are again worked over the beam to soften further if possible4 ,they are then rinsed and again worked over the beam4 ,drenching follows with #aj per cent4 of bran on the pelt weight1 the operation commencing at #he to #ie ,f41 and lasting till next morning4 ,the skins are next scudded thoroughly to remove all dirt1 but carefully so as not to damage the grain4 ,in tanning1 sumach and oak bark are the staple materials4 ,sumach gives a much lighter colour1 and hence it is used alone for goods that are to be dyed the lighter shades1 but oak bark is a faster tannage and more preferable for dyeing in those cases where blacks and very dark shades are wanted4 ,for ordinary purposes a blend is usually employed4 ,a feature of oak bark1 also1 is that it tends to make a firmer leather1 so that the proportion used must be adjusted with this fact in mind as well as the question of colour4 ,for firmer moroccos the skins may pass through a handler round of oak-bark liquors 7#aj-bj7 in which a certain amount of sumach is added to the liquors4 ,the sumach is leached and assists both in tanning and bleaching as the liquor works through the round4 ,the old liquor is run to a paddle1 and the tannage is commenced by paddling the drenched skins in this liquor4 ,it is advantageous both for the tannage and for the efficient spending of the sumach if this liquor be slightly warmed4 ,in the early pit liquors the goods are very frequently handled4 ,there is1 however1 the usual tendency of the times to save labour in this direction1 and hence it is common to have several paddles with liquors of gradually increasing strength1 followed by a shorter round of handlers in which the handling is more infrequent4 ,instead of paddles latticed drums may be inserted into pits containing liquors4 ,these1 however1 are not quite so convenient4 ,in some tanneries1 especially where sumach only is employed1 the tannage is in paddles throughout4 ,a new liquor is made up with fresh sumach and is used repeatedly until exhausted4 ,a three-paddle system sometimes obtains1 in which case the operation closely resembles the three-pit system of liming 7,part ,i41 ,section ,,ii471 and the skins pass through an old liquor1 a medium liquor and a fresh liquor4 ,the goods need not be paddled the whole day through1 and indeed in the later stages this is undesirable4 ,the packs remain several days in each liquor and take up to #ad days to tan4 ,two to three bags of sumach are needed for about #bj dozen goatskins4 ,this method of tanning is efficient and convenient for bold-grain finishes1 on account of the constant tumbling and bending of the skins which tends to work up a grain4 ,for very soft leathers and fine-grain finishes1 however1 the bag-tannage or bottle tannage is favoured4 ,in this method the pelt is stitched up by machine to form a bag1 grain outwards1 leaving a neck in the hind shank4 ,the bag is nearly filled with a fairly strong infusion of sumach1 inflated with air and tied up at the neck4 ,the bags are then placed into a vat of warm sumach liquor1 in which they just float4 ,the bags are pushed down and the liquor stirred up1 so that the goods are in constant motion4 ,after a few hours they are piled on a rack1 and the tan liquor of the interior is caused to diffuse through the skins by the pressure due to the weight of the pile4 ,the bags are refilled with fresh and stronger sumach liquor and the process is repeated4 ,the skins are thus lightly but effectively tanned in about #bd hours1 and the leather has very fine grain and soft feel4 ,however tanned the skins are dried out after tanning1 and sorted in the crust according to size and colour4 ,the larger skins are preferred for upholstery and the smaller for fancy goods and bookbinding4 ,to illustrate the course of finishing operations1 the case of hard-grain morocco for bookbinding may be given as typical4 ,the goods are wet back with warm water and drummed for #a-b hours in warm sumac to prepare for dyeing4 ,they are then struck out by machine1 sammed and shaved4 ,dyeing follows1 with acid colours1 in a drum4 ,the goods are run first in a little water and the dyestuff added very gradually through a hollow axle4 ,the acid required 7preferably formic7 is added later to develop the full shade4 ,warm solutions are used1 and the dye bath is practically exhausted4 ,the goods are next placed in cold water to wash off superfluous liquor and free the skins from acid4 ,they are then horsed to drain1 struck out and hung up to samm4 ,they are seasoned with milk and water and piled to temper4 ,they are tooth rolled in the glazing machine two ways3 right-hand shank to left fore shank and vice vers1 and piled again4 ,after wetting back again they are wet grained by hand with a cork board in four directions3 belly to belly1 shank to shank1 and across as before1 and finally from neck to butt4 ,they are immediately hung up in a warm shed to dry1 and to fix the grain4 ,they are then softened by breaking down with a rubber board1 top seasoned1 piled to temper and dry1 brushed lightly1 piled again1 brushed more heavily1 and dried out4 ,they are finally softened by graining in three directions3 shank to shank and across1 and neck to butt4 ,they are then brushed again4 ,if these skins are wanted for upholstery they are shaved after dyeing1 and nailed on boards to samm4 ,they are also dried out in a cooler shed or stove1 to ensure softness4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp4 #ci1 #ee1 #hi1 #aaa1 #bjd1 #cdd1 #cif4 ,,section ,,iii4--,,sealskins ,a special class of morocco leather is manufactured from the skins of seals4 ,this should not be confused with the sealskin of popular parlance1 which is manufactured from the skin of a different animal4 ,all the fin-footed mammals 7,pinnipedia71 except the walrus1 are termed seals1 but they are divided into two families4 ,the ,otariid are known by their possession of small but distinct external ears3 into this class fall the fur-seals whose skin is dressed with the fur on1 for women's jackets1 muffs and caps4 ,the ,phocid are that family without external ears3 the skins of many species 7,phoce ,greenlandica1 ,phoco barbata1 etc47 of this family are unhaired and given a vegetable tannage1 thus forming the raw material of sealskin morocco leather4 ,it is with the latter that this section will deal4 ,as the seal is a marine animal and is partial to the colder seas1 its skin is very oily4 ,the skins are imported in a salted condition from both the ,arctic and ,antarctic regions4 ,north ,europe1 ,north ,america and ,newfoundland supply many skins1 and the southern material is supplied chiefly through the ,cape4 ,sealskin shares with goatskin the properties of compact texture1 strength of fibre1 and great durability1 all of which fit it for the manufacture of moroccos for upholstery1 bookbinding1 etc4 ,it is1 however1 readily distinguishable from goatskin by its characteristic grain pattern4 ,in soaking sealskins the object is not only to soften thoroughly1 but also to effect the recovery of as much seal oil as possible before the liming commences4 ,this is desired because the oil is in itself a valuable bye-product1 and because its removal is essential to a satisfactory liming and tannage4 ,the removal of the oil is materially assisted by raising its temperature1 so that the soaking of sealskins is often done with warm water 7#he-hh ,f471 after which treatment they are laid over the beam and scraped with a blunt knife on both flesh and grain4 ,the oil flows away into a special receptacle4 ,this treatment is repeated until the bulk of loose oil is removed4 ,the process is known as blubbering or brushing over4 ,after some soaking the skins are drummed to ensure softness4 ,the skins are then fleshed4 ,more oil may be obtained from the fleshings4 ,by fleshing before liming a more regular action of the lime is obtained4 ,this is necessary to kill the grease still remaining in the skin4 ,a long and mellow liming is given for the same reason4 ,fully three weeks are given1 and old limes are much preferred1 partly to obtain the maximum lipolytic action and partly to avoid the intense ribbing of the pelt which new limes so easily impart to the older animals4 ,these ribs are very difficult to eliminate in the subsequent work4 ,some factories find it necessary to finish up in new limes1 however1 in order to plump and split the compact fibre bundles into their component fibrils4 ,the plumped pelt is also easier to split green4 ,no sulphides are usually employed4 ,sweating 7see ,section ,,iv47 is sometimes used for depilation1 and in this case the ribbing of the pelt does not take place4 ,the puering is unusually thorough with sealskins4 ,this is to obtain the maximum softness and take full advantage of the lipolytic action4 ,the puer liquor is fully #ie ,f41 and the skins are paddled for about three hours1 or until fully pulled down and completely delimed4 ,scudding follows1 now usually by machine4 ,the skins are then well drenched4 ,the action is intensified by the use of peameal in addition to the bran4 ,about #aj per cent4 of the mixture on the weight of pelt is used4 ,it is customary1 however1 to drench at a lower temperature 7#fh-gj7 than in the case of goatskins 7,section ,,ii471 but the goods are left in the drench overnight only1 as is usual in drenching4 ,it is quite possible that drenches worked differently may have also a somewhat different fermentation and be due to other organisms than the symbiotic bacteria discovered by ,wood4 ,it is equally possible that the acids produced are also different1 in relative proportion1 if not in nature1 and that consequently there is a real difference in the practical effect4 ,in the ,author's opinion1 the great probability is that in the drench are several fermentations1 and that if the action be reduced by lowering the temperature1 but intensified by adding peameal to the bran1 some of these fermentations are encouraged at the expense of others4 ,the tannage of sealskins depends upon the size of the skins1 the purpose for which they are intended1 and whether they have been split or not in the limed state4 ,the largest and coarsest skins intended for boot uppers1 and those which have been heavily scratched on the grain and are only suitable for enamels1 are given a tannage which may last about #e weeks4 ,the liquors are made from oak bark and mimosa bark1 and are made up to #ce with gambier and possibly myrabolans extract4 ,for fancy work also heavy skins are used1 but a softer tannage is needed4 ,if for blacks the tannage is with gambier and chestnut extract4 ,two sets of handlers are given 7#aj-ae and #ae-bj71 using only gambier in the green sets4 ,they are well sumached after tanning to bleach and to mordant4 ,if for colours1 only sumach and oak bark are employed4 ,the skins are first paddled for #c-d days in sumach liquors1 in which they are coloured through4 ,the liquors may be warmed2 this quickens the tannage and also leaches the sumach4 ,the skins are then split1 and the grains pass through a handler set with liquors made from oak bark 7#h-bd74 ,the skins are in this set for #c weeks1 in the first half of which they are very frequently handled4 ,they are finished off by paddling for #a or #b days in a fresh liquor containing much sumach1 which mordants the skins and bleaches the bark tannage4 ,the flesh splits are given a drum tannage in chestnut and quebracho extracts4 ,if small skins are being tanned for bookbinding purposes1 sumach only is employed1 and usually the tannage is entirely in paddles4 ,in finishing many types of grain may be obtained1 in blacks and in colours4 ,the finishing of black levant may1 however1 be selected as a typical case4 ,the skins are soaked back1 tempered1 and either split or shaved1 according to their substance and the size of grain wanted4 ,the thin skins of course give the fine grains4 ,mixed tannages need scouring and possibly sumaching4 ,the skins are then oiled up with linseed oil1 sammed1 set out and blacked4 ,in this last operation the grain is brushed over with a solution of logwood and ammonia1 and afterwards with the iron mordant which often contains glue4 ,they are next hung up for a while and then wet grained in four directions--belly to belly1 shank to shank1 across1 and neck to butt4 ,after hanging up in a hot stove to set the grain1 they are cooled1 fluffed on the flesh1 and seasoned on the grain with a solution of milk and blood4 ,a little black dyestuff may be added to the season4 ,the season is well brushed in1 the skins dried somewhat1 and then glazed4 ,they are then grained four ways again as above1 dried out in the stove1 and lightly oiled with warm linseed oil on the grain4 ,,reference4 ,bennett1 ,manufacture of ,leather1 #dj1 #ef1 #ij1 #aab1 #bjf1 #bea1 #cab1 #cdf1 #chc4 ,,section ,,iv4--,,sheepskins ,the most numerous class of skins for light leathers is from the common sheep4 ,these skins have particular value inasmuch as they include the wool as well as the pelt4 ,this wool1 which is actually the most valuable part of the sheep's skin1 is the raw material of our woollen industries1 and is one of the most important of animal proteids4 ,we have1 therefore1 in this section to consider this dual value of sheepskins1 the proteid of the epidermis 7wool71 and the proteid of the dermis 7pelt72 one the raw material of the woollen industry1 the other the principal raw material of the light leather trade4 ,the first problem is to separate the two proteids4 ,with other skins and hides the ordinary liming processes were sufficient and appropriate1 but in the case of sheepskins the method is unsuitable1 because the exposure of the wool to the action of caustic lime and possibly other alkalies would seriously impair its quality and reduce its commercial value4 ,hence this separation of wool from pelt is usually quite a separate business1 viz4 that of the fellmonger1 whose occupation it is to collect the sheepskins from butchers and farmers1 to separate the two important constituent proteids1 and to hand the wool in one direction to the wool stapler1 who sorts it according to quality1 and to hand the pelt in another direction to the light leather tanner1 who tans and finishes the pelt to fit it for light upper work1 fancy goods1 etc4 ,in the first instance1 therefore1 we have to consider the work of the fellmonger1 the separation of wool and pelt4 ,in this work the wool receives first consideration1 and the raw material of the fellmonger is usually classified accordingly into long wools1 short wools1 and mountain breeds4 ,the skins vary very largely in quality of wool and in quality of pelt1 being influenced very strongly by the conditions under which the sheep lived1 and by the precise breed of animal from which the skin has been taken4 ,as in the case of hides 7,part ,i41 ,section ,i471 animals exposed to extremes of weather develop the best pelts1 whereas those sheep which have been carefully bred and reared for the sake of their wool yield a thin and poor class of pelt4 ,in ,britain1 and more especially in ,england1 are reared the finest and most valuable sheep4 ,this is evident from the prices paid for them by foreigners and colonial breeders when seeking new blood for their flocks and fresh stock for their lands4 ,as much as #ajjj guineas have been paid by an ,argentine firm for a single ,lincoln ram4 ,long wools are obtained from some of the best and most extensively bred animals4 ,the ,cotswolds are the largest1 and probably the original breed of ,england are still found on the ,cotswold ,hills4 ,they have long wool1 white fleeces1 white faces1 and white legs1 and have no horns4 ,the wool is fine1 but the pelts are particularly greasy1 especially along the back4 ,a later breed originating in the ,midlands was called the ,leicester long wool4 ,this breed gives a great cut of wool and much coarse mutton4 ,it is very extensively distributed in the ,north of ,england and has been much crossed1 so that many sub-breeds are now well known1 e4g4 the ,border ,leicester--the general utility sheep of ,scotland--and the ,yorkshire ,leicester or ,mashams1 much bred in ,wensleydale4 ,lincolns are another long wool found only on the ,lincolnshire ,wolds4 ,they also have white faces and shanks and yield a large pelt with fine grain4 ,they give a big crop of wool4 ,devons are a smaller breed common in ,somerset1 ,devon and ,cornwall4 ,they yield a fairly long wool of great strength1 but not quite white4 ,romney ,marsh sheep 7,kents7 are also long wools4 ,they have white legs1 white faces1 a tuft of wool on the head1 and no horns4 ,the pelt is large and good4 ,roscommons are an ,irish cross breed with much ,leicester blood4 ,they yield a long wool and a spready pelt4 ,short wools are typified by the ,down sheep4 ,these sheep are extensively bred on the chalk lands which comprise a very large percentage of the southern counties of ,england4 ,the ,south ,downs are the best and most important1 the breed being the general utility sheep of ,england4 ,they are small but well-shaped animals with grey faces1 no horns and fine close wool4 ,the pelt is only fair1 but the mutton is excellent and provides the meat sold in our best shops4 ,this breed has largely stocked ,new ,zealand4 ,the ,south ,down is a somewhat delicate animal1 and has therefore been largely crossed with ,cotswolds and other breeds4 ,many well-known cross-breeds are found in the eastern and southern counties4 ,the ,suffolks1 for example1 are found in the eastern counties4 ,they have black heads1 faces and legs4 ,oxfords and ,hampshires are similar1 but larger4 ,shropshires are another hardy cross-breed1 which yield a heavier fleece4 ,all the cross-breeds are larger than the ,south ,down and yield bigger pelts4 ,mountain breeds yield wool of varying quality but give the best pelts4 ,the ,cheviots--much favoured by the ,scotch farmers--have a wool of medium length but with much hair in it4 ,they have white faces and legs and no horns1 and yield excellent pelts4 ,the ,black-faced ,mountain ,sheep have longer wool but coarse1 and yield good pelts4 ,they are kept in the hilly parts of ,north ,england and in the ,scottish ,highlands4 ,lonks yield a large and good pelt1 but very coarse wool4 ,the mutton is good4 ,they are a very large breed with much curved horns and black faces4 ,there are also some small breeds1 soft wools1 ,shetlands1 and ,welsh ,mountain ,sheep4 ,the wool of the last two is poor1 but the ,welsh pelts are valued for their fine grain4 ,there are large numbers of sheepskins also imported1 from ,south and ,central ,america1 and from ,australia1 ,new ,zealand and the ,cape4 ,the colonies1 however1 have often done their own fellmongering1 and we have imported pickled pelts4 ,they now tan the skins also1 and many tanned sheepskins are now imported4 ,there are also many ,indian skins imported after tannage with turwash bark 7cp4 ,e4,i4 ,goat1 ,section ,,ii474 ,the depilation is brought about by sweating 7or staling7 and by painting4 ,the immediate object of both these types of method is to avoid using any thing which will affect the wool4 ,the sweating process is the most ancient method of unhairing and is used in ,america for hides as well as sheepskins4 ,it consists of a more or less regulated putrefaction4 ,the loosening of hair or wool has long been accepted as evidence that putrefaction had commenced in a hide or skin1 and it is the aim of the sweating process to stop the action at that stage1 before any damage has been done to the pelt4 ,this aim is achieved rather imperfectly by suspending the goods in closed chambers and regulating the temperature and humidity by means of steam and water4 ,such chambers are known as sweat pits or tainting stoves4 ,in the case of sheepskins the warm-sweat system is generally used1 and the operation is carried out at #ge-hj ,f4 ,a satisfactory yield of wool is obtained in good condition1 but the pelt is very liable to suffer bacterial damage and show weak grain4 ,the skins are first cleaned by a few soaks in clean fresh water1 with intermediate help from a burring machine which presents a rapidly revolving set of spiral blades to the wool1 and in the presence of a good stream of water quickly removes all dirt from the wool4 ,the skins then enter the tainting stove1 and the operation is commenced by a slight injection of live steam4 ,in summer1 about a week is sufficient to loosen the hair1 but in winter up to two weeks may be necessary4 ,little control of the process is possible1 and all that can be done is to watch the goods carefully near the end of the operation4 ,in one variety of this method of unwoolling the skins are painted on the flesh side with a creamy mixture of lime and water and piled for a day or two until the pelt is distinctly plumped4 ,they are then washed with fresh water to remove the excess of lime1 drained1 and then enter the tainting stove4 ,by this method the pelts are obtained in better condition and are less liable to damage by local excess of putrefaction4 ,in unwoolling the skins are placed over a beam and the true wool is pulled out by hand4 ,the wool is graded as it is pulled and different qualities kept separate3 ewe wool1 lamb wool1 hog wool1 etc4 ,the hair is next removed from face and shanks by means of a blunt rubbing knife1 and the pelt then immersed in water4 ,in the other method of depilation1 by painting1 advantage is taken of the loose texture of the sheepskin fibre and of the fact that the wool root is nearly halfway through the skin4 ,the flesh side of the clean skin is painted with a creamy mixture of lime in a strong solution of sodium sulphide 7#ad-bd ,beaum74 ,care is taken to keep the depilatant off the wool4 ,the skins are folded flesh to flesh and left for a few hours or until next day before unwoolling1 according to the strength of the sulphide solution4 ,the depilatory action is entirely chemical1 being due to the solvent action of the sulphide on the hair root4 ,the lime is sometimes omitted4 ,after pulling1 the skins are opened up and washed in fresh water4 ,the various classes of wool are sold to the wool-stapler and so to the woollen industry4 ,as this is a mechanical rather than chemical industry1 its discussion is beyond the scope of this volume4 ,however unwoolled1 the pelt still needs further treatment by the fellmonger4 ,it needs liming and unhairing4 ,this is done in the ordinary way in pits of milk of lime1 through which the goods pass from old to new limes in the course of about a week4 ,this plumps the fibres1 separates the fibrils and kills the grease4 ,paddles are used also to save handling4 ,shearlings are sometimes limed #i-ad days and unwoolled without sweating or painting4 ,after liming the skins are unhaired and fleshed1 and placed in clean strong limes until sold to the tanner4 ,sheepskin pelts are sometimes preserved by pickling4 ,this consists in placing them first in a solution of sulphuric acid 7about #c_/d per cent47 together with some common salt4 ,the pelts swell up and imbibe the acid solution4 ,they are then placed in saturated brine1 which causes a very complete repression of the swelling1 the pelts being apparently leathered4 ,in this condition or partly dried out they may be kept for years4 ,the forces at work in this phenomenon are somewhat complex 7see ,part ,v41 ,section ,i474 ,the skins may be depickled by paddling in a #aj per cent4 salt solution to which weak alkalies such as borax1 whitening1 carbonate and bicarbonate of soda1 etc41 have been added4 ,the leather manufacturer classifies sheepskins according to the size of the pelts4 ,the large skins are tanned for light upper leathers and similar work4 ,these are called basils4 ,many large skins are also split green into skivers which after vegetable tannage are finished for fancy goods1 bookbinding1 etc4 ,the fleshes are often oil-tanned for chamois leather 7,part ,,iv41 ,section ,,iii474 ,medium-sized skins such as are obtained from the ,down sheep are tanned for roans1 and finished as a kind of morocco leather4 ,small skins are mostly tawed 7,part ,,iv41 ,section ,i47 for glove leathers1 but some are made into roller leather by vegetable tannage4 ,basils1 which represent the heaviest sheepskin work1 are tanned and finished in the following manner4 ,the limed pelts are first bated lightly at about #hj ,f4 for two days1 scudded and drenched4 ,they are sometimes puered1 but more often merely delimed with organic acids4 ,in this last case they are first paddled in warm water to remove excess of lime1 and a mixture of organic acids is very slowly added at definite intervals4 ,when nearly free from caustic alkali the skins are removed and drenched overnight4 ,there are two types of tannage4 ,the ,west of ,england tannage is similar to those noted for sealskins when oak bark and sumach are employed 7,section ,,iii474 ,there is also the tendency to paddle more and handle less1 and to use the stronger tanning materials such as myrabs1 gambier and other extracts4 ,after about #ab hours' tannage in paddles they are coloured through1 and are then degreased by hydraulic pressure4 ,the skins are piled in the press with layers of sawdust or bran between them1 and the pressure applied very slowly4 ,much grease runs out1 for the natural sheepskin contains up to #ae per cent4 of oil and fat4 ,degreasing may be postponed till tannage is complete1 and the grease can then be extracted by solvents 7benzene1 acetone1 etc474 ,degreasing after part tannage is usually considered preferable1 and the skins may be tanned out in pit or paddle in about a week4 ,the ,scotch tannage is with larch bark from ,pinus larix1 which contains up to #ac per cent4 of a rather mellow catechol tan4 ,this material has also some sugars and yields sour and plumping liquors4 ,the basils are paddled in weak liquors 7#h-aa7 for about #b days1 and when struck through are degreased by hydraulic pressure4 ,they are then soaked back and tanned out in stronger liquors 7#aa-bj71 which takes up to one week4 ,they are then dried out and sorted in the crust4 ,the finishing depends of course upon the purpose in view4 ,if for linings they are soaked1 shaved1 sumached1 struck out well1 nailed on boards and dried right out4 ,they are next stained with a solution of starch1 milk and red dyestuff4 ,after drying they are glazed by machine and softened with a hand board4 ,for fancy slippers the crust skins are starched and stained directly1 then staked 7see ,part ,,iii41 ,section ,,ii471 fluffed1 seasoned and glazed4 ,if intended for leggings and gaiters a flesh finish is given4 ,the skins are soaked1 stretched1 shaved and sumached4 ,they are then rinsed1 drained1 sammed and stained4 ,a brown stain mixed with linseed jelly is usual4 ,this is spread evenly over the flesh and glassed in4 ,the skins are dried out1 restained if necessary1 and staked to raise a nap4 ,basils for gaiters are dyed in paddle and fluffed over the emery wheel4 ,skivers are split in the limed state and sometimes immediately degreased4 ,they are next puered at #he ,f4 for about #c hours in a paddle1 and scudded4 ,they are drenched at a low temperature 7#fh-gj ,f471 but often #b or #c days4 ,they are again scudded and then rinsed and sent to tan4 ,the skivers are tanned in a few days by sumach liquors working the goods up from mellow to fresh as usual4 ,the liquors are warmed4 ,care must be taken that the goods do not tear4 ,a great variety of finish is possible1 but the paste grain skiver for fancy goods and the plain finish for hat leathers are sufficiently typical4 ,for paste grains they are soaked and cleared for dyeing by immersion in very weak sulphuric acid1 excess of which is carefully washed out with water4 ,paddle-dyeing follows1 and is preferred to drum dyeing as the skins are so liable to tear4 ,after being struck out they are pasted1 by spreading on to the flesh a glue jelly1 using first the hand1 then a stiff brush and finally a cloth4 ,the goods are then dried out4 ,they are then seasoned1 partly dried and printed cross-grain4 ,they are next grained two ways lightly2 shank to shank1 and across1 lightly tooth-rolled and glazed4 ,they are regrained two ways as before1 dried out1 and finally softened with a graining board4 ,they are sometimes sized on the grain to fix the pattern and give a gloss4 ,for hat leathers the skins are first soaked1 sumached and struck out4 ,if for white or cream finishes they are now lead-bleached4 ,this consists of pigment dyeing with lead sulphate4 ,they are immersed alternately in lead acetate and in sulphuric acid solutions until precipitation is sufficient4 ,they are then dyed to shade4 ,if for browns it is common to mordant with titanium and use basic dyestuffs1 paddling afterwards in sumach to fix the dye4 ,after dyeing the goods are struck out again1 starched1 and dried out on boards4 ,they are again starched and rolled to give the plain finish4 ,roans are not split4 ,they are degreased1 puered1 scudded and drenched overnight at #ie ,f4 ,they are tanned with sumach usually in pits1 and take rather longer than usual to tan4 ,they are finished in much the same style as goatskins for morocco leather1 but as the sheepskin has little natural grain it needs embossing or printing according to the type required4 ,if for hard grains1 the skins are soaked1 sumached1 seasoned1 dried1 glazed and damped back for printing4 ,this is done by the hard grain roller1 and the goods are dried out to fix the pattern4 ,they are damped back1 sammed1 and grained in four directions 7cp4 ,section ,,ii471 dried out and boarded to soften4 ,if for straight grains they are printed with a straight-grain roller1 or grained neck to butt4 ,after tooth rolling they are boarded1 dried and glazed4 ,they are softened down and aired off in a cool store4 ,roller leather is a special class of sheepskin leather which is used to cover the rollers used in cotton spinning4 ,the essential requirements are that a smooth plain finish should be given1 and the leather must not stretch or be greasy4 ,for this purpose small sheepskins with a fine small grain are chosen1 such as those obtained from the ,welsh mountain sheep4 ,the pelts are machine fleshed1 short haired and often puered1 but the deliming is also brought about by organic acids also4 ,the pelts are drenched in pits fitted with paddles1 which are used to stir up the infusion occasionally4 ,a thorough scudding is given4 ,for the smooth-grain finish it is necessary to tan in weak liquors1 and to give plenty of time so as to ensure complete penetration4 ,an oak-bark tannage is preferred1 but a little extract is usual to assist4 ,the goods are coloured through in paddle1 like basils1 and are then degreased by hydraulic pressure4 ,this should be as complete as possible1 and a little heat is used to assist the escape of grease4 ,the pressed skins1 moreover1 must be quite freed from creases1 and this is attained first by paddling in warm water to remove sawdust1 and then by drumming in fairly hot water1 in which they are left overnight4 ,the skins are tanned out in suspenders1 taking about #c weeks4 ,the crust skins need careful sorting1 and are soaked and hand shaved4 ,they are sumached in drum1 rinsed1 struck out1 sammed and set4 ,the striking and setting should be thorough1 in order to get rid of stretch4 ,they are next filled by coating with linseed jelly or similar material1 and dried out on boards in a thoroughly stretched condition4 ,they are then trimmed1 seasoned and rolled with a steel roller4 ,they are then staked or perched1 fluffed1 reseasoned1 dried and glazed4 ,they are carefully short-haired1 glazed again and finally ironed4 ,e4,i4 sheepskins are imported in a tanned condition4 ,these are soaked back and the turwar bark tannage stripped as far as possible by drumming with soda for #bj-cj minutes at #ie ,f42 after washing they are soured in weak 7#a_/b per cent47 sulphuric acid solution1 and retanned with sumach paste for an hour1 drumming at #ajj ,f4 ,they may then be finished for basils1 moroccos or roller leather as described above1 but are often finished as imitation glac kid4 ,in this case they are drum dyed1 lightly fat-liquored 7see ,part ,,iii41 ,section ,,iv471 struck out and dried4 ,they are staked by machine1 fluffed1 seasoned and glazed4 ,they may be re-staked and reglazed if desired4 ,,references4 ,a4 ,seymour ,jones1 ,the ,sheep and its ,skin4 ,bennett1 ,manufacture of ,leather1 pp4 #cj1 #he1 #ajg1 #bjh1 #cdi-ced1 #che4 ,,section ,v4--,,calfskins ,calfskins are the raw material for many classes of leather4 ,the term itself is rather broad4 ,a calfskin may be obtained from a very young animal and weigh only a very few pounds1 or it may be anything just short of a kip4 ,goat1 seal1 and sheep skins are obtained from adult animals1 but calfskins from the young of a large animal4 ,thus there are many grades of quality1 according to age1 and the material must be chosen with regard to the purpose in view4 ,some of these purposes have already been discussed4 ,heavy calf is treated much like kip as a curried leather for upper work4 ,even lighter skins are given the waxed calf and satin calf finishes1 and make upper leather of excellent quality4 ,to produce such leathers the treatment is much the same as described in ,part ,i41 ,section ,,viii4 ,calfskins were also used for very light upper work1 in which they were not so heavily greased in finishing1 but rather dyed and finished as a light leather4 ,in this direction1 however1 the vegetable tannage has been almost completely superseded by the mineral tannages1 first by calf kid1 an alumed leather 7,part ,,iv41 ,section ,i471 and afterwards by the now popular chrome tannage of box calf1 willow calf1 glac calf1 dull calf1 etc4 7,part ,,iii41 ,section ,,iii474 ,in this section1 therefore1 we have only to consider calfskins as used to make a vegetable-tanned light leather1 such as may be employed in bookbinding and in the manufacture of fancy goods4 ,for these purposes the skins receive a mellow liming of #b-a_/b - #c weeks4 ,no sulphide need be employed1 as the goods are soon fit to unhair4 ,in such a mellow liming it is important that the bacterial activity is not too prominent1 and hence it becomes advantageous to work the liming systematically in the form of a round of pits4 ,to avoid over-plumping in the newest limes some old liquor is used in making up a new pit1 and its bacterial activity is reduced by adding it to the new caustic lime whilst slaking4 ,thus for a pack of #bjj-bej skins1 #ad-af stone of lime may be slaked with about #cj gallons of old lime1 and the pit filled up with water4 ,if it be necessary to shorten the process and to use sulphide1 this should be added only to the tail liquors of the round1 and with it should be added1 if possible1 some calcium chloride to reduce the harshness of the soda4 ,the skins should be puered thoroughly to obtain the necessary softness1 bate-shaved if desirable1 and drenched with #h per cent4 of bran overnight4 ,in tanning for fancy work and for dark colours1 the goods are coloured off and evenly struck through with sumach liquors1 and then tanned further with liquors made from oak bark1 myrabolans or chestnut extract4 ,the methods are very closely similar to those used for goatskins and sealskins 7,part ,,ii41 ,sections ,,ii4 and ,,iii471 and need not be described in further detail4 ,the tannage is finished off in sumach4 ,for bookbinding work1 however1 a pure sumach tannage is given1 using liquor slightly warm 7#gj ,f474 ,paddle tannages are common1 but for bookbinding the bag or bottle tannage is often preferred4 ,the skins are sewn together in pairs1 grain outwards1 and nearly filled with warm sumach infusion1 just as described for goatskins4 ,they are then handled in old sumach liquors for about #c days1 and piled to drain and press4 ,at this stage the bag is cut open1 the goods worked on the flesh1 and the tannage is completed with separated skins in newer sumach liquors1 handling at least once a day for #d-e days1 as necessary4 ,in finishing there is the usual variety1 but a plain ungrained finish is most typical1 as the smooth and fine grain of the young animal lends itself to this type of finish better than the skins of goat and seal1 and gives a better quality leather than those from the sheep4 ,the crust skins are wet back with water at about #aaj ,f41 and1 if necessary1 sammed and shaved4 ,sumaching follows1 the operation being carried out in a drum for #a-b hours4 ,the skins are then well struck out4 ,striking and setting should always be thorough for a plain finish1 and this case forms no exception4 ,dyeing follows next1 the paddle being often preferred to the drum1 which is liable to work up a grain4 ,the dyed skins are placed in cold water for a while and again well struck out4 ,they are often nailed on boards to samm1 and are then set out1 lightly oiled with linseed oil and dried out in a cool shed4 ,seasoning follows1 with milk and water only4 ,the operation may be done with either brush or sponge1 after which the goods are piled grain to grain and flesh to flesh to regulate4 ,they may be next perched to soften and fluffed if desired4 ,after top seasoning with milk1 water and albumin the skins are hung up for a while1 piled to regulate and brushed1 first lightly and then more vigorously4 ,they may be then oiled very lightly and dried out in a cool stove to ensure a soft leather4 ,,reference4 ,bennett1 ,manufacture of ,leather1 pp4 #ee1 #hd1 #aje1 #bja1 #bjg1 #cjc4 ,,section ,,vi4--,,japanned ,,and ,,enamelled ,,leathers ,the leathers which receive a japanned or enamelled finish are usually vegetable tannages1 and so may be discussed at this stage4 ,they are popularly known as patent leather1 but for no obvious reason4 ,the chief object is to obtain a leather with an exceedingly bright and permanent gloss or polish1 and this is attained by coating the leather several times with suitable varnishes4 ,the great difficulties are to prevent the varnish cracking when the leather is bent or in use1 and to prevent it peeling off from the leather4 ,almost all classes of vegetable tannage are japanned and enamelled4 ,hides are split and enamelled for carriage1 motor car and upholstery leathers1 and enamelled calf1 seal and sheep skins are used for boot uppers1 toe caps1 dress shoes1 slippers1 ladies' and children's belts1 hat leathers1 and so on4 ,broadly speaking1 a japanned leather is a smooth finish and is usually black1 whilst an enamelled leather is a grain finish with a grain pattern worked up1 and more often in colours4 ,hence japanned leathers are often made from flesh splits or leathers with a damaged grain4 ,it is in any case advantageous to buff the grain lightly1 for this permits the varnishes to sink rather deeper and get a firmer grip1 and avoids the too sudden transition from phase to phase which is one cause of stripping or peeling4 ,many flesh splits1 however1 are printed or embossed to give an artificial grain and are then enamelled1 which tends to fix the embossed pattern4 ,almost any method of preparing dressing hides for upper or bag work will yield a suitable leather for enamelling and japanning 7see ,part ,i41 ,section ,,viii42 and ,section ,,ix474 ,if anything the liming should be somewhat longer and mellower in order to eliminate grease1 as the natural grease of the hide causes the stripping of some varnishes4 ,in finishing it is important to obtain even substance1 or the varnish is liable to crack4 ,hides are soaked and sammed in1 and often split4 ,sometimes they are split twice1 giving grain1 middle and flesh1 the two former being enamelled and the last japanned4 ,other goods are shaved very smooth4 ,the goods should be next thoroughly scoured and stoned to get as much stretch as possible removed4 ,they are often sumached1 washed in warm water1 slicked out again and sammed4 ,they are then lightly buffed on the grain1 and after oiling lightly are thoroughly set out and dried4 ,embossing or printing for enamels is done before the goods are quite dry4 ,considerable difference of opinion obtains as to the best oil to use in the above oiling4 ,linseed oil is widely preferred as being most likely to agree with varnishes made from linseed oil4 ,some manufacturers of japans do not dislike the use of mineral oil1 but strongly object to cod oil1 tallow or other stuffing greases as tending to cause the varnish to strip or peel4 ,other manufacturers1 on the other hand1 will not have leather with mineral oil in it1 and indicate that nothing but cod oil should be used4 ,in all probability these various preferences are determined by the nature of the varnish1 which differs widely in various parts of the globe4 ,in this country the varnishes are made largely from linseed oil by boiling it with driers4 ,this oil contains much triglyceride of an unsaturated relative of stearic acid4 ,the double bonds are very susceptible to oxidation with the production of resinous bodies of unknown constitution4 ,this phenomenon is known as drying the oil1 and has been extensively used in the manufacture of linoleums4 ,the driers are either oxidizing agents or oxygen carriers1 such as litharge1 ,prussian blue1 raw umber1 manganese dioxide1 manganese borate1 and resinate4 ,prussian blue is most preferred for ,british japans1 as it always materially assists the attainment of the desired black colour4 ,the exact details of the boiling1 and the manufacture of the varnishes is still largely the trade secret of the master japanners1 and differs indeed for the various stages of japanning4 ,the varnish for the earlier coats is boiled longer1 and the drying carried further1 than in the case of the later coats4 ,this is partly to obtain a product of such stiffness that it will not penetrate the leather4 ,the driers and the pigments should be finely powdered and thoroughly mixed in4 ,the boiling takes several days when at a low temperature1 but if done in #bd hours the temperature may be up to #egj ,f4 ,in the later coats driers are often not used1 and the product is often mixed with copal varnish1 pyroxylin varnish1 etc41 which greatly help in obtaining smoothness and gloss4 ,turpentine1 petroleum spirit and other solvents are also used to thin the varnishes4 ,before boiling1 the oil is often purified by a preliminary heating with nitric acid1 rose spirit and other oxidizing agents1 which precipitate impurities and thereby assist in obtaining a bright gloss4 ,before the application of the varnishes1 the leather is first dried thoroughly in a stretched condition4 ,this is accomplished by nailing down on boards which fit like movable shelves into a stove1 a closed chamber heated by steam pipes4 ,the temperature of the stove varies widely in different factories1 from #adj-bjj ,f41 according to the nature of the varnishes4 ,the first coat of warm and rather stiff japan is laid over the hot leather in a warm room1 being spread over first by hand1 then by a serrated slicker1 and then again smoothed by hand4 ,the goods are then put into the stove for several hours to dry4 ,when dry the surface is pumiced and brushed and a second coat applied in a similar manner1 but with increased care4 ,this is repeated with finer japans until the desired result is obtained4 ,brushes are used to apply the later coats4 ,up to seven coats may be applied for the production of a smooth japan--three coats of ground japan1 two coats of thinner japan1 and two coats of finishing varnish4 ,after the stoving is complete1 the product is given a few days under ordinary atmospheric conditions to permit the reabsorption of moisture to the usual extent4 ,enamelled leathers are then grained to develop the pattern4 ,,reference4 ,bennett1 ,manufacture of ,leather1 p4 #chj4 ,,part ,,iii4--,,chrome ,,leather ,,section ,i4--,,the ,,nature ,,of ,,chrome ,,leathers ,in these days the manufacture of chrome leather has attained a position hardly less in importance than that occupied by the ancient method of tanning by means of the vegetable tanning materials1 and large quantities of hides and skins are now chrome tanned after preparatory processes analogous to those described in connection with vegetable tannages 7,part ,,ii41 ,section ,,ii42 and ,part ,,ii41 ,section ,i474 ,chrome leathers are made by tanning pelts with the salts of chromium1 and are typical of what are known as mineral tannages1 in which inorganic salts are the tanning agents4 ,tannage with alum and salt 7see ,part ,,iv41 ,section ,i47 is one of the earliest mineral tannages1 but is now of relatively minor importance4 ,chrome tanning was first investigated by ,knapp 7#aheh71 who experimented with chromic chloride made basic by adding alkali1 but his conclusions were unfavourable to the process4 ,a patent was taken out later by ,cavallin in which skins were to be tanned by treating with potassium dichromate and then with ferrous sulphate which reduced the former to chromic salts1 being itself converted into ferric salt4 ,the product1 which was a combination of iron-chrome tannage1 did not yield a satisfactory commercial leather4 ,another patent1 taken out in #ahgi by ,heinzerling1 specified the use of potassium dichromate and alum4 ,this in effect was a combination chrome-alumina tannage4 ,the alum had its own tanning action and the dichromate was reduced to chromic salts by the organic matter of the skin itself and by the greases employed in dressing4 ,the process1 however1 was not a commercial success4 ,in #ahha patents were obtained by ,eitner1 an ,austrian1 whose process was a combination chrome and fat tannage4 ,the chrome was employed as basic chromium sulphate made by adding common soda to a solution of chrome alum until a salt corresponding to the formula ,cr7,,oh7,,so#d was obtained4 ,such a solution is now known to be perfectly satisfactory1 but at first it proved difficult to devise satisfactory finishing processes1 and to supplement the chrome tannage with the fat tannage4 ,the first undoubted commercial success in chrome tanning was obtained by the process of ,augustas ,schultz1 whose patent was the now widely known two-bath process1 in which the skins are treated successively with a chromic acid solution and with an acidified solution of hypo 7sodium thiosulphate74 ,the first bath was made up commercially of potassium dichromate and hydrochloric acid1 so that1 strictly speaking1 it contained potassium chloride also4 ,the second bath contained1 in effect1 sulphurous acid1 which reduced the chromic acid in the skin fibres to the tanning chrome salts4 ,free sulphur is also formed in this bath and in the skin1 and contributes to the characteristic product obtained by this process of tanning4 ,many minor deviations from the original process of ,schultz have been introduced1 but the main features have been unchanged1 and this method of tanning is widely employed at the present time for both light and heavy chrome leather4 ,in #ahic tanning by basic chromic salts was revived and the use of the basic chloride was patented by ,martin ,dennis1 who offered such a tanning solution for sale4 ,the validity of the patent has always been doubtful on account of the previous work of ,knapp and others1 but the process itself was commercially satisfactory1 and the many variants of this and of the basic sulphate tannages are now generally known as the one-bath process in contradistinction to the variants of the ,schultz process1 and are widely used for all classes of chrome leather4 ,a one-bath process which deserves special mention was published in #ahig by ,prof4 ,h4 ,r4 ,procter4 ,in this the tanning liquor was made by reducing potassium dichromate in the presence of a limited amount of hydrochloric or sulphuric acid by adding glucose4 ,although a basic chrome salt is the chief tanning agent thus produced1 there is little doubt that the organic oxidation products play an essential part in producing the fullness and mellowness of the leather thus tanned1 but their nature and mode of action has not yet been fully made clear though lyotrope influence is probable4 ,more recently ,balderston has suggested the suitability of sulphurous acid as reducing agent4 ,a stream of sulphur dioxide gas is passed through a solution of sodium dichromate until reduction is complete4 ,the resulting chrome liquor has been favourably reported upon by some chrome tanners4 ,bisulphite of soda has also often been used as the reducing agent4 ,other organic substances are also often used1 instead of glucose1 to reduce the dichromate4 ,theory of ,chrome ,tannage4--,as to the theory of chrome tanning there is still considerable difference of opinion and much room for experiment4 ,some leather chemists regard the tannage as differing essentially from the vegetable tannages4 ,mr4 ,j4 ,a4 ,wilson has even suggested that the proteid molecule is in time partly hydrolyzed with the formation of a chromic salt with the acid groups4 ,the author1 however1 strongly favours the view that in chrome tanning changes take place which are closely analogous to those which occur in vegetable tannage1 the differences being mainly of degree4 ,thus the hide gel is immersed into a lyophile sol--the chrome liquor--and there follows lyotrope influence1 adsorption1 gelation of the tanning sol1 as well as diffusion into the gel1 and finally also1 probably1 precipitation of the tanning sol at this interface4 ,in chrome tannage the lyotrope influence is much more prominent than in vegetable tannage1 but the effect is in the same sense1 viz41 to reduce the imbibition of the hide gel4 ,thus the potassium sulphate in a chrome alum liquor has its own specific action of this kind and contributes to the leather formation4 ,unhydrolyzed chromium sulphate and the sodium sulphate formed in making basic act also in the same sense4 ,the tanning sol is probably chromium hydrate1 formed by the hydrolysis of chromium sulphate3 it is a lyophile or emulsoid sol and is in consequence very strongly adsorbed by the hide gel4 ,this adsorption1 involving a concentration of lyophile sol1 is the first stage in gelation1 which occupies a relatively more prominent place in chrome than in vegetable tannage4 ,some diffusion into the gel also occurs1 and both the gelation and diffusion of the sol are affected by lyotrope influence1 but to a greater extent than in the vegetable tannage4 ,thus far the analogy is almost complete4 ,there remains the question of the precipitation of the tanning colloid at the interface4 ,this is a point which has not yet been thoroughly investigated1 and which offers considerable difficulty to a clear understanding1 but the matter may be probably summarized thus3 the adsorbed chromium hydrate is precipitated at the interface of gel and sol to some extent1 chiefly through the neutralization of its charge by the oppositely charged ions of the electrolytes present1 but possibly also--in the last stages of manufacture by the mutual precipitation of oppositely charged gel and sol4 ,to illustrate the matter1 the case of a basic chrome alum liquor will be considered4 ,the chromium hydrate sol is primarily a positive sol1 just like ferric and aluminium hydrate sols3 i4e4 in water they are somewhat exceptional in that they adsorb ,h rather than ,,oh-4 ,to cause precipitation therefore it is necessary to make the sol less positive and more negative4 ,the positive charge of the sol1 however1 is greater than in water1 because of the free acid formed in the hydrolysis1 which results in the adsorption of more hydrions by the sol4 ,hence to ensure precipitation steps must be taken to reduce the adsorption of hydrions by the chromium hydrate sol4 ,in practice such steps are taken1 and to such an extent that there can be little doubt that the chrome sol is not far from its isoelectric point4 ,amongst these steps are 7#a7 making the liquor basic1 i4e4 adding alkali to neutralize much of the free acid1 which involves a considerable reduction in the stabilizing effect of the hydrions2 7#b7 the adsorption of hydrions by the hide gel when first immersed in approximately neutral condition2 7#c7 the operation of the valency rule that the predominant ionic effect in discharging is due to the multivalent anions4 ,in this case the divalent ,,so#d-- ions assist materially in discharging the positive charge on the chrome sol2 7#d7 the final process of neutralization in which still more alkali is added4 ,the operation of the valency rule is the most complex of these factors1 for there is also to be considered the stabilizing effect of the kations1 especially of the trivalent kation ,cr from the unhydrolyzed chromium sulphate4 ,it is quite possible also that in the last stages of chrome tanning there are zones of non-precipitation due to the total effect of multivalent ions1 and it is quite conceivable that the chrome sol may change its sign1 i4e4 become a negative sol and thus give also a mutual precipitation with the hide-gel4 ,this is particularly probable where a local excess of alkali occurs in neutralization4 ,however that may be1 it is probable that most of the tannage is accomplished by chromium hydrate in acid solution1 and it is therefore legitimate to conclude that adsorption and gelation have a relatively greater part in chrome tannage4 ,the operation of the valency rule makes it easy to understand why basic chlorides do not tan so well as sulphates2 the precipitating anion is only monovalent 7,cl-7 and chromic chloride contains no substance analogous to the potassium sulphate of chrome alum and hence contains a less concentration of the precipitating anion4 ,hence also the stabilizing influence of common salt added to a basic alum liquor1 the effect being to replace partially the divalent ,,so#d-- by the monovalent ,cl-4 ,lyotrope influence1 however1 may be here at work4 ,it is possible to make out a rather weak case that the tanning sol is not chromium hydrate at all1 but a basic salt of chrome also in colloidal solution1 and to contend that this salt1 like most substances1 forms a negative sol1 but in practice not negative enough1 hence the desirability of alkali1 divalent anions1 etc4 ,from this point of view the analogy with vegetable tannage becomes more complete and the stabilizing effect of the soda salts of organic acids becomes easy to understand4 ,it is highly probable that the electrical properties of the chrome sol need closer investigation on account of the complexity due to the prominent effect of multivalent ions4 ,it is desirable to bear in mind the remarkable phenomenon observed by ,burton 7,phil4 ,mag41 #aije1 vi1 #ab1 #dgb71 who added various concentrations of aluminium sulphate to a silver sol 7negative74 ,he observed 7#a7 a zone of non-precipitation due to protection2 7#b7 a zone of precipitation due to the trivalent kation2 7#c7 a second zone of non-precipitation due to protection after the sol has passed through the isoelectric point and become a positive sol2 7#d7 a second zone of precipitation due to the precipitating effect of the anion on the now positive sol4 ,it seems to the writer that similar phenomena may possibly occur in chrome tanning1 for whatever the sol actually is1 it is not far from the isoelectric point4 ,a few observations on the vegetable-chrome combination tannages will not be out of place at this stage4 ,wilson refers to the well-known practical fact that chrome leather can take up about as much vegetable tan as if it were unchromed pelt1 and considers this evidence that the two tannages are of fundamentally different nature4 ,in mineral-tanned leathers the metal is combined with carboxyl groups1 while in vegetable-tanned leather the tannin is combined with the amino groups4 ,this strongly suggests the possibility that the two methods of tanning are to some extent independent of one another1 and that a piece of leather tanned by one method may remain as capable of being tanned by the other method as though it were still raw pelt 7,collegium 7,london71 #aiag1 #aaj-aaa74 ,to the writer1 however1 it seems that the facts are evidence for the contrary proposition1 that the tannages are fundamentally of the same nature4 ,on the adsorption theory1 one would expect chrome leather to adsorb as much tan as pelt2 the readily adsorbable tan is the same1 and the chrome leather is an adsorbent of very much the same order of specific surface as pelt4 ,the adsorption theory would find it difficult to account for chrome leather not adsorbing as much tan as pelt4 ,it is quite conceivable that a chrome leather could adsorb more tan than pelt1 owing to the more complete isolation of the fibrils by the chrome tannage and to their being coated over by a more adsorbent gel4 ,adsorption is often deliberately increased by a preparatory adsorption4 ,thus sumach-tanned goatskins are wet back from the crust and retanned in sumach before dyeing1 to coat the fibres with a fresh and more adsorbent gel and so ensure the even and thorough adsorption of the dyestuff4 ,mordanting fabrics has a similar object1--the adsorption of colloidogenic substances which give rise to an adsorbent gel on the fibre4 ,unless vegetable-tanned leather is so much loaded with tan that its specific surface is effectively reduced1 one would similarly expect that vegetable-tanned leather would adsorb the chrome sol4 ,this1 of course1 is exactly the case of semi-chrome leather4 ,if1 on the chemical combination theory1 the vegetable tan combines with the amino groups and the chrome with carboxyl groups1 it is natural to inquire which groups the dyestuffs combine with4 ,as either tannage does not interfere with the adsorption of dye1 are we to conclude similarly that tanning and dyeing are fundamentally different processes8 ,those who favour this chemical combination theory1 and who offer equations for the formation of vegetable and of chrome leather1 should likewise suggest an equation for the formation of leather from pelt by the action of dyestuffs--a practical though hardly an economic process4 ,the remarks made earlier in this volume 7,part ,i41 ,section ,,iii47 as to the occurrence of what have been called irreversible changes subsequent to the mutual precipitation of oppositely charged gel and sol1 are equally applicable to the chrome tannages4 ,chrome tannage was once thought to embrace such irreversible changes1 but the process can now be reversed with ease4 ,the reversibility of the chrome tannage is an easier proposition than that of vegetable tannage1 partly because the leather is comparatively much less tanned1 and partly because the acidity or alkalinity of the stripping agent may be adjusted1 as desired1 without the oxidation trouble4 ,in approaching this question from the theoretical side one must consider mainly whether to solate the tanning agent to a positive or to a negative sol4 ,our imperfect knowledge of the electrical forces in operation in the chrome tannage is thus a serious drawback1 but the evidence on the whole points to the precipitation being effected by a negative sol near its isoelectric point but in faintly acid solution4 ,hence1 we should theoretically expect that reversion should take place into a negative sol in nearly neutral or even faintly alkaline solution4 ,thus1 suitable stripping agents for chrome leather would be the alkali salts of organic acids 7especially if multivalent74 ,now1 ,procter and ,wilson have recently accomplished this stripping of chrome leather by the use of such salts4 ,they approached the question from an empirical and practical point of view and found that ,rochelle salt1 sodium citrate1 and sodium lactate would strip the chrome tannage with ease4 ,this important and very creditable achievement will have great practical and commercial importance4 ,procter and ,wilson have deliberately and carefully refrained from offering an exact explanation of this reversible action1 but point out that all their stripping agents are salts of hydroxy-acids1 and strongly insist that these form soluble complexes with the chrome4 ,whilst not denying this in the least1 the present author would point out that according to the views advanced in this book1 the salts of organic acids which do not contain hydroxyl groups should1 when combined with a monacid base1 also strip the chrome tannage4 ,this he has found to be the case4 ,thus the chrome tannage is reversible in solutions of ammonium or potassium oxalate and of ammonium acetate4 ,with these salts the full effect of multivalent anions is not attained1 so that somewhat strong solutions are necessary4 ,a #aj per cent4 solution of ammonium acetate shows some stripping effect after a few days1 but a #dj per cent4 solution after a few hours4 ,saturated ammonium oxalate is only a #d4b per cent4 solution1 but shows a stripping effect in #b-c days4 ,potassium oxalate 7#cc per cent47 shows distinct stripping in #bd hours4 ,potassium acetate and sodium acetate show only slight action1 because the solution is too alkaline1 but strip if acetic acid be added until litmus is just reddened4 ,it is noteworthy from a theoretical point of view that a #dj per cent4 solution of ammonium acetate is distinctly acid1 and indeed smells of acetic acid4 ,there can be little doubt that such stripping actions are also connected with the solubility of the stripping agent in the gel1 for the liquid must pass through the walls of the gel to dilute the liquid in the interior4 ,this view fits in with the facts that hydroxy acids and ammonium salts are particularly efficient1 for the tendency of chrome to form ammonia-complexes as well as hydroxy complexes is well known4 ,from this point of view we should not expect a stripping action from a salt such as disodium phosphate1 which would form an insoluble substance4 ,actually sodium phosphate does not strip1 and indeed reduces the stripping power of ammonium acetate4 ,similarly1 we might expect some stripping action by ammonia and ammonium chloride1 with the formation of chrome ammonia complexes4 ,this actually occurs1 a pink solution being obtained4 ,sodium sulphite does not strip1 possibly partly on account of its too great alkalinity1 but is interesting theoretically to observe that sodium sulphite as well as ,rochelle salt will strip salt stains 7see ,yocum's patent1 ,collegium 7,london71 #aiag1 #f2 also ,procter and ,wilson1 loc4 cit474 ,this points to the formation of a negative sol1 and suggests many other substances for removing salt stains4 ,special ,qualities of ,chrome ,leather4--,a few words on the special peculiarities of the leather formed by chroming will not be out of place at this stage4 ,one of the greatest disadvantages of the chrome tannage has been the absence of what is known as the crust or rough leather stage4 ,in chrome tanning1 the finishing operations have had to follow on immediately after the tannage4 ,chrome leather1 after tanning1 may be dried out like other leathers1 but if thoroughly dried1 or if kept in a dried condition for any time1 it will not wet back again with water4 ,various suggestions have been made to overcome this difficulty but none yet have found much favour in practice4 ,the discovery of the reversibility of the tannage1 however1 ought to solve this difficulty1 and the author would suggest that any of the substances used for dechroming might also be suitable for wetting in chrome leather which has been well dried out4 ,a piece of chrome leather1 dried out well after neutralizing1 and kept in a warm place for four years1 wetted back easily in ammonium acetate1 in the author's laboratory4 ,another peculiarity of the chrome tannage is that any defects in the raw material always seem more obvious in chrome than in vegetable leather4 ,this often necessitates the use of a better quality hide or skin4 ,weak grain or loose grain becomes very obvious4 ,the presence of short hair which both unhairing and scudding have failed to remove also is usually more evident4 ,a more serious disadvantage of chrome leather is its tendency to stretch4 ,in the case of belting leather this feature is an obvious nuisance1 and has inevitably led manufacturers to use powerful stretching machines upon the goods before they are marketed4 ,in chrome sole leather also there is a tendency to spread and throw the boot out of shape4 ,further disadvantages arise from the fact that the chrome tannage is an empty tannage4 ,compared with the vegetable tannage1 very little of the tanning agent is adsorbed4 ,hence there is little matter of any kind between the hide fibres isolated during tannage4 ,the inevitable effect of this is that the leather has not the same solidity and firmness1 and needs filling out with other materials4 ,a commercial consequence is also that it is impossible to obtain the same yield of leather from any given quantity of raw material4 ,in trade parlance chrome tannage does not give good weight4 ,another consequence is that 7even when well filled with greases in finishing7 chrome leather tends to be woolly on the flesh side or at cut edges4 ,on the other hand1 chrome tanning has very many advantages over the older process4 ,the most obvious of these is the great saving in time4 ,many chrome tannages involve only a day or two1 and none more than a week or two4 ,a chrome leather factory therefore needs less capital on account of the quicker turnover4 ,if1 moreover1 the market be unfavourable1 a chrome tanner can stop or reduce his output in a very short time1 whereas a vegetable tanner is committed to many weeks' supply of the goods he is manufacturing4 ,another notable advantage of chrome leather is its durability4 ,in the finishing processes more grease is usually employed than in vegetable tannage1 and this has a preservative effect upon leathers which often get wet4 ,chrome sole leather and hydraulic leathers are cases in point4 ,chrome leather will also stand changes of temperature and friction much better than vegetable tannages4 ,the light chrome tannage results1 further1 in yielding a leather which has great tensile strength1 and it is not surprising to find that chrome harness and chrome picking bands are highly thought of4 ,the empty nature of the tannage necessitates the use of stuffing greases1 but such large proportions of these may be used that chrome tannage becomes obviously suitable if one wishes to produce a waterproof leather4 ,hence the popularity of chrome tannage for waterproof soling and hydraulic leathers4 ,the advantages of the chrome process are very real1 and very obviously such as will appeal to manufacturers4 ,chrome leathers have now been for some time in the forefront as far as boot-uppers are concerned1 especially for the best quality goods1 in which the popular box-calf and glac kid are so largely employed4 ,there seems little doubt that this will continue to be the case4 ,it is an unfortunate fact that in this important branch of tanning1 ,british manufacturers have not quite risen to the occasion4 ,their products have in the past been faced with very serious competition from ,continental and ,american manufacturers of chrome uppers1 and there can be no doubt that these competitors produced a better article1 and produced it more economically4 ,the disorganization of the ,continental factories owing to the war should give ,british manufacturers a valuable opportunity of putting such businesses on a better basis4 ,for sole leather also the chrome tannage makes constant headway1 and the relative proportion of it becomes gradually greater4 ,a great impetus to chrome sole leather has been given by the war conditions of ,britain4 ,owing to the submarine campaigns of ,germany the tonnage question became all-important1 and the bulky imports of vegetable tanning materials became a serious item4 ,british tanners were therefore encouraged to make more chrome sole and less vegetable sole4 ,the urgent need of leather for our armies also assisted in the same sense4 ,the production of chrome sole progressed therefore enormously during #aiag and #aiah1 and although some reaction will doubtless occur1 there seems little doubt that chrome sole leather has taken a definite and permanent leap forward4 ,once the general public fully appreciate its qualities of waterproofness and durability its future will be assured4 ,on the whole the position and prospects of chrome tanning are good4 ,the chrome tannages are making headway in all directions1 and undoubtedly threaten the existence of many of the older processes of vegetable tanning4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 pp4 #aih-bbj4 ,bennett1 ,manufacture of ,leather1 pp4 #baj1 #cee4 ,bennett1 ,j4,s4,l4,t4,c41 #aiag1 #agf4 ,stiasny1 ,collegium1 #aijh1 #aag4 ,,section ,,ii4--,,general ,,methods ,,of ,,chrome ,,leather ,,manufacture ,it has been previously pointed out that the chrome tannage is an empty one2 the primary principle in the wet work of goods for chrome leather is to avoid anything which will make this feature more obvious4 ,in the vegetable tannages relatively larger amounts of the tanning agents are used1 and these fill the interfibrillar spaces2 indeed1 as we have seen 7,part ,i41 ,sections ,,iii41 ,v4 and ,,vi471 effort is made to increase these spaces and to fill them to their maximum capacity1 thus yielding a leather of which #ej per cent4 is the tanning agent4 ,in chrome tanning1 however1 the tanning agent may only be approximately #e per cent4 of the finished leather1 so that any trouble taken to split the hide fibres or to dissolve hide substance is usually not only superfluous1 but also calculated to enhance the emptiness4 ,the governing principle of all the preparatory processes for chrome tannage is therefore the conservation of hide substance1 and this principle determines the modifications of the processes of soaking1 liming1 and deliming1 which are in vogue4 ,now1 in most of these processes there is usually some loss of hide substance1 and it is the particular problem of chrome tanning to reduce this loss to a minimum in each stage4 ,whether the loss of hide substance be due to alkaline or fermentive hydrolysis1 or to solation of the hide gel1 the effect is increased by swelling1 and in the wet-work for chrome1 therefore1 any variations in the degree of swelling are objectionable4 ,the preparatory processes should be carried out with as little change as possible in the volume and elasticity of the pelt4 ,whether also the loss of hide be due to hydrolysis or solation1 it is increased by time1 hence short processes are 7other things being equal7 much to be preferred4 ,fermentive hydrolysis is minimized by cleanliness1 alkaline hydrolysis by avoiding strongly alkaline liquors1 and solation of collagen is reduced by both1 and also by avoiding1 as far as possible1 the presence of calcium and ammonium salts4 ,soaking should be quick and clean4 ,the use of the paddle or drum gives the greatest efficiency and also assists in procuring the softness so essential to the bulk of chrome leathers4 ,liming chrome leather satisfactorily is almost an impossible ideal4 ,every conceivable arrangement has some objection to it4 ,the time of the process may be shortened either by the use of sulphide or by the use of mellow or old limes4 ,to shorten time by the use of sodium sulphide unfortunately involves the employment of more alkali than is desirable1 with a consequent plumping effect and tendency to harshness4 ,if sufficient sulphide be used to make the liming very short1 then the grease is not killed 7saponified or emulsified74 ,if the harshness and alkalinity be removed by using also an excess of calcium chloride1 then the lyotrope influence of this substance enhances the solation of the hide gel4 ,on the other hand the use of old lime liquors avoids the plumping effect1 but increases considerably the bacterial activity1 and the bacterial enzymes produce both hydrolysis and solation of the pelt4 ,in practice what is generally done is to shorten time by both methods and so to admit both disadvantages to a limited extent4 ,this is theoretically more sound than would appear1 for in mellow limes sulphide has less plumping power but is just as strong a depilatant2 whilst1 on the other hand1 a mellow liming shortened by sulphide is less objectionable as there is some evidence that bacterial activity is relatively less in the first few days4 ,hence a mellow sulphide liming of #g-aj days is very common in practice1 but sometimes a #c-d days' process with more sulphide is also found satisfactory4 ,it would seem probable that the real solution of the problem would be found by a different process altogether4 ,in this connection it is interesting to note that a ,continental proposal to unhair by enzyme action only has been found most practicable with goods for chrome1 and1 in the author's opinion1 some development on these lines1 in which a lipolytic enzyme is used in addition to a proteolytic1 might solve the difficulty1 and give a rapid depilation which dispenses with liming1 plumping and deliming with the consequent loss of valuable hide substance4 ,in the usual short1 mellow1 sulphide liming it is clear that there is not much advantage in a round or set of pits4 ,hence the one-pit system is popular on account of the less labour involved4 ,the above remarks are less applicable in the case of chrome sole leather4 ,in this case weight is a great consideration and plumping is necessary4 ,in such leather the chrome tannage is supplemented by the use of waxes1 which fill up the spaces between the fibres and give solidity and waterproofness to the finished article4 ,with this leather an ordinary sole leather liming in sharp liquors is not unsuitable1 handling the goods from mellow to fresh1 but there is1 on the whole1 a tendency to shorten the process to about a week by using more sulphide4 ,processes for deliming pelt for chrome leather should also be chosen by our guiding principle of hide substance conservation4 ,here again short processes involving little change in swelling should be preferred4 ,now1 the ordinary bating and puering processes give 7#a7 neutralization of lime by organic acids combined with weak bases2 7#b7 the solation of some hide substance2 and 7#c7 a pulling down effect on the swollen pelt4 ,now1 neutralization is quite superfluous1 as the acids of the chrome liquor 7one-bath or two-bath7 can quite well accomplish this2 the solvent effect is undesirable altogether2 and the pulling down effect is also unnecessary if the goods are not plumped up4 ,with any method of liming1 however1 some plumping is obtained1 and this creates a problem of practical importance4 ,in the huge quantities of pelt which go for chrome upper leathers1 a primary consideration is the soft1 kind1 or mellow feel of the grain in the finished leather4 ,this is obtained only by tanning the pelt when the grain at least is in a thoroughly deplumped and inelastic condition4 ,it is essential to delime not only so that the alkaline plumping effect is completely removed1 but also so that no acid plumping effect succeeds it4 ,the practical problem is to decide whether1 in any particular instance1 dung puers and bates are necessary to obtain this result4 ,bating is clearly not very desirable1 on account of the length of the process1 during which hide substance would be lost unnecessarily1 and also because there will usually be a slight alkaline swelling4 ,puering with dog-dung infusions is preferable2 it is not such a long process1 the liquor is just acid to phenolphthalein1 and the action is more intense1 and by puering for a short time only the loss of hide may be confined to the grain and flesh only1 whilst the desired inelasticity of grain-pelt is soon obtained4 ,many large firms have admittedly found themselves unable to dispense with puering1 but others have succeeded in substituting for it the use of non-swelling deliming and lyotrope agents like ammonium chloride and boric acid4 ,in all cases it is futile to delime or puer the grain and then allow the goods to stand until the centre lime has diffused outwards4 ,the goods must pass into the chrome liquors when in the correct condition4 ,for heavy chrome leather a surface deliming with boric acid is all that is necessary4 ,even that is superfluous when the goods are to be pickled before tanning4 ,types of ,two-bath ,chrome ,tannage4--,although the original process of the ,schultz patent is quite a practicable one1 many modifications have been introduced4 ,these modifications have been made to suit the class of goods under treatment1 to suit the particular mode of application which is available or suitable1 and to effect economies of chrome and other material1 and of time1 and also to combine with the tannage a pickling effect or a partial alum tannage4 ,other modifications arise from the precise acid1 neutral1 or alkaline condition of the pelt1 being for example obviously necessary when pickled stock replace neutral pelts4 ,the many two-bath processes which have been found useful have been classified previously by the author#f into three types3 7#a7 ,the ,schultz type1 in which such quantities of dichromate and acid are used that there is no excess of free acid 7other than chromic71 but an excess of unaltered dichromate2 7#b7 the ,acid type1 in which the chromic acid is completely free and the liquor contains also some excess of mineral acid also2 and 7#c7 the ,neutral type1 in which neither of these main constituents is in excess1 just sufficient mineral acid having been used to liberate all the chromic acid from the dichromate4 ,footnote #f3 ,types of ,two-bath ,chrome ,tannage1 ,leather1 #aiji1 #bbg-bei4 ,now3-- ,k#b;,cr#b,o#g #b;,h,cl #b,k,cl #b;,cr,o#c ,h#b,o #bjd #gc ,taking the commercial hydrochloric acid as a #cj per cent4 solution1 #gc parts will be obtained in about #bej parts of commercial acid4 ,hence #bid parts dichromate need #bej parts commercial hydrochloric acid for the above reaction2#g in other words1 #e per cent4 dichromate needs #d-a_/d per cent4 commercial acid4 ,similarly #f per cent4 and #d per cent4 of dichromate need #e4a per cent4 and #c4d per cent4 respectively of commercial acid4 ,if therefore such quantities be used we have the so-called ,neutral type of chroming bath4 ,if less quantities of acid be used we have the ,schultz type1 and if greater quantities of acid be used we have the ,acid type4 ,the original ,schultz patent used #e per cent4 dichromate and #b-a_/b per cent4 hydrochloric acid1 and well exemplifies its type1 for there is much undecomposed dichromate4 ,the composition of some chroming baths in common use on a practical scale are given below under the heading of their type3-- ---------------------------------------- ----------------- ,type4 ,dichromate4 ,hydrochloric ,salt4 ,aluminium ,acid4 ,sulphate4 ---------------------------------------- ----------------- #e #b-a_/b -- -- #e #b-a_/b -- #c ,schultz #e #b-a_/b #e -- #e #b-a_/b #aj -- #f #c -- -- ---------------------------------------- ----------------- #d #d -- -- #d #d #e -- #e #e #e #c ,acid #e #e #aj -- #f #f #ae -- #c #c #ae #d #b #d #aj -- #d #ae #bd -- ---------------------------------------- ----------------- #e #d-a_/d #e -- #e #d -- #b-a_/b ,neutral ,chromic acid #e -- #e -- #f -- #h -- #d -- #aj -- ---------------------------------------- ----------------- ,footnote #g3 ,commercial acids of course vary in strength1 and the amount needed varies accordingly4 ,all the figures are percentages of the weight of pelt4 ,as ,k#b;,cr#b,o#g has a molecular weight of #bid1 and ,na#b;,cr#b,o#gb;,h#b,o a molecular weight of #bih1 in practice they may be considered as interchangeable1 weight for weight4 ,the sodium salt is cheaper and more often used4 ,the corresponding amount of chromic acid1 #b;,cr,o#c1 has an equivalent weight of #bjj1 hence any weight of dichromate may in practice be substituted by two-thirds the weight of commercial chromic acid4 ,equivalent weights of commercial sulphuric acid are sometimes used in place of hydrochloric4 ,the quantity depends upon the strength of the sulphuric acid used4 ,aluminium sulphate1 ,al#b7,,so#d7cah;,h#b,o 7mol4 wt4 #fff71 may be replaced by ordinary potash alum1 ,k#b,,so#d;,al#b7,,so#d7cbd;,h#b,o 7mol4 wt4 #idh74 ,in practice #g parts of the former and #aj parts of the latter may be considered equivalent4 ,it should be remembered that both these salts are hydrolyzed in solution1 and therefore increase slightly the amount of free acid present4 ,their presence decreases the amount of chrome taken up1 and as little or no alumina is found in the leather1 there is usually small advantage in their employment4 ,the use of salt is common but often unnecessary4 ,it is considered desirable in baths of the acid type to prevent swelling by the excess of acid1 and in baths made up from commercial chromic acid to replace correspondingly that normally formed from the reaction of dichromate and acid4 ,it is used also in all baths which are intended to treat pickled goods4 ,like all electrolytes its presence decreases the adsorption of chromic acid4 ,all these conceivable modifications will make good leather1 and the choice of a process often depends largely upon market prices4 ,on the whole the tendency is to prefer the neutral or acid type1 on account of the greater ease and completeness with which the bath may be exhausted4 ,pickled stock may be depickled before tanning1 by a bath of salt1 mixed with borax1 whitening1 or basic alum solutions4 ,it may also be placed direct in the chroming bath1 but the amount of acid thus added with the goods must be determined and allowed for when making up the bath4 ,no allowance is usually necessary1 however1 if the pickle consist only of alum and salt4 ,the chroming operation is carried out usually in drums or paddles4 ,drums are preferable because more concentrated baths may be used2 these solutions penetrate quicker and are easier to exhaust economically4 ,they are also preferable for hides and heavy skins4 ,paddles are preferable where grain is important1 and for light skins in which little time is needed4 ,small variations in the ratio of chrome to pelt1 or in concentration of liquor1 have little influence upon the resulting leather4 ,the analytical investigation and control of chroming baths is usually simple4 ,a suitable volume of liquor is titrated with ,n_/#aj thiosulphate after acidifying with hydrochloric acid and adding potassium iodide4 ,the operation should be conducted in a stoppered bottle1 and the liquor allowed to stand for #aj-ae minutes after adding the iodide and before titrating4 ,a little fresh starch infusion should be added towards the end of the reaction4 ,each c4c4 ,n_/#aj thiosulphate corresponds to #j4jjcc gram ,cr,o#c or #j4jjdi gram ,k#b;,cr#b,o#g4 ,the same volume of liquor should also be titrated with ,n_/#aj caustic soda and phenolphthalein4 ,potassium chromate is neutral to this indicator1 i4e4 chromic acid acts as a dibasic acid4 ,any excess of hydrochloric acid is also titrated4 ,more indicator should be added towards the end of the titration1 as it is often oxidized4 ,each c4c4 ,n_/#aj soda corresponds to #j4jje gram ,cr,o#c1 #j4ja gram half-bound ,cr,o#c 7i4e4 present as dichromate71 #j4jadg gram ,k#b;,cr#b,o#g1 or #j4jjcfe gram ,h,cl4 ,if a c4c4 ,n_/#aj thiosulphate and b c4c4 ,n_/#aj soda be needed the type of chroming bath may be seen at a glance-- ---------------------------------------- ----------------------- ,if ,the type is ,the bath contains ---------------------------------------- ----------------------- b is greater than #a_/c;a ,schultz potassium dichromate but is less than #b_/c;a and chromic acid b is greater than #b_/c;a ,acid chromic acid and free hydrochloric acid b equals #a_/c;a ,neutral chromic acid only ---------------------------------------- ----------------------- ,if #aj c4c4 chrome liquor require a and b c4c4 of thiosulphate and soda respectively-- ,i4 #aj c4c4 of a ,schultz bath contain 7b - #a_/c;a7 #j4ja gram ,cr,o#c and 7a#j4jjcc7 - 7b - #a_/c;a7 #j4ja #a4dg grams ,k#b;,cr#b,o#g ,,ii4 #aj c4c4 of an acid bath contain 7a#j4jjcc7 grams ,cr,o#c and 7b - #b_/c;a7 #j4jjcfe grams ,h,cl ,,iii4 #aj c4c4 of a neutral bath 7a#j4jjcc7 grams ,cr,o#c or 7b#j4jje7 grams _/ ,the second bath of the two-bath chrome tannage consists of a solution of sodium thiosulphate acidified with hydrochloric acid4 ,the reactions in this bath are somewhat complicated1 several occurring simultaneously4 ,broadly speaking1 the final result is due to 7#a7 the reduction of the chromic acid to a chromic salt by the sulphurous acid2 7#b7 the formation of a basic chromic salt owing to the excess of thiosulphate2 7#c7 the reaction of the added acid and thiosulphate to give free sulphur1 which is deposited in and on the leather4 ,the relative intensity of these effects is variable1 according to the conditions of operation1 e4g4 the amounts of chemicals used1 their concentration1 the nature and condition of the goods1 the time of application1 the manner of application1 etc4 ,in practice the most favourable conditions are usually discovered empirically1 but1 broadly speaking1 the goods are usually added soon after the thiosulphate and acid are well mixed4 ,there is some evidence that the reduction is in steps1 intermediate products such as sodium tetrathionate and chromium dioxide are known to be formed4 ,the goods change from yellow to dark brown1 then to green1 and finally to the familiar blue4 ,the sulphur makes the final colour a lighter blue than in the case of a one-bath tannage1 hence the two-bath process is often preferred for colours4 ,on account of the empirical character of this hypo bath1 it is impossible to fix any exact relation between the quantities of material used in the chroming bath1 and the quantities of hypo and acid used in the reducing bath4 ,the following rules1 therefore1 must be understood as rough approximations for practical use1 and though they have been empirically discovered their theoretical significance is often fairly obvious4 #a4 ,the amount of hypo necessary is almost directly proportional to the amount of dichromate used4 ,in chroming with baths of the acid or neutral type1 the percentage of hypo should be about three times the percentage of dichromate used4 ,thus #d per cent4 dichromate needs #ab per cent4 hypo2 and #f per cent4 dichromate needs #ah per cent4 hypo on the pelt weight4 ,in baths of the ,schultz type a less proportion of hypo may suffice1 but the #aj per cent4 hypo for #e per cent4 dichromate1 recommended by the ,schultz patent1 is generally considered rather insufficient4 #b4 ,the proportion of hypo is increased somewhat for the heavier classes of goods1 and may even reach #bj per cent4 of the pelt weight4 #c4 ,an increase in the proportion of hypo is usual with an increase in the amount of free acid in an acid chroming bath4 #d4 ,the percentage of hydrochloric acid in the reducing bath is roughly half that of the hypo1 but is the most variable factor4 ,the quantity varies with the rate and mode of addition1 the class of goods under treatment1 and the composition of the chroming bath4 #e4 ,in baths of the ,schultz and neutral type it is better to add some acid to the hypo bath before adding the goods1 but this is less essential for goods from an acid chroming bath4 #f4 ,in the case of goods from acid chroming baths1 the amount of acid used in the reducing bath is an inverse function of the excess of acid in the first bath1 e4g4 take the following two processes3-- ---------------------------------------- --------------------------- ,chroming bath4 ,hypo bath4 ---------------------------------------- ------------------------- ,dichromate4 ,hydrochloric acid4 ,hypo4 ,hydrochloric acid4 ---------------------------------------- ------------------------- #d #d #ab #e #d #ae #ae #a ---------------------------------------- ------------------------- #g4 ,there should be some excess of hypo at the end of the process4 ,this acts as a feeble alkali1 and commences the neutralization4 ,the process can be carried out in paddles or in drums as preferred1 for reasons similar to those applicable in the case of the first bath4 ,on the whole1 however1 drums are less popular for the second bath1 for the dilute solutions of the paddle effect some economy of sulphurous acid1 which is apt to escape into the air4 ,a preliminary hypo dip is sometimes used to prevent the bleeding of the chromic acid4 ,the use of many other reducing agents has been suggested as substitutes for hypo4 ,sulphides1 sulphuretted hydrogen1 polysulphides1 sulphites1 bisulphites1 hydrogen peroxide1 nitrous acid1 lactic acid1 etc41 have been used1 but none are so easy to manipulate as thiosulphate4 ,types of ,one-bath ,chrome ,tannage4--,the one-bath process is simpler than the two-bath process inasmuch as only one kind of liquor is involved1 viz4 one in which the chromium is in the chromic state4 ,hence the variants of the one-bath process consist mainly of variations in the composition of this liquor4 ,the chief point of variation is in the readiness with which chromium hydrate is adsorbed4 ,this is determined by the extent to which the chromic salt is hydrolyzed to form the tanning sol and free acid1 and by the concentration and nature of this free acid as well as of other substances4 ,it is difficult unfortunately to express these factors in terms which are comparable under general conditions4 ,chromic salts are usually hydrolyzed to some extent1 but this extent is very different even in water1 according to the nature of the acid radical4 ,the degree of hydrolysis is also largely affected by the extent to which the solution has been made basic by the addition of alkalies4 ,by the neutralization of the free acid in this way there is further hydrolysis1 the extent of which is again influenced by the nature of the acid radical involved and other dissolved substances1 especially of organic matters4 ,again1 the hydrolysis is largely affected by the concentration of the solution even when the proportions of the ingredients are constant1 and this is practically important on account of the necessity for exhausting the chrome liquors economically4 ,nor is the matter entirely one of degree of hydrolysis1 for 7as we have noted in the preceding section7 the electrical condition of the chroming sol is of great importance owing to the operation of the valency rule and the possibility of zones of non-precipitation4 ,the alkaline1 neutral or acid condition of the goods when first introduced has also its influence on all these points4 ,it will be readily understood1 therefore1 that there is some difficulty in expressing the tanning power of a chrome liquor4 ,as near as can be yet said this is determined by 7#a7 the concentration of the actual tanning sol1 and 7#b7 its nearness to the isoelectric point4 ,now1 these points are not readily determined by analytical methods1 and the best that can yet be done is to determine the conditions which have large influence upon these points4 ,thus the degree to which the liquor is made basic by adding alkali is known1 and can be expressed in formul by assuming that the acid neutralized by this alkali is replaced in the chrome salt by hydroxy groups4 ,chromic chloride1 ,cr#b;,cl#f1 with the addition of soda to correspond to half the acid formed upon complete hydrolysis1 would be considered then to be a solution of the salt1 ,cr#b7,,oh7#c;,cl#c4 ,this has given rise to the conception of the basicity of a chrome liquor1 which may be expressed in many ways1 the most common of which in practice is the number of grams ,,so#d still combined with #eb grams ,cr4 ,thus the salt corresponding to the composition ,cr7,,oh7,,so#d is said to have a basicity of #if4 ,the practical importance of such determinations of basicity has been much exaggerated1 for they are but a rough guide to the degree of hydrolysis of the chrome and to the extent to which the sol is positive4 ,thus if the chrome salt be actually a sulphate1 a liquor of basicity #if has about the same practical value as a chloride liquor of basicity #gb1 and in each case the figures are of little significance if many organic substances be present4 ,if1 however1 as is usual in practice1 there be approximately the same acid radicals throughout the tannage and about the same relative proportion of organic matters or of inorganic salts1 then these determinations have some practical value for comparative purposes4 ,the determination is itself simple3 a portion of liquor is titrated direct with caustic soda4 ,the titration is at boiling-point1 and is continued until a permanent pink is obtained with phenolphthalein4 ,the amount of ,,so#d corresponding to the soda required is then relative to the amount of ,cr in the same volume of liquor4 ,a chromium estimation is therefore also necessary and is most readily done by evaporating a portion of liquor to dryness1 igniting the residue and oxidizing the chrome to chromate by heating in a muffle furnace with magnesia and sodium carbonate in equal parts1 or fusing in a blowpipe with sodium and potassium carbonates in equal parts4 ,the oxidized residue is dissolved in hydrochloric acid and titrated with thiosulphate as described for the two-bath process4 ,another attempt to determine the practical value of a chrome liquor is the empirical test suggested by ,mc,candlish1 in which #aj c4c4 of the liquor is titrated with standard alkali until the precipitation point is reached and a turbidity appears4 ,the figure thus indicates approximately the degree of nearness to the precipitation point and the amount of free acid in the liquor4 ,the author has found this a useful test taken in conjunction with the basicity determination4 ,it is best expressed in the same units1 e4g4 grams ,,so#d per #eb grams ,cr4 ,another method is the determination of the hydrion concentration of the liquor4 ,this has useful possibilities for research work1 but is usually too laborious for rapid commercial control4 ,the results1 moreover1 are not less empirical1 for the hydrion concentration of the liquor indicates but imperfectly the electrical condition of the particles of the tanning sol4 ,in classifying one-bath liquors into types1 it is best to take together those in which the usual basicity and acidity determinations have at any rate approximate comparative value1 and this is determined in the main by the method by which the liquor is manufactured4 ,broadly speaking1 there are three types of chrome liquor3 7#a7 those made from chromic salts by adding suitable amounts of alkali2 7#b7 those made from sodium dichromate by reduction with organic matter2 and 7#c7 those made from sodium dichromate by reduction with sulphurous acid or its salts4 ,of the first type the most common is that in which chrome alum 7a bye-product of the dyeing industry7 is the starting-point4 ,to a solution of this a solution of washing soda is gradually added1 with constant stirring1 until the salt corresponding with the formula ,cr7,,oh7,,so#d is obtained4 ,now3-- ,k#b,,so#d;,cr#b7,,so#d7cbd;,h#b,o ,na#b,,so#d _/ #iih ,na#b;,,co#caj;,h#b,o _/ #bhf #b;,cr7,,oh7,,so#d ,k#b,,so#d ,,co#b #cc;,h#b,o ,hence1 in practice1 for every ten parts of chrome alum #b4hf parts of soda crystals 7or #a4jf parts anhydrous soda7 are used4 ,a convenient stock solution is of #aj per cent4 strength4 ,thus #aj lbs4 of chrome alum is dissolved1 made basic1 and made up to #aj gallons4 ,to dissolve the alum a mechanical stirrer is necessary1 for the water must not be more than warm4 ,the disadvantage of this liquor is the limited solubility of chrome alum and the need for its solution in the cold4 ,liquors may be also made by dissolving chromium hydrate in hydrochloric acid1 and making basic to correspond to the formula ,cr#b7,,oh7#c;,cl#c4 ,many preparations are on the market containing both chlorides and sulphates with appropriate basicity4 ,chrome alum liquors have been less often used in ,britain of recent years owing to the high price of chrome alum1 caused in part by the presence in the salt of potassium1 all the salts of which have been scarce and dear under war conditions4 ,of the second type ,procter's glucose liquor is a good example4 ,use #e lbs4 sulphuric acid1 #f lbs4 sodium dichromate1 and #g lbs4 of glucose1 or quantities in similar proportion4 ,the dichromate is first dissolved1 and the acid added gradually4 ,the glucose is then added cautiously on account of the brisk effervescence of carbon dioxide4 ,a glucose of good quality is necessary1 and the proportion to be used is not quite definite1 for sufficient only is needed to effect the reduction1 and this amount is influenced by the rate of addition and temperature of the mixture4 ,the reduction should be careful and regular1 or the oxidation products will be irregular and have a varying effect upon the tanning4 ,molasses can be substituted for glucose1 in amounts varying with its strength4 ,of the third type the most common is that in which the dichromate is reduced by sulphuric acid and sodium bisulphite4 ,solid bisulphite may be used1 but it is usually dear1 and solutions are more commonly employed4 ,into this type fall also the liquors formed by passing sulphur dioxide gas into dichromate solution4 ,stock liquors of this type have the advantage that strong solutions may be made 7up to #ah per cent4 ,cr#b,o#c72 they have the disadvantage that they are liable to contain excess of free sulphurous acid4 ,the method of application of chrome liquors is usually by paddling or drumming the goods in solutions of appropriate strength--broadly speaking1 paddles used for lighter goods and plain finishes1 and slowly revolving drums for heavier hides and grained finishes4 ,heavy chrome leather is often tanned in pits by suspension just as in vegetable tanning4 ,in such instances rockers may be usefully employed4 ,in any case1 the goods are successively brought into contact with liquors of increasing strength1 as in vegetable tannage1 and the liquors are thus most conveniently exhausted economically4 ,the green goods thus receive first nearly spent liquor and finish out of fresh strong liquor4 ,the goods may be1 of course1 handled from drum to drum1 or from pit to pit1 but the modern tendency is to save labour by moving the liquors instead4 ,thus in drum tanning the liquor is run out and pumped into the next drum4 ,in pits air ejectors have proved suitable1 not only as lift pumps1 but also as agitators of the liquor in which goods are suspended4 ,the press system is also used4 ,finishing ,operations4--,in nearly all cases the chrome leather has to be neutralized after tanning4 ,this consists in removing the acid reversibly adsorbed4 ,this removal is necessary to the finishing processes1 as well as to bring the tanning sol into condition for more permanent tannage4 ,neutralization gets rid of soluble chrome salts as well as free mineral acid1 and is the final stage in rendering the tanning sol less positive1 and perhaps even negative4 ,it is brought about by the use of weak alkalies1 of which borax is the easiest and safest1 but not the cheapest4 ,sodium silicate1 phosphate1 carbonate1 and bicarbonate have been also used1 and a mixture of soda and an ammonium salt has been suggested by ,stiasny4 ,whitening has also been tried1 but is very slow-acting4 ,considerable economy in alkali may be effected by a thorough washing of the leather before using the alkali4 ,if the water be hard1 so much the better1 and if warm water be available the process is hastened4 ,for most leathers it is necessary to remove excess of alkali just as much as excess of acid1 so that a thorough washing in water generally follows the treatment with alkali4 ,anything from #a_/d to #c per cent4 borax 7or its equivalent7 on the pelt weight may be used1 and1 generally speaking1 it is better to use solutions as dilute as practicable in order to avoid local over-neutralization and tender leather4 ,fat liquoring is a process which is very largely typical of chrome leather manufacture2 it consists in drumming the goods with an oil emulsion1 the grease of which is entirely taken up by the leather4 ,it thus strongly resembles drum stuffing 7,part ,i41 ,section ,,iv47 in method1 but the fat liquor is such that it mixes easily with water1 and usually contains soap in order to assist in this sense1 and may sometimes indeed consist of soap only4 ,mineral oil is also used frequently in fat liquors4 ,the object of fat liquoring is to give softness1 pliability1 or waterproofness1 and to feed the empty chrome tannage4 ,it is also used as a preparation for more complete impregnation of grease1 e4g4 as in stuffing chrome harness1 and in dipping chrome sole leather4 ,fat liquors are usually made by dissolving the soap in boiling water and gradually adding the oil with constant agitation4 ,perfect emulsification is essential1 and this is assisted by the use of casein1 albumen1 gelatine1 starch1 egg yolk in addition to soap and oil4 ,soda and borax also assist1 and degras and sod oil are also useful and are admissible where the leather is to receive a dull finish4 ,the operation of fat liquoring is greatly assisted by heat1 and temperatures of about #aaj to #acj ,f4 are usual4 ,chrome leather may be dyed before or after fat liquoring3 if before1 the fat liquor sometimes tends to alter the shade2 if after1 the dyeing tends to be uneven4 ,logwood extract and iron salts are largely used for blacks4 ,it is common to mordant chrome leather with vegetable tanning before dyeing4 ,sumach and gambier are often used for this purpose1 and the usual fixing agents 7tartar emetic1 titanium salts1 etc47 may also be used4 ,of the mechanical finishing operations staking is the most characteristic4 ,it is now done entirely by machines1 and the primary purpose is to soften the leather1 which otherwise dries out in a non-pliant and stiff condition4 ,in the staking machine1 the blade is fixed between two rollers1 which are however on the other side of the leather4 ,the leather is held by the operator1 and the machine head pulls a fold of the leather over the blade4 ,seasoning and glazing are also common for many chrome leathers4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 pp4 #aih-bbj4 ,bennett1 ,manufacture of ,leather1 pp4 #baj1 #cab1 #cee1 #cge4 ,bennett1 ,types of ,two-bath ,chrome ,tannage1 ,leather1 #aiji1 ,aug4 and ,sept4 ,,section ,,iii4--,,chrome ,,calf ,the tannage of calfskins by the chrome processes for the manufacture of upper leathers is one of the most extensive branches of leather manufacture4 ,the deservedly popular box calf is typical of these leathers1 and the observations of this section are primarily applicable to it4 ,a chrome-tanned calf skin1 fat liquored and blacked1 provides as suitable an upper leather as could be desired for ordinary boots4 ,it is at once supple and durable4 ,it is also sufficiently waterproof1 but can be given a bright glazed finish4 ,in regard to the wet work for chrome calf1 the general principles and methods discussed in the previous section are much to the point4 ,it is essential to avoid undue plumping and the loss of hide substance4 ,the skins should be washed clean as soon as possible4 ,three fresh waters are desirable1 the goods remaining only a short time in each4 ,salted skins need more time1 but the liquors must be kept sweet4 ,drumming the skins in running water is very suitable for the first and last stages of soaking4 ,the liming should be short but not sharp1 i4e4 mellow sulphide limes are suitable1 depilation being carried out after about #g days4 ,the one-pit system is usual1 but two liquors may be given1 the green goods being first inserted into a used liquor1 and after handling reinserted into the same pit with a new lime liquor made up with lime1 sulphide and a proportion of the old liquor4 ,scudding should be carefully done1 as hair on the finished leather is very objectionable4 ,in deliming it is essential to have the grain of the skins thoroughly relaxed and pulled down4 ,the finished box calf should have a characteristic soft and silky feel1 and this is only attained by procuring the inelastic pelt4 ,it is not surprising that a light puering is a popular method for attaining this1 but there is also a tendency to use artificial bates such as are made from ammonium chloride and pancreatin1 together with organic acids1 or non-swelling acids like boric acid4 ,drenching is also common after a preliminary deliming with acid4 ,the skins may be half or two-thirds delimed with lactic acid1 rinsed and drenched over night at #he ,f4 with #f per cent4 bran on the pelt weight4 ,less acid may be also used1 in tepid water1 and the drench made up with #aj per cent4 bran and a little pea meal4 ,it is very common to pickle the skins in #e per cent4 alum and #e to #aj per cent4 salt before tanning4 ,this is often of doubtful advantage1 but sometimes prevents drawn grain when the goods are moved rapidly into strong chrome liquors4 ,this pickling is said to give fullness to the leather4 ,the tannage of box calf is usually by the one-bath process1 though the two-bath process gives quite as good a result and is sometimes used4 ,again1 drum tannages are the most popular on account of their speed and the economy of chrome4 ,the practical problem is to use up all the chrome1 and to tan quickly without drawing the goods4 ,it is1 in any case1 usual to commence the tannage in a used and nearly spent liquor and finish in a fresh liquor4 ,the most appropriate way depends largely upon local convenience1 the number of drums available1 supply of labour1 etc4 ,in a one-drum system the goods may be started in an old liquor1 which is run off when exhausted by the green goods4 ,fresh stock solution is then added at intervals of an hour or two and the drumming continued till tannage is complete1 which is usually in less than #bd hours4 ,the remaining liquor is used to commence the tannage of the next pack4 ,in another system the operation is similar except that the liquors are weaker1 and the goods are then removed and finished in another drum4 ,a three-liquor system1 however1 is often combined with a one-drum method2 the goods are thus not handled4 ,the liquors are run off and pumped to other drums1 the once-used liquor to a drum containing goods already treated with a twice-used liquor2 the twice-used liquor to a drum containing green goods1 and the thrice-used liquor pumped to the drain4 ,in any of these methods the chrome alum liquor is suitable1 using #aj per cent4 alum and #c per cent4 soda on the pelt weight4 ,the glucose liquor has also proved very suitable for chrome calf1 and the liquors made with sulphurous acid or its salts have increasing popularity on account of lower costs4 ,many tanners use bought liquors--chrome extracts which are supposed to be specially devised to suit the tannage of chrome calf4 ,when thoroughly tanned through1 as can be readily judged from a sectional cut of the leather1 and also by the strength of the liquor remaining1 the goods are horsed in pelt overnight1 and are then ready for finishing4 ,in finishing box calf the neutralization should be thorough1 or the acid may cause trouble in dyeing and fat liquoring4 ,imperfect removal of excess chrome salts may cause the formation of chrome soaps which are very difficult to remove2 the goods should therefore be well washed4 ,there are two general types of treatment before blacking4 ,in one1 the skins are first well washed with water at #aaj ,f41 neutralized with about #c per cent4 borax1 and well washed again4 ,striking follows and is usually very thorough1 partly because it assists in producing evenly the characteristic box grain1 and partly because the finished leather is sold by the square foot4 ,machine striking is now almost universal1 and may be done several times at different stages in the drying4 ,when half dry 7sammed7 the skins are shaved by machine and1 at this stage usually1 weighed4 ,dyeing and fat liquoring then follows4 ,in the other type1 the goods are merely washed1 and then struck out1 sammed1 shaved and weighed4 ,the skins are then neutralized1 washed and immediately dyed and fat liquored4 ,the advantages of this latter course are that the goods remain in the drum for the last four processes1 which is economical of labour1 and also that by neutralizing immediately before dyeing and fat liquoring there is less danger of a further diffusion of acid4 ,in dyeing logwood extract is largely used1 occasionally a little fustic is used also1 and by using a striker of iron and copper sulphates a good black is obtained4 ,logwood is often used also in conjunction with coal-tar dyestuffs4 ,the goods are first warmed in the drum up to #adj ,f41 and the dyestuff solution gradually run into the drum whilst it is revolving4 ,up to #c_/d hour may be necessary to exhaust the bath1 the goods being constantly drummed4 ,the fat liquor is then run in similarly1 and the drumming continued until the grease is all absorbed by the leather1 which may take another hour4 ,the skins are horsed till next day1 during which time the grease penetrates more completely4 ,the skins are now dried out1 sometimes by suspending from the hind shanks and sometimes by nailing on boards or wooden frames4 ,they are damped back for staking by leaving for #a-a_/b to #b days in moist sawdust4 ,after staking they are dried strained in a stove at about #aje ,f4 ,in finishing off1 the grain is cleared by sponging with #aj per cent4 lactic acid1 and seasoned with a mixture of milk1 blood and black dyestuff4 ,when dry on the surface the skins are glazed by machine1 and grained two ways--neck to butt and belly to belly4 ,they are usually reseasoned1 dried out1 reglazed1 regrained1 lightly oiled with mineral oil1 and finally trimmed4 ,these various operations are fairly typical1 but there is obviously ample scope for divergence4 ,thus one may fat liquor before dyeing1 and the skins may be staked before drying out1 and may be re-staked after glazing4 ,much so-called box calf is not made from calf skins4 ,a very close approximation1 however1 is obtained from rather older animals1 and box-kip is largely manufactured by similar methods4 ,light hides are also widely used1 being similarly treated except that they are split and also cut into two along the spine4 ,the finished article is sold as box-sides4 ,to yield the characteristic grain pattern1 the goods are frequently printed and embossed4 ,even the flesh splits are sometimes made into box calf imitations1 some filling material being used and an artificial grain pattern embossed4 ,willow calf typifies the chrome calf which is finished in colours4 ,the soaking1 liming and deliming processes are the same as for box calf4 ,the tannage1 however1 is generally by the two-bath process on account of the lighter colour thereby obtained4 ,this colour is largely due to the deposition of sulphur in and on the leather in the second bath4 ,in one tanning process the skins are first pickled in #b per cent4 hydrochloric acid and #aj per cent4 salt4 ,they are then drummed in solution containing #b per cent4 dichromate 7strength #a in #fj7 for about half an hour4 ,a solution containing #d per cent4 dichromate1 #c-a_/b per cent4 hydrochloric acid1 and #e per cent4 salt is gradually added1 and the skins drummed until well struck through4 ,they are then horsed overnight and struck out and passed through a hypo dip1--a #b per cent4 solution of thiosulphate1--and then into the reducing bath1 which contains #aj per cent4 of thiosulphate1 to which #e per cent4 hydrochloric acid is added4 ,another process employs paddles instead of drums4 ,the chroming liquor is made up with #d-a_/b per cent4 chromic acid and #aj per cent4 salt4 ,the bath is exhausted by commencing the tannage of a succeeding pack4 ,the skins are reduced as in the last process4 ,in another process the acid type of chroming bath is used4 ,the skins are paddled with a solution containing #e per cent4 dichromate1 #e per cent4 hydrochloric acid1 #b per cent4 aluminium sulphate1 and #aj per cent4 salt4 ,in the reducing bath #ad per cent4 hypo and #d per cent4 hydrochloric acid are used4 ,in yet another process the skins are pickled first in #e per cent4 aluminium sulphate1 #g-a_/b per cent4 salt1 and #c per cent4 sulphuric acid1 and are then dried out and sorted4 ,the tannage proper is in the drum1 using #f per cent4 dichromate1 #e per cent4 hydrochloric acid1 and #e per cent4 salt4 ,in the reducing drum #ae per cent4 hypo is used and #d-a_/b per cent4 hydrochloric acid4 ,whichever process of tanning has been used1 the skins are neutralized and washed thoroughly1 as for box calf1 sammed and shaved4 ,in dyeing1 the skins are first mordanted with a filtered infusion of leaf sumach1 used at #aaj ,f4 for half an hour4 ,as fixing agent1 #d oz4 tartar emetic per dozen skins is then added and the drumming continued for half an hour4 ,the goods are washed1 struck out and drum dyed at #adj ,f4 with basic colours1 and immediately fat liquored4 ,in the fat liquors olive oil and castor oil1 with the corresponding soaps1 have been popular1 but substitutes are now used on economical grounds4 ,the skins are next horsed a while1 well struck out again and dried strained4 ,they are now finished off as for box calf1 except that it is usual to grain only one way--neck to butt--and the season should consist of milk1 water and albumin only1 though sometimes other mucilagenous matters are added4 ,as with box calf1 the finishing may be varied in many ways4 ,the skins may be dyed with acid colours after fat liquoring4 ,for pale shades direct dyes are used without a mordant4 ,for darker shades of brown and red1 the dyewoods are used both as mordants and ground colours1 and titanium salts are useful as fixing agents4 ,both the box and willow finish are largely a matter of public taste1 and the fashion varies from time to time on such points as to whether the grain should be one way or two ways1 and whether it should be faint or bold4 ,there are also other common finishes besides the typical box grain4 ,glac calf is made much in the same way as box calf1 but there is no graining at all4 ,the goods are usually seasoned and glazed three times4 ,small skins are preferred for this finish4 ,dull calf is also a plain finish4 ,the leather contains more grease1 and the fat liquor is made up with greater proportions of degras4 ,the goods are not seasoned or glazed1 but ironed1 sized with gum1 oil1 soap and logwood1 and after brushing are dried and rolled4 ,in both these plain finishes a one-bath paddle or pit tannage is common1 in order to ensure the smooth finish4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 p4 #aih4 ,bennett1 ,manufacture of ,leather1 pp4 #ee1 #hd1 #aje1 #bbg1 #cfj-cfc1 #cge4 ,bennett1 ,theory and ,practice in ,wetwork of ,chrome ,calf1 ,shoe and ,leather ,reporter1 ,sept41 #aiji4 ,,section ,,iv4--,,chrome ,,goat ,,and ,,sheep ,immense quantities of goat and sheep skins are chrome tanned for upper leathers4 ,most of them are manufactured into the well-known and popular ,glac kid1 to the manufacture of which this section is chiefly devoted4 ,to be quite strict1 glac kid should be made from kid skins1 but actually comparatively few of such skins are used1 they being reserved rather for glove leathers4 ,the popular upper leather is made from goatskins4 ,chrome goat is deservedly popular2 it is an ideal upper leather for shoes and light boots4 ,as compared with chrome calf 7thickness and other factors being equal71 it is not only softer and more pliant1 but also more durable4 ,it is usually1 however1 not quite so thick1 and perhaps therefore not quite so warm and waterproof4 ,the popularity of glac is probably enhanced by the brighter and more glassy finish than is usual with box4 ,as the supply of goatskins is unfortunately too limited1 an even more widely used glac upper leather is made from sheepskins1 and often sold as glac kid4 ,from what has been previously said as to the quality of goat and sheepskin leathers 7,part ,,ii41 ,sections ,,ii4 and ,,iv471 it will be readily understood that glac sheep is by no means so good a leather as glac goat4 ,it is perhaps as soft1 but is more spongy and loose textured1 and is neither so waterproof nor so durable as chrome goat4 ,the ubiquitous sheep1 however1 provides an immense supply of raw material1 and the resulting leather1 which should strictly be regarded as a glac kid imitation1 finds a ready sale4 ,when well finished it is indeed a good imitation in respect of appearance1 and this fact1 together with its comparatively low cost1 causes it to meet an undoubted public need4 ,the production of glac goat will first be considered4 ,the soaking process is quite similar to that before described for the production of goatskin moroccos 7q4v47 and need not be here repeated4 ,the liming is similar in many respects also1 but from what was said in ,section ,,ii4 about the undesirability of excessive plumping of pelt for chrome leather1 it will be clear that caustic soda should be omitted from the limes4 ,the liming should also be shorter for glac than for moroccos1 and this is attained both by using a greater proportion of sulphide and by using mellower lime liquors1 preferably the latter1 as soft pelts are better ensured4 ,calcium chloride has sometimes been added to the limes3 this reacts with the soda from the sulphide1 yielding salt and probably precipitating lime1 and has its own lyotrope influence1 thus reducing the plumping effect possibly in two ways4 ,to obtain either effect it is necessary to use considerable amounts of calcium chloride4 ,as goatskins are so tight fibred1 a longer liming and a greater loss of collagen is permissible than with most pelts for chrome4 ,the deliming operations should be exceedingly thorough in order to obtain the desired softness and the smooth grain4 ,puering is largely used to the full extent1 i4e4 the goods are thoroughly pulled down at #he-ij ,f41 and are carefully delimed in the puer liquor4 ,after puering it is common to give a low temperature drench 7#fj-fe ,f471 which of course acts slowly over a day or two4 ,the skins must be well scudded after puering or after drenching2 sometimes after both4 ,the drenching is often substituted for purely deliming processes1 of which may be mentioned the use of boric acid and also the use of warm solutions of the commercial organic acids 7lactic1 formic1 acetic1 butyric1 etc471 together with calcium chloride4 ,in place of the chloride1 a salt of the acid may be employed1 and the deliming bath may be regenerated by oxalic acid and used repeatedly4 ,sometimes puering is omitted and the desired result obtained by washing in warm water1 nearly deliming with warm solutions of organic acid1 washing again and drenching4 ,skins are also washed often after drenching4 ,in tanning chrome goat for glac the two-bath process is mostly preferred4 ,this is partly because the sulphur deposited in the reducing bath assists materially in producing the mellowness and fullness which are so essential1 and partly because a large proportion of skins are finished in colours4 ,the two-bath process also lends itself to a paddle tannage1 which is necessary for the smooth grain finish4 ,one or two illustrative processes may be given4 ,one process presents many points of resemblance to the first process suggested for willow calf in ,section ,,iii4 7q4v474 ,the skins are first pickled in a paddle with #b per cent4 hydrochloric acid and #aj per cent4 salt1 and then pass into the chroming paddle1 which contains at first only #b per cent4 dichromate4 ,subsequently #d per cent4 dichromate1 #c-a_/b per cent4 hydrochloric acid1 and #e per cent4 salt are added to the paddle liquor1 and the skins paddled until well struck through4 ,after being horsed overnight the skins are struck out by machine1 passed through a hypo dip if desired1 and reduced with #ab per cent4 of thiosulphate and about #e per cent4 of acid4 ,the skins may be left overnight in the hypo paddle1 and the excess of thiosulphate1 which is a feeble alkali1 commences the neutralization4 ,in another process the chroming bath is made up of #e-a_/b per cent4 chromic acid and #f-a_/b per cent4 of salt1 and to this paddle liquor #b or #c per cent4 of aluminium sulphate may be added if desired4 ,the reduction is with #ad per cent4 hypo and #g per cent4 hydrochloric acid4 ,a little of the acid is added to the reducing bath2 when the liquor turns milky1 the skins are rapidly inserted1 and the rest of the acid gradually added4 ,in the finishing processes the mechanical operation of striking is very prominent1 on account of the necessity of obtaining area and smooth grain4 ,the skin of goats has rather a tendency to bold grain1 and this enhances the need of striking4 ,most manufacturers lay great stress upon thorough neutralization and washing4 ,an important point also is that the staking should be carried out at the proper condition of dryness4 ,if either too damp or too dry1 the requisite mellow feel is not obtained4 ,there is1 of course1 ample scope for variation and ingenuity1 and the following processes for blacks and colours must be taken as broadly typical4 ,the skins from the reducing bath are first machine-struck1 and then immediately neutralized with one per cent4 borax until this is thoroughly used up1 and the skins are then paddled for many hours in running water4 ,they are again struck out and lightly shaved1 possibly after a little drying4 ,there is a tendency to save time by using a stronger borax solution1 and by using warm or tepid water1 and some factories save borax by washing well first in warm water4 ,if for blacks a common plan is to dye grain and flesh a violet-blue and then black the grain only with logwood and iron4 ,the skins are drum dyed blue with a coal-tar dyestuff1 drumming half an hour in the solution at #aaj ,f41 and again struck out4 ,they are then paired or pleated1 and rapidly passed successively through three vats containing respectively cold weak ammonia1 a logwood and fustic infusion at #abj ,f41 and a solution of ferrous sulphate containing a little copper sulphate4 ,the skins must be immediately washed well to remove excess of iron4 ,instead of this process the skins may be passed through vats containing coal-tar blacks4 ,instead of blue backing the skins may be drum-dyed black on flesh and grain with either coal-tar blacks or with logwood and iron4 ,in the latter case the skins must be drummed in water for an hour to remove excess of iron4 ,however dyed1 the skins are often struck out again after dyeing1 and sammed slightly for fat liquoring4 ,neatsfoot oil is a popular ingredient of the fat liquor4 ,the skins are drummed dry for a few minutes in a hot drum1 and the fat liquor added at #acj ,f41 and the drumming continued after the grease has been taken up in order that it may be thoroughly distributed4 ,the skins are struck out again1 rapidly dried out1 and wet back for staking in damp sawdust4 ,the staking should be thorough1 and1 if necessary1 repeated when the goods are rather drier4 ,in finishing off the skins may be fluffed if desired1 and are then cleared by sponging with #aj per cent4 lactic or acetic acid4 ,they are then seasoned and glazed after some drying4 ,this is repeated until the required gloss has been obtained4 ,they are finally oiled lightly with a mixture of linseed and mineral oils4 ,on finishing dull kid a heavier fat liquor is given1 in which degras is used1 and the skins are not seasoned and glazed1 but are ironed and oiled4 ,in finishing for coloured glac1 the skins are mordanted before dyeing by the use of dyewood extracts1 antimony and titanium salts being used as fixing agents4 ,the fat liquor should contain less soap and more egg yolk1 and for fancy shades even egg yolk only is sometimes used4 ,the production of chrome glac sheep follows the same general lines as glac goat4 ,there is less difficulty in obtaining smooth grain1 so that striking is perhaps less prominent1 and drum tannages are preferred1 whether one bath or two bath4 ,the skins are received after fellmongering 7see ,part ,,ii41 ,section ,,iv47 and need thorough puering to remove scud1 and may be then rinsed through boric acid4 ,pickling is very common with these goods4 ,in the pickled state they are often sorted out before tanning4 ,the pickling is usually a one-bath process in which vitriol and salt or else alum and salt are used1 but sometimes all three substances4 ,the skins may indeed be received in a pickled state4 ,they may be depickled by paddling with salt and borax1 bicarbonate1 or basic alum solution4 ,they may also be tanned without depickling if the composition of the pickle be allowed for in the first chroming liquor4 ,a commonly used pickle consists of #c per cent4 aluminium sulphate and #i per cent4 salt4 ,if these goods are to be dried out1 flour also may be used with the pickle1 which thus becomes practically a light preliminary alum tannage 7see ,part ,,iv41 ,section ,i474 ,a commonly used acid pickle is of #e per cent4 commercial sulphuric acid and #be per cent4 salt4 ,the delimed or depickled stock may be tanned as now described4 ,the two-bath process may be used with drums4 ,the chroming bath contains #e per cent4 dichromate1 #e per cent4 hydrochloric acid1 and #aj per cent4 salt4 ,after the skins are thoroughly penetrated they are horsed overnight and reduced with #bj per cent4 thiosulphate1 up to #g per cent4 of hydrochloric acid being added after half an hour in thiosulphate only4 ,alum pickled or tawed skins are wet back by drumming for about an hour in water1 and are then tanned by the one-bath process in drums4 ,only a few hours are needed4 ,towards the end of the operation about #a_/b per cent4 of bicarbonate of soda may be added to the chrome liquor4 ,acid pickled skins may be wet back with #aj per cent4 salt1 and depickled by adding a basic alum solution and the chrome tannage superimposed after about half an hour without handling the goods4 ,the basic chrome alum liquor is suitable for this purpose4 ,in finishing glac sheep much the same methods are used as in the case of glac goat4 ,sheepskins are perhaps more lightly fat liquored1 being naturally soft and porous4 ,degreasing is often necessary to obtain an even finish4 ,as sheep gives an empty pelt and chrome an empty tannage1 a slight retannage is often given in gambier1 especially for blacks1 in which case the skins are well mordanted4 ,this retannage makes the leather less stretchy4 ,logwood and iron blacks are usual4 ,for colours1 fustic or sumach are the usual mordants1 with tartar emetic to fix4 ,if for glove leathers1 skins pickled in alum and salt or tawed should be preferred1 and flour may be used in the fat liquor4 ,sheepskin splits are sometimes given a chrome tannage and finished as chrome chamois4 ,this leather may be used for linings1 but not for polishing silver on account of the sulphur originating from the reduction bath4 ,the splits are puered heavily1 and pickled in #f per cent4 vitriol and #bd per cent4 salt4 ,they are paddled in this pickle liquor1 and #d per cent4 dichromate added in successive portions4 ,the fleshes are horsed overnight and reduced in #ae per cent4 thiosulphate1 to which a little hydrochloric acid is added if needed4 ,in finishing the splits are washed in warm water1 neutralized in weak soda1 and washed again4 ,they are sammed by machine striking1 and fat liquored1 using much soap4 ,they are then horsed1 struck and dried out4 ,they are staked several times after damping back1 drying out again between stakings4 ,they are finally fluffed4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 p4 #aih4 ,bennett1 ,manufacture of ,leather1 pp4 #ee1 #hd1 #aje1 #bcj1 #cfd4 ,bennett1 ,theory and ,practice in ,wetwork of ,chrome ,goat1 ,shoe and ,leather ,reporter1 ,sept41 #aiaj ,,section ,v4--,,heavy ,,chrome ,,leathers ,the term heavy chrome leather is taken to include chrome sole leather1 chrome strap and harness butts1 waterproof chrome upper leathers1 motor butts and picking band butts4 ,these will be discussed in turn4 ,chrome sole leather1 as stated in ,section ,i41 has made headway in ,britain during the ,european ,war1 the ,army authorities having recognized its great advantages in durability and waterproofness4 ,at the time of writing1 however1 its manufacture has received a set back1 and many factories are reducing their output4 ,the primary cause of this is that the ,army purchases have largely ceased1 whilst the general public have not yet been educated to its value4 ,men who take chrome uppers for granted talk of chrome sole as a leather substitute with an implication that it is of inferior value4 ,it must be recognized1 too1 that there is some interested opposition to its development4 ,cobblers and bootmakers complain that it ruins their tools1 being so hard to cut4 ,now1 it is manifestly impossible for it to be soft to cut and hard to wear out2 the complaint is therefore an excellent testimonial4 ,there is also a stupid fear that an article which lasts twice as long will reduce repairs and retail sales by #ej per cent4 ,even the manufacturer has sometimes a suspicion that a demand reduced in proportion to durability will not be balanced by an extended export trade4 ,these points of view will become minor considerations when the public realize its relative economy1 and when the community as a whole grasp that a durable article is a natural asset4 ,meanwhile credit is due to those firms who persevere in their pioneering work of educating the public4 ,the manufacture of chrome sole leather presents many analogies with the vegetable tannages4 ,the soaking and liming should be about identical1 but the hides for chrome are generally given more sulphide and the depilation is reduced to about a week4 ,the methods used for deliming differ widely in different factories4 ,some delime completely with mineral acids1 some even pickle in acid and salt1 whilst others merely delime the grain with boric acid4 ,the last is really quite sufficient4 ,again1 in tanning one finds similar divergences of method4 ,drum tanning is practised1 but tannage in pits by suspension is more usual1 though1 as this last involves more dilute liquors1 it involves also greater time to tan4 ,in drum tannages a few days only are sufficient4 ,in pit tanning at least a week is given1 but sometimes up to a month1 according to the strength of the final liquor and the rate of progress of the goods into stronger liquors4 ,liquors containing over #a per cent4 of chromium may easily be spent out so as to contain only #j4ja per cent4 ,labour and time are saved in pit tanning by the use of rockers4 ,the press system of avoiding handling1 however1 so complicates the analytical control that its advantage is doubtful1 a better way being to shift the liquors by an air ejector1 which may also be used as an agitator of the liquor and thus abolish the need for rockers 7,forsare patent74 ,chrome butts are tanned out in suspension4 ,no floats or layers are used4 ,the neutralization need not be so thorough as for light chrome uppers1 as dyeing is not practised and trouble does not arise with emulsions made from sulphonated oils4 ,thorough washing is advisable1 and the butts are usually then cut into bends and may be oiled before drying if desired4 ,the bends are dried strained1 to obtain flatness and smooth grain1 for no machines1 such as strikers and rollers1 are usually employed4 ,it is necessary to dry very thoroughly1 for the bends are waterproofed by dipping the dry leather into molten waxes4 ,the most commonly used wax and the cheapest is paraffin wax with a m4p4 of about #abg ,f4 ,it is rather a brittle wax1 however1 and as the finished leather consists of up to one-third of the wax1 it is better to use at least some proportion of hard fat1 ,japan wax or ceresin wax1 to obtain a stuffing material with less crystalline texture4 ,the use of #aj-cj per cent4 rosin in the stuffing grease is also usual4 ,this prevents the leather from being so slippery when in wear4 ,the stuffing should take place at temperatures from #aej-aie ,f41 according to the melting-point of the grease employed4 ,the bends are taken out and laid in pile to cool and set in a flat condition1 and are then finished4 ,the chrome tannage of butts for strapping and harness backs1 and for motor butts and picking bands may be similar to that for chrome sole1 but drum tannages are more common and the two-bath process is often used4 ,in the latter case the acid chroming bath is preferred1 using #f per cent4 of dichromate and of acid1 with up to #ae per cent4 of salt1 and reducing with #ae per cent4 thiosulphate and acid as needed4 ,this process assists in the production of the light colour which is preferred in the case of some of these leathers4 ,strap butts after tanning are very thoroughly washed with cold water in pits1 and repeatedly struck out by machine between the washings4 ,they are then oiled with heavy mineral oil1 and stretched by powerful machines4 ,they are dried and curried during the stretching4 ,degras1 wool fat and vaseline are greases used1 and the drying and stretching finished off at #abj ,f4 ,they are then fluffed on the flesh1 ,french-chalked and heavily rolled4 ,harness backs are neutralized1 machine sammed1 and lightly fat liquored with #d-a_/b per cent4 soap4 ,they are then struck and oiled with heavy mineral oil and dried for stuffing4 ,hand stuffing1 drum stuffing1 and burning in are all used 7see ,part ,i41 ,section ,,iv474 ,stearin1 paraffin wax1 ceresin wax1 wool fat1 sod oil and mineral oil are the greases employed4 ,the butts are blacked after stuffing with lamp black and oil1 glassed well and buck-tallowed on the grain4 ,motor butts are fat liquored lightly1 using soap only4 ,they have to be softened1 therefore1 during the drying by being mechanically worked4 ,a boarding machine is repeatedly used during the drying4 ,they are finished off with ,french chalk on flesh and grain4 ,picking band butts are neutralized by using warm water and then borax solution1 and are then sammed by machine and very heavily fat liquored with cod oil and tallow and hard soap1 to which degras may also be added4 ,up to #bj per cent4 of greases 7on the pelt weight7 may be used4 ,they are well drummed in this1 struck out1 ,french chalked1 and dried out4 ,they are softened finally by machine4 ,waterproof chrome upper leathers are manufactured usually from hides tanned by the two-bath process1 which is said to give a mellower leather4 ,the neutral type of chroming bath is common4 ,the butts are neutralized1 machine sammed and struck1 and then fat liquored with #b per cent4 each of neatsfoot oil and soft soap4 ,they are then sammed1 shaved and blacked on the grain with logwood and iron1 and dried further4 ,they are stuffed then by brushing with an abundant amount of concentrated fat liquor4 ,this gives the waterproofness4 ,they are staked after drying further1 and often grained three ways4 ,a further waterproof finish is given consisting of a fat liquor containing beeswax4 ,they are finally brushed and re-oiled with linseed oil1 to which some mineral oil may be added4 ,this leather is much the most durable type for a shooting boot1 or where waterproof uppers are desirable4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 p4 #aih4 ,bennett1 ,manufacture of ,leather1 pp4 #bcd1 #cfh4 ,,part ,,iv4--,,miscellaneous ,,tannages ,,section ,i4--,,alum ,,tannages ,the use of alum for making pelt into leather is several centuries old4 ,it was the first case of what are called mineral tannages4 ,the tannage is closely analogous in theory to the chrome tannages discussed in ,part ,,iii41 and if soda be added to ordinary potash alum in solution1 a basic alum liquor is obtained which is quite capable of yielding a satisfactory leather1 and which is thus a strict analogy of the basic chrome alum liquor described in ,part ,,iii41 ,section ,,ii4 ,the range of basicity which is practicable is very limited1 however1 and it is much more usual to use common salt with the alum instead of soda4 ,the alum is1 of course1 hydrolyzed and free sulphuric acid is quickly adsorbed1 whilst the colloidal solution of alumina is adsorbed also but more slowly4 ,the adsorbed acid tends to swell the pelt and to cause it to take up the alumina less readily4 ,the function of the salt is to repress the swelling by a pickling action4 ,the actual result is thus partly due to the alum tannage and partly due to the temporary tannage given by the pickle4 ,hence such tannages are not firmly fixed1 nor is the result water-resisting1 for much of the tanning material may be washed out4 ,if1 however1 such leathers be stored for a time in a dry condition1 the alumina becomes much more firmly fixed1 owing probably to a further dehydration of the alumina gel deposited upon the fibres4 ,the tannage is thus relatively more irreversible1 and such storage is practised in commerce for this purpose1 being known as the ageing of the leather4 ,it will be understood that it is possible to use too great a proportion of salt1 the hygroscopic nature of which would keep the leather moist and thus interfere with a glossy finish4 ,about one-third the weight of the alum used is usually sufficient4 ,all that has been said in ,part ,,iii4 as to the empty nature of the chrome tannage is equally applicable to the alum tannages4 ,it is as necessary therefore to employ filling agents4 ,a fat liquor is quite satisfactory for many purposes1 but is too dark coloured and greasy for glove leather4 ,egg yolk is the favourite emulsion in these cases4 ,it contains about #cj per cent4 of an oil very similar to olein and in very perfect emulsion4 ,olive oil is also largely olein and is also used1 being emulsified by the egg yolk and effectively reducing the proportion required of this expensive material4 ,flour is also used as a filling agent4 ,it acts also as a whitening agent and as an emulsifier4 ,its use enables the tanner to obtain the required fullness without so much greasiness4 ,thus softness and fullness may be obtained1 and yet a glossy finish be possible4 ,it will be clear that the more flour is used1 the more oil may also be used4 ,the materials mentioned1 viz4 alum1 salt1 flour1 egg yolk and olive oil1 are all mixed together into a paste with some amount of water4 ,the goods are drummed in this paste and then dried out4 ,this operation is known as tawing4 ,the goods are then aged for several weeks and finished as required4 ,the manufacture of glove kid from lambskins and kid skins is the most typical example of alum tannage4 ,lambskins are unwoolled very usually by painting the flesh with a mixture of lime and sodium sulphide4 ,there must not be too much of the latter on account of its tendency to give harshness1 a fatal defect in glove kid4 ,the addition of calcium chloride is desirable1 and the skins1 which should be pulled as soon as possible1 should be quickly placed in soft water or weak lime4 ,for kidskins a set of lime liquors may be used1 and in preference to sodium sulphide red arsenic is employed4 ,about one per cent4 realgar on the weight of the lime is used1 but more often larger quantities are preferred1 even up to #f per cent4 ,the liming is thus shortened to #d or #e days4 ,fresh lime liquors are sometimes used without any sulphides4 ,another method is to place the skins in a paste of lime to which realgar has been added in slaking4 ,in any method it is necessary to saponify or emulsify the grease on the grain1 or difficulties occur in dyeing and finishing4 ,skins which are to be tawed for glove kid are both puered and drenched4 ,they are heavily puered at #gj ,f4 for #c hours1 or even longer for the heavier skins4 ,after scudding they are drenched with #aj per cent4 bran and some pea meal at #ie ,f4 for a few hours only4 ,in preparing the tawing paste1 the flour should be mixed with tepid water2 the egg yolk should also be diluted with tepid water slightly1 and strained if necessary1 and then added to the flour4 ,the oil is then carefully mixed in4 ,the alum and salt are dissolved separately at #aaj ,f4 and added to the flour and oil4 ,the tawing paste should be used at about #aje ,f4 ,for every hundred medium-sized lambskins there will be required3 #aj lbs4 flour in #b-a_/b gallons water1 #a quart preserved egg yolk1 #c-c_/d lbs4 alum and #a-a_/d lbs4 salt4 ,the skins are drummed in this for an hour or so and dried out on poles rapidly1 but not with great heat4 ,this is essential to get stretch4 ,they are next wet back1 staked1 dried and staked again4 ,they are then aged4 ,to wet back for dyeing and finishing the skins are drawn through warm water and then drummed in water at #ie ,f4 for #ae minutes to wet evenly and thoroughly4 ,this liquor1 which contains much of the tawing material1 is run off and replaced by the dye solution1 e4g4 fustic or turmeric1 with which the goods are drummed for half an hour4 ,iron1 chrome or copper salts may be used for saddening4 ,after this bottom colour is obtained1 a coal tar colour is added for topping and the drumming continued until the required shade is obtained4 ,the excess liquor is now run off1 and the materials lost in soaking are replaced by drumming further with egg yolk and salt for #ae minutes4 ,this is known as re-egging4 ,blacks are obtained with logwood and iron4 ,after re-egging1 the skins are dried out and staked4 ,they are seasoned with a weak emulsion of soap and oil1 dried1 oiled lightly with linseed oil1 ironed1 re-oiled and finally brushed4 ,whites are undyed1 and #aj lbs4 ,french chalk per #ajj skins is used in re-egging4 ,calf kid is a once popular but now obsolete upper leather made by tawing calfskins4 ,the skins were well plumped in limes1 delimed by washing and drenching1 tawed much as for glove kid1 split1 dried out rapidly1 staked and aged4 ,they were finished dull and black with soap and wax4 ,the various white leathers used for belts1 laces1 whip lashes1 aprons1 covers for stoppered bottles1 etc41 are very usually made with an alum tannage4 ,alum1 salt and flour only are used4 ,whitening is also mixed in and acts as neutralizing agent as well as pigment dye4 ,wool rugs are manufactured from suitable sheepskins by an alum tannage4 ,they are first well cleaned1 using soap on wool and flesh4 ,they are next degreased by painting with fuller's earth paste and drying4 ,they are tawed by painting the flesh with a strong solution of alum and salt1 or even by rubbing on the solid salts4 ,they are dried out1 aged and sorted for suitable colours4 ,the dyeing is rather difficult1 as many artificial dyestuffs are of no use4 ,it is usual to bleach the skins first in a weak solution of bleaching powder1 and afterwards to dye with infusions of the dyewoods1 e4g4 logwood1 fustic1 sandalwood1 terra japonica1 quercitron bark1 turmeric1 indigo1 etc4 ,vat dyeing is usual4 ,after dyeing1 retanning with alum and salt is necessary1 on account of the loss of these in bleaching and dyeing4 ,rugs are usually finished black1 white1 grey1 brown1 walnut1 crimson1 blue or green4 ,,references4 ,procter1 ,principles of ,leather ,manufacture1 pp4 #ahd1 #bcf4 ,bennett1 ,manufacture of ,leather1 pp4 #bci1 #cga4 ,,section ,,ii4--,,fat ,,tannages ,for the manufacture of a permanent leather the essential requirements are that the fibres of the hide or skins gel should be dried in a separate condition1 and that they should be coated by some waterproof or insoluble material4 ,many substances fulfil the first but not the second of these conditions4 ,for example1 the dehydration only may be accomplished more or less by salt 7as in curing hides71 still better by salt if a little mineral acid be used 7as in pickling71 and by other salts such as potassium carbonate and ammonium sulphate1 and dehydrating agents such as alcohol4 ,such temporary leathers1 however1 are not water-resisting1 as the second requirement has not been fulfilled1 viz4 the coating of the fibres with some more or less waterproof material4 ,thus if pelts dehydrated with alcohol be treated with an alcoholic solution of stearic acid1 the second condition is fulfilled and a permanent leather is obtained4 ,now1 many tanning agents accomplish these two requirements only imperfectly4 ,as we have noted in the preceding section1 the alum-tanned leathers are not very water resisting1 and much of the tannage will wash out4 ,leathers made by the vegetable tannages usually contain some excess of vegetable tanning matters which are soluble in and removed by water1 though much tannin can no longer be thus removed1 owing to the mutual precipitation of the oppositely charged tannin sol and hide gel4 ,the necessity for fulfilling the second requirement mentioned is one reason for the practice of following these tannages by applications of oil1 fat or of both4 ,in this way the isolated fibres are not only dried separately1 but are coated with a typical water-resisting material4 ,in the fat tannages an attempt is made to fulfil this second requirement without the use of any specific tanning agent for producing the first requirements2 i4e4 an attempt is made to dry the fibres separately in an untanned condition1 and to coat them simultaneously with fat so that a permanent leather is obtained4 ,it is only possible to do this1 if the pelt is constantly during drying subjected to mechanical working1 e4g4 by twisting1 folding1 bending1 drumming1 staking1 etc4 ,the resulting leather is often called rawhide leather1 and presents a real advantage over other leathers in its great tensile strength4 ,where toughness is an essential quality1 there is much to be said for the fat tannages4 ,it is also possible1 of course1 to effect compromises between ordinary tannages and the straight fat tannages2 thus picking band butts1 which must be tough1 are often very lightly tanned with oak bark or chrome1 and then given what is practically a heavy fat tannage4 ,in the most typical of fat tannages1 moreover1 it is often common to colour the goods by a brief immersion in a weak vegetable tan liquor4 ,further1 the employment of fats in the currying of dressing leather is in effect a fat tannage superimposed upon the vegetable tannage4 7,see ,combination ,tannages1 ,section ,,vi47 ,the fat tannage is undoubtedly one of the earliest methods for making leather4 ,prehistoric man discovered that the skins of animals killed in hunting could1 by alternately rubbing with fats and then drying slightly1 be eventually converted into a useful leather1 whereas without the fat it was stiff and horny4 ,even yet similar methods are in use1 thongs of raw hide being continually twisted during drying1 with intermittent application of fats4 ,in the modern fat tannages drums are used to give the necessary mechanical working to the goods4 ,the raw hide leather produced in the ,u4,s4,a4 is made by drumming the nearly delimed goods with tallow and neatsfoot oil4 ,in this country the fat tannages have been typified by the ,crown and ,helvetia leathers4 ,the hides are thoroughly limed in mellow limes1 and after the beam work are delimed by drenching1 scudded1 and sometimes fleshed again1 and then coloured off in tan liquor4 ,after partial drying1 they are drummed warm for some hours to ensure isolation of the fibres4 ,after further drying they are coated with the tanning paste1 which consists essentially of soft fats and flour to produce partial emulsification4 ,equal parts of soft fats and of flour may be used1 to which may be added smaller proportions of degras1 cod oil1 mutton tallow1 salt1 together with about #be per cent4 water4 ,the goods are coated with this mixture1 drummed1 and dried further1 and this routine repeated as often as necessary to fill the interstices thoroughly with fat4 ,the temperature in the drum may reach #ie ,f4 ,in finishing an attempt is made to stuff further with grease4 ,the goods are thoroughly set out1 dried a little1 and coated again1 flesh and grain1 with a mixture of tallow1 cod oil1 glycerine and degras1 and dried further4 ,the excess grease is slicked off and the goods again set out and grained4 ,they are then dried out4 ,,references4 ,bennett1 ,manufacture of ,leather1 pp4 #bde1 #bdf and #cgf4 ,procter1 ,principles of ,leather ,manufacture1 p4 #cgh4 ,,section ,,iii4--,,oil ,,tannages ,there are very obvious analogies between the fat tannages discussed in ,section ,,ii4 and the oil tannages now to be dealt with1 but there is nevertheless a distinct departure in principle involved4 ,in the oil tannages the mechanical treatment is generally more vigorous1 and the drying process is conducted at a much higher temperature1 with the result that there is a vigorous oxidation of the oil4 ,this results in the formation of insoluble oxidation products which coat the fibre and play an essential part in the production of a permanent leather4 ,pungent vapours are evolved in the drying operations1 amongst which is acrolein and probably also other aldehydes1 and it is thought by ,procter that these aldehydes also are essential tanning agents and typical of the process 7cf4 ,section ,,iv474 ,fahrion considers that the tanning action is due solely to unsaturated fatty acids with more than one double linkage4 ,garelli and ,apostolo1 however1 believe that the tannage is due to a coating of fatty acid whether saturated or not4 ,these observers made leather with stearic and palmatic acids in colloidal aqueous solution4 ,the manufacture of chamois leather from the flesh splits of sheepskins comprises the largest and most typical branch of the oil tannages4 ,the sheep pelts are split in the limed state1 and the fleshes are given another sharp liming which may last up to a fortnight4 ,they are next frized1 i4e4 scraped over the beam with a sharp two-handled knife1 to remove roughness and loose fat4 ,the goods are next thoroughly washed in running water and drenched4 ,a paddle drench is often preferred1 and if not used the handling should be frequent4 ,paddling drenching reduces the time required from about #af hours to about #f hours4 ,an hour or more in a hydraulic press removes superfluous liquor and some more grease4 ,the fleshes are separated1 cooled and then stocked for #cj minutes to equalize the moisture in them4 ,after removing from the stocks they are sprinkled on both sides with cod oil and thrown back into the stocks for a few hours4 ,they are then dried cold for a day or two4 ,the stocks used are similar to those once popular for softening dried hides during soaking1 and consist of two heavy hammers which fall alternately upon the goods which are contained in a curved box below4 ,the result is a mechanical kneading action4 ,the fleshes are again sprinkled with cod oil1 restocked for a few hours and dried again1 this time at #ajj ,f4 ,they are then repeatedly sprinkled1 stocked and dried1 the last operation being conducted always at an increasing temperature until finally the final heater is even up to #afj ,f4 ,as the operation proceeds it is advantageous to hang the splits also nearer one another1 and in the final heater they are quite close4 ,the next stage is to pack the goods quickly into suitable boxes and allow them to heat1 i4e4 to oxidize further4 ,this is a rather critical stage in the process1 and to prevent overheating 7burns7 it is often necessary to open out and repack into another box1 with possibly some little intermediate cooling4 ,they are turned over thus repeatedly until the oxidation is complete1 and then spread out to cool4 ,the fleshes are now a dark brown colour1 and are next treated to remove excess of oxidized oil products4 ,the goods are dipped through water at #aaj ,f4 and then subjected to hydraulic pressure4 ,the grease and water which exude are allowed to separate by settling1 and the thick yellow oil so obtained1 known as degras1 forms a valuable material for leather dressing1 as it more readily emulsifies with water than many oils1 and impart this quality to other greases mixed with it4 ,a further quantity of a similar oil is obtained by paddling the goods with a weak soda solution4 ,the liquor obtained is treated with sulphuric acid to neutralize the alkali1 and the grease recovered is known as sod oil4 ,the fleshes are now well washed with hot water 7#adj ,f471 fat liquored with cod oil and soft soap1 machine sammed1 either by a wringer or a centrifuge1 and then dried out4 ,much chamois leather is also made in ,france by closely similar methods4 ,the skins are usually oiled on tables and folded up before stocking4 ,other marine oils 7seal1 whale1 etc47 replace cod oil4 ,generally speaking the oxidation is more moderate1 and the grease from the hydraulic press 7moellon7 is mixed with other fish oils to form commercial degras4 ,an inferior quality of degras is obtained by subsequent treatment with soda4 ,the crust chamois obtained as above has only to be thoroughly staked to soften1 grounded and fluffed to raise the nap1 and then trimmed1 and the ordinary wash-leather is obtained4 ,if intended for glove leathers superior skins are selected4 ,these are fluffed carefully upon emery wheels1 using first a coarse surface and eventually a fine surface so that a fine velvet effect is attained4 ,the skins are next bleached4 ,in the sun bleach or grass bleach the goods are soaked in a #a-a_/b per cent4 soft soap solution and exposed to sunlight after being wrung4 ,they are bleached in about #c days in summer1 but nearly a fortnight may be necessary in winter4 ,in the permanganate bleach1 which is less tedious1 the skins are first degreased by soaking in a warm #c_/d per cent4 solution of soda crystals and then drumming for #cj minutes in water at #ie ,f4 ,they are then paddled in a #a_/h per cent4 solution of commercial permanganate for an hour at the same temperature1 rinsed through water1 and the brown manganese dioxide is then removed by paddling or drumming the goods in a #c per cent4 solution of sodium bisulphite to which hydrochloric acid is added as required4 ,the goods are well washed in warm water1 and are then tucked1 i4e4 placed in a vat of boiling water containing a little soft soap1 just for a few seconds4 ,the goods shrink and curl up1 and they are then dried out at #abj-adj ,f4 to fix the tuck4 ,they are then staked1 fluffed1 and dyed4 ,in dyeing with coal tar colours the alizarin colours may be used after mordanting with chrome alum4 ,direct dyes1 natural dyestuffs and pigment dyes are also used4 ,the goods are struck out after dyeing1 lightly fat liquored with commercial egg yolk1 dried out at #aaj to #abj ,f41 staked and fluffed on the face side4 ,buff leather is a similar leather made from hides4 ,they are limed mellow for a fortnight1 unhaired1 fleshed1 and then limed again for another week in sharp limes4 ,the grain is then split off1 and the goods rinsed and scudded1 slightly delimed and hung up to dry4 ,they are then treated in much the same way as fleshes for chamois1 but lime is often added to the cod oil used in stocking4 ,buck leather is a similar product obtained from deerskins1 but much mock buck is made from cheaper raw material4 ,,references4 ,bennett1 ,manufacture of ,leather1 pp4 #bdg-bej and #cgf-cgi4 ,procter1 ,principles of ,leather ,manufacture1 p4 #cgh4 ,,section ,,iv4--,,formaldehyde ,,tannage ,the use of formalin for hardening gelatin has long been known1 but it was left for ,payne and ,pullman to devise a commercial process for tanning pelt into leather by means of formaldehyde 7,h,,cho7 solutions4 ,their process1 which was patented1 specified the use of alkalies in conjunction with formaldehyde or other aldehydes4 ,the function of the alkalies is not very obvious1 for it has been shown that formaldehyde will tan also in neutral and in acid solution4 ,the precise action of the aldehydes is also as yet somewhat obscure1 but it is noteworthy that very small proportions of formalin will give a complete tannage4 ,it is probable that the action of formaldehyde is not perfectly analogous with that of its homologues1 for it is a most reactive substance1 and will certainly with proteids undergo reactions which are not analogous to those with other aldehydes4 ,the leather obtained by tanning with formalin is quite white and resembles buff leather1 but has advantages over the latter in that no bleaching is necessary4 ,according to the patent specifications the pelt should be drummed in water and the tanning liquor--a solution of formalin and sodium carbonate--added gradually at #ae-minute intervals4 ,up to #f hours for light skins1 and up to #dh hours for heavy hides1 are required for complete tannage4 ,the temperature is raised during the process from #ajj to #aah ,f4 ,the tanning liquor may be made from #af lbs4 of commercial formalin 7#cf per cent4 formaldehyde7 and #cb lbs4 soda 7#hj per cent4 ,na#b;,,co#c7 in #aj-ae gallons of water4 ,this should be added1 one gallon at a time1 to #d cwt4 pelt in #ajj-abj gallons of water4 ,after tannage is complete the goods should be paddled with a #a-a_/b per cent4 solution of ammonium sulphate to remove the soda1 and nourished in a solution of soft soap and salt1 about #b-a_/d per cent4 of each on the weight of pelt4 ,the goods are then dried out1 and may be finished like chamois1 buff1 and buck leathers 7,section ,,iii474 ,,references4 ,payne and ,pullman1 ,english ,patent #ahih1 #bhgb4 ,bennett1 ,manufacture of ,leather1 pp4 #bej and #cgi4 ,,section ,v4--,,synthetic ,,tanning ,,materials ,in spite of much valuable work on the constitution of the vegetable tannins and the compounds usually associated with them1 such as that of ,e4 ,fischer1 ,k4 ,freudenberg and their collaborators on gallo-tannic acid1 and that of ,a4 ,g4 ,perkin on ellagic acid and catechin1 we are still in the dark with respect to the constitution of the tannins which are of commercial importance1 and any synthetic production of these materials is thus out of the question as yet4 ,attempts1 however1 have been made to produce artificially substances which possess similar properties to the tannins and which may be used for converting pelt into leather4 ,into this category fall some of the earlier attempts to synthesize gallo-tannic acid by heating gallic acid with condensing reagents4 ,the first commercial success in this direction was attained by ,stiasny1 who produced condensation products of the phenolsulphonic acids1 to which products he gave the general name of syntans 7synthetic tannins74 ,the ,badische ,co4 placed one of these products on the market as ,neradol ,d1 and later took out subsidiary patents for the manufacture of similar products by slightly differing methods of productions4 ,since the outbreak of the ,european ,war such patent rights have been suspended1 and several ,british firms have been manufacturing synthetic tanning materials by similar methods1 but doubtless with developments and improvements of their own discovery4 ,these products 7e4g4 ,cresyntan1 ,maxyntan1 ,paradol1 ,syntan1 etc47 are now in use in many factories1 and assist rather than substitute the vegetable tannins in producing leather of the desired colour and quality4 ,these synthetic tanning materials resemble the vegetable tannins in the following respects4 ,they are organic acids containing phenolic groups4 ,they are semi-colloidal1 passing slowly through semipermeable membranes4 ,they precipitate gelatin1 basic dyestuffs and lead acetate1 give a violet-blue colour with ferric salts1 and convert hide into an undoubted leather4 ,they differ from the vegetable tannins in that they contain sulphur and sulphonic acid groups1 but they agree in that both are aromatic derivatives4 ,in each case the tanning effect is diminished by alkalies1 but the synthetic materials are the more sensitive4 ,methods of ,manufacture4--,there are1 broadly speaking1 three types of method by which these condensation products are produced1 viz41 condensation by formaldehyde1 condensation by phosphorus trichloride or similar reagents1 and condensation by heat alone4 ,illustrative methods will now be given4 ,condensation by formaldehyde was the first method used4 ,the procedure is given by the ,austrian patent #eh1dje4 ,a phenol1 e4g4 crude cresylic acid1 is heated with the equivalent amount of sulphuric acid for a few hours to #ajj-baj ,c41 cooled1 and formaldehyde added slowly whilst cooling and stirring1 in the proportion of one molecule of formaldehyde to #b molecules of phenol4 ,the free mineral acid is neutralized1 and the resulting product is the syntan ,neradol4 ,by this procedure only water-soluble products are obtained1 but an alternative process is to heat the phenols in slightly acid solution1 and then to render soluble the resinous products obtained by treating with sulphuric acid4 ,the proportion of formaldehyde to phenol used led ,steasny to conclude that the resulting products were diphenyl-methane derivatives which polymerize to form molecules of considerable size4 ,the formaldehyde supplies the carbon bridge4 ,this view was criticized by ,a4 ,g4 ,green as too simple1 and he suggested the alternative theory that polymerization does not take place at all1 but that more advanced or higher condensation products are formed2 he thought that o-hydroxy-benzyl alcohols were first produced1 that these condensed with another molecule1 and afterwards the process was repeated4 ,the result was a colourless dyestuff4 ,this view receives some support from the other types of method of manufacture4 ,with the use of other condensing reagents the procedure may be as in the process of the ,b4,a4,s4,f4 7,fr4 pat4 #dea1hge-f71 thus3 #bbe parts of o-cresol-sulphonic acid are heated to #fj ,c4 for #d hours with #bfb4e parts of phosphorus oxychloride4 ,the excess of oxychloride is removed by distillation under reduced pressure and the residue washed with dilute hydrochloric acid4 ,condensation by heat alone is illustrated by the method given in the same patents1 thus3 phenol-p-sulphonic acid is heated to #acj ,c4 for #bd hours under a pressure of #bj mm4 or in a current of dry air at atmospheric pressure4 ,the product may be used direct or may be purified by dissolving in water1 neutralizing with caustic soda1 filtering and evaporating to dryness4 ,a white powder is obtained which tans when its solution is acidified4 ,an alternative is to mix phenol with sulphuric acid and heat the mixture to #adj ,c4 for #gb hours under #bj mm4 pressure and purify as before4 ,methods of ,use4--,the synthetic tanning materials may be put to many uses4 ,when well manufactured they make practically a white leather1 and this fact makes a valuable opening for their use in connection with light leather tannages and the dressing of rugs4 ,it is also claimed that they improve the colour usually obtained in the ordinary vegetable tannages4 ,if used in the suspenders to the extent of #e-aj per cent4 they are said to brighten the colour throughout the tannage4 ,if used in bleaching and finishing they are said to lighten the colour of the finished leather4 ,about #e per cent4 on the weight of the goods may be added to the bleach or vat liquors2 they may be also mixed with sumac during finishing1 and in effect act as a sumac substitute2 solutions are also brushed over the grain before oiling1 with a view to obtaining good colour4 ,it is also claimed that their use prevents vegetable-tanned leather from becoming red under the action of sunlight4 ,the syntans are also used to lighten the colour of chrome leather1 even of chrome sole leather after it has been dipped4 ,it is claimed also that syntans produce a tough leather1 and if used for heavy leather in the early stages they give a tough grain and assist in avoiding a cracky grain4 ,on this account they are also recommended for retanning ,e4,i4 tanned kips4 ,when used in heavy leather suspenders they are said to get rid of lime blast 7,ca,c,o#c7 and to quicken the tannage1 i4e4 to enable the same weight to be obtained in less time4 ,procter suggests that a tannage of commercial value might be obtained by blending them with wood pulp extract4 ,if used alone for tanning a series of pits containing liquors of #d to #cg ,bkr4 may be used1 but drum tannages may be given using liquors of #ad-bi ,bkr41 the goods being tanned in #f-h hours4 ,about #cj per cent4 of syntans are said to be necessary for complete tannage4 ,,references4 ,e4 ,stiasny1 ,a ,new ,synthetic ,tannin1 ,collegium1 #aiac1 #adb-ade4 7,see also ,j4,s4,c4,i41 ,abs4 #aiac1 #ejj47 ,e4 ,stiasny1 ,syntans--,new ,artificial ,tanning ,materials1 ,j4,s4,c4,i41 #aiac1 #gge4 ,patents3--,austrian #eh1dje4 ,german #bfb1eeh1 ,sept4 #ab1 #aiaa4 ,french #dea1hge1 ,dec4 #ac1 #aiab2 #dea1hgf1 ,dec4 #ac1 #aiab2 #dea1hgg1 ,dec4 #ac1 #aiab4 ,,section ,,vi4--,,combination ,,tannages ,the formation of leather being due to the adsorption of colloidogenic substances at the interface of the tanning liquor and the hide gel1 there is the obvious possibility that several such substances may be used simultaneously1 and that the resulting leather may be due to the combined effect of these substances4 ,indeed1 the average vegetable tannage consists of such a combination tannage1 each tanning material contributing its own individual tannin and characteristic astringent non-tannins4 ,there is evidently also the possibility that the different types of tannage discussed above might be used either simultaneously or successively1 and that a leather might be obtained which combines to some extent the qualities of each of the types in combination4 ,it is such a case that is generally called a combination tannage4 ,there are many conceivable combinations1 and in this section will be chiefly discussed a few which have demonstrated some commercial possibilities4 ,some of these have already received notice in the preceding sections4 ,the manufacture of curried dressing leathers is a combination of vegetable and fat tannages4 ,the manufacture of waterproof chrome uppers illustrates a combination of chrome and fat tannages4 ,the use of syntans in conjunction with vegetable tanning materials is also a combination tannage4 ,the case of chamois leather is possibly a combination of aldehyde tannage with fatty acid tannage4 ,two-bath chrome leather is a combination of chrome1 sulphur and fat tannage4 ,formaldehyde and vegetable tannage is also a known possibility4 ,it is clear that there are possibilities of endless complexity1 and that what normally may appear as a simple tannage is in reality a very complex combination tannage4 ,from this standpoint one might instructively consider the successive adsorptions involved in a goatskin tanned first with syntans1 then with oak bark1 retanned in sumac1 mordanted with chrome1 dyed with coal-tar dyestuffs and finally oiled with linseed oil4 ,it will be easily seen that in a very strict sense nearly all tannages are combinations4 ,usually1 however1 the term combination tannage is confined to those cases where the main tanning agents not only differ in type1 but where none are in predominant quantity4 ,a typical case is that of semichrome leather1 in which a vegetable tannage is succeeded by a chrome tannage4 ,e4,i4 tanned sheep and goat skins are rather heavily stripped of their vegetable tannage and heavy oiling1 by drumming with warm soda solutions1 and after washing with water are chromed with the one-bath process2 they are neutralized1 dyed1 fat liquored and finished for glac upper leather4 ,in a precisely similar way kips and split hides which have received vegetable tannage are stripped and retanned in chrome and finished as for box calf1 of which they are a good imitation4 ,such vegetable-chrome combination tannages possess many of the properties of chrome leather4 ,to chrome the pelt first and afterwards to subject it to vegetable tannage is also an obvious possibility1 but has not yet been made a commercial success in this country1 but has been increasingly used in the ,u4,s4,a4 during the ,war4 ,another typical case of combination tannage is the dongola leather produced by the use of gambier and of alum and salt4 ,this is a vegetable-alum combination1 and yields a good quality leather for light uppers1 gloves1 etc4 ,goatskins for glazed dongola are paddled tanned in gambier liquors1 and alum and salt are subsequently added4 ,they are tanned in #bd hours1 well washed1 and are fat liquored without ageing4 ,the ,e4,i4 tanned skins may also be stripped with soda1 and retanned in alum and salt1 using flour also if desired4 ,dull dongola are first tawed and then retanned in gambier liquor4 ,sude and velvet calf are also tawed and retanned with gambier4 ,yet another case of combination tannage is that of sheepskins for glac uppers1 which are first tawed thoroughly with alum1 salt and flour and dried out for sorting1 and are then retanned in chrome by the one-bath process1 and finished as usual4 ,closely related to this is the method of pickling in alum and salt and then chrome tanning4 ,another case is the combined one-bath1 two-bath method of chrome tanning4 ,the goods are chromed by a one-bath liquor containing dichromate 7say #b per cent471 and then pass into a reducing bath4 ,there is not much advantage in such procedure1 however4 ,from a strictly commercial point of view the dongola and semichrome leathers have proved the most successful combination tannages1 but there seem to be possibilities in combinations of the vegetable tannins with synthetic tanning materials4 ,many other substances are known to tan1 e4g4 iron salts1 cerium salts1 sulphur1 quinones1 fatty acids1 the halogens1 etc41 etc42 hence there is always the possibility that new useful combination tannages may be discovered4 ,,references4 ,bennett1 ,manufacture of ,leather1 pp4 #bdc1 #cgd-e4 ,procter1 ,principles of ,leather ,manufacture1 p4 #bcf4 ,,section ,,vii4--,,the ,,evolution ,,of ,,the ,,leather ,,industry ,the leather trades are amongst the oldest of all industries1 but their evolution has been much more rapid during the last two or three decades than at any other period of their history4 ,the ,european ,war1 moreover1 has caused the commencement of another period of rapid development1 and it is the aim of this section to point out some of the principal lines of change which have already become apparent4 ,many of these lines of evolution in the methods of manufacture have been previously discussed in their appropriate sections4 ,they may all be summarized as attempts at more economical production4 ,prominent amongst them is the persistent effort to attain quicker processes4 ,during the last twenty-five years the time necessary to produce the heavy leathers has been reduced from #ab months to as many weeks4 ,the tendency is to reduce the time further still1 but this is of course increasingly difficult to accomplish4 ,on the other hand1 it is more urgent to strive in this direction than ever1 because a needless week involves more capital lying idle than ever before4 ,moreover1 as most leather factories are now large works1 a saving even of #bd hours has become a serious item in economic production4 ,hence in liming1 bating1 tanning1 drying and in warehousing there are increased efforts to make a quicker turnover4 ,a good illustration of this speeding up in modern tanneries is the adoption by all large factories of much more rapid methods of extracting tannin4 ,on the old press-leach system liquors may be percolating through the material for possibly a fortnight4 ,the extract manufacturer reduces this operation to about two days4 ,steam generated from the spent bark is used to heat the extracting vats1 and to work a vacuum pan or evaporator whereby more water can be used and a more complete as well as a more rapid extraction obtained4 ,the evaporator also makes easy the preparation of the strong liquors used in modern tanning4 ,hand-in-hand with quicker production and manipulation are the attempts to obtain a larger turnover4 ,it is realized that the big business attains cheap production4 ,even before the war the smaller factories were disappearing4 ,a small tannery must now either extend or close down4 ,this has been better realized in the heavy than in the light leather trades4 ,in the sole leather tanneries very often many thousand hides per week are put into work1 but in the glac kid factories there is nothing yet to correspond to the output of ,american glac factories1 which sometimes reaches three or four thousand dozen a day4 ,another very prominent feature of factory evolution is the increased use of labour-saving machinery4 ,this practice has been in operation for a considerable time1 but with marked acceleration during the last few years owing to the labour shortage occasioned by military service4 ,this development of machine work has largely dispensed with that labour which involved any skill or training4 ,the journeyman currier is now practically extinct4 ,in the beam house1 too1 fleshing1 unhairing and scudding are rapidly becoming machine instead of hand operations4 ,many devices are now being adopted also which reduce the quantity of unskilled labour needed4 ,instead of handling the goods from pit to pit1 modern tanneries aim at moving the liquors4 ,thus in the ,forsare and ,tilston systems of liming1 hides are placed in a pit and lie undisturbed until ready for depilation1 the soak liquors and lime liquors being supplied and run off just as required1 whilst these liquors are agitated as often as desired by means of a current of compressed air4 ,this agitation replaces the handling up and down once practised4 ,in the tanyard proper the same tendency is at work1 rockers are increasingly preferred to handlers1 and an inversion of the press leach system permits the exhaustion of tan liquors by a gravity flow1 and so avoids the handling forward from pit to pit4 ,there is also a tendency to install lifts1 overhead runways1 trucks on lines1 motor lorries1 etc41 to replace carrying1 barrowing1 carting1 etc41 and so to arrange the tannery that the minimum transport is needed4 ,all these lines of evolution involve more intensive production1 and necessitate much more careful supervision4 ,it is not surprising1 therefore1 that the industry now feels that scientific oversight and administration are essential4 ,a dozen years ago the trade chemists were largely unqualified men1 whose work lay solely in the laboratory1 and consisted mainly in the analysis of materials bought4 ,to-day all large tanneries have qualified chemists1 and it is realized that they are the practical tanners4 ,their function is so to control the manufacturing processes that all waste is avoided1 and so to correlate and co-ordinate the manufacturing results with the analytical and experimental records of the laboratory1 that constant improvements are made in the methods of production4 ,the extended use of machinery1 and the necessity for economy in coal and power1 give the engineer also very large scope for useful work4 ,modern business conditions1 moreover1 have made necessary more skilful clerical work and accountancy in the large offices of a modern tannery4 ,in the creation of cordial relationships between capital and labour in the leather trades1 there has been unfortunately little progress4 ,the leather trade is not a sweated industry4 ,its workers have always enjoyed reasonable hours of work4 ,in most factories an approximate #dh-;hour working week 7involving no night work7 has long been in operation4 ,the industry1 however1 is not one in which high wages obtain4 ,the average tannery worker receives a wage which is never much above the level of subsistence4 ,this is mostly due to the fact that he is usually a quite unskilled labourer1 and is therefore on the bottom rung of the labour ladder4 ,in addition to this the work itself is often distressingly monotonous1 and makes little demand upon the intelligence of the worker4 ,the trade consequently offers little attraction to the intelligent labourer4 ,the old system of apprenticeship is now quite obsolete1 partly owing to the rapidity of the changes in the methods of manufacture1 partly to the specialization of labour which results from the development of large factories1 and partly also1 because to understand modern tanning involves a better general education than most workmen receive4 ,it is indeed frequently difficult to find competent under-foremen for the different departments of the modern leather factory4 ,until recently leather workers have been either unorganized or badly organized1 and their views and complaints have been confused and sporadic1 but during the war period there has been a very rapid extension of trade union movements1 and consequently a more articulate expression of the demands for democratization as well as a greater share in the fruits of the industry4 ,in the leather trades1 however1 the gulf between the unskilled labourers and the wealthy employers is perhaps unusually wide1 and there is little disposition on the part of capital to recognize the equity of either of the above demands of labour4 ,generally speaking1 the leather trade firms are not public but private companies4 ,there is absolutely no trace of co-partnership or profit-sharing schemes1 or of co-operative production4 ,there is little recognition that the trades' prosperity should be shared in any way by the workpeople1 and still less recognition of any right to a voice in industrial conditions4 ,this condition of affairs has an ominous reaction upon the attitude of labour1 which believes that it is producing great wealth but not obtaining much more than subsistence4 ,it is not the function of this volume to pronounce a verdict upon the wages question or upon the democratization of the leather trades1 but one may be permitted earnestly to hope that if such be the future lines of development1 there will be also1 as an absolutely essential part of any such schemes1 a much higher standard of education amongst the workers1 for this is the only satisfactory guarantee that the voice of labour in council will have any practical value1 or that higher wages will be at all wisely used by the recipients4 ,in his instructive and valuable volume on ,the ,evolution of ,industry1 ,prof4 ,mac,gregor points out that modern industry has evolved three outstanding types1 viz4 the ,co-operative ,movement1 the ,trusts1 and the methods of ,public ,trading4 ,he also suggests that these types tend to blend4 ,in the leather industry co-operative and municipal production are unheard of1 but the industry has certainly developed along the lines of the large trusts4 ,large businesses have replaced small1 and later still have formed local federations1 which in turn have combined to form the ,united ,tanners' ,federation4 ,war conditions have certainly stimulated evolution towards the trust type4 ,the ,united ,tanners' ,federation has become possessed of powers which were not originally contemplated1 such as the purchase and distribution to its members of hides1 bark1 extract1 sulphide and other materials4 ,how far some of these arrangements will be permanent is problematical1 but one beneficial result is that the allied trades have certainly realized more thoroughly their unity of interests4 ,this is shown by the much freer collaboration of the tanners1 and by the encouragement now given to similar collaboration between their chemists4 ,more evidence is found in the proposals for combined research4 ,there is also considerable reason to believe that there is some movement in the direction of partial ,state control4 ,there is little doubt that evolution along trust lines will make this less difficult and possibly more desirable4 ,the country cannot afford the spectacle of a ,leather ,trust permanently at war with a ,labourers' ,union4 ,the public has realized that the well-being of the leather industry is vital to the national safety4 ,it has realized that the leather trades are great producers of national wealth1 and that increased production with the development of the export trade will materially assist to restore the country's financial position4 ,it has realized also its own right to protection from bad leather and from exorbitant prices4 ,on all these grounds it is probable1 though there may be some reaction from the present position1 that the ,state1 which has already got its fingers in the pie1 will refuse to draw them out altogether4 ,the ,imperial aspect of the question affords some further justification for this attitude4 ,the leather trades operate very largely upon imported material1 and it is clearly desirable that there should be close co-operation between the home industry and the colonial supplies of material4 ,here too the war has also given a great stimulus in this direction4 ,indian myrabolans has long been a staple tanning material4 ,south ,african wattle bark has during the last few years replaced almost completely1 and probably to a large extent permanently1 ,turkish valonia4 ,there has also been great increase in the imports of ,indian kips and of ,south ,african hides1 and it is not at all an impossible proposition to maintain a self-contained ,imperial ,leather ,trade1 should this be necessary4 ,french chestnut extract1 and quebracho extract1 however1 are much too valuable tanning materials to exclude for merely sentimental reasons4 ,these instances indicate possible advantages in ,imperial co-operation1 but also show the need for caution in the elaboration of such schemes4 ,although a partial1 and indeed increasing1 measure of ,state ,control is probable1 there has been as yet no serious proposal to nationalize the leather industry4 ,such a proposition1 indeed1 is hardly ripe even for discussion4 ,until the nationalization of transport and of mines is a proved success1 and until the merely distributive undertakings of the municipalities 7e4g4 of coal and of milk and other foods7 are past the experimental stage1 any proposition to nationalize the leather trades seems premature4 ,it is noteworthy1 however1 that in ,queensland1 ,australia1 the ,government have the right to commence and to administer ,state ,tanneries4 ,any progress in the direction either of democratization or of nationalization1 has been certainly postponed by the sudden and unprecedented trade slump which commenced in the earlier part of #aibj4 ,this depression1 in spite of heavy falls in the prices of raw materials1 has made economic production a much more difficult problem4 ,it has undoubtedly given a further stimulus to evolution towards the trust type1 and created a further tendency towards the closing of the smaller factories1 and the employment of labour-saving devices4 ,when the general fall in prices has made an appreciable fall in the cost of living1 some reduction in the leather workers' wages1 together with more efficient work1 will also contribute to the solution of the difficulty4 ,it is chiefly to be desired1 however1 that the export trade should be restored4 ,the realization of this hope depends largely upon the establishment of peace and prosperity abroad1 and the consequent stabilization of the various foreign exchanges4 ,,part ,v4--,,gelatine ,,and ,,glue4 ,,section ,i4--,,properties ,,of ,,gelatine ,,and ,,glue ,many of the chemical properties of gelatine1 especially those which distinguish it from other proteins1 have been described in the ,introduction to this volume1 and need no further comment4 ,in this section its colloid nature and behaviour will chiefly be considered1 for these points have greatest importance from the standpoint of industrial chemistry4 ,it is hoped1 moreover1 that this section will be of interest not only to the chemist concerned in the manufacture of gelatine and glue1 but that it will be of value also to those concerned in leather manufacture4 ,the difference between the collagen which composes the hide fibre and the high-grade gelatines is so small that for many practical purposes it may be considered negligible4 ,thus the description of the behaviour of a gelatine gel is very largely applicable to a hide gel also4 ,gelatine has been crystallized by von ,weimarn by evaporating a dilute solution in aqueous alcohol whilst in a desiccator containing potassium carbonate1 the temperature being maintained at #fj-gj ,c4 ,the carbonate takes up water only1 and the concentration of the alcohol therefore slowly increases until the gelatine is no longer soluble4 ,gelatine is usually found and known in the colloid state1 however1 and its behaviour in this state only is of practical importance4 ,the fundamental idea of modern colloid chemistry is that colloids are heterogeneous systems1 usually two-phased1 in which one phase is liquid and the other phase either liquid or solid4 ,the latter phase1 which is divided into small separate volumes1 is known as the disperse phase1 whilst the other is the continuous phase or dispersion medium4 ,the dispersity is the degree to which the reduction of the dimensions of the disperse phase has been carried1 and is best expressed numerically in terms of specific surface1 i4e4 surface area divided by volume1 but it is also often expressed as the thickness or diameter of a film or particle4 ,when the dispersity is not high1 we have ordinary suspensions and emulsions1 which with increasing dispersity merge into the typical colloids4 ,by analogy1 colloids have been divided into suspensoids and emulsoids1 when the disperse phase is solid and liquid respectively4 ,the classification1 however1 has not been found satisfactory1 for some systems in which the disperse phase is undoubtedly liquid1 exhibit characteristic properties of suspensoids1 and vice vers4 ,a more satisfactory division1 therefore1 is found in the presence or absence of affinity between the two phases1 the systems being termed lyophile and lyophobe respectively4 ,if water be the continuous phase the terms hydrophile and hydrophobe are often used4 ,broadly speaking1 the lyophile colloids correspond to the emulsoids1 and the lyophobe colloids to the suspensoids4 ,gelatine is a typical hydrophile colloid4 ,another fundamental idea of colloid chemistry is that the great extension of surface involved in a high dispersity causes the surface energy to be no longer a negligible fraction of the total energy of the system1 and that the recent advances in knowledge respecting surface phenomena may be called in to assist in the explanation of the special properties of the colloid state4 ,particles which exhibit the ,brownian movement1 about #aj7-e7 cm4 diameter1 down to the limit of microscopic visibility 7#aj7-c7 cm47 are termed microns4 ,particles less than this1 but just visible in the ultra-microscope 7#eaj7-g7 cm47 are termed submicrons4 ,particles still less1 approximately #aj7-g7 cm41 have been shown to exist1 and are termed amicrons4 ,the dimensions of molecules such as may exist in true solutions are of the order of #aj7-h7 cm4 ,a colloid sol may contain particles of various sizes4 ,thus a gelatine sol 7like other lyophile systems7 contains chiefly amicrons1 but submicrons are also observable4 #a4 ,,the ,,continuous ,,phase ,owing to the contractile force of surface tension1 it is concluded that the surface layer of a liquid is under very great pressure1 much greater than the bulk of the liquid4 ,any extension of the surface of the liquid naturally causes a corresponding extension of the proportion of liquid which is thus compressed4 ,if in a beaker of water there be placed a porous substance1 such as animal charcoal1 there is a great extension of the surface of the water1 and a corresponding increase in the amount of compressed water4 ,if instead there be substituted a large number of very small particles of a substance1 a still further increase in the amount of compressed water is involved4 ,as the specific surface of the substance inserted is increased1 and its amount1 the proportion of compressed and denser water increases also1 until it is a practically appreciable percentage of the total volume4 ,it is clear also that the extent of the zone of compression will be determined also by the nature of the substance with which the water is in contact at its surface1 i4e4 by the extent to which it is hydrophile1 and this indeed may be the more important factor4 ,now in a gelatine sol we have the necessary conditions for a system in which the compressed water bears an unusually large ratio to the total1 owing to the enormous surface developed by the minute particles of the disperse phase 7amicrons7 and to the unusually wide zone of compression surrounding each particle caused by the strongly hydrophile nature of gelatine4 ,it should be pointed out that these zones of compression do not involve any abrupt transition from the zone of non-compression1 the layer nearest the particle is under the greatest pressure1 and the concentric layers under less and less pressures1 the actual compression being thus an inverse function of the distance from the particle4 ,now if there be a gradual increase in the concentration of the sol1 the time will come when these zones of compression begin to come in contact1 and the system will then show a considerably increased viscosity4 ,with further increase in concentration the zones of compression will overlap throughout the system1 and when the layers under considerable pressure are thus continuous1 the whole system will acquire a rigidity much greater than water and approaching that of a solid body4 ,this is a gelatine gel1 or jelly4 ,with increasing concentration the jelly becomes increasingly rigid1 and if it be eventually dried out under suitable conditions it forms what is practically solid body--gelatine--which1 however1 still contains from #ab to #ah per cent4 of water4 ,it will be clear that1 in the case of gelatine jellies 7e4g4 of #c-aj per cent4 strength71 an increase in temperature will cause an increase in the kinetic energy of the particles and effectively reduce the zones of compression4 ,indeed1 they may be reduced to such an extent that they are no longer in contact1 and the rigidity due to the continuous contact of the layers of great compression will then disappear2 as we say usually1 the jelly melts4 ,on cooling1 the decreased kinetic energy of the water molecules results in the return of the state of compression1 with rapidly increasing viscosity and eventual gelation2 as we say usually1 the jelly sets4 ,neither of these changes takes place at a definite temperature 7like a melting-point71 and in melting 7solation7 or in setting 7gelation7 the temperature-viscosity curve is quite continuous4 ,by various arbitrary devices1 however1 approximate melting and setting points may approximately be determined4 ,the results also vary somewhat with the concentration of the gel or sol4 ,gels between #e and #ae per cent4 strong melt about #bf-cj ,c4 and set at #ah-bf ,c4 ,on this view1 we must regard a gelatine gel as a continuous network of water under great compression1 and in this network are zones of still greater compression1 which surround the particles of the disperse phase--the gelatine itself1 and zones of less compression which in a weak gel1 at any rate1 have a compression equal to or much the same as the normal state of compression in water4 ,one consequence of this system is1 that when a piece of gelatine swells1 there is a considerable enlargement in the zones of compression2 in other words1 some1 at least1 of the imbibed water is compressed4 ,now the compression of water means that work is done1 and when gelatine swells1 therefore1 we expect--and actually find--that heat is liberated 7#e4g cal per g4 gel74 ,hence also by the ,le ,chatelier theorem1 we expect--and find--that gelatine swells best in cold water4 ,further1 the compression of water involves a decrease in volume1 and we therefore expect--and actually find--that the volume of the swollen jelly is appreciably less than the volume of gelatine plus the volume of water imbibed4 ,another consequence of such a compressed system is that a gelatine jelly1 even in water1 will have a surface tension towards water just as the water itself has such a tension to the water vapour above the liquid4 ,this interfacial tension of the jelly will of course have a contractile effect1 and will tend to resist swelling and to limit it as far as it possibly can4 ,this force1 tending to contract the jelly and resist imbibition is therefore one of the main influences at work in the swelling of gelatine1 and is one of the two principal factors which determine the extent of the maximum swelling when equilibrium is established4 ,the force tending to resist swelling is1 in the ultimate1 just surface tension4 ,its actual magnitude depends1 of course1 mainly upon the extent of compression in the dispersion medium of the gel1 and will be a resultant which is a function of this compression4 ,the magnitude will thus vary with the average compression in the continuous network of compressed water4 ,it will be obvious that as the jelly swells the power of resisting the swelling will decrease1 and the interfacial tension with the external water will tend to disappear4 ,if the force tending to swell were great enough the swelling would continue until the zones of compression were no longer in contact and the gel would become sol4 ,as suggested above1 it is probable that the extent of the zones of compression is determined by another factor in addition to the great development of surface4 ,that factor is connected if not identical with that power which makes the system lyophile1 and is evidently connected also with the solubility of the disperse phase1 and may indeed be electrochemical forces tending to form a series of hydrates1 or at least to cause an orientation or definite arrangements of the water molecules in the zone of compression4 ,this idea receives some support from the hydrate theory of solution1 and the zones of compression and orientation are the colloid analogue of the hydrates supposed to exist in solutions of electrolytes4 ,the extension of such zones on cooling are then analogous with the series of hydrates formed1 for instance1 by manganese chloride with #b1 #d1 #f1 #aa1 or #ab molecules of water when crystallized at temperatures of #bj1 #ae1 -#ba1 -#cj1 and -#dh ,c4 respectively1 the idea being that the salts most hydrated in solution crystallize with most water4 ,as the compression is the result of two factors1 one of which depends upon the nature of the disperse phase1 we expect--and find--in other lyophile systems a considerable variation in their power of gelation4 ,some indeed1 though very viscous1 e4g4 egg albumin1 never quite set like gelatine1 and others 7e4g4 agar-agar7 set to a stiff gel from a much weaker sol than gelatine4 ,when the zones of compression are large1 as in gelatine1 the magnitude of the compressing force on the outermost part of the zone is relatively small1 and it is not surprising that time is necessary for the victory of this force over the kinetic energy of the water molecules4 ,hence we find a #e per cent4 jelly sets readily on cooling1 but its elasticity increases steadily for many hours after it has set4 ,this phenomenon1 known as hysteresis1 we should expect--and find--to be much more marked in a case where the zone of compression is unusually large 7e4g4 an agar gel74 ,we should also expect--and find--that hysteresis is more marked in a high-grade gelatine than in a low-grade gelatine where both eventually form gels of equal elasticity4 ,we should expect too--and we find--that hysteresis is more prominent in weak gels than in strong4 ,these points are of obvious importance in testing gelatine by its elasticity1 e4g4 the well-known finger test4 ,there are also other facts and considerations which have an important bearing upon the point under discussion4 ,it is necessary ultimately to regard true solutions of electrolytes and other bodies as heterogeneous1 though perhaps of a rather different order4 ,from this point of view molecules and ions existing in an aqueous solution will present a surface and have associated zones of compression analogous with those suggested for the minute particles of gelatine4 ,now recent investigations have shown that the essential physical properties of water are affected by dissolved substances in a definite manner and to a fixed extent1 and that these substances exhibit a sequence in order of their effect4 ,this sequence is also exhibited in the essential properties of water as solvent and as dispersion medium for colloid sols4 ,the sequence is known as the lyotrope series4 ,thus the numerical value of the compressibility of aqueous solutions is reduced below that of water by salts which1 with the same kation1 exhibit an effect in the following order3-- ,,co#c ,,so#d ,cl ,br ,,no#c ,i ,this same order is observed1 in the effect on the increased values for the surface tension1 density and viscosity of these solutions4 ,on the other hand1 the kations have a similar sequence of effects1 ,mg ,,nh#d ,li ,k ,na ,rb ,cs which appears when salts of the same anion are chosen4 ,it is not surprising to find that this lyotrope series exhibit an analogous influence on the chemical reactions of water1 e4g4 the hydrolysis of esters4 ,in the hydrolysis by acids ,,so#d retards the action1 the other anions and the kations accelerate it1 in the lyotrope order4 ,in the hydrolysis by bases the series is reversed4 ,similarly the lyotrope series exert the same order of effect upon the inversion of cane sugar and other reactions4 ,this lyotrope influence has also been shown to exert considerable effect in the behaviour of lyophile sols4 ,with the lyophobe sols the addition of foreign substances apparently affects the disperse phase only1 but with the lyophile sols the effect on the continuous phase is also important1 and may overshadow the other4 ,now1 in gelatine and in hide gels and tanning sols we are dealing with lyophile systems1 and there are many points of behaviour in which lyotrope influences become prominent4 ,similar effects are observed upon other lyophile sols 7e4g4 albumin1 agar-agar1 etc47 which differ widely in chemical nature4 ,thus the salting out of albumin 7reversible precipitation7 is influenced by sodium salts in lyotropic sequence as follows4 ,the anions hinder precipitation2 in order of precipitating power they are3 citrate tartrate ,,so#d acetate ,cl ,,no#c ,cl,o#c ,i ,,cns ,the sulphates illustrate the kation effect1 which is independent and which favours precipitation3 ,li ,k ,na ,,nh#d ,mg ,if the experiments be carried out in faintly acid solution this order of effect is exactly reversed1 iodide and thiocyanate having the greatest effect and citrates the least4 ,the coagulation temperature of albumin and the coagulation by other organic substances are similarly influenced by the lyotrope series4 ,lyotrope influence also exerts a powerful effect on the behaviour of gelatine sols and gels4 ,the gelation temperature is influenced thus3-- raised by ,,so#d citrate tartrate acetate lowered by ,cl ,cl,o#c ,,no#c ,br ,i ,the kation effect 7small7 is ,na ,k ,,nh#d ,mg ,other lyotrope substances raise or lower the temperature thus3-- glucose glycerol--7,h#b,o7--alcohol urea ,the effect on gelation is also illustrated by the change of viscosity of the sol with time4 ,the same lyotrope order is found4 ,in the salting out or precipitating of gelatine with salts1 the order of anions is lyotrope3 ,,so#d citrate tartrate acetate ,cl ,also the osmotic pressure of gelatine sols is markedly lowered by neutral electrolytes in lyotrope sequence3 ,cl ,,so#d ,,no#c ,br ,i ,,cns ,similarly lyotrope influences are shown in the modulus of elasticity3 substances which favour gelation increase elasticity1 whilst substances which favour solation decrease elasticity4 ,the order is again lyotrope4 ,the permeability of the gel is affected by lyotrope influences2 alcohol and glycerol reduce diffusion through gelatine 7or agar72 and urea1 chloride and iodide increase it4 7,similarly the diffusion of sols through semipermeable membranes is affected by lyotrope influence47 ,the lyotrope series also influence the optical activity of gelatine sols and the double refraction of strained gels4 ,the swelling of gelatine 7and other gels7 is very strongly influenced by the lyotrope substances and merits more attention than it has received4 ,hence this lyotrope influence exerts a profound effect in the manufacture of gelatin1 and perhaps even greater in the manufacture of leather4 ,this is only to be expected4 ,if a gel comprise a continuous network of compressed water1 as suggested above1 the presence of other substances in the gel which cause increases or decreases in the compression must modify accordingly the properties which depend upon this state of compression1 such as the viscosity of the melted gel1 the rate of gelation1 the elasticity of the gel1 and the rate and extent of its imbibition4 ,this indeed we find to be the case4 ,now the substances which affect the compressibility1 surface tension1 etc41 of water least1 i4e4 the substances producing little or no compression of water1 are just those which reduce the compression of water in a gelatine jelly1 and cause a decreased viscosity1 elasticity1 surface tension1 etc41 and which therefore naturally allow the gel to swell more than in pure water4 ,conversely1 the substances which cause the greatest compression of water1 the greatest increase in its surface tension and viscosity1 are also the substances which increase the compression1 viscosity1 elasticity1 and surface tension of gels1 and which therefore hinder imbibition4 ,the effect on swelling is as follows3-- ,sodium sulphate tartrate citrate acetate2 alcohol glucose cane sugar2 7water7 chlorides-potassium sodium ammonium2 sodium chlorate nitrate bromide iodide thiocyanate urea4 ,as the amount of compression will depend upon the amount of substance1 we expect--and find--that the effect is usually additive1 and that suitable mixtures of substances having an effect in the opposite sense will produce no change4 ,the interpretation of lyotrope influence is of course somewhat speculative1 but considered as a surface phenomenon1 the surface specific of the molecules and ions of the lyotrope substance must be one of the factors involved4 ,one naturally also connects the effect with solubility and the tendency to form hydrates in solution1 the zones of compression being zones of orientation and of electrochemical attraction4 ,the hydrate theory of solution again affords an instructive commentary4 ,the fact that1 broadly speaking1 the polyvalent anions and the monovalent anions also group themselves together1 suggests that electrical forces are at work1 and the order of effect of monovalent anions almost suggests that what are called residual valencies are in operation4 ,it is difficult to resist the conclusion that in the lyotrope influence1 in the crystallizing of salts1 and in the formation of a gel1 we have zones of compression and orientation which are manifestations of the same forces--surface and electrical2 the chief differences in the case of gelatine being that the zones are larger and that the electrical effect is perhaps of less definite magnitude4 ,however these things may be1 the fact of water compression determines the rigidity of the gel1 and the changes in this compression of the continuous phase determine the surface tension resultant which hinders swelling1 and which is one of the two main factors fixing both the rate at which gelatine swells in water1 and the final volume attained by the gel4 ,before leaving this point1 it is desirable to note the effect on the swelling of gelatine of the extremes of this lyotrope influence4 ,substances like iodides1 thiocyanates and urea prevent a gelatine sol from setting to a gel at all1 and a piece of gelatine in such solutions swells rapidly until it solates4 ,on the other hand1 sulphates1 tartrates1 etc41 make a stiffer gel on account of the enhanced compression4 ,gelatine in such solutions may swell1 but at a much slower rate than in water and with a decreased maximum extent4 ,a gelatine gel may in such solutions not only fail to swell at all1 but actually contract and in some cases1 indeed1 be practically dehydrated4 ,if a gel be in a very concentrated solution of such a substance1 it may be that the lyotrope compression in the external solution is greater than the compression in the dispersion medium of the gel2 in which case the surface tension effect is reversed1 and the external solution tends to increase in volume and the gel to contract4 ,hence we find that the saturated solutions of such substances as ammonium sulphate and potassium carbonate will dehydrate a gel almost completely1 and will also1 by a similar action on pelt1 make a kind of white leather4 ,it is important to remember this contractile effect of strong solutions of salts1 because it is very easy to confuse this effect with a similar result produced in another manner1 viz41 by a reduction of the force tending to swell4 #b4 ,,the ,,disperse ,,phase ,a very important feature of the colloid state is that the particles of the disperse phase appear to possess an electric charge1 and if this charge be removed a colloid sol no longer remains such1 but precipitates1 flocculates1 coagulates1 etc4 ,as to the origin of this charge several theories have been advanced1 but the most generally accepted is that it is a result of the adsorption of electrically charged ions by the particles of the disperse phase4 ,the enormous specific surface possessed by this phase renders it particularly liable to such adsorption4 ,this view harmonizes well also with the general behaviour1 of colloid sols and gels1 in endosmosis1 kataphoresis1 precipitation1 etc4 ,according to this point of view the particles of the disperse phase are surrounded by a surface layer in which these ions are in much greater concentration than in the volume concentration of the dispersion medium4 ,the hydrion and hydroxyl ion are particularly liable to such adsorption4 ,in the case of a lyophile colloid1 like gelatine1 the charge may be either positive or negative1 according to the nature of the predominant ions in the dispersion medium1 and the amount of adsorption is determined by the concentration of these ions in accordance with the adsorption law4 ,in effect1 therefore1 the particles of the disperse phase each carry an electric charge of the same nature1 and as similarly charged bodies repel one another1 the particles of the disperse phase will tend to separate and to occupy a bigger volume4 ,it is the author's opinion that this repulsion of similarly charged particles is the cause of the swelling of gelatine4 ,the amount of charge and force--tending to swell--is due possibly to several ionic adsorptions1 which may be considered to operate independently1 and the power of repulsion is determined by the nett charge1 which in the case of a positive colloid is positive1 and in the case of a negative colloid is negative4 ,as ions possess different electric charges1 the charge on the disperse phase is subject to the valency rule4 ,now the repulsive force between two similar and similarly charged bodies is proportional to the amount of charge and is inversely proportional to the square of the distance between them4 ,the amount of charge on a colloid particle will be determined by the dispersity--best signified by the specific surface 7s7--and by the operation of the adsorption law y mac7#a_/n7 ,the distance between the particles varies with the degree of swelling1 and is determined by the cube root of the volume of the gel 7v74 ,hence if ,f be the force tending to make the gelatine swell1 we may write ,f ,q_/7d#b7 7sy7_/v7#b_/c7 ,now with all electrolytes1 even with water1 we have both positively and negatively charged ions1 and y is consequently determined by the difference in the amounts adsorbed4 ,hence in the case of an electrolyte with an equal number of oppositely charged ions y ma#a;c7#a_/n#a7 - ma#b;c7#a_/n#b71 where a#a1 a#b1 and n#a1 n#b1 are the appropriate constants for the particular ions concerned4 ,hence at constant temperature1 pressure1 etc41 we may write ,f sm7 a#a;c7#a_/n#a7 - a#b;c7#a_/n#b7 7 _/ v7#b_/c7 ,the force tending to make a piece of gelatine swell is proportional to its mass1 which is perhaps fairly obvious4 ,the swelling force is also an inverse function of the volume of the gel1 and as swelling proceeds therefore the force tending to swell further decreases4 ,the force tending to swell is proportional to the specific surface of the disperse phase1 other factors being constant4 ,to illustrate this one has only to imagine that one particle of the disperse phase be split into two particles each carrying half the original charge4 ,it is clear that a new repulsive force becomes operative1 which did not before influence the swelling1 and that the distance between the particles is halved4 ,in the swelling of gelatine1 however1 we may consider the dispersity constant for constant temperature1 and if we consider unit mass we see that the force causing swelling depends upon the operation of the adsorption law and upon the degree to which the gel is already swollen4 ,in the swelling of 7say7 one gram of gelatine to its maximum1 both the contractile force of surface tension and the expanding force of electrical repulsion are in operation4 ,at the commencement the latter is much the greater force--hence the rapid imbibition4 ,both these forces decrease in magnitude as the swelling proceeds1 but the force tending to swell decreases at a more rapid rate1 and the time comes when it has decreased to the precise value of the force tending to resist swelling4 ,at this point equilibrium is established and the maximum swelling attained4 ,obviously this maximum will in many cases be determined largely by the value of a#a;c7#a_/n#a7 - a#b;c7#a_/n#b74 ,this factor1 therefore1 demands particular consideration4 ,now1 unfortunately1 the adsorption law constants for the different ions have not yet been numerically determined1 so that we are still somewhat in the dark as to the operation of ionic adsorptions4 ,it is possible1 however1 to form conclusions of a qualitative or relative order1 and these are such as to throw much light upon the question at issue4 ,in the first place1 we know that in general the various ions are not usually very widely different in the extent to which they are liable to be adsorbed4 ,if this were otherwise1 the valency rule would hardly operate so well in endosmosis1 kataphoresis1 and precipitation4 ,in consequence we must expect the differences between the ions to appear in small rather than in large concentrations1 the amounts adsorbed being under those conditions more affected by changes in the volume concentration4 ,at the larger concentrations1 therefore1 the value of a#a;c7#a_/n#a7 - a#b;c7#a_/n#b7 is small1 and the force causing swelling often tends to zero4 ,there are1 however1 noticeable differences at lower concentrations4 ,thus we know that if a substance be primarily a positive colloid1 it will absorb kations more readily than anions4 ,as gelatine falls into this class1 we may therefore conclude that usually a#a a#b4 ,further1 it often happens that very adsorbable substances are less affected by concentration changes1 and in the case under consideration1 therefore1 we should expect that n#a n#b4 ,moreover1 we know that the hydrion and hydroxyl ion are much more readily adsorbed than other ions1 i4e4 have a large value for a4 ,hence in the case of gelatine we expect that a#a;c7#a_/n#a7 - a#b;c7#a_/n#b7 will have a comparatively large value when one of the ions is ,h or ,,oh-4 ,also we know that organic anions are usually much more strongly adsorbed than inorganic anions1 and hence that in such cases a#a is more nearly approached by the value of a#b4 ,it should be emphasized perhaps1 at this point1 that these various considerations are not based upon any facts relating to the phenomena of imbibition in gels1 or in gelatine in particular1 but are based upon the behaviour of colloids in endosmosis1 kataphoresis1 electrolytic precipitation1 adsorption1 etc4 ,illustration3 ,,fig4 #a4 ,now if we select a few simple figures which are in accord with the above considerations1 we can examine the value of the factor a#a;c7#a_/n#a7 - a#b;c7#a_/n#b7 in a purely illustrative and typical way1 and at any rate form some idea as to the manner in which it is likely to vary4 ,the figures might be3-- ,ion4 n4 a4 ---------------------------------------- --- ,hydrion or hydroxylion #bj #aj ,kation of a metal #ae #g ,organic anion #aj #h ,inorganic anion #f #f ,for the sake of simplicity we can assume that these ions are all monovalent4 ,the ions adsorbed by unit mass will then be #aj;c7#a_/bj71 etc4 ,if these hypothetical adsorption isotherms be plotted as usual we get the fairly typical curves shown in ,fig4 #a4 ,now in practice there are always two of these ions1 each giving its own specific effect in opposite senses1 and the difference 7 a#a;c7#a_/n#a7 - a#b;c7#a_/n#b7 7 represents the nett charge adsorbed4 ,hence we have the following combinations3-- ,inorganic acid #aj;c7#a_/bj7 - #f;c7#a_/f7 ,organic acid #aj;c7#a_/bj7 - #h;c7#a_/aj7 ,alkali #aj;c7#a_/bj7 - #g;c7#a_/ae7 ,inorganic salt #g;c7#a_/ae7 - #f;c7#a_/f7 ,if we plot these values of nett adsorption against the concentration we obtain the curves shown in ,fig4 #b4 ,illustration3 ,,fig4 #b4 ,on the assumption that the nett charge adsorbed is the dominant factor in determining the maximum swelling at equilibrium1 one must therefore regard the curves of ,fig4 #b as representing the changes in volume of the swollen gel as the concentration is increased4 ,now in type these curves correspond to those obtained by experiment from hydrochloric acid1 acetic acid1 caustic soda1 and common salt4 ,the maximum swelling with hydrochloric acid increases rapidly with the concentration at first and then rapidly decreases1 though not at such a great rate4 ,the swelling with acetic acid increases less rapidly and to a less maximum1 but decreases more slowly4 ,with common salt there is a slight swelling followed by contraction4 ,caustic soda gives a rapid increase in volume at first1 afterwards much less so1 and finally yields an exceedingly slow decrease4 ,the correspondence of these facts with the type-curves inevitably suggests that the phenomenon of swelling might be accounted for1 in part at least1 along these lines4 ,of course it is not likely that the simple figures selected for the illustration of the argument are either relatively or absolutely correct4 ,thus we know that the adsorption curve for hydrions and hydroxylions are not likely to be quite identical1 as assumed above4 ,as gelatin is primarily slightly positive1 it is probable that the values of a and of n for hydrion adsorption will be relatively slightly greater4 ,the relative values supposed1 however1 are near enough to illustrate the contention that the type of the maximum volume curve can be explained on this assumption of different adsorption isotherms for each of the ions4 ,if the remarks on the compression of the continuous phase be recalled1 it will be obvious that in the present paragraphs we have been giving the question of equilibrium-volume a rather one-sided consideration4 ,the volume of the gel when equilibrium is established may be determined in type by the nett charge adsorbed by the disperse phase1 but it will be modified also by the lyotrope influence of the particular substance on the continuous phase4 ,when gelatine swells in solutions the influences on both phases are always in operation1 and either upon occasion may become predominant4 ,in the case of neutral organic substances1 such as cane-sugar1 the lyotrope influence is the determining factor4 ,in the case of neutral salts the predominant influence is decided by the place occupied by the salts in the lyotrope series4 ,if at either end of the series the lyotrope influence is uppermost and the effect of ionic adsorptions is practically swamped4 ,thus sodium sulphate and sodium iodide hinder and promote imbibition respectively as could be expected from their strong lyotrope power4 ,on the other hand1 in the case of sodium chloride1 which has comparatively feeble lyotrope influence1 the relatively different adsorptions of its ions comes to the fore4 ,with acids and alkalies the relatively large adsorption of the hydrion and hydroxylion causes this to be the predominant influence1 but we must concede the possibility that purely lyotrope influences may be at work in some cases1 and especially at the greater concentrations4 ,indeed1 it is sometimes a difficult problem to decide whether an increase or decrease in swelling is due to lyotrope or adsorptive influence1 but1 broadly speaking1 we can expect strong lyotrope effects at either end of the series and also at large concentrations1 and we can expect strong adsorptive effects in dilute solutions1 in the middle of the lyotrope series and in the case of alkalies and acids4 ,for much of the above explanation of the nature and behaviour of gelatine1 the author must himself take responsibility1 and in this section he has freely quoted from his own papers upon the subject 7see ,references74 ,he claims that his view of a gelatine gel as involving a network of compressed water1 liable to modification by lyotrope influence upon the continuous phase and by ionic adsorptions of the disperse phase1 is most in harmony with the recent advances in our knowledge of colloids2 that much of the theory is a necessary corollary of those discoveries2 and also that he has found this view to be a sound guide in practice1 both in tanning and in gelatine manufacture4 ,many other theories have been advanced1 but most are generalizations over too limited a field1 and from experiments with only a few substances1 and show little or no correlation with the wider facts of colloid behaviour4 ,that of ,procter1 for example1 discards altogether the idea of a two-phased structure of the gel as an unproved and rather gratuitous assumption1 dismisses surface tension considerations as more complicated and less verified1 and adsorption as wholly empirical1 whilst it ignores lyotrope influence and the analogy with agar gels completely4 ,procter's theory applies mainly to the swelling of gelatine by acids1 which swelling he considers to be due to the osmotic pressure of the anion of a highly ionizable salt formed by the chemical combination of the acid with gelatine4 ,on this assumption1 mathematical considerations show that the electric charge on the gelatine is given by the expression z sqrt7#d;ex e#b71 where z the amount of ion taken up1 x the concentration of the surrounding solution1 and e the excess concentration of diffusible ions in the jelly4 ,the property of gelatine and glue which is chiefly used in classifying them into grades of different commercial value1 is the strength of the jelly obtained as compared with any arbitrary standard gelatine4 ,an enormous number of other physical tests have been devised1 but none are nearly so simple or so reliable4 ,gelatine is unfortunately very liable to hydrolysis even by water1 and long before any amido-acids1 etc41 have appeared there is a change to a not greatly hydrolyzed product 7sometimes called beta gelatine7 which has lost the power of setting to an elastic gel4 ,it is thus the lyophile nature which has been altered1 and the fall in elasticity corresponds to the fall in power of compressing water1 which is proportional to the concentration of alpha gelatine4 ,now the elasticity of a gelatine gel varies as the square of the concentration4 ,hence if one so arranges the concentrations of standard and unknown samples that gels of equal elasticity are obtained1 the concentration of alpha gelatine is the same in both gels1 and the relative amounts of alpha gelatine in the original samples are inversely proportional to the weights used to give gels of equal elasticity4 ,the strength of a gelatine or glue is therefore usually stated as the number of grams of a standard gelatine which will yield a gel with elasticity equal to that from #ajj grams of the gelatine or glue being tested4 ,elasticity is matched by lightly pressing with the finger-tips4 ,it is also possible to grade samples of gelatine and glue by the estimation of peptones1 whose amount indicates the degree of hydrolysis4 ,nitrogen is estimated by ,kjeldahl's method in the sample and in the precipitate obtained by saturating a solution with zinc sulphate4 ,the difference is calculated as peptones by multiplying by #e4cc4 ,trotman and ,hackford say that the results are in the same sequence as those of the finger test4 ,the method1 however1 is much more laborious than the finger test4 ,gelatine is also graded according to the results of bleaching and clarifying1 but with quite arbitrary standards1 largely determined by the fancy of the customer4 ,chemical analyses1 involving estimations of ash1 lime1 fat1 acid1 water1 insoluble matter1 and poisonous metals1 e4g4 arsenic1 copper1 zinc and lead1 are of value for special cases according to the destiny of the goods4 ,special physical tests1 such as breaking strain and foam test1 are also of some little value in special cases4 ,,references4 ,the ,chemistry of ,colloids1 ,w4 ,w4 ,taylor4 #aiae4 ,handbook of ,colloid ,chemistry1 ,w4 ,ostwald4 #aiai4 ,chemistry of ,colloids1 ,zsigmondy and ,spear4 #aiah4 ,introduction to the ,chemistry and ,physics of ,colloids1 ,e4 ,hatschek4 ,surface ,tension and ,surface ,energy1 ,willows and ,hatschek4 ,chemistry of ,colloids1 ,v4 ,pschl4 ,grundzge d4 ,dispersoid ,chemie1 von ,weimarn4 ,the ,lyotrope ,series and the ,theory of ,tanning1 ,bennett1 ,j4,s4,l4,t4,c41 #aiag1 p4 #acj4 ,the ,swelling of ,gelatine1 ,bennett1 ,j4,s4,l4,t4,c1 #aiah1 p4 #dj4 ,the ,swelling of ,gelatine1 ,procter1 ,j4,c4,s4 ,trans41 #aiad1 #aje1 #cac2 and ,koll4 ,chem4 ,beihefts1 #aiaa1 #b1 #bcd4 ,the ,swelling of ,gelatinous ,tissues1 ,procter1 ,j4,s4,c4,i41 ,april #af1 #aiaf4 ,summary of ,procter's ,views1 and ,bibliography1 ,collegium 7,london71 p4 #c1 #aiag4 ,lyotrope ,influence and ,adsorption in the theory of wet work1 ,bennett1 ,j4,s4,t4,c41 #aibj1 p4 #ge4 ,for the finger test1 see-- ,glue and ,glue ,testing1 ,rideal1 #bnd ed41 p4 #aeh4 ,leather ,trades' ,chemistry1 ,trotman1 p4 #bda4 ,,section ,,ii4--,,raw ,,materials ,,and ,,preliminary ,,treatment ,the raw materials for the manufacture of gelatine and glue may be classified according to their origin4 ,the preliminary treatment1 which comprises chiefly purifying and cleansing operations1 is varied according to type of manufacturing process for which it is a preparation4 ,in the case of hide or skin gelatine1 the raw material is a bye-product of the leather industry4 ,after the hides or skins have passed through the preparatory processes which convert them into pelt 7see ,part ,i41 ,section ,,ii471 they are so trimmed that all that is left will make a useful leather4 ,these trimmings or roundings include ears and noses1 the udders of cows and heifers1 and also include parts from the butt1 belly and shanks which are collectively termed pieces4 ,the operation of fleshing 7,part ,i41 ,section ,,ii471 in which fat and flesh are cut from that side of the hides and skins which was next the flesh1 also involves cutting into the collagen to some extent1 and these fleshings comprise another very large class of raw material4 ,the fleshings obtained by hand labour contain distinctly more hide substances than those obtained by machine work1 and their commercial value to the gelatine manufacturer is of course proportionate to the collagen content4 ,some hides and skins are split in the pelt 7,part ,i41 ,section ,,ix42 ,part ,,ii41 ,sections ,,ii41 ,,iii4 and ,,iv471 and the flesh split1 though sometimes made into leather1 is also used in making gelatine1 a high quality being obtained from such material4 ,minor sources of material are tendons and cartilages1 and also hides and skins which have been too much damaged by partial putrefaction or by accidents to make sound leather4 ,of course the material from the hides for heavy leathers form the greater bulk of raw material for skin gelatine which is thus derived principally from ox hides but sheep and goat skin pieces have also an important place4 ,the skins of other animals1 such as dogs1 cats1 hares and rabbits not usually made into leather can also be depilated and used for making skin gelatine and glue4 ,horse hide fleshings and pieces are sometimes used1 but are notorious for the poor quality of their product4 ,they seem to contain less alpha gelatin4 ,all these materials are of course readily putrescible and must be put into work without much loss of time4 ,when it is impossible to convey them from the tannery to the gelatine factory quickly enough1 e4g4 foreign material1 the glue stock is dried out completely and sold in that condition4 ,in the manufacture of pickers from limed pelt there is some superfluous material1 and this is cut into shavings and dried4 ,this picker waste also forms a useful source of raw material4 ,skin gelatine material is not very strong in gelatine-substance4 ,the fleshings1 pieces1 etc41 contain much water1 even up to #hj per cent4 ,this1 however1 is very variable1 and only a practical test or a hide substance determination can indicate the commercial value of any particular material4 ,this value1 moreover1 is determined not only by the yield and quality of the gelatine which can be obtained1 but also by the yield of grease1 the valuable bye-product4 ,the preliminary treatment of material for skin gelatine consists essentially of liming and of washing4 ,the object of each process is to purify4 ,liming has much the same action on hide pieces1 etc41 as on hides1 and indeed the liming treatment is somewhat superfluous on cuttings from well-limed hides4 ,the material is plumped up and the partially hydrolyzed products are taken into solution4 ,lime also acts as mild antiseptic1 stops any putrefaction and liberates ammonia formed by fermentation in transit to the factory4 ,when plumping is particularly wanted 7as in wetting in dry stock7 caustic soda is sometimes used as an assistant 7cf4 dried hides74 ,sodium sulphide has also been used for this purpose4 ,the liming is in brick pits1 an excess of undissolved lime being always used4 ,it is advantageous frequently to disturb or agitate the goods in the lime pits4 ,up to ten weeks liming has sometimes been given1 but about three weeks is now generally considered sufficient1 and the tendency is to shorten the time4 ,the lime and soda have also a detergent action on soiled stock1 and they probably assist in hydrolyzing the pigments of the hair roots and sheaths4 ,they also saponify and emulsify the grease1 and it is obvious1 therefore1 that liming can be carried too far4 ,slaked lime1 of course1 must always be used4 ,after liming the soaked1 softened and plumped stock is washed as thoroughly as possible4 ,to do this it is necessary to supply repeated batches of clean cold water4 ,some manufacturers1 however1 use the warm water from the evaporators4 ,wooden vats or brick pits with arrangements for agitation1 for draining off and for inspection1 are used for this purpose4 ,the agitation may be carried out by means of revolving shafts or drums with projecting curved spokes or vanes4 ,an ,american patent 7,hoeveler's glue stock washer7 involves the use of a paddle wheel4 ,it is combined with a settling tank to gather particles of stock4 ,in the washing the chalk1 excess lime1 dirt1 etc41 are quickly removed and a slow deliming process is commenced4 ,the sediment from the washers and wash waters has some value in making fertilizers4 ,deliming cannot be carried on further than certain limits by water alone4 ,hence acid is often added to finish off the process4 ,hydrochloric acid has the advantage of forming soluble salts1 but if they are not removed completely their lyotrope influence is to weaken the gelatine4 ,sulphuric and sulphurous acids are even cheaper1 and the lyotrope influence of their salts is in the opposite sense4 ,the latter also has the advantage of destroying sulphides1 an important advantage for food gelatines4 ,whatever acid is used1 however1 it is evident that an abundance of pure cold water is the fundamental requirement of a pure product4 ,it is a sound maxim in gelatine manufacture to avoid1 if at all possible1 the addition of any soluble substance1 for it is always present in a more concentrated state in the finished article4 ,thus if its solubility be even moderate1 one is likely to attain supersaturation in the cake and consequently a dull product4 ,further1 lyotrope influences can never strengthen a gel very much1 but may and often do weaken it very considerably4 ,hence the aim of most manufacturers in the preliminary treatment is so to delime that a nearly neutral and salt-free product is obtained4 ,an exception is the case of skin gelatine in which excess of sulphurous acid is used4 ,this process has for its object not only deliming and purifying1 but also a bleaching action4 ,in the case of bone gelatine1 the raw material is such that there are much longer and more elaborate preparatory processes4 ,this arises from the fact that about half the bones of animals consists of mineral matter1 chiefly calcium phosphate4 ,bones1 of course1 vary in composition to some extent1 and those from younger animals contain distinctly less of the mineral constituents4 ,approximately speaking1 bones have the following average composition3-- ,gelatinous matter #ba-a_/b per cent4 ,fat #ab-a_/b ,calcium phosphate #dh ,calcium carbonate #c ,alkali salts1 silica1 etc4 #b-a_/b ,water #ab-a_/b -------- #ajj ,it will be seen1 therefore1 that the manufacture of bone gelatine and of a comparatively large proportion of phosphate involves the recovery and purification of much fatty matter4 ,the manufacturing processes are naturally subject to considerable variation4 ,one respect in which they differ is the stage in which grease is removed4 ,sometimes this is simply done as the need and occasion arise1 and it is skimmed out in the acid or water extractions1 but it is now more usual to have a special degreasing process4 ,there are1 moreover1 two quite distinct types of manufacture4 ,in one of these 7the boiling process7 the routine bears some resemblance to that for skin gelatine4 ,in this process the bones are washed and cleansed and then immediately subjected to extraction with water4 ,this removes the gelatinous matter and leaves the phosphate and earthy matters behind4 ,grease may be removed before the water extraction1 but is also sometimes removed by skimming off during the extraction1 as is usual in the case of skin gelatine4 ,this procedure is now not much favoured unless only a low-grade glue is required4 ,in the other type of manufacture 7the acid process7 the material is first degreased1 and then the mineral matter is extracted or dissolved by acids1 leaving the gelatinous matter behind for subsequent refinement and solution4 ,the acid process has long been preferred for high-class bone gelatine1 and hence needs further discussion4 ,the degreasing operation was once brought about by steaming only1 but is now accomplished with the assistance of fat solvents4 ,the object of cleansing is not only to remove dirt1 but also fleshy matter which often adheres to the bones4 ,this may contain a little gelatine1 but consists mainly of other proteins and insoluble fibre1 neither of which are wanted in the water extraction4 ,the mill consists of a large cylinder of stout wire gauze4 ,this revolves round the axis of the cylinder1 and the bones are fed in at one end by a hopper and are discharged at the other4 ,the revolution of the mill causes the friction which polishes off the fleshy matter4 ,the dirt and flesh fall through the gauze and are sent to the fertilizer factory4 ,the polishings are sometimes further separated by a similar machine4 ,raw bones may thus yield nearly #fj per cent4 of degreased bones1 and about #ef per cent4 cleansed bones ready for extraction1 and #c or #d per cent4 bone meal4 ,the next stage is the extraction of the mineral matters by acid1 for which purpose hydrochloric acid has proved very suitable1 as both phosphate and carbonate of lime are dissolved by it4 ,the usual counter-current system of extraction is used cp4 ,leaching and extract manufacture1 ,part ,i41 ,section ,,iii41 p4 #ce4 ,the process is methodical and regular1 the acid liquor passing successively through a battery of six vats in such a manner that the liquor richest in lime salts comes into contact with the bones most recently charged2 the fresh acid thus acts upon the nearly extracted bones4 ,the hydrochloric acid used is of #h to #aj per cent4 strength 7#e to #g ,b474 ,stronger acid is apt to hydrolyze 7rot7 the gelatine1 whilst weaker acid takes longer time4 ,the process takes #h to #aj days1 though up to #ad days is sometimes given1 and1 on the other hand1 the process has been occasionally reduced to #d days4 ,the gelatinous matter undissolved has the shape of the original bone1 but is much swollen4 ,when the acid liquor is saturated with lime salt1 the liquor is drawn off from below the vats and sent to the phosphate precipitation tanks4 ,the phosphate is usually precipitated by adding just sufficient milk of lime to neutralize the hydrochloric acid4 ,the precipitated phosphate is then well washed by decantation to remove calcium chloride4 ,it is then drained1 and dried at a low temperature4 ,as a large bulk of phosphate is obtained it is often filter-pressed and dried quickly in long revolving chambers through which a current of air is passed4 ,the phosphate is sometimes also precipitated by ammonia4 ,it is then more easily washed and dried1 and the ammonium chloride is recovered and may be used to regenerate ammonia1 or be sold as a valuable bye-product4 ,sometimes the acid liquor is not used for making precipitated phosphate1 but is evaporated with animal charcoal and silica and then distilled to make phosphorus4 ,the next stage is the purification by washing of the gelatinous matter which remains4 ,the vat is filled up with pure cold water and the material allowed to steep for six or seven hours4 ,the acid and salts remaining diffuse outwards into the water4 ,this is drained off and replaced by fresh water1 and the procedure repeated half a dozen times or as often as necessary4 ,the end is said to be determined by the absence of a precipitate on adding silver nitrate to the wash water1 or by the absence of any action on blue litmus paper4 ,it will be seen1 however1 that there are two actions involved1 one being the removal of calcium chloride and the other the removal of excess acid4 ,the former is the easier1 and is almost necessarily brought about by the latter4 ,hence in some factories the neutralization is brought about1 therefore1 by the addition of a certain quantity of soda1 or more usually by lime1 and the material is sometimes submitted to a veritable liming by which it remains in milk of lime for about three weeks1 the lime liquor being renewed several times4 ,the product is finally washed again to remove excess lime4 ,this is carried out in a rotating vessel through which passes a continuous stream of water4 ,if a slightly acid gelatine is required1 however1 the lime and liming are both superfluous1 and the procedure is simply to wash as thoroughly as possible and then to immerse the material in a #a per cent4 sulphurous acid solution for #c hours to bleach1 and then to proceed with the water extraction or solution of the gelatine4 ,the hydrochloric acid used for these processes should be as pure as possible1 and the degreasing as thorough as possible1 for1 if not1 a gelatine with a bad odour is liable to be obtained4 ,instead of using hydrochloric acid for the solution of mineral matter1 sulphurous acid is sometimes employed1 and has the advantages that its bleaching effect is thereby obtained throughout the process1 and that it is recoverable for subsequent use4 ,the ,bergmann process1 most generally favoured1 is described very concisely by ,rideal thus3 ,a sulphurous acid solution is made to circulate over the bones in a series of closed tanks1 the solution being continually enriched with sulphurous acid from a cylinder of the liquefied gas4 ,the resulting liquor1 containing an acid calcium phosphate and calcium bisulphite1 is heated by steam in a leaden digestor1 when the excess of sulphurous acid is liberated and passes back to the tanks1 while neutral calcium phosphate and sulphite are precipitated4 ,the latter is decomposed by an equivalent of hydrochloric acid1 setting free the remaining sulphurous acid1 which is returned to the tanks1 leaving calcium chloride in solution1 and neutral calcium phosphate in suspension4 ,not more than #e per cent4 of sulphurous acid is said to be lost in this process1 and the gelatine is more thoroughly bleached4 ,it is subsequently well washed before extraction4 ,recovery and ,purification of ,grease4--,the degreasing operation1 which is applied usually to bones and to skin glue scutch1 was once brought about by steaming only1 but is now accomplished with the assistance of fat solvents1 though in the latter case steaming together with mechanical centrifugal force has proved sufficiently successful4 ,on the ,continent carbon disulphide was once largely used as solvent1 and in this country benzene has been employed1 but their low volatility and high inflammability1 as well as their expense1 make both these substances somewhat unsuitable1 and it is now usual to make use of petroleum oils1 whether ,scotch1 ,american or ,russian4 ,a fraction which boils about the same temperature as water is usually employed1 and all of it must be volatile under #bhj ,f4 ,before the actual grease extraction the bones should be sorted over and unsuitable substances 7horns1 gravel1 iron1 etc47 removed4 ,they are also usually put through a mill and roughly crushed or broken4 ,the actual grease extraction plant consists of large copper vessels which will each take #e tons of bones4 ,these extractors are arranged in sets so that the degreasing is proceeding in some whilst the others are being emptied and recharged4 ,the doors for charging and emptying must be securely fastened4 ,when the extractor is charged the solvent is run in and heated by a steam coil which eventually causes it to distil4 ,after some hours the remainder1 which has dissolved much grease1 is run off1 and a fresh lot of solvent is added and heated up4 ,after four such extractions only about #a_/d per cent4 of grease remains in the bones4 ,to remove the remainder of the solvent high-pressure steam 7#hj lbs47 is blown through the bones4 ,the extractor is then opened and the degreased and somewhat dried bones are mechanically conveyed to the cleansing mill4 ,the grease solutions obtained are subjected again to steam with a view to removing the solvent and obtaining it for repeated use in this sense4 ,the efficient distillation and recovery of the solvent is indeed an essential element in the success of the process4 ,the greases obtained1 whether by the use of fat solvents or by skimming off during extraction1 or in any other way1 are mixed together as is appropriate to their origin and purity1 and subjected to further purification1 the object of which is to remove gelatinous and albuminous matters1 and to decompose lime or soda soaps4 ,the precise methods of purification are1 of course1 dependent mainly upon the impurities known to be present1 but the readiest method is to give the grease further steaming or boiling with water1 and so effect by washing and by solvent action the elimination of non-fatty matters4 ,in many cases it is found advantageous to employ mineral acids or oxidizing agents to assist the process4 ,the process may be repeated as often as is desired4 ,the recovered and purified greases are often of a high standard of purity1 and the best are quite fit for edible purposes4 ,the large extension of the margarine industry in this country has indeed caused a larger proportion than ever of this bye-product to be so used4 ,in some cases it is found commercially advantageous to submit the grease to action of the filter press1 and so to separate it into solid and liquid portions1 the former containing a much larger proportion of stearin1 and the latter of olein4 ,much of the grease from the gelatine trade is also found suitable for soap manufacture1 and is therefore a valuable source of glycerine4 ,other ,raw ,materials4--,whilst hide pieces and fleshings1 and animal bones1 comprise the principal raw material for the manufacture of gelatine and glue1 there are also minor sources of raw material which1 though often not suitable for gelatine manufacture1 will yield a satisfactory glue4 ,thus the skins1 bladders and bones of fish form the source of fish glue4 ,sole skins1 indeed1 when deodorized by chlorine and decolorized by animal charcoal1 are made into gelatine4 ,the bladders of some fish 7e4g4 the sturgeon7 are washed1 purified and dried with rolling to make isinglass1 a form of natural gelatine in which the original fibrous structure is retained4 ,there is a limited demand for this material for clarifying purposes by brewers1 wine merchants and cooks4 ,leather waste may sometimes be used to make a low-grade glue4 ,vegetable-tanned leather offers much difficulty unless very lightly and recently tanned4 ,the tannage must be stripped by drumming with weak alkalies1 e4g4 borax1 sodium sulphite1 or weak soda4 ,chrome leather may be stripped easily and completely by ,rochelle salt and other salts of hydroxy acids 7,procter and ,wilson71 and also by ammonia acetate1 oxalate and similar salts 7,bennett71 also by certain organic acids 7,lamb74 ,processes are patented by which chrome leather is digested with lime to make glue1 the chromium hydrate being insolubilized4 ,viscous and tenacious substances are also obtained from some vegetable matters and are called glue4 ,,references4 ,glue and ,glue ,testing1 ,s4 ,rideal1 ,d4,sc41 #bnd ed42 ,skin ,gelatine and ,glue1 pp4 #be-dh2 ,bone ,gelatine and ,glue1 pp4 #ei-ff4 ,gelatine1 ,glue and their ,allied ,products1 ,t4 ,lambert1 pp4 #aa-eb4 ,encyclopedie chimique1 ,fremy1 tome x4 ,,section ,,iii4--,,extraction ,the term extraction is applied to that essential process by which the gelatinous matter from whatever raw material is used1 is actually dissolved in water and removed from the rest of the material4 ,extraction is often termed boiling or cooking4 ,whether one is treating hide fleshings and pieces or whether one is dealing with raw or acidulated bones1 the general principles of extraction are much the same1 and most of this section is equally applicable to any class of material4 ,the chief principle of extraction is so to arrange the process that both the material and the extracted liquor are maintained at high temperatures for the shortest possible time4 ,as we have observed1 gelatine is readily hydrolyzed by hot water1 and as hot water is needed for its extraction or solution1 care must be taken to remove the solution as soon as possible from the source of heat4 ,in practice this can only be done somewhat imperfectly1 as it is necessary to obtain a gelatine sol of several per cent4 strength before removing it from the extraction vessel4 ,the stronger this sol is made before removal1 the less the time1 trouble and expense is incurred in evaporation subsequently1 but the more is the exposure to heat with consequent weakening of the gelatine4 ,hence in practice it is necessary to compromise4 ,the matter is complicated further by the necessity of obtaining a clear sol1 for which it is desirable that the sol obtained in extraction should not be too concentrated1 as impurities settle and filter much more readily from weaker and less viscous sols4 ,it will be understood1 therefore1 that whatever material is being extracted1 the most favoured procedure is to extract in fractions4 ,the first fraction1 which is least exposed to hydrolytic decomposition1 produces the highest quality products1 and the subsequent fractions 7nearly always two more1 and sometimes several7 yield products which gradually become of inferior quality owing to the number of times the raw material has been re-heated4 ,within limits1 the precise temperature of extraction does not have the importance one would expect4 ,lambert suggests the temperature of #ahe ,f4 as suitable for both skin and bone gelatine1 and most manufacturers would1 on the whole1 endorse this4 ,if1 however1 a higher temperature be preferred1 the hydrolytic action is increased in intensity but decreased in its time of operation1 whilst if a lower temperature be adopted the decomposition is retarded in speed1 but is increased in totality because of the longer time needed to obtain a suitable strength of liquor4 ,thus1 with care1 much the same result is obtained by extraction at near boiling-point for a short time as by extraction at #afj ,f4 for a long time4 ,the higher temperatures have the definite advantage of speed1 whilst the lower temperatures have the advantage that one may choose to be satisfied with a weaker extract1 and so gain a little in the strength of the gel1 by throwing more work on the evaporator4 ,one other point should1 however1 be borne in mind in this connection1 viz4 that a gelatine sol kept at temperatures above #ahe ,f4 begins to deteriorate in colour4 ,whilst1 therefore1 much depends upon the precise class of material1 it is broadly true to say that the higher temperatures are advantageous for glue1 whilst the lower temperatures are preferable for the highest quality gelatine4 ,extraction in open vats is used both for skin and bone gelatine4 ,it is usually preferred when it is intended to extract at the lower temperatures1 and it is usually adopted also when the material is such that the extraction is comparatively rapid1 as for example in the case of skin gelatine and bones by the acid process4 ,the vats themselves are often constructed of wood1 in which case they are heated by a copper 7or brass7 steam coil4 ,they may be constructed also of iron1 cast or wrought1 the former being cheaper1 less liable to corrosion1 but more liable to fracture4 ,in the case of iron vessels the heating may also be done by a steam coil beneath a false bottom1 but it is sometimes arranged that iron vats are heated by a steam jacket1 and even by a hot-water jacket4 ,heating in either wood or iron vessels has been brought about by direct application of raw steam1 but the results are both uncertain and unsatisfactory owing to local overheating4 ,whatever appliances are used agitation of the material or liquor is advantageous4 ,extraction in closed vats is also used4 ,this is generally associated with extraction at higher temperatures1 and more often also with the manufacture of glue than of gelatine4 ,it has been used on the ,continent for skin glue1 and in this country for bone gelatine and glue by the boiling process4 ,in this system of working the vessels are usually made of #c_/h-;inch steel plates1 and will take a charge of #c to #e tons of material4 ,it is claimed for the system that there is a lessened steam consumption as well as lesser manipulation1 that strong liquors are more easily and quickly obtained1 and that the material may be more thoroughly exhausted4 ,extraction is sometimes made by steam and water playing alternately on the material1 but many manufacturers prefer the use of direct steam1 keeping the pressure at #ae lbs4 for about #b hours4 ,the pressure is then reduced considerably and the process finished off by spraying the material with water4 ,from such a procedure a #bj per cent4 glue sol may be obtained4 ,it is common to work such extractors in couples or in batteries of four to six4 ,it will be readily understood that the process is suitable for making bone glue when the phosphate has not been dissolved4 ,the high temperature is in this case almost necessary to ensure thorough extraction4 ,it will be equally clear that the process is not so suitable in the manufacture of a strong gel4 ,as alternatives to the systems of fractional extraction1 several processes have been devised in which the extraction is continuous4 ,amongst these is the tower system1 in which the material is placed upon a series of perforated shelves arranged inside a steam-tight cylinder or tower4 ,water is admitted from the top and trickles down over the material whilst steam is admitted from the bottom4 ,superheated steam is sometimes used4 ,the material may thus be digested with a minimum amount of water1 and the sol passes out of the apparatus and from the action of heat soon after it is formed4 ,from bones the sol obtained is of good colour1 but is somewhat dull4 ,several variants of this process have been patented4 ,another continuous system of extraction is that involving the use of the ,archimedean screw4 ,the material is fed into one end of a cylinder carried along and discharged at the other end by the screw4 ,the cylinder is of metal gauze and is steam jacketed4 7,lehmann's patent1 #aiab47 ,continuous systems1 involving a battery of digestors connected by pipes1 have also been devised4 ,arrangements are made of course for admitting water and steam as required4 ,,references4 ,glue and ,glue ,testing1 by ,s4 ,rideal1 ,d4,sc41 #bnd ed41 pp4 #dg-ef and #fa4 ,gelatine1 ,glue and their ,allied ,products1 by ,t4 ,lambert1 pp4 #ba-bd1 #dj1 #db-dd1 #di and #ea4 ,encyclopedie chimique1 ,fremy1 tome x41 p4 #hc4 ,,patents4 ,edison3 ,u4,s4,a4 patent1 #aijb1 #gjcbjd4 ,bertram3 ,english patent1 #ahib1 #iea4 ,dorenburg3 ,german patent1 #aiaa1 #bcifgf4 ,lehmann3 ,french patent1 #aiab1 #ddaedh4 ,,section ,,iv4--,,clarification ,,and ,,decolorization ,after the raw material has been appropriately prepared and an aqueous extract or gelatine sol obtained therefrom1 there are certain refinements necessary before the weak sol is evaporated4 ,these purifying processes include 7#a7 clarification1 7#b7 decolorization1 and 7#c7 bleaching4 ,whilst most manufacturers have more or less successfully solved the problems involved in these processes1 the practical methods that are in common use have been evolved and elaborated in a purely empirical way1 and the underlying principles have been very imperfectly recognized1 and indeed often confused and misunderstood4 ,hence it is even yet not uncommon to find these terms rather loosely used1 and it is one aim of this section to define and distinguish these various operations in principle as well as in practice4 ,clarification consists essentially in the removal of suspended matters1 with the consequent production of a sol or gel which is bright1 clear1 and apparently homogeneous4 ,bleaching consists essentially in destroying the colouring matters of the sol by chemical action1 such as oxidation or reduction4 ,decolorization involves the removal rather than the destruction of colouring matters1 and does not therefore imply a chemical action in the ordinary sense4 ,clarification may be now considered more particularly4 ,it is necessary in this connection to consider what is meant by suspended matter4 ,the modern view is that the difference between a true solution and a muddy liquor or an emulsion is one chiefly of degree4 ,if the particles of matter in suspension or emulsion 7the disperse phase7 be reduced in size they eventually merge into colloidal sols which are sometimes analogously named suspensoids and emulsoids1 if further reduced in size into suspensides and emulsides1 and with further reduction into true solutions4 ,on this view not only suspensions and emulsions1 but also sols1 solutides and solutions are all heterogeneous4 ,now in practice the clarifying of a gelatine sol involves only the removal of the particles which are evident to sight4 ,what is needed is that the product should make a sol or gel which to the naked eye appears to be optically clear both to reflected and to transmitted light4 ,if desired1 the limit could be expressed in terms of dispersity or specific surface4 ,now it is a comparatively easy matter to remove the coarser substances which often pass into the sol1 e4g4 undissolved portions of raw material or the insoluble portions1 such as the hair1 the grain 7hyaline layer71 and the elastic fibres of skin gelatine material1 and the fibres which even remain in extracting acidulated bones4 ,a more difficult proposition is the removal of still finer particles which may be almost said to be in colloidal solution1 but which at any rate are so large that they cause a visible opalescence or even a turbidity of the gelatine sol4 ,a more difficult task also is the removal of minute particles of grease1 which are an exceedingly common cause of turbidity and which are often very effectively emulsified in the sol4 ,now at this stage it is necessary to point out that besides the difference in the size of the particles of the disperse phase1 there is another important difference involved1 viz4 that the particles of a colloid sol carry an electric charge owing to the adsorption of electrically charged ions of the electrolytes 7salts1 acids or alkalies7 present4 ,if this charge be removed the colloid is precipitated 7coagulated1 flocculated7 and is then filtered off with comparative ease4 ,this precipitation can be brought about by a reduction or elimination of the potential difference between the disperse phase and the continuous phase4 ,the electric charge given by the adsorbed ions may be reduced by dilution1 for dilution causes a lessened adsorption of the charging ions4 ,hence the well-known practical fact that it is more satisfactory to filter a dilute gelatine sol4 ,further1 the electric charge may be reduced also by causing the adsorption of an ion of opposite charge4 ,this is the principle underlying the precipitation 7of any colloid7 by adding electrolytes4 ,it is essential here to consider which ions are most likely to be adsorbed1 and also to bear in mind what charge they carry4 ,now the hydrion 7,h7 of acids and the hydroxyl ion 7,,oh-7 of alkalies are most strongly adsorbed1 so that to precipitate a negative sol1 acid is very effective1 whilst with a positive sol an alkali is an appropriate precipitant4 ,further1 it is known that organic ions are usually more strongly adsorbed1 hence when precipitating from an alkaline sol 7negative sol71 one should preferably select an inorganic or mineral acid rather than an organic acid4 ,thus in clarifying an alkaline gelatine sol1 hydrochloric or sulphuric acid is to be preferred to acetic or lactic acid4 ,again1 it is necessary to remember that a divalent ion carries twice the charge of a univalent ion1 hence the precipitating power of an electrolyte depends upon the valency of the ion whose electric charge is opposite to that on the sol 7,hardy's valency rule74 ,thus a negative sol is most easily precipitated by a monobasic acid4 ,thus hydrochloric acid is better than sulphuric1 on account of the stabilizing effect of the divalent ,,so#d-- ion on a negative sol4 ,in such a sol1 also1 the valency rule indicates that the multivalent kations1 e4g4 iron1 ,fe2 chromium1 ,cr2 and aluminium1 ,al1 should have great precipitating and clarifying effect4 ,this of course is known to be the case1 aluminium salts having long been used4 ,the rule indicates1 also1 that aluminium chloride would be better than the sulphate or than potash alum4 ,another feature of precipitation worthy of mention is the phenomenon of acclimatization4 ,this describes the fact that when the precipitating reagent is added very slowly1 or a little at a time1 a larger amount must be used1 and the slower the addition the greater the excess required4 ,hence in precipitating matters from an alkaline gelatine sol the acid1 if practicable1 should be added all at once4 ,in any case it is clear that one should aim at filtering a gelatine sol when it is near the iso-electric point1 which is stable enough for gelatine itself1 but a point of instability for many undesired impurities4 ,yet another phenomenon of colloid chemistry is concerned1 viz4 protection4 ,the particles it is desired to precipitate not only adsorb ions of electrolytes1 but also the gelatine sol itself1 and the particles1 thus covered by a layer of a stable emulsoid sol1 attain much of the stability of this gelatine sol4 ,unfortunately for gelatine manufacturers1 gelatine possesses very great powers as protective colloid1 and this no doubt greatly enhances the practical difficulty of obtaining a clear and bright sol or gel4 ,here again dilution of the sol reduces the adsorption and correspondingly reduces1 to some extent1 the difficulty4 ,with regard to the turbidity or opalescence in a gelatine sol due to minute globules of grease1 the case presents some analogy to the coarser colloid solutions1 but the analogy has its limits1 for an emulsion of grease is not an emulsoid sol4 ,doubtless the grease globules exhibit adsorptive phenomena1 in which case the valency rule comes into force2 the gelatine1 also1 by lowering interfacial tension1 assists in protecting the emulsion2 but grease emulsions are certainly stabilized in alkaline media 7hence the detergent effect of soap1 soda1 borax1 etc471 and it is undoubtedly easier to separate the emulsion by making the medium acid4 ,hence the practical fact that an acid sol is more easily clarified from grease than an alkaline or even than a neutral one4 ,the next stage in clarification is the separation of precipitated matters and of the coalesced particles of grease4 ,this may be attained by the two processes usual in such a problem of chemical engineering1 viz4 sedimentation and filtration4 ,after precipitation1 therefore1 the sol should be allowed to stand for some hours1 during which time the precipitate not only flocculates but also settles to the bottom1 and the globules of grease coalesce further and rise to the top1 from which they may be skimmed off4 ,sedimentation alone is both too slow and too incomplete to be sufficient for proper clarification1 and in these days it is always supplemented by the use of the filter-press4 ,this well-known appliance can easily be adapted to the local requirements of the manufacturer4 ,as speed of working is an essential requirement it is necessary to have a large filtering surface1 and this may be done either by increasing the number of plates in the press or by increasing the area of the plates used4 ,the large plates1 however1 are often cumbrous and inconvenient1 and if of metal are very heavy4 ,the plates may be constructed of well-seasoned wood1 or in the case of alkaline gelatine and glues1 even of iron4 ,the framework is in any case usually iron4 ,acid gelatines and glues may have wooden plates1 but acid-proof alloys are sometimes used to make them4 ,where it is essential to filter quickly two presses may be arranged in parallel1 thus doubling the active filtering surface4 ,when it is essential to obtain the highest possible clarity1 two presses may be worked in series1 which1 in effect1 means that the sol is filtered twice4 ,in using the filter press for gelatine and glue it is most necessary to observe the most scrupulous cleanliness1 and the plates must be frequently washed and sterilized4 ,rideal recommends weak chlorine water or bleaching powder solution for this purpose4 ,the process of decolorization1 by which colouring matters are removed without being chemically altered or destroyed1 usually precedes or takes place concurrently with the filtration4 ,the underlying principle of this operation is adsorption4 ,the colouring matters are usually in colloidal solution and most frequently are emulsoids1 hence they are substances which are known to be exceedingly susceptible to positive adsorption4 ,it is probable1 also1 that in a gelatine sol are particles which cause turbidity1 though not coloured1 and which are capable of being adsorbed4 ,hence the adsorption of colouring matters not only makes the sol more colourless1 but in all probability makes it brighter and clearer4 ,further1 decolorization by adsorption probably also involves the removal of the last traces of emulsified grease4 ,it will be clear1 therefore1 that in the improvement in brightness and colour of a gelatine sol1 adsorption fulfils a triple usefulness4 ,the ordinary processes of dyeing fabrics or leather are adsorption processes1 and the decolorization of gelatine sols consists essentially of the same process1 except that the concentration of the dyestuff is much less1 and the liquor remaining1 instead of the adsorbent1 is the primary consideration4 ,decolorization of gelatine sols may be effected by any substance with a large specific surface4 ,indeed1 a great variety of adsorbents are actually used in practice1 and each factory has its favourite material or mixture1 and its favourite mode1 place1 and time of application1 determined partly by the nature of the adsorbent and partly by the precise form of apparatus used4 ,amongst the adsorbents which have received special favour are sand1 kieselguhr1 asbestos1 animal charcoal1 wood pulp fibre1 albumin and alumina4 ,sand is very effective1 but a comparatively large weight is needed1 and its cleansing for repeated use is troublesome4 ,on the other hand1 it may be completely renovated by ignition4 ,kieselguhr is a very powerful adsorbent1 and only a little will do much good2 it is1 however1 hardly sufficient alone4 ,animal charcoal has great specific surface1 but its pores are very small for viscous liquors1 and its use is less suitable in the case of gelatine than in the decolorization of liquors which may be boiled4 ,wood pulp fibre is a very popular decolorizing material1 not only in gelatine but also in other trades4 ,its short1 woolly fibres give a clarifying as well as a decolorizing effect4 ,it may thus act as a mechanical filter for suspended matter and grease1 as well as an adsorbent for colouring matters present as sols4 ,its two functions1 however1 are often confused4 ,it may be regenerated for repeated use by careful washing1 and special pulp-washing machines are manufactured and sold for the purpose4 ,detergents are usually employed in the wash waters4 ,asbestos is also a good adsorbent1 and its long fibres make it much less liable to non-operating channels and bursts4 ,it also has the advantage that1 if desired1 it may be regenerated by ignition4 ,it forms a very useful mixture with pulp fibre4 ,all the above decolorizing materials are insoluble and hydrophobe1 and act in virtue of their finely divided conditions1 which causes them to have a large specific surface2 but there is another type or branch of substances1 whose effect is due to surface action of rather a different type4 ,these are the hydrophile gels4 ,in a gelatine sol the colloid particles have largely adsorbed the colouring matters which it is desired to remove4 ,this adsorption1 which is after all only an equilibrium1 is reduced by introducing another very strong adsorbent4 ,this latter1 by adsorption from the continuous phase1 reduces the adsorption of colouring matters by the gelatine particles4 ,in the case under discussion another lyophile colloid is introduced1 and after bringing about such an action is removed by appropriate means4 ,the use of albumin has long been known for such a purpose1 its special advantage being that after its admixture and adsorptive action1 it may easily be removed by raising the temperature above #gj ,c41 when coagulation takes place1 and by subsequent mechanical filtration4 ,the coagulated albumin takes down the adsorbed colouring matters4 ,albumin has been used in this way not only for gelatine and glue liquors1 but also for tanning extracts 7,part ,i41 ,section ,,iii47 and other commercial preparations4 ,into this class of decolorizing agents fall the insoluble inorganic gels which have been advocated by ,w4 ,gordon ,bennett1 e4g4 alumina cream4 ,freshly precipitated alumina hydrate is a colloid gel with very considerable adsorptive powers4 ,it has also the advantage that it is quite insoluble1 easily removed in filtration1 and has a powerful adsorptive action upon other objectionable impurities1 especially the poisonous metals1 arsenic1 copper1 zinc and lead4 ,its use is an undoubted advantage when in addition to the other clarifying agents and adsorbents4 ,it is conceivable1 in some cases1 that when alum is employed as clarifying agent in an alkaline gelatine liquor1 some alumina may be formed1 and as such contribute to the total effect4 ,,section ,v4--,,bleaching ,the adsorption law indicates that however much colouring matter is removed from the volume concentration 7continuous phase7 there must always be some left4 ,after all that the decolorization processes can do1 there still remains much colour that can only be removed by a chemical action of the ordinary sense4 ,the amount of colouring matter of this kind is not large1 but it is a deep red-brown1 and when the gelatine sol has been evaporated and dried out the final product1 if untreated1 possesses this typical colour1 and is known as glue4 ,if1 before gelation1 a chemical bleaching action is applied to destroy this pigment1 the product may be then dried out in a nearly colourless condition and is known as gelatine4 ,gelatine1 therefore1 is simply bleached glue4 ,many other definitions have been given1 and many elaborate distinctions drawn1 but the fact of bleaching is the essential difference4 ,in these days when gelatine is so valuable1 the higher-grade products are nearly always bleached1 and the term glue is consequently more often applied to a lower-grade product1 and is sometimes used in a sense implying this fact4 ,if it be desired to manufacture gelatine1 it is fairly obvious that the task is lightened by observing the axiom that prevention is better than cure4 ,if steps are taken to prevent the presence or development of such colouring matter1 a great advantage is attained1 for not only is the problem of bleaching easier1 but also quicker and less expensive in chemicals4 ,the nature of the colouring matters is but imperfectly investigated1 but in the case of skin gelatine the pigment of the hair roots and epidermis is doubtless one factor4 ,a long liming is said to assist in its destruction1 possibly because this completes the loosening of epithelial structures and possibly because the alkali causes some hydrolysis of the pigment4 ,in both skin and bone gelatine sols1 however1 there is a considerable tendency to develop the brown colouring matter typical of glue4 ,this tendency is enhanced by an increase in temperature and also by the presence of acid or alkali4 ,these facts seem to indicate that its development is associated with a partial hydrolysis of the gelatine in some direction4 ,rideal says this colouring matter is allied to caramel4 ,in harmony with this is the experience that its development is greatest in products which have been burnt1 i4e4 subjected to unusually high temperature4 ,the practical maxims which arise from these considerations are fairly obvious and widely known1 viz4 to conduct the extraction and evaporation at as low a temperature as possible and in as neutral a condition as practicable4 ,the temperature is particularly important during evaporation 7see ,section ,,vi474 ,fortunately for manufacturers of gelatine1 the colouring matter to be attacked is very susceptible both to reduction and to oxidation1 and both types of bleach are widely used in practice4 ,it is somewhat curious that the same colouring matter should be destructible both by reduction and by oxidation1 but there is no doubt that each type gives a perfectly satisfactory bleaching action and can result in a practically colourless gelatine4 ,on the other hand1 the reduction is the more unstable reaction1 for the glue colour slowly develops again in the gelatine on keeping it1 even in a dried condition4 ,gelatine bleached by oxidation1 however1 retains its colour quite well1 and even tends to improve with keeping4 ,it is quite possible that quite different reactions are involved in the two processes1 but in the light of the above facts it is somewhat surprising to observe ,rideal's statement that reduction followed by oxidation has been successful in practice4 ,although there is a wide choice of reducing and of oxidizing agents1 those which are suitable for application to gelatine cover a very limited field4 ,this limitation arises not so much from the ineffectiveness of the bleach1 as from the other effects of these substances upon the purity of the product and upon the elasticity of the gel which it can yield4 ,especially important is the lyotrope influence of the bleaching agent4 ,many reactive substances are ruled out simply because they either insolubilize the gelatine or weaken the gel it makes4 ,others are inadmissible on account of their poisonous nature4 ,it must never be forgotten that whatever is used in bleaching is1 like the gelatine itself1 much concentrated during evaporation and drying4 ,its possible percentage in the finished product should be considered1 and also the possibility that in these finishing operations what is present may not remain in solution1 owing to supersaturation4 ,bleaching by ,reduction4--,of all the reducing agents suggested1 sulphurous acid has proved to be much the most suitable and successful4 ,it has been used with equal success both for bone and for skin gelatine1 but on the whole has proved more suitable for the former4 ,sulphurous acid can fulfil in this instance a double function1 viz4 that of acid solvent for the bone phosphate1 and that of bleaching agent also4 ,as it penetrates the bone material1 dissolving the phosphate1 it also exercises its bleaching influence on the gelatinous part of the material4 ,changes of liquor tend to complete both actions1 so that a counter-current system is found most convenient4 ,the acid process for the manufacture of bone gelatine has been previously described 7,section ,,ii471 and the use of sulphurous acid in this connection is typified in the ,bergmann process4 ,in this process bleaching is in effect merely a continued treatment4 ,in the case of skin gelatine1 also1 sulphurous acid may fulfil a double function1 viz4 that of deliming agent as well as of bleaching agent4 ,in such instance it is necessary to use excess of bleaching acid1 some acting as deliming material and the remainder as bleaching agent4 ,as it is desirable to get rid of the lime and soda salts1 several changes of liquor are given to the goods1 possibly with intermediate washing4 ,here again approximation to a counter-current system is of advantage1 as the employment of used bleach liquors for deliming purposes effects considerable economy of sulphurous acid4 ,indeed1 there need be no waste acid at all4 ,whether the material be for bone or skin gelatine1 however1 it will be seen that the extraction is conducted in an acid condition and the resulting sol is also acid4 ,most usually the decolorization and filtration processes are also conducted with such an acid sol4 ,from what has been said 7,section ,,iv47 of the value of dibasic inorganic acids as clarifying agents1 it will be understood that the presence of sulphurous acid at this stage is of great advantage in the production of a clear and bright gelatine4 ,indeed1 it is well known in trade circles that sulphurous acid gelatines are usually of exceptional clarity and brightness4 ,the disadvantage of sulphurous acid processes is also found in the same fact that both sol1 gel and cake are in an acid condition4 ,to complete the bleach it is sometimes necessary to add sulphurous acid to the sol after extraction1 or even after evaporation1 but this is to be avoided if possible4 ,usually the ideal attempted is that the bleaching action should be as much as possible before extraction2 the excess of sulphurous acid is then washed off just before the extraction1 as far as practicable1 and the rest is boiled off during extraction4 ,the ideal is practically never attained1 for the acid is strongly adsorbed1 and the result is that the finished article is always an acid gelatine1 and sometimes indeed very decidedly such4 ,the acid condition is objectionable in the case of some forms of filter press on account of the solvent action on the metals1 and is objectionable in evaporation for similar reasons4 ,acid gelatines are also objectionable for many purposes for which gelatine is usually sold1 and this limits the commercial possibilities of the product thus obtained4 ,sulphurous acid is itself1 of course1 a gas1 and whilst the gas itself has been used for treating the material 7e4g4 bones71 it has been found not only more convenient but also more effective to use an aqueous solution4 ,this is mainly because it is possible to attain a greater adsorption in a liquor4 ,unfortunately1 however1 sulphurous acid is not a very soluble gas1 and although #h-aj per cent4 solutions may be1 with great care1 obtained1 they are really supersaturated and readily yield the gas1 even with slight mechanical agitation4 ,solutions even of #b to #c per cent4 strength are also liable to this1 and the general experience is that #a to #b per cent4 solutions are most economical and convenient for practical purposes4 ,as the freight on weak solutions is prohibitive1 the manufacturer using sulphurous acid is faced with the necessity either of purchasing cylinders of sulphur dioxide liquefied by pressure or making the gas and solution himself4 ,the former is the most convenient course when only small amounts are required1 but the latter preferable for a gelatine factory of any size4 ,sulphurous acid is easily manufactured by burning sulphur and leading the fumes by induced draught up a scrubber down which water slowly trickles4 ,forced draught may also be used1 as in the ,sachsenburg plant4 ,of the other reducing agents which have been used1 sodium hydrosulphite 7,na#b,,so#b7 deserves mention4 ,it is a very powerful reducing agent1 and has been found most useful when employed as an assistant to sulphurous acid4 ,this reagent is usually added to the sol1 after evaporation and before gelation4 ,it is sold as a white powder1 usually under trade names4 ,sometimes a mixture of bisulphite and powdered zinc replaces it1 but this is objectionable for pure food gelatines4 ,its use also involves an impurity in the finished article1 and a greater amount of inorganic ash4 ,bleaching by ,oxidation4--,many oxidizing agents have been suggested for bleaching gelatine1 but most of them have some practical disadvantage4 ,most of them contradict the maxim 7previously noted7 that it is desirable to avoid adding any soluble substance1 as this involves a permanent impurity1 possibly concentrated to supersaturation in the finishing processes1 and possibly involving a disadvantageous lyotrope influence4 ,there is another objection to oxidizing agents also2 whilst their bleaching action on the pigments is undoubted1 some of them have also a special action upon the gelatine itself which is in reality akin to tanning1 and may indeed involve an insolubilization of the gelatine4 ,thus1 chlorine gas 7which ,meunier patented for tanning7 has been used for bleaching gelatine1 but the conditions of success have not yet been thoroughly elucidated1 and it is problematical indeed whether the process is consistent with best results4 ,hypochlorites and bleaching powder have also a similar action1 which has been utilized with some success in practice4 ,rideal suggests that a suitable concentration for these reagents is #a3bjjj1 and emphasizes the care necessary4 ,an advantage of all these chlorinations is the formation of the strongly antiseptic chloramines1 which preserve the gelatine from putrefaction4 ,ozone has also been tried as an oxidation bleach for gelatine1 but not successfully1 partly on account of difficulties in controlling the quantity used4 ,peroxide of soda has also been used1 but it is not only alkaline1 but liable to contain sodium hydrate and carbonate as impurities1 and this involves neutralization either before use or in the gelatine sol1 and the consequent presence of sodium salts in the finished article4 ,peroxide of calcium is open to the same objections1 except that calcium is more easily removed from the sol than sodium4 ,rideal's suggestion for removing this lime1 viz4 precipitation by a current of carbonic acid1 merits attention in this and in other directions also4 ,rideal also states that in the case of an acid bone gelatine1 a good peroxide of lime is almost an ideal reagent for bleaching1 inasmuch as the lime carries down phosphate1 several impurities and colouring matters4 ,it thus acts as bleach1 as neutralizing agent1 and as precipitant1 and the precipitate itself is a strong adsorbent4 ,on account of its freedom from bases1 and because its residue is simply water1 peroxide of hydrogen has been found of great service in practice1 and in most factories it has shown itself superior not only to the other peroxides1 but also to all other oxidizing agents4 ,its application is simple1 a concentrated solution being added to the gelatine sol before or after evaporation4 ,it is the most fool-proof of all the oxidizing agents used in bleaching1 and it yields the purest product4 ,its bleaching action is perfectly satisfactory1 but only in a non-acid sol4 ,hydrogen peroxide is moderately stable in acid solution1 and its bleaching action is best in slightly alkaline solution4 ,an acid sol bleaches too slowly1 or not at all2 an alkaline sol induces evolution of oxygen and consequent waste4 ,the great disadvantage of peroxide of hydrogen is its great expense1 which is enhanced by an increasing demand for it in other industries4 ,a minor disadvantage is its instability1 which leads to loss in transit and storage4 ,it is sold usually in strengths indicated by the volume of oxygen obtained from unit volume of the solution1 when treated with permanganate in a nitrometer 7e4g4 #ae vols4 peroxide74 ,it is a fortunate feature of both the oxidizing and reducing agents usually employed in bleaching1 that they have considerable antiseptic power4 ,this assists materially in preserving the gelatine from putrefaction during the critical period between extraction and concentration4 ,,references4 ,glue and ,glue ,testing1 ,s4 ,rideal1 ,d4,sc41 #bnd ed41 pp4 #fa-ff1 #gh-hb4 ,gelatine1 ,glue1 and ,allied ,products1 ,t4 ,lambert1 pp4 #bi1 #cj1 #di1 #ea4 ,chemical ,engineering1 ,j4,r4 ,san4 ,inst41 ,no4 #b1 #aiaj4 ,s4 ,rideal4 ,on adsorption phenomena3 #a4 ,chemistry of ,colloids1 ,dr4 ,w4 ,w4 ,taylor4 #b4 ,chemistry of ,colloids1 ,v4 ,pschl4 #c4 ,chemistry of ,colloids1 ,zsigmondy and ,spear4 #d4 ,chemistry and ,physics of ,colloids1 ,e4 ,halschek4 #e4 ,surface ,tension and ,surface ,energy1 ,willows and ,hatschek4 ,,section ,,vi4--,,evaporation ,the evaporation of the weak gelatine sols 7#c-i per cent47 obtained by the processes described in previous sections into sols of such concentration 7#bj-ee per cent47 that they readily set to a stiff gel on cooling1 is now an essential feature of gelatine manufacture1 and is one of the most important processes4 ,in the early days of this industry1 manufacturers aimed at obtaining a concentrated sol1 as this saved time in drying1 and so reduced the possibilities of putrefaction4 ,the advent of evaporation has reduced these possibilities to a minimum1 and has also enormously reduced the space required and the capital outlay needed in the drying sheds4 ,it has1 in addition1 given the practical advantages involved in dealing up to the last minute with a much less viscous liquor4 ,as the liquors extracted are weaker1 the extraction is more complete and the decolorization more easily effected4 ,the earliest attempts at evaporation were not very successful1 partly on account of the prolonged stewing which ruined the setting power1 and partly because of the poor economy of heat4 ,thus in the open evaporators the sol was maintained at a high temperature for a long period1 and this process only proved suitable for low-grade products4 ,a great stride forward was made by ,howard's invention of the ,vacuum ,pan4 ,this made it possible to undertake concentration at much lower temperatures1 a most important improvement in the case of gelatine and other organic matters easily damaged by heat4 ,the process1 however1 was still slow1 and the sol exposed to heat for a long time1 as must be the case when evaporation takes place in bulk4 ,these disadvantages were still fatal to the production of the highest-grade gelatine4 ,there were also the practical difficulties of entrainment 7blowing over71 in which parts of the sol were carried away by the escaping vapour1 and also of incrustation which so rapidly reduces the heating efficiency and evaporative capacity of the machine4 ,the vacuum pan1 however1 presented two decided advantages--evaporation at a low temperature1 and1 as a corollary1 the possibility of utilizing exhaust steam to attain this temperature4 ,whilst the vacuum pan was a satisfactory machine for many branches of chemical engineering1 the problem of evaporation was still unsolved for gelatine liquor because of the stewing involved1 until the advent of the film evaporator1 which dealt with the liquor not in bulk1 but in a continuous stream4 ,in this way the product was only exposed to heat for a comparatively short time4 ,many evaporators of this type came into being1 and rapid improvement was made in the constructional details4 ,the film evaporators retained usually the advantage of evaporation in vacuo1 so that it was now possible to evaporate gelatine sols by exposure for a short time to a comparatively low temperature4 ,of this type of evaporator1 the ,lillie1 ,yaryan1 ,schwager1 ,claassen1 ,greiner1 ,blair ,campbell1 and the ,kestner machines are well-known examples4 ,a further advance in solving this problem was the application of the principle of multiple-effect evaporation4 ,the vapour driven off during evaporation possesses of course many heat units1 and is of very considerable volume4 ,in multiple-effect evaporators this vapour is used to work a similar evaporator1 and the evaporated liquor passes immediately into what is practically a second machine1 and is further evaporated by the heat from the vapour just driven from it4 ,such an arrangement would be termed a double-effect evaporator4 ,the vapour from the second effect may of course be similarly used to operate a third effect1 and the vapour from this to work a fourth effect1 and so on4 ,thus1 we may have triple effect1 quadruple effect1 etc41 even up to octuple effect4 ,the great advantage of multiple-effect evaporation is in the saving of costly steam4 ,reavell gives the following figures to illustrate the economy thus obtained3-- ,,water ,,evaporated ,,per #ajj ,,units ,,steam4 ---------------------------------------- ------- ,single4 ,double4 ,triple4 ,quadruple4 ---------------------------------------- ------- #ie #aej #bbj #cjj ---------------------------------------- ------- ,there is naturally a limit beyond which the capital cost of the machine neutralizes the advantage of steam economy1 and it is seldom that octuple effects are used4 ,there are probably more triple effects in use than any other machine4 ,an essential and important part of the modern evaporator is the condenser1 in which the vapour from the last effect is conducted into water 7jet condensers7 or over cooled surfaces 7surface condensers71 with a view to producing and maintaining the vacuum4 ,a lasting vacuum cannot be maintained without an air-pump1 as air is often introduced 7#a7 with the steam1 having entered the boiler dissolved in the feed water2 7#b7 by leakage from the atmosphere into the condenser and the connected vacuous spaces2 and 7#c7 in jet condensers1 in solution with the circulating condenser water4 ,that from the first two sources may be reduced1 but the third is beyond control3 hence if high vacua are necessary1 surface condensers are to be preferred4 ,dissolved air is usually #e-bj per cent4 of the water volume1 and is least for sea-water4 ,it should be noted that water leaving a surface condenser is in a very air-free state1 and therefore particularly suitable for boiler supply4 ,apart from the capital cost of a condenser the chief cost of maintaining a vacuum is in pumping the circulating water1 of which up to #gj lbs4 is usual per lb4 of steam condensed4 ,if ,w weight of steam condensed 7lbs4 per hour72 ,q weight of cooling water circulated 7lbs4 per hour7 ,ti inlet temperature 7 ,f47 of cooling water2 ,to outlet temperature 7 ,f47 of cooling water2 then ,to ,ti #ajej7,w_/,q7 ,it will be understood that for high vacua1 low temperature of cooling water 7,ti7 is more important than copious supply 7,q_/,w74 ,it is advantageous1 however1 to choose a site yielding plenty of cold water1 such as a river or canal side4 ,otherwise it is often necessary to use cooling towers or spray nozzles4 ,the cooling is by evaporation 7 #fj to #hj per cent4 of ,w71 cold water replacing that evaporated1 and yielding water #ge to #hj ,f4 ,if ,ti #hj ,f4 and ,q_/,w #gj1 a vacuum of #bh4cd is possible1 but the #j4cd should be allowed for the partial pressure of the air1 determined exactly by the air entering and by the displacement of the air-pump4 ,another feature of the modern evaporator is the heater or calorifier1 by which the liquor to be evaporated is led in a continuous rapid stream through heated tubes immediately prior to its entry into the first effect4 ,it is the aim of the heater to raise the temperature of the liquor to the temperature of evaporation1 and so to avoid this being necessary in the first effect4 ,the heater thus further avoids stewing1 ensures steady running1 and effectively increases the capacity of a machine4 ,it is noteworthy that superheated steam is not desirable for working an evaporator4 ,the principle of evaporation by steam is not merely that the temperature of the liquor is raised to boiling point2 it is that in the condensation of the heating steam its latent heat is yielded to the liquor being evaporated4 ,to evaporate quickly1 therefore1 the heating steam must condense rapidly4 ,hence1 as superheated steam has a rate of condensation #bj-cj times slower than saturated steam1 the latter is much to be preferred4 ,a slight superheating1 however1 may be justifiable where the steam has any distance to travel before use4 ,it is the fact that it is the latent heat of steam which is mainly utilized which gives steam its great practical advantage over hot non-condensable gases4 ,steam in condensing yields an enormously greater number of heat units per lb4 than hot waste gases4 ,steam has also the advantage of more constant temperature4 ,the capacity and efficiency of an evaporator depends upon a good many factors1 some of which are worthy of discussion at this point4 ,the transference of heat and the amount of evaporation are directly proportional to the mean temperature difference between the heating steam and the liquor being evaporated4 ,these temperatures1 however1 both vary somewhat1 the steam losing part of its pressure and temperature as it passes along the heating surface2 the liquid generally increases in temperature4 ,the mean difference in temperature1 moreover1 is not the arithmetic mean between the smallest and largest temperature differences1 but is given by the following expressions1 which yield results not wide apart3-- ,if thetaa temperature difference at commencement2 thetae end2 and thetam mean temperature difference2 then thetam 7thetaa - thetae7 _/ log7thetaa _/ thetae7 or 7thetaa - thetae7 _/ n7#a - nth root of7thetae _/ thetaa77 ,this mean temperature difference is in practice usually spoken of as the temperature head or heat drop4 ,it will be clear that this temperature head is increased by using steam at higher pressure 7temperature71 and by evaporating under reduced pressure4 ,since most liquids have their boiling points reduced about #dj ,c4 by operating in vacuo1 the advantage of the vacuum is apparent4 ,it should be remembered that the temperature head has not the same value in any part of the scale3 it has more value higher up the scale1 because the steam is denser and more heat units come in contact with a given area in a given time4 ,it must also be remembered that whilst the pressure gauge is a most useful indicator of steam temperature1 it is not necessarily accurate4 ,the pressure in the hot space is the sum of the pressures of air and steam1 and since the temperature 7the important condition7 of the hot space depends upon the pressure of the steam1 and not on the sum of the pressures1 the temperature in a steam space is always rather lower than would be supposed from the pressure indicated by the gauge4 ,the transference of heat is influenced by the velocity of both the heating fluid and the fluid being heated over the heating surface4 ,the more rapidly each fluid moves1 the more rapid is the transference of heat1 because a greater number of particles of both fluids are brought to the heating surface in any given time4 ,this is popularly known as the effect of circulation1 and is illustrated by the advantage of stirring a liquid being heated in bulk4 ,in the film evaporators the circulation is through tubes at high speed 7up to #b miles a minute71 and the maximum effect in this sense is thus obtained4 ,the increase in heat transference is not directly proportional to the increase in velocity1 but in a lower ratio1 sometimes approximately the square root of the velocity4 ,in such a case1 if either velocity be quadrupled1 the heat transference is doubled4 ,other advantages of high velocity are that the heating steam more readily sweeps away condensed steam from the heating surface1 and the high-speed film similarly scours away incrustations on the interior of the tubes4 ,the transference of heat is also proportional to the conductivity of the metal forming the heating surface4 ,for gelatine liquors1 copper tubes are almost invariably employed1 the advantage being great even when price is taken into consideration4 ,the following conductivity coefficients illustrate this point 7calories per hour through #a sq4 metre of metal #a metre thick1 with a temperature difference of #a ,c473-- ,copper444#ccj ,iron44444#ef ,steel4444#bb-dj ,tin444444#ed ,zinc44444#aje ,lead44444#bh ,the coefficient of heat transmission decreases the more with increasing thickness of wall1 the worse conductor is the metal4 ,for copper tubes1 however1 this decrease is usually unimportant4 ,the transference of heat is also much influenced by the viscosity of the liquor being evaporated2 the greater the viscosity1 the lower the coefficient of heat transmission4 ,unfortunately for this process of evaporation1 gelatine sols are exceedingly viscous1 and thus the difficulty in obtaining a concentrated sol is thus greatly enhanced4 ,the transference of heat is often greatly hindered by incrustations of the tubes1 which incrustations generally conduct heat very badly4 ,thus the relative heat conductivities of copper and chalk are as #ajjj3e4 ,the amount of heat transferred is of course determined also by the area of the heating surface4 ,the amount of evaporation needed thus determines the number of tubes 7of standard size7 in the evaporator1 and thus the capacity of the machine4 ,an evaporator should have its heating surface area chosen with a view to the duty required of it4 ,in practice the working of an evaporator is often not a very difficult matter1 and large numbers of machines are operated by unskilled labour4 ,troubles generally arise from inconstant steam pressure1 incrustation1 leakages of air1 which reduce the vacuum1 the temperature head1 and hinder heat transmission4 ,for the evaporation of gelatine liquors the ,yaryan1 the ,kestner1 and the ,blair-,campbell film evaporators are the most widely used4 ,the velocity of the liquor through some of these machines is so great that occasionally no vacuum is used4 ,the temperature obtained is high 7#bjj ,f471 but the time is very short1 if rapid cooling of the evaporated liquor is arranged4 ,,references4 ,evaporating1 ,condensing and ,cooling ,apparatus1 by ,e4 ,hausbrand4 ,scott1 ,greenwood ,son 7#aiaf ,ed474 ,evaporation1 by ,e4 ,kappeschaar4 ,norman ,rodger 7#aiad74 ,evaporation in the ,chemical ,industry1 by ,j4,a4 ,reavell1 ,m4,i4,mech4,e41 ,j4,s4,c4,i41 #aiah1 ,april #aath4 ,glue and ,glue ,testing1 ,s4 ,rideal1 ,d4,sc41 pp4 #ef-ei4 ,gelatine1 ,glue1 and their ,allied ,products1 ,t4 ,lambert1 pp4 #bf-bi4 ,notes on ,condensing ,plant1 ,j4,m4 ,newton1 ,b4,sc41 ,j4 ,junior ,inst4 ,engineers1 ,aug41 #aiab4 ,,section ,,vii4--,,cooling ,,and ,,drying ,the conversion of a gelatine sol into cakes of gelatine has been much simplified by the advent of the evaporator4 ,before this machine was used much trouble was experienced with putrefaction1 and in hot and thundery weather1 especially on the ,continent1 it was often necessary to suspend operations4 ,evaporation has1 however1 materially contributed to the possibility of rapid and satisfactory cooling and drying4 ,from the time the weak sol is decolorized and bleached1 the finishing processes consist essentially in the removal of water4 ,this is now usually done partly by evaporation of the sol1 and partly by the desiccation of the gel4 ,there is an obvious elasticity in method1 and factory practice does actually vary considerably in the relative proportions of these two alternatives4 ,some factories evaporate to a #bj per cent4 sol1 approximately1 and rely upon drying sheds and lofts to complete the desiccation3 other factories evaporate up to a #ee per cent4 gelatine sol1 and so can manage with less shed room4 ,something depends upon local conditions1 but the main issue is between the cost of steam in evaporation and the cost of land and buildings required for sheds4 ,on the whole the modern tendency is to evaporate more1 for this course has the additional advantage of speed1 involving both a quicker turnover and less liability of putrefaction4 ,lower-grade products need relatively greater evaporation to form a gel of equal rigidity4 ,after evaporation and bleaching1 the concentrated sol is first cooled rapidly until it has set to a stiff gel1 then cut up into cakes according to the size required1 these being dried out on network frames arranged in tiers1 through which a draught of air is usually forced or induced4 ,this general description is of course applicable to many factories with innumerable variations in detail1 most of which variations originate in local convenience and are unessential parts of the manufacture4 ,an essential principle is that the cooling or gelation should be done rapidly1 not only to avoid putrefaction but also to avoid the action of heat on the elasticity of the gel4 ,a hot sol or gel is liable to hydrolysis and loss of setting power1 and should have its temperature quickly reduced1 but a warm sol or gel 7say #ajj ,f47 is most liable to putrefaction1 so that the cooling should be continued quickly4 ,on the other hand1 the gel should not be frozen4 ,for cooling purposes a copious supply of cold water is most usually employed1 but some factories have installed refrigerators4 ,these plants operate by the rapid evaporation of liquefied gases such as carbon dioxide1 sulphur dioxide1 or ammonia1 so arranged as to cool a solution of common salt1 which forms the circulating liquor and is returned after use to the refrigerator4 ,where such plants are used1 it is natural that their use should be extended to the drying sheds to cool the air entering in the height of summer4 ,in some factories the cooling is attained neither by cold water nor cooled brine1 but merely by cold air4 ,the kind of vessel in which gelation is induced varies widely in different factories4 ,for lower-grade products metal boxes are used1 heavily galvanized iron being the most common material4 ,if the liquor be muddy1 deep boxes are preferred1 but if clear1 rapid cooling is best attained by having them long and shallow1 and so exposing a relatively greater area to the cooling action4 ,in either case the boxes may contain up to #a_/b cwt4 of jelly4 ,lambert mentions boxes #bd #f1 which are #e deep2 ,cavalier suggests rectangular moulds holding #cj litres4 ,in place of galvanized sheet iron1 boxes of sheet zinc or of wood lined with zinc are sometimes used4 ,in any case the most scrupulous cleanliness should be observed in all cooling-house work1 and in some factories the most elaborate precautions are taken for cleansing vessels1 tools1 floors1 etc41 and even for their disinfection and sterilization4 ,iron1 tinned iron1 and copper cooling vessels are ruled out on account of their tendency to rust and tarnish1 and the last is unjustifiably expensive4 ,many of these vessels are unsuitable for pure food gelatines in which traces of copper1 zinc and arsenic are held to be very objectionable4 ,for the best gelatines1 therefore1 a very shallow vessel 7#a_/d to #a_/b deep7 with a sheet glass bottom is preferred1 and the concentrated sol is run on to this for gelation4 ,glue 7or gelatine7 which has set in this way is sometimes called cast glue4 ,that which sets in metal boxes in blocks is termed cut glue1 because the blocks of jelly need subsequently to be cut into slabs of the desired size and shape4 ,jelly blocks may be cut by hand with the wire knife which yields a characteristic wavy appearance to the finished product4 ,this may also be done by machinery1 the block of gel being placed on a series of correctly spaced wires and forced through the network by hydraulic pressure4 ,a cutting machine 7,schneible7 has also been used to cut up blocks of jelly into slices of the required thickness1 but these machines have not made great headway in this country4 ,it will be clear that cast glue is cooled more rapidly than glue in blocks2 it is therefore not surprising to note ,lambert's statement that the former comprises the larger proportion on the market4 ,the cut or cast cakes are next placed upon network frames1 and a series of such frames are placed on a bogey4 ,the bogey is run along tram lines into the drying tunnel1 through which air is forced or induced by a fan4 ,many such bogeys are1 of course1 passed into each tunnel1 and as many tunnels as required may be constructed4 ,care is necessary to expose the cakes evenly to the action of the air4 ,it is mostly necessary to warm the air at the inlet by means of steam pipes and so increase its drying power4 ,this is especially necessary in winter or wet weather4 ,in summer1 however1 it is often arranged that the air is cooled before entering the sheds4 ,this is accomplished by passing the air through pipes from a refrigerator4 ,when heated air is used1 it is stated by ,lambert that the maximum temperature should be #be4e ,c4 7#gh ,f472 ,rideal considers #ba ,c4 7#gj ,f47 should be the maximum4 ,in all cases the drying power of the air is easily ascertained from a wet-and-dry bulb thermometer1 and the amount of air passing along the shed from a wind gauge4 ,lambert states that drying normally occupies four to five days4 ,the final product is still a gel1 of course1 and contains from #aj to #ah per cent4 of water4 ,it appears1 however1 very hard and solid4 ,the dried cakes are removed from the frames and transferred to the warehouse1 where they are sorted according to quality and packed in bags or tin-lined boxes4 ,some material is ground to powder4 ,the network of the drying frames has been made from many materials4 ,cotton or string netting is very common1 but is liable to sag and to get dirty4 ,it also has a short life4 ,ordinary galvanized iron soon loses its galvanizing cover1 and the iron then is liable to rust4 ,attempts have been made to use sheet zinc and other alloys1 which are cut or punched into nets with square or diamond-shaped holes4 ,these were found to warp and break4 ,rideal's conclusion1 which is confirmed by the general experience1 is that the best material is a heavily galvanized iron wire netting4 ,he suggests that it should have #ae to #be per cent4 of its weight of zinc1 and that it should be strengthened by stiffer ribs arranged both longitudinally and transversely4 ,many attempts have been made1 and many patents taken out1 with the object of making the cooling1 cutting1 and drying processes as continuous and as quick as possible1 and with a view to saving labour1 which is rather costly at this stage4 ,these attempts1 however1 have only met with indifferent success4 ,a common idea is that a continuous supply should fall upon a revolving appliance1 and be instantly congealed in a thin state1 which last lends itself to more rapid desiccation4 ,vacuum drying has also been attempted4 ,,references4 ,glue and ,glue ,testing1 ,s4 ,rideal1 ,d4,sc41 pp4 #fh-gd4 ,glue1 ,gelatine1 and ,allied ,products1 ,t4 ,lambert1 pp4 #cj-ce4 ,chem4 ,zeit41 #aiaa1 #he1 #ag 7,cavalier74 ,,patents4 ,eng4 ,patent 7#ahid7 #aa1dbf 7,hewitt74 ,eng4 ,patent 7#ahih7 #b1djj 7,brauer74 ,fr4 ,patent 7#aiji7 #cih1eih 7,lehmann71 ,j4,s4,c4,i41 #aiji1 #hig4 ,u4,s4 ,patent 7#aiab7 #a1jdg1afe 7,american ,glue ,co474 ,,section ,,viii4--,,uses ,,of ,,gelatine ,,and ,,glue ,gelatine and glue have both been put to an immense variety of uses1 and the list is constantly extending4 ,indeed1 no one who considers the following account of their applications can doubt that gelatine and glue have become a necessary part of our civilization4 ,gelatine for edible purposes certainly forms a very considerable part of the total used1 and great pains are now taken to obtain a pure product4 ,thus1 a gelatine with more than #a4d parts per million of arsenic1 or more than #cj parts per million of copper1 is not considered good enough for pure food4 ,the food value of gelatine1 compared with other proteids1 is exceedingly low2 its use in this connection has no connection with the calories of heat energy it will yield4 ,it is used almost entirely because of its property of forming a gel4 ,table jellies form1 of course1 one popular use of gelatin1 but the manufacture of sweets makes also a great demand upon the gelatine trade4 ,culinary operations often require a little gelatine1 especially is it used in pies and soups4 ,an extension of the same idea is found in its employment for many manufactured foods1 e4g4 tinned meats1 meat extracts1 and the concentrated foods4 ,the use of gelatine in connection with the first of these received a big impetus during the war period4 ,in gelatine for any of these purposes1 the presence of excess of sulphurous acid is objectionable1 as its taste is easily noticed4 ,gelatine for medicinal purposes finds an ever-growing number of applications4 ,gelatine capsules for holding greasy liquids and solutions of nauseous drugs are increasingly popular1 for the dose may be swallowed without unpleasantness4 ,in making these capsules some sugar is also used1 and the finished article is often protected from atmospheric moisture by treatment with a weak solution of alum4 ,in a similar way pills are often coated with a #cc per cent4 gelatine sol4 ,such pills are not only pleasanter to swallow1 but are less liable1 after being dried1 to stick together in the box4 ,alcohol solutions of drugs 7or essences1 perfumes1 etc47 may be suitably stored in gelatine instead of metal tubes4 ,medicated wines are detannated by gelatine before the addition of drugs which would have been precipitated by the tannin4 ,the ,british ,pharmacopoeia specifies four kinds of ,lamell1 which are small discs of gelatin and glycerin1 each containing a minute but definite dose of some powerful alkaloid4 ,glycerin jelly is a mixture of gelatin glycerin with some water4 ,it is used for chapped and rough hands2 the mixture is also used for glycerin suppositories1 and for mounting microscopic sections4 ,the mixture also forms the basis of gelato-glycerin1 used in nasal bougies1 and of glyco-gelatin for medicated lozenges4 ,gelatine insolubilised by formalin 7formo-gelatin7 has been used for making tabloids1 wound dressings1 and artificial silk4 ,gelatine is in constant demand for bacteriological work1 for which purpose a high-grade product is desired4 ,nutrient media for the culture of bacteria are solidified by #aj-ae per cent4 of gelatin1 and the growth of colonies of bacteria often show typical formations4 ,by inoculating into a melted and sterile quantity and setting quickly in a flat dish after mixing1 the number of bacteria in the volume introduced can be judged from the number of colonies which develop4 ,bacteria are also distinguished often as liquefying or non-liquefying according to their type of culture on nutrient gelatine media4 ,gelatine for such work should be neutral and of high clarity4 ,the gelatine required for photographic purposes is also a high-class product4 ,it should be neutral1 colourless1 and free from chlorides and other mineral salts4 ,grease also is objectionable4 ,gelatine is used in the numerous carbon processes1 in which the principle is that gelatine is made insoluble in water by the action of potassium dichromate under the action of light4 ,it is used also in ,poiteoin process for copying engineering drawings1 which is based upon the power of a ferric salt to render gelatine insoluble so long as it is not exposed to the actinic rays4 ,gelatine is used in the manufacture of the crystalline glass used for decorative purposes4 ,advantage is taken of the immense contractile force it exerts on drying4 ,when ground glass is coated with gelatine1 and the latter dried1 it tears away the surface of the glass itself1 and leaves peculiar fern-like patterns4 ,inorganic salts dissolved in the sol influence the nature of the pattern obtained4 ,gelatine is used also very largely in the textile trades1 for finishing coloured yarns and threads1 for sizing woollen and worsted warps1 and for thickening the dyestuffs used in printing fabrics4 ,it is also used for finishing white straw hats2 as a size in the manufacture of high-class papers1 and as a wax substitute for covering corks and bottle necks4 ,glue is used instead of gelatine in all cases where colour is not a matter of much moment4 ,the fact that it has not been bleached makes no difference to its suitability in such a case1 and the cost is substantially reduced4 ,thus1 for dark-coloured straw hats1 textiles1 sweets1 papers1 and in all suitable woolwork1 glue is used in place of the more expensive article4 ,a very large quantity of glue is used in the manufacture of matches1 where it functions as the material binding the head to the stem4 ,a #ae-ej per cent4 sol is used1 containing nitrate or chlorate of potash as oxidizing agent4 ,the mixture is kept at #ch ,c4 and the phosphorus cautiously added1 and when this is emulsified1 the friction ingredients 7sand1 glass1 etc47 are also added4 ,the glue acts also in preventing premature oxidation4 ,glue is also used in making the match-boxes1 and similarly in making sand1 emery1 and glass papers and cloths4 ,there is a large consumption of glue by joiners1 carpenters1 cabinet-makers1 and all kinds of woodwork and fancy work4 ,it is used in the manufacture of furniture of all kinds1 of pianos1 organs1 billiard tables1 panels1 picture frames1 and of toys and brushes4 ,mixed with white lead1 chalk1 and sawdust1 it forms a composition used for mirror frames1 rosettes1 etc4 ,glue is used for veneering1 for mosaics1 plaques1 trays1 fingerplates1 leather wall coverings1 and for staining floors4 ,there is also a considerable sale for glue in bookbinding1 for which a sweet1 light-coloured1 and strong product is required4 ,it has been found particularly suitable for leather bindings where the grain has been artificially printed or embossed1 and in finishing and gilding4 ,the compositions used for printing rollers all contain gelatine or glue together with sugar or glycerin and possibly oil and soap4 ,they are often hardened with formalin4 ,similar mixtures are used for the beds of hectographs4 ,glue 7together with waste leather7 is used in the manufacture of imitation leather and leather substitutes4 ,cotton and wool fibres are often incorporated1 and sometimes textile fabrics4 ,much glue is converted into size1 which is a weak gel used as a filling rather than as an adhesive agent4 ,a low-grade glue is often therefore preferred for such purposes1 as having body rather than strength4 ,size is often sold in cake1 but sometimes in the form of the gel itself1 in which case it may never have been evaporated4 ,indeed1 size is often overboiled glue1 made by crude and out-of-date methods4 ,it is largely used in the paper trade1 and for wallpapers1 millboards1 papier-mache1 paper and cardboard boxes1 etc4 ,mixed with logwood and iron1 and possibly alum1 it formed the blue size once largely used by bootmakers as a foundation for blacking1 and is similarly used in currying4 ,size is also used in making oil paints and varnishes4 ,distemper is a size with which is incorporated whiting or gypsum and coloured pigments4 ,in all applications of size1 it is common to use antiseptics4 ,salicylic acid has been widely used in this sense4 ,low-grade glue is used for the manufacture of cheap brushes and for fly-papers4 ,innumerable patents have been taken out and mixtures invented for the production of plastic materials1 which frequently involve gelatine or glue4 ,thus1 gelatine and glue are used in making plaster casts1 and for imitation ivory1 wood1 stone1 and rubber4 ,many of these inventions have been investigated by ,rideal1 who points out the features common to most of them4 ,usually a viscous sol is thickened by the addition of inert fibres and powders1 and with the object of making the preparation more waterproof it is customary to incorporate oils1 fats1 waxes1 tars1 and resins before the gel is set4 ,the surface is hardened by tanning with formalin or tannin solution1 finally painted or varnished4 ,equally innumerable are the inventions1 recipes1 and patents for making glues that shall remain liquid4 ,the convenience of this ideal is obvious1 but many of the suggestions are useless4 ,it is quite easy to incorporate into a gel substances which keep it liquid--any soluble substances with a lyotrope influence of the iodide type will do this--but these also prevent the glue setting when used4 ,even in small quantity they will influence the tenacity of the joint4 ,other methods depend upon a partial hydrolysis of the protein4 ,amongst the most successful of these attempts are to dissolve #c parts of glue either in #ab-ae parts saccharate of lime1 or in #i parts of #cc per cent4 acetic acid4 ,many special glues and cements are made from commercial glue1 according to the purpose required4 ,marine glue contains no glue2 it is made from shellac and rubber mixed with benzene or naphtha4 ,its advantage is waterproofness4 ,,references4 ,glue and ,glue ,testing1 ,s4 ,rideal1 ,d4,sc41 #bnd ed4 ,uses of ,glue1 chap4 iii4 p4 #hc4 ,uses of ,gelatine1 chap4 iv4 p4 #ajj4 ,special ,glues1 p4 #ajh4 ,liquid ,glues1 p4 #aai4 ,gelatine1 ,glue1 and their ,allied ,products1 ,t4 ,lambert4 ,uses of ,glue and ,gelatine1 chap4 ix4 p4 #hj4 ,liquid ,glues and ,cements1 chap4 viii4 p4 #fi4 ,,section ,,ix4--,,the ,,evolution ,,of ,,the ,,gelatine ,,and ,,glue ,,industry ,the manufacture of gelatine and allied products has received a great stimulus in this country from the circumstances arising from the ,european ,war4 ,the large restriction of continental--especially ,french and ,belgian--supplies of gelatine1 led to greater demands for the ,british-made product1 and resulted not merely in a period of greater prosperity1 but in a period in which much greater efforts were made to supply a high-grade article in larger quantities4 ,most manufacturers strove to make high-class gelatine rather than low-grade glue1 great extensions were made1 and many new businesses were established4 ,the development of the leather trades1 more particularly in respect of greater production1 caused a bigger supply of raw material for skin gelatine1 and the slaughter of home animals for food caused a more plentiful supply of bones4 ,at the same time it was realized that greater production not only reduced working costs1 but also that a bigger turnover in any one factory involved a proportionately less capital outlay4 ,these facts tend to counterbalance the heavy freight on the raw materials4 ,production is thus not only on a larger scale but more intensive4 ,one of the greatest difficulties of this industry is to produce a regular or standard article1 for the raw material is so exceedingly variable in quality2 that for skin gelatine tends also to become less valuable4 ,in such a case1 as ,rideal has truly remarked1 to ensure that supplies to customers shall be always up to sample1 which is often a matter of contract--exact and regular working1 strict cleanliness1 observance of temperatures and other physical data1 and scientific supervision1 are clearly necessary4 ,rule of thumb is never quite certain to produce the same article twice4 ,in past years ,british methods of manufacture have been far too empirical4 ,as in other industries1 rule of thumb must inevitably be replaced by scientific principle4 ,the advances in colloid chemistry of this last decade or so have1 in the author's opinion1 supplied the clue to this line of development4 ,in the preceding pages emphasis has been laid upon the importance of the adsorption law1 the lyotrope series1 and the valency rule4 ,the manufacturer or supervisor who understands and can apply these generalizations will find his task vastly easier and his factory more efficient4 ,much remains to be learnt1 however1 and the industry would certainly benefit by research work1 for which there is a fertile field4 ,there is also considerable room for improvement in the methods of chemical engineering usually employed4 ,whilst the heat engineers have certainly done much to solve the question of evaporation and drying1 there is still great scope in the more economical application of heat in extraction1 and the last word can hardly have been said on the problem of clarification and decolorization4 ,there is indeed almost as much scope for research by the chemical engineer as by the colloid chemist4 ,the industry also exhibits1 in common with the leather and many other trades1 the same tendency to save labour1 both by careful arrangement of the factory and by the installing of mechanical labour-saving devices4 ,thus1 lifts1 runways1 hoists1 and trucks are increasingly used to move the solids1 and pipes and pumps to move the liquors4 ,as ever1 there is scope for the mechanical engineer4 ,if some of these problems are vigorously tackled during the present reconstruction period1 there is little doubt that the gelatine and glue industry will be in a much better position to cope with all possible competition in the future4 ,from what has been said in ,section ,,viii4 as to the wide uses of gelatine and glue1 it will be seen that general prosperity in trade is conducive to better trade conditions in the gelatine and glue industry4 ,it is similarly true that a general trade slump affects the glue trade adversely4 ,the severe trade depression which commenced in #aibj has had this effect1 and has made economic production much more difficult as well as more essential4 ,as often is the case1 the larger factories and firms can better face the difficulties1 and there can be little doubt that if the depression be long continued there will be a tendency for the smaller factories to be closed down and for the larger firms to unite4 ,as in the leather trade1 both the ,war boom and the ,peace slump have caused the gelatine and glue trade to develop along the lines of the great trusts4 ,it may be reasonably expected1 moreover1 that these will be intimately connected with the leather trusts4 ,this fact1 together with the heavy freight charges on the raw material1 tends also to make the skin glue factories gravitate towards the leather centres4 ,,part ,,vi4--,,miscellaneous ,,proteins ,,and ,,bye-,,products ,,section ,i4--,,bye-,,products ,,of ,,the ,,leather ,,trades ,in the leather trades by far the most important and valuable bye-products are obtained from the hides and skins themselves1 and all these are obtained before the tannage proper is commenced4 ,the leather trades use only the dermis 7corium7 or true skin for the manufacture of leather1 and as we have noted 7,part ,i41 ,section ,,ii47 this prepared and purified dermis is called pelt4 ,the cuttings and trimmings from the pelt form the most valuable bye-product of the leather trades1 and are the raw material of the gelatine and glue industries 7,part ,v41 ,section ,,ii474 ,many portions of the pelt1 indeed1 such as ears1 noses1 and cows' udders1 are quite useless for any other purposes4 ,other portions1 such as cheeks1 faces1 and even bellies1 may be made either into glue or leather according to the state of trade4 ,hardly less important to the same industry are the cuttings of adipose tissue removed in fleshing the hides and skins4 ,these1 though yielding less protein1 yield also1 however1 the valuable animal greases 7,part ,v41 ,section ,,ii474 ,to obtain both these products in a purer condition the removal of flesh after soaking1 but before liming 7,part ,i41 ,section ,,ii471 has been favoured by some1 especially in ,america4 ,amongst the epithelial structures of the hides and skins1 we have several protein bye-products which have some commercial value4 ,the horns of cattle are now almost invariably removed before reaching the leather manufacturer1 but have some little value4 ,this part of the epidermis is not solid keratin4 ,a pith is easily removed after boiling in water4 ,the outer parts1 too1 are often coarse and somewhat damaged1 but if removed by scraping reveal often a rather beautiful structure of varying colour4 ,there is some opening for this product in the manufacture of small articles of horn1 but much of it1 together with hoofs1 is roasted and crushed for making fertilizers4 ,the hair of cattle1 goat1 etc41 has also a commercial value4 ,this is removed after liming1 and needs subsequent purification 7,part ,i41 ,section ,,ii474 ,the hair is well washed with water1 using either repeated changes or a continuous supply1 the operation being carried out in paddles or similar machines which stir up the hair in the water4 ,when clean1 the hair is transferred to a centrifugal machine or spinner1 in which much adhering water is removed4 ,this is a great assistance in drying out1 which is the next and final operation4 ,in drying1 the hair is laid upon steam-heated boxes or pipes1 and a current of warmed air passed over or through it by means of a fan4 ,it is better to have the hair turned occasionally4 ,this ensures quicker as well as more even drying4 ,the product is made up into large bales and sold for the manufacture of felts1 mattresses1 etc4 ,white hair is usually kept separate and commands a larger price4 ,the power consumed in driving the washing machinery1 the centrifuges and the drying fan1 together with the fuel required for the drying steam1 and the labour involved throughout1 make it doubtful whether this bye-product is worth either the capital outlay or the working costs necessitated4 ,many manufacturers avoid this treatment altogether1 therefore1 and the wet limed hair is sold direct to the fertilizer factory4 ,a less price is obtained1 but much expense is saved4 ,especially when the animals have only their short summer coats1 this course is preferred4 ,in the case of the wool from sheepskins the product is much more valuable4 ,the wool1 indeed1 is often the primary consideration4 ,unfortunately this sometimes results in the neglect of the pelt4 ,the removal of wool from sheepskins forms a special industry known as fellmongering1 which has been previously described 7,part ,,ii41 ,section ,,iv474 ,pains are taken to clean the wool even before removal from the pelt1 by the liberal use of water and the burring machine4 ,there is much variation in quality1 and care is taken to keep the various grades separate1 even during the pulling operation4 ,from the fellmonger the wool passes to the wool stapler1 and forms the basis of one of our most important mechanical industries1 the manufacture of woollen cloths4 ,wool is also removed from sheep by the periodic shearing1 and in this case does not reach the fellmonger at all4 ,apart from the raw material itself1 there are few bye-products of the leather trades which are of commercial importance4 ,the sludge from the pits of the limeyard contains1 in addition to much lime and chalk1 a certain proportion of protein matter4 ,this is derived partly from the blood and dung associated with the hide1 partly from the solution of the corium hide substance1 partly from the solution of the softer keratins1 and partly also undissolved and loose hair4 ,this bye-product is rather difficult to deal with1 as it will not easily dry4 ,it is indeed sometimes a problem to dispose of it1 except in rural districts1 where the farmers appreciate its manurial value and will usually cart it away for a nominal fee4 ,where possible1 it is better to let it drain and settle on land1 and pile it up in heaps to dry further4 ,soak-pit sludge has a distinctly greater value as manure1 on account of the greater proportion of dung proteins4 ,as some lime is often used in these pits1 the product is a really useful fertilizer4 ,the only other bye-product of the leather trades is waste leather itself4 ,for small pieces of leather there is always some little opening in producing small articles1 such as washers for taps1 etc41 and there is also the possibility of shredding or pulping and making an artificial leather4 ,the best leather substitutes1 indeed1 are made from waste leather4 ,nevertheless1 there is always a certain amount of waste leather which only finds an outlet in the fertilizer factory4 ,such material is usually steamed or roasted to make it brittle1 and then crushed in a disintegrator4 ,it is then mixed in with other materials1 but is sometimes solubilized by the action of sulphuric acid4 ,leather seldom contains less than #cj per cent4 protein4 ,,references4 ,chemical ,fertilizers and ,parasiticides1 ,s4,h4 ,collins1 ,m4,s41 ,f4,i4,c4 7,companion volume in this series on ,industrial ,chemistry47 ,wool ,wastes1 ,part ,,ii41 ,section ,v41 p4 #ge4 ,hoofs1 ,horns1 ,leather1 ,part ,,iii41 ,section ,,ii41 p4 #aae4 ,gelatine1 ,glue1 and ,allied ,products1 ,t4 ,lambert4 ,,section ,,ii4--,,bye-,,products ,,of ,,the ,,gelatine ,,and ,,glue ,,trades ,from the skin gelatine and glue trades the most valuable bye-product is the grease1 which is obtained from the fleshings of the adipose tissue4 ,these fleshings are themselves a bye-product of the leather trades4 ,the recovery and purification of this grease has been dealt with previously 7,part ,v41 ,section ,,ii474 ,in the skin glue trade the only other bye-product is the residue from the extraction process 7,part ,v41 ,section ,,iii474 ,this residue is known usually as glue scutch1 and is composed of the proteins of the skin which are insoluble in hot water4 ,these insoluble portions are obtained from all layers of the skin4 ,there is much hair often in scutch1 the hyaline or glassy layer 7grain71 and the elastic fibres of the corium are also insoluble1 and a proportion is derived from the fibres of the adipose tissue on the flesh side4 ,all these portions are fairly rich in nitrogen1 and the scutch has1 therefore1 considerable value to makers of fertilizers4 ,it is liable to contain also a percentage of grease1 which is usually removed by steaming under hydraulic pressure4 ,this process recovers a valuable bye-product and increases the manurial value of the scutch4 ,there is always left in scutch some of the gelatinous skin substance which1 strictly speaking1 should have been removed during extraction4 ,there is1 however1 a practical limit beyond which it does not pay to do this4 ,when this limit is reached the cost of steam in extracting1 and also in evaporating and drying1 together with the loss of time and labour involved by occupation of the plant1 is greater than the value of the possible product4 ,from the bone-glue industry1 the grease is similarly a valuable bye-product1 but there is also another of equal importance1 viz4 the phosphate of lime1 which comprises about half the raw material4 ,as previously described in ,part ,,iv41 ,section ,,ii41 this is usually extracted after the grease1 by solution in weak hydrochloric acid4 ,the solution is neutralized in lead-lined vats with milk of lime1 a precipitate of di- and tri-calcium phosphates being obtained4 ,calcium chloride is left in solution1 and the precipitate should be1 therefore1 well washed if it be desired to have dry phosphate4 ,the bone-glue industry is1 generally speaking1 much more intimately connected with the fertilizer trades than the skin-glue trades1 indeed the extraction of the bones for glue is not always advisable1 in which case the protein matter as well as the phosphatic matter of the bones are employed for making bone manures4 ,for details of this industry the reader is referred to a companion volume in this series on ,chemical ,fertilizers4 ,,references4 ,chemical ,fertilizers and ,parasiticides1 ,s4,h4 ,collins1 ,m4,sc4 ,bones1 ,part ,,ii41 ,section ,v41 p4 #gb4 ,precipitated ,bone ,phosphate1 ,part ,,iii41 ,section ,,iii41 p4 #aeg4 ,bone ,manures1 ,part ,,iii41 ,section ,v41 p4 #agc4 ,gelatine1 ,glue1 and ,allied ,products1 ,t4 ,lambert4 ,,section ,,iii4--,,food ,,proteins ,although there are those who consider that animal proteins are both undesirable and unnecessary as foods1 it is nevertheless true that man is almost universally a carnivorous animal4 ,the animal world provides mankind with one of its chief sources of food1 and especially of protein foods4 ,protein foods are unquestionably essential1 and animal protein foods differ chiefly from those of vegetable origin in the fact that they contain generally much more protein4 ,of the proteins noted in our ,introduction1 the keratins have no value as foods2 the gelatins have some value as culinary material1 but little actual food value2 whilst the albumins comprise practically all the useful animal food proteins4 ,whilst the actual flesh of animals is the principal source of food proteins--both as to quantity and food value--other parts of animals1 e4g4 kidneys1 liver1 blood1 brains1 tongue1 are used and relished4 ,the most important sources of animal food proteins are from fish1 fowl1 sheep1 cattle1 and pigs1 the meat from these being roughly in the same sequence as to digestibility4 ,there are1 however1 many other animals of which the flesh is quite edible1 but most of the above are specially farmed and propagated primarily for their food value4 ,as the animal food proteins are exceedingly putrescible1 they are usually consumed within a short time of the animal being killed4 ,it is perhaps natural1 therefore1 that many efforts have been made to discover means of preserving such foods4 ,these efforts form the basis of some important industries1 and though they can hardly be included as chemical industries1 it will not be out of place in this volume to point out that these efforts present analogies with1 as well as differences from the methods used for preserving hides and skins 7,part ,i41 ,section ,i474 ,the curing of hides and skins is a temporary preservation from putrefaction until the opportunity is convenient for the permanent preservation 7i4e4 tannage74 ,the preservation of meats is analogous to curing inasmuch as more drastic treatment might indeed make them non-putrescible1 but would also render them indigestible and unsuitable for food4 ,thus drying1 salting1 drying and salting1 pickling and freezing1 are just as suitable for preserving food proteins as for hide and skin proteins4 ,hence we have dried meats1 salt bacon1 pickled beef1 frozen mutton1 etc4 ,to a limited extent smoking 7fish1 bacon1 etc47 has been employed as a cure4 ,when it has been applied to skins it is usually combined with a fat tannage4 ,there is1 however1 one method of preservation of proteins1 inapplicable to skins1 which has been eminently successful and useful for food proteins1 viz4 sterilization by boiling4 ,the food has been placed in tins1 hermetically sealed1 and thoroughly sterilized4 ,hence have appeared corned beef1 tinned tongue1 sardines1 etc41 which merely illustrate the immense possibilities involved4 ,a noteworthy advantage of this method of preserving animal food proteins1 is that the food is already cooked and prepared for immediate consumption4 ,another line of effort is the preparation of concentrated foods4 ,just as animal foods are on the whole more concentrated in protein than vegetable foods1 so these prepared animal foods are more concentrated than animal flesh1 and generally also more soluble4 ,such preparations of animal protein are obviously useful when there is difficulty in swallowing and when journeys are necessary into regions of poor food supply4 ,it is a little doubtful1 one must say1 whether the concentration is as great in some cases as is claimed4 ,yet another industry based upon the animal proteins is the manufacture of meat-extracts4 ,these are not merely concentrated extracts of animal flesh1 but contain especially the stimulative properties of animal food proteins4 ,there is now little doubt of the value of these preparations as stimulants1 and it is claimed for them that they not only have food value1 but also that they increase the food value of other foods used with them4 ,together with these products may be classed all the miscellaneous tonic foods1 in which proteins are blended with carbohydrates and often also with drugs4 ,these aim at the cure of specific disorders1 such as nervous debility1 sleeplessness1 etc4 ,their claims are often extravagant4 ,amongst all the multitude of prepared foods1 there deserve particular mention the partly predigested foods4 ,in cases where the digestive functions are weak or disordered these products have been of real service4 ,one of the most useful and valuable of animal food proteins is obtained from hen eggs4 ,the white of eggs is almost pure albumin1 and there is much protein in the yolk also4 ,eggs are now produced and imported by the million1 and form a most important item in the country's dietary1 the protein being in a very easily digestible form4 ,it is also necessary to refer to the importance of cows' milk as a source of animal food protein4 ,the amount of protein in milk 7#d-e per cent47 is not large1 but it is united with fats1 carbohydrates1 salts1 and vitamines in such proportions1 that milk is about the only article which may reasonably present a claim of being a complete food4 ,milk1 moreover1 forms the staple diet of infants and young children1 so that its protein is certainly of great importance4 ,as an infant food1 cows' milk is not altogether ideal4 ,even when the proportions of fat1 carbohydrate1 and protein have been adjusted to resemble human milk1 there remains the difficulty that some of the proteins of milk 7especially the casein7 are too indigestible for young infants4 ,this difficulty has been only partly surmounted by those industries engaged in manufacturing infant foods4 ,some claim to remove the bulk of the casein2 others to have rendered it digestible by treatment with enzymes2 others1 again1 simply claim to supply concentrated cows' milk4 ,tinned milk1 generally concentrated to some extent1 now forms a useful addition to animal food products4 ,the casein of milk also finds some outlet for industrial purposes4 ,when treated with formaldehyde it yields an artificial horn much used for the preparation of imitation tortoiseshell4 ,skim milk is treated with caustic soda or carbonate of soda1 the casein precipitated by acid1 pressed1 impregnated with formaldehyde1 and dried4 ,the product is termed galalith4 ,it can be distinguished from real tortoiseshell by the action of fuming nitric acid 7see ,j4,c4,s4,i41 #aiji1 #aja74 ,the utilization of the blood of animals1 which is very rich in protein1 as a foodstuff has long been known1 but has met with a good deal of prejudice in this country4 ,this prejudice has arisen not merely from the objection to blood as food1 but also from the fact that such foods have been particularly liable to putrefaction and hence to cause poisoning4 ,the shortage of all foodstuffs occasioned by the ,european ,war did much to overcome this prejudice1 and there were considerable developments in the manufacture of black pudding and similar preparations of animal blood4 ,the same circumstances made it necessary to consider more seriously the possibilities of other butchers' offal as human food1 and resulted in new preparations of tinned animal proteins being placed on the food market4 ,the author would like to record his opinion that by no means the last word has been said on the question of drying as a method for preserving animal food proteins4 ,there is much to be said for this method on every ground in theory1 and it is evidently an increasing success in practice4 ,dried milk has been followed by dried eggs1 and in view of the success of the method when applied to fruits and vegetables1 there seems a prospect of better success in respect of dried meats4 ,after all1 animal food proteins are chiefly lyophile colloids1 and though desiccation presents some practical difficulties1 the subsequent imbibition 7assisted perhaps by lyotrope influences7 seems to be the ideal method for restoring preserved protein to its original condition4 ,in conclusion1 it will be interesting to note in the subjoined table1 the relative importance of the different sources of supply of both animal and vegetable food protein4 ,the figures are taken from the report of a ,committee of the ,royal ,society4 ,they show the average quantities of food materials 7imported and home produced7 available for the ,united ,kingdom during the five years #aiji-aiac inclusive1 together with the amounts of protein1 fat1 and carbohydrate present and the energy value4 ,this information formed the basis of the ,committee's recommendations as to economy of protein during the war shortage4 ,these recommendations included the more economical production of meat by slaughtering cattle younger and the saving of #ee1jjj metric tons of protein annually by adopting cheese-making as a general practice in place of butter-making4 ,metric tons4 ,energy -------------------------------- value1 ,protein4 ,fat4 ,carbo- millions of hydrate calories4 ---------------------------------------- ---------------------------- ,cereals #edi1jjj #fc1jjj #c1fbh1jjj #ag1gab1jjj ,meat #cef1jjj #gii1jjj -- #h1hij1jjj ,poultry1 eggs1 game1 #db1jjj #ca1jjj -- #dfa1jjj and rabbits ,fish #ia1jjj #ag1jjj -- #eca1jjj ,dairy produce1 including #aii1jjj #fhf1jjj #beh1jjj #h1bec1jjj lard and margarine ,fruit #i1jjj #ad1jjj #bbb1jjj #a1jgg1jjj ,vegetables #abj1jjj #aj1jjj #a1jca1jjj #d1hab1jjj ,sugars 7including cocoa1 #e1jjj #ah1jjj #a1egb1jjj #f1fcc1jjj etc47 ,other cottage and farm produce #fg1jjj #ac1jjj #eea1jjj #b1fee1jjj ,,section ,,iv4--,,miscellaneous ,,animal ,,proteins ,the excreta of animals include animal proteins of great importance to agriculture and horticulture1 forming the staple supplies of manure4 ,the manure of animals should contain not only the solid waste material and undigested food1 but also the urine1 which contains much nitrogen1 and hence makes considerable difference to the value of the product as a fertilizer4 ,if the animals are fed on rich foods1 the manure obtained is correspondingly richer1 especially in its protein content4 ,the value of dung manures depends not merely upon the protein content1 but also upon its content of phosphate and potash1 as well as other organic matter4 ,the protein breaks down into simpler nitrogenous compounds1 and eventually1 through ammonium carbonate1 it becomes nitrate4 ,nitrogenous manures darken leaves and increase growth considerably4 ,dung manures are deficient in phosphates and potash and are of value partly as nitrogenous manures producing growth1 and partly as dressings of organic matter for soil4 ,from both points of view it is desirable that the manure should be well decayed4 ,fresh dung manures are both wasteful and injurious to soil1 except perhaps to very stiff clays4 ,they are wasteful inasmuch as much ammonia escapes1 and injurious inasmuch as they cause the denitrification of the valuable nitrates already in the soil4 ,when possible dung manures should be kept under cover4 ,free exposure to air and rain will sometimes reduce its value by one half4 ,it should be stored until sweet1 and until the straw has rotted and become short4 ,this takes usually several months4 ,a ton of well-rotted farmyard manure contains very approximately #aj-ab lbs4 nitrogen1 about the same amount of potash1 and about half that quantity of phosphates4 ,it is1 however1 very variable4 ,horse manure is rather richer than cow manure1 but more liable to loss on storage4 ,pig manure is intermediate between them4 ,sheep manure is distinctly richer in protein1 and has therefore greater value as nitrogenous fertilizers4 ,poultry droppings are richer still1 perhaps partly because they include the urinary products4 ,when fresh they contain #ah-be lbs4 nitrogen1 #ab-bd lbs4 phosphate1 and #f-ab lbs4 potash per ton4 ,when dried they have about double the value4 ,pigeon manure is even richer1 and the pigeon loft scrapings have a manurial value about double that of dry hen manure1 and eight times that of farmyard manure4 ,guano is much decayed droppings of sea birds on the tropical coasts of ,africa and ,america4 ,the supplies are now quite exhausted1 and the market guanos are chiefly artificial fertilizers4 99 99 99 99 99 ,there is one other animal protein which must be referred to before this volume is concluded1 viz4 silk4 ,this is obtained from the cocoon of the silkworm1 which is the general name given to the larv of certain bombycid moths4 ,these larv feed on the leaves of the mulberry1 and when ready to pupate produce a considerable supply of a soft and delicate thread which is wound round about the larva itself4 ,this is the raw silk1 and it is unwound from the cocoon in a machine called the silk-reel1 and may then be wound into a thread4 ,two or more threads twisted together form thrown-silk4 ,silk threads are also woven into cloth of characteristic texture and appearance4 ,this protein thus forms the raw material of one of the most important textile industries4 99 99 99 99 99 ,from the fish trade there is much animal protein1 which is useless for food purposes and which1 to avoid nuisance1 it is necessary to convert promptly in fertilizers4 ,during the herring season there is the disposal in this way of the heads1 tails1 and the guts4 ,many fish are incidentally caught which1 being valueless as food1 are yet useful as manure4 ,after the extraction of oil from fish livers the residue is suitable for a similar purpose4 ,these residues are steamed1 dried1 and ground up1 forming fish manure1 rich in nitrogen and often also in phosphate4 ,,references4 ,chemical ,fertilizers and ,parisiticides1 ,s4 ,h4 ,collins1 ,m4,sc4 ,organic ,nitrogen ,fertilizers1 ,part ,,iii41 ,section ,,ii41 p4 #aje4 ,fish ,manure1 p4 #aaj4 ,,index ,acclimatization in colloid systems1 #bcf ,acid1 ellagic1 #bi gallic1 #bi sulphurous1 #bbg1 #bdc ,acid process for bone gelatine1 #bdc ,acids1 for deliming1 #bc for pickling1 #aad in sour liquors1 #bi1 #dd ,adsorption1 law of1 #dc methods of clarification1 #bcd nature of1 #da of ions by gelatine1 #baa ,african hides1 #ae ,albumins1 #d1 #bdj1 #bgd1 #bgg ,algarobilla1 #cb ,alum1 #bcf1 #bdj ,american hides1 #ad ,animal excreta1 #bgi ,arsenic sulphide1 #bj ,asiatic hides1 #ad ,astringency of liquors1 #dd ,bacteria in soaks1 #af limes1 #bj bates1 #bd tan liquors1 #bi ,bag leather1 #hf ,band-knife splitting1 #eb ,bark1 hemlock1 #cd1 #dj mallet1 #cd mangrove1 #ce1 #da mimosa1 #cc oak1 #cd pine1 #cd1 #da willow1 #cb ,basic dyestuffs1 #ig ,basils1 #aae ,bating1 #bd1 #id ,belting leather1 #fe ,blair-,campbell evaporator1 #bdi ,bleaching leather1 #fb glue1 #bda ,block ,gambier1 #dj ,bloom1 #bi ,boiling process for glue1 #bbc ,bone gelatine1 #bbc manure1 #bgc meal1 #bbd ,bones1 #bbc ,bookbinding leather1 #ajd1 #ajf1 #aag1 #abj ,boric acid1 #bc ,bottle tannage1 #ajc ,box calf1 #aef ,bridle leather1 #ga ,british hides1 #h ,brushing leather1 #fc ,buck leather1 #aha ,buff leather1 #aha ,buffing1 #eb ,burning in1 #ed ,butt1 #bb ,bye-products of the gelatine trade1 #bgb of the leather trades1 #bfh ,calcium sulphydrate1 #bb ,calf skins1 #gf1 #abj1 #aef ,casein1 #bgf ,cast glue1 #beg ,catechin1 #cb ,catechol tans1 #cb ,caustic soda1 #ah1 #bj ,centrifugal fan1 #ej ,chamois leather1 #aha ,cheeks1 #bfh ,chemistry of colloids1 #bja ,chestnut extract1 #cf ,chlorine bleach for glue1 #bdf ,chrome calf1 #aef goat1 #afc hide1 #agj sheep1 #afc ,chrome tannage1 #abg-agd finishing operations1 #aec general methods1 #aci history of1 #abg one bath1 #adi special qualities of1 #acf theory of1 #abi two-bath process1 #adb ,clarification of gelatine1 #bcd ,coefficient of conductivity1 #bec ,colloid chemistry1 #bja ,combination tannages1 #aia ,concentrated foods1 #bge ,condenser water1 #bea ,conductivity coefficient1 #bec ,continental hides1 #ad ,crown leather1 #agh ,cube gambier1 #dj ,curing hides1 drying1 #ac dry-salting1 #ac freezing1 #ac salting1 #ab sterilizing1 #ad ,currying1 #di ,cut glue1 #beg ,decolorization of glue1 #bch ,deerskins1 #ib1 #aha ,degreasing bones1 #bbd1 #bbg leather1 #aae ,deliming1 #bc ,depilation1 #ai ,divi-divi1 #cb ,dongola leather1 #aia ,drenching1 #be1 #ie ,dressing leather1 #bd1 #fe-ib ,drum stuffing1 #ec tanning1 #fc ,drying gelatine and glue1 #bee hides1 #ac leather1 #ej ,dung bates1 #bd manures1 #bgi puers1 #id ,dyeing leather1 #if ,ears1 #bbj1 #bfh ,eggs1 #bgf ,elastic fibres1 #f1 #bgb ,ellagic acid1 #bi ,enamelled leather1 #abc ,enzymes1 #bd1 #be1 #id1 #ie ,erodin1 #id ,evaporation1 #cg1 #bdh ,evaporators1 ,blair ,campbell1 #bdi ,kestner1 #bdi ,yaryan1 #bdi ,evolution of gelatine industry1 #bfe of leather industry1 #aid ,extraction of gelatine and glue1 #bcj-bcc of grease1 #aae1 #bbd1 #bbg of phosphate1 #bbd of tannin1 #ce ,extracts of meat1 #bge of tanning material1 #cg-da ,faces1 #bbj1 #bfh ,fan drying gelatine1 #beg leather1 #ej ,fat liquoring1 #aed tannages1 #agh ,federation of ,tanners1 #ajh ,fellmongering1 #aac ,fermentation in bates and puers1 #bd1 #id in drenches1 #be in limes1 #bj1 #ba ,fertilizers1 #bfi1 #bgi ,filter press1 #bch ,finger test1 #bah ,finishing chrome leather1 #aec heavy leather1 #di light leather1 #if ,fish glue1 #bbh manure1 #bhj ,fleshing1 #bb ,flocculation1 #bcg ,food proteins1 #bgd ,foods1 concentrated1 #bge dried1 #bgg ,formaldehyde tannage1 #ahe ,fractional extraction of glue1 #bcj ,galalith1 #bgg ,gallic acid1 #bi ,galls1 #cb ,gambier1 #dj ,gelatine1 bleaching1 #bda clarification of1 #bcd decolorization1 #bcd drying of1 #bee evaporation of1 #bdh extraction of1 #bcj properties of1 #bjj raw material for1 #bbj uses of1 #bfj ,glac calf1 #aef goat and sheep1 #afc ,glazing1 #ig1 #aee ,glove leather1 #agd ,glue 7see ,,gelatine7 difference from gelatine1 #bda ,goatskins1 #ii1 #afc ,graining1 #ig ,grease in bones and scutch1 #bbd1 #bbg in skins1 #aae ,guano1 #bgh ,hair1 removal of1 #bb ,handlers1 #dg ,hard-grain morocco1 #aag ,harness leather1 #ga1 #agj ,heavy leather1 #g-ib chrome leather1 #agj ,helvetia leather1 #agi ,hemlock bark1 #cd ,hides1 ,american1 #ad ,african1 #ae ,asiatic1 #ad ,british1 #h ,continental1 #ad dried1 #ac dry-salted1 #ac fresh1 #h frozen1 #ac salted1 #ab ,hoofs1 #bfh ,horns1 #bfh ,hyaline layer1 #bgb ,hydrophile colloids1 #bdj ,hydrophobe colloids1 #bdj ,hydrosulphite of soda1 #bde ,hypo bath1 #abh1 #adg ,imitation box calf1 #aei glac kid1 #afc ,imperial aspect of leather trade1 #aih ,increase in strength of tan liquor1 #dd ,incrustation1 #bed ,influence of ,lyotrope series1 #bjf-bji ,intensive production1 #aid1 #bfe ,interfibrillar substance1 #bd ,iron and logwood1 #ge1 #hc1 #aji ,jacking leather1 #ea ,japanned leather1 #abc ,jelly1 #bjc1 #beh ,keratins1 #d of epidermis1 #bgb ,kestner evaporator1 #bdi ,kid skins1 #afc1 #agd ,kips1 #h1 #gf1 #aei 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