The manufacture of leather: being a description of all of the processes for the tanning, tawing, currying, finishing

Front matter

CX3PYRIGHT DEPOSIT

THE

MANUFACTURE OF LEATHER:

Preface

Considering the importance of the leather industry, it seems strange that up to the present time it should in technical literature have been so much neglected.

There is not in England nor is there in America a single current book broadly treating all the branches of this subject, and the object of the present volume is fully to explain the details of manufacturing all kinds of leather in common use, and produced from hides and skins by the agency of the usual tanning substances.

The author has not been satisfied to make use of the matter found in obsolete books, but has preferred to present a view of the state of the art as it to-day exists in the United States.

The tools, machines, and in fact nearly all the mechanical appliances illustrated in the present treatise are of American origin, and in common use in the numerous tanneries and leather-finishing shops of the country.

The collection, compilation, and collation of the vast amount of technical and detailed information attainable relating to the various processes, and to the construction of the numerous machines herein described, have required almost herculean labor. But the work has been greatly aided by many of the leading tanners and curriers of the United States, who have not only placed at the author's disposal every opportunity for personal observation, but have promptly and courteously responded to

IV PREFACE.

his letters when containing requests for information. It is doubtful if such facilities as have been extended to him would be granted to a like professional writer on technical subjects in any other country in tlje world.

The enormous development of American leather manufacturing industries is a source of much congratulation. There are of course in this manufacture, as in all others, times of depression, but the natural facilities for obtaining the raw material, the great ingenuity of our people, and the steady increase in the export demand, added to the large home consumption of leather, are certain to keep the United States in the position of the leading leather-producing country of the world.

The invention and employment of a large number of mechanical appliances have done much to stimulate and cheapen leather production in the times just passed, and those manufacturers who have clung to the old-fasliioned metliods of tanning and finishing leather by hand have found their business absorbed by more enterprising firms.

Sucli results were only natural, and it is therefore in the future very desirable that those now in the business should keep fully abreast of the improvements in the art. When a machine or process has, after fair trial and investigation, proved to be an improvement upon old methods, it is simply suicidal to a business not to employ it. Every new method or contrivance is not necessarily an improvement: but the success of small tanners and curriers in the future lies solel}^ in the discriminative adoption of labor-saving machines and time-saving processes.

It is among those who j)roduce leather on a small scale that many chemical experiments in depilating, bating, and tanning could be conducted without serious loss or inconvenience, and it is urgently recommended that in the future more attention be given to this subject than it has received in the past. Every

PREFACE. V

process or machine used in leather manufacture that has been patented in the United States since 1790 to the close of the year 1883 is mentioned in this work. Ten volumes of the size of the present one would not have been sufl&cient to describe them all in full, but a printed copy of any patent issued since the year 1866 will, on receipt of twenty -five cents, be sent by the Commissioner of Patents to any address in the postal union. The patents issued prior to 1866 require to be copied in manuscript, and are therefore charged for by the United States Government according to the number of words contained in them. Thus there is by means of the present volume placed at the disposal of any person who desires it, an opportunity to become fully acquainted with every step and improvement in leather manufacture made in the United States during nearly a century.

The author desires to acknowledge the assistance which he has received from Dr. Thomas Antisell, Mr. John P. Chapman, and Prof. Benjamin S. Hedrick, examiners in the United States Patent Office, all of whom have most kindly and willingly aided him in many ways. The numerous and valuable lists of patents contained in this volume could not have been perfected but for the facilities which the above-named gentlemen have extended.

Prof. William H. Seaman, assistant examiner, early manifested his interest in the work, and his suggestions from the first have proved valuable.

Col. Weston Flint, and his assistants in the scientific library of the United States Patent Office, have also greatly aided the author in his researches, and to them also he desires to acknowledge his indebtedness.

To the enterprising publishers of this volume much credit is due. They have most kindly responded to every suggestion of the author, and have cooperated with him in every particular, sparing neither time, labor, nor expense.

VI PREFACE,

The chernistr}'- relating to leather, skin, and tannins has been compiled from the best German and French authorities, and due credit is given for all such matter in the proper places in the volume.

It is earnestl}^ hoped by the undersigned that his long labors will not prove unfruitful, and that many persons will be benefited by his work.

CHARLES T. DAVIS. <

1114 Pennsylvania Avenue,

Washington, D. C, Nov. 22, 1884.

Chapter I

HJDES AND SKINS — THE VARIETIES OF HIDES AND SKINS USED FOR LEATHER — REMOVING HIDES AND SKINS FROM ANIMALS — SELECTING HIDES AND SKINS — FRAUDULENTLY INCREASING THE WEIGHT OF HIDES — PRESERVING HIDES — LIST OF AMERICAN PATENTS FOR PRE- SERVING HIDES-^COMMERCIAL CLASSIFICATION OP HIDES.

PAGE

Historical facts relating to the use of Hides and Skins of Animals . 33

Early facts in regard to flocks and herds as given in the Old Testament . 34

Cattle breeding in the United States ; the Empii-e of Nature divided into three Kingdoms — Mineral, Vegetable, and Animal ; their connection with the Leather Industry ; the Mineral Kingdom ; the Vegetable Kingdom . . . . . . . . . . . 35

The Animal Kingdom ; the Skins which are applicable to the Manufacture of l^eather ; Historical facts regarding the Manufacture of Leather 86

Surmises as to the manner of the origin of the Art of Tanning . . 37

Varieties of Hides and Skins used for Leather ; Classification of Tanned Leather and of the parts of Hides ; Hides, Kips .... 38

Skins ; Mammiferous Animals, and their application to the wants of Man ; the Common Ox — its Flesh, Horns, Cartilages, Bone, Hair, etc. ; Glue ; Effect of the improvement of the Breed of Cattle on their Hides 39

Hides from UnimproAred Breeds preferred by the Tanner ; Cattle-Skins the chief source of supply for Tanneries ; whence procured and the Characteristics of those from the Various Countries . . . .40

Heavy Hides and Medium Weight Hides, Calf-Skins, Sheep- Skins, I^amb-Skins whence derived, and Varieties of Leather which they produce . . . . . . . . . . . .41

Sheep and Lamb- Skins, the next in impor'_tance to Ox Hides as sources of Leather ; the value of a Breed of Sheep for the Tanner in inverse proportion to its value as Wool ; Some of the uses of Sheep and Lamb Skins; Goat Skins .......... 42

Horse Hides, and the Skins of the Ass, Zebra, Quagga, etc. ; Horse Leather and the importance of this Industry ; Seal- Skins . . .43

Vm CONTENTS.

VAGE

Hog-Skins, Dog-Skins, Porpoise- Skins, Hippopotamus, and Elephant Hides ; Alligator Skins, the Alligator Leather Industry in the United States ; Characteristics and Uses of Alligator Leather ... 44

Kangaroo-Skins and the Leathers which they produce ; Buffalo Hides, Deer-Skins, Shark and Rhinoceros Skins, AValrus Hides ; Removing Hides and Skins from Animals ........ 45

Directions urgently recommended in Flaying Hides and Skins ; Importance of these dii'ections ......... 46

Selecting Hides and Skins; the Hides of Oxen, Bulls, and Cows; the Hides of Animals dying of disease ; Criteria for guiding the purchaser in distinguishing the quality of Hides and Skins . . . .47

Hides of Animals dying from contagious diseases should be rejected or handled with great care ; danger of handling such Hides ; Poisoning by Bacterium, AntTirax producing Malignant Carbuncles : Disinfecting I'anneries and other places where Skins are stored ; Importance of thorough Cleansing of the Store-room ...... 48

Fraudulently increasing the Weight of Hides by the employment of Sulphuric Acid ; Tests for the Detection of this Fraud ; Preserving Hides ; Mode of Salting ; Delane's Method the one generally employed . 49

Quantity of Salt required; Glauber's Salt for Salting Hides; Other Materials for Preserving Hides ; Moret's Composition for Impregnating Hides and Skins and Preserving them so as to be capable of being unhaired by a simple immersion in water ...... 50

The Preparation and Application of Moret's Composition . . .51

Advantages claimed for Moret's Composition ; Rock's Liquid for Curing Hides 52

Sabath6 and Jourdan's Process ; Napier's Process, Sacc's Process, Wickersheimer's Process ......... 53

List of all Patents issued by the Government of the United States of America for Preserving Hides from 1790 to 1883 inclusive ; Commercial Classification of Hides ; Dry Flint ; Dry Salted ; Green Hides . . 54

Green Salted Hides ; Part Cured Hides ; Damaged Hides ; Glue Stock ; Branded Hides ; etc. . . . . . . . . .55

CHAPTER IL

SYNOPSIS OF THE HISTORY OF TANNING — COMMERCIAL VARIETIES OF

LEATHER.

Synopsis of the History of Tanning ; Conditions upon which an Art must rest in order to improve ; Facts in reference to the history of Leather derived from the Old Testament ....... 5C

Colored Leather described by Ezekiel as early as 593 B. C. as in use by Babylonians, Chaldeans, Pecods, Shoas, Koas, and all the Assyrians ; Testimony of Herodotus in regard to the use of Leather; Early use

CONTENTS. IX

PAGE

of Leather by the Greeks, Phoenicians, Germans, and Britons ; Testimony of Homer and Hesiod ........ 57

Early expressions regarding the use of Leather ; the legend of St. Crispin ; the names of the early discoverers and improvers of the Processes of Tanning Leather ; Discoveries of MacBride (1768), Seguin (1 795), and Banks (1801); MacBride's Process of Raising by Sulphuric Acid; Seguin's Method by which Hides and Skins were Tanned in a shorter time, and Banks's discovery of the Tanning Property of Terra Japonica

(Catechu) 58

The English discovery of the Art of Varnishing Leather ; the introduction of the art of preparing AVater-Proof Leather by Ballamy, Von Hildebrandt, Edward, and others ; Little done by science in regard to the Improvement of the Art of Tanning ; Great improvements made in Apparatus, especially in the United States ..... 59

Skill not force, Chemical Knowledge not steam power, which in the future must cheapen and accelerate the Process of Tanning ; our inventors must aim to be good Chemists, as well as good Mechanics ; Room for inquiry after Tanning Materials and as to the Hide itself and its Structure .... ...... 60

The System of Tanning or Tawing by means of Chromium Compounds by Dr. Heinzerling in Germany ....... 61

The claims of Dr. Heinzerling as to the meritorious and original features of his Process ; Experiments of David Kircaldy, London, on Bark- Tanned and Chrome Leather ; Advantages which seem to be offered by the Chrome Process . . . . . . . • .62

Localities in which Dr. Heinzerling's Process, is in use ; Not yet full}' passed critical stages of practical experiment ; Commercial varieties of Leather ; Characteristic properties of Leather ; Leather Chemically considered .......... 63

Tawing and the class of Skins to which it is applied ; Tawing practised by the Romans ; Introduced into Hungary in the 1 2th Century ; Chamois Dressing invented in Hungary ; the Hungarians celebrated in early times for their White Leather ; French and Dane's Leather made from Lamb and Goat- Skins for the manufacture of Kid Gloves . 64 Red or Bark Tanning the oldest Method of Tanning ; Leather similar to Morocco and Cordovan made by the Ancient Orientals ; Persian and Babylonish Leather ; the art of making Leather brought from Asia into Europe ; the Turks, Russians, and Hungarians, the most celebrated Tanners in the first centuries of the Christian era ; Cordovan, Morocco, Shagreen, and Russia Leather ...... 65

The Morocco Leather Industry in the United States ; Decline of the Morocco and Chamois Leather Industries in Russia; the Tanning- Industry in Russia . . . . . . . . . .66

Shagreen and Russia Leather . . . . . . . .67

X CONTENTS.

Hungarian Leather ; Parchment ; Artificial Parchment ... 68

The use of Parchment, and where most hirgely produced ; Alum Leather ;

JBazil ; BufF Leather ; Chamois, Shammy, or Shamoy Leather ;

Enamelled Leather . . . . . . . . . .69

Enamelled Leather first manufactured in the United States in Newark, N.

J. ; Fair Leather ; Juncten ; Japanned, Patent and varnished Leathers

first made in the United States at Newark, N. J.; Oil Leather;

Roan; Russet; Saffian Leather ; Mogador Leather ; Skiver . . 70 Split Leather ; Wash Leather ; Whang ; White Leather or Tawed

Leather; List of names applied to Leathers in Commerce . . 71

Artificial Leather and its uses ; Vegetable Leather . . . .7?

Artificial Leather produced in Boston, Mass.; Importance of the Leather

Industry in the United States ........ 73

^ CHAPTER IIL

STATISTICS OF THE TANNING INTERESTS IN THE UNITED STATES.

Statement of the number of Tanneries in the United States ; Capital ; Hemlock and Oak Bark used ; Hides and Skins Tanned and the total value of products for the year 1880 . ... . . .74

The leading States engaged in this Industry . . . . . .76

Increase of Tanneries in Virginia, Tennessee, and other Southern States ; Exports and Imports of Leather ; the Leather Industry in Italy . 77

The Leather Industry of the United States rivals those of England, Germany, and Austria, and our exports should be largely increased ; Objections of English Tanners to our Leather ..... 78

Imports and Exports of Hides, Skins, Bark for Tanning, Cutch, and Gambir, Tallow, Fish Oils, etc., into and out of the United States for the twelve months ending June 30, 1882, and June 30, 1883, respectively ; Number of Leather Currying Establishments in the United States and their product in 1880 ; Importance of this Industry in Massachusetts . . . . . . . . . . .79

Table of the Leather Currying industry of the twelve leading States, representing nine-tenths of the whole business ..... 80

CHAPTER IV.

EXAMINATION OE LEATHERS.

Importance of the determination of the value and quality of Leather by chemico-technical examination; Marquis's Method — 1. Determination of fat and resin . . . . . . . . . .81

2. Determination of Lime in Leather. 3. Determination of the Tanning constituents : Method proposed by Heinzerling ; Determination of AVater ; Percentage of Ash ; Importance of determining the amount of Lime in Leather . . . . . . . . . . 82

• CONTENTS. XI

PAGE

Percentage of Fat . . . . . . . . . .83

To determine the Sebaoie Acid ; Determination of Nitrogen ; Plan proposed by Muntz; Barrentrapp-Will Method ; Cori'in, formulae of Reimer 84

Tanning Substance. 1. Tannic Acid ; Defects of Marquis's Method for determining Tannic Acid ; Mittenzweig's Method. 2. Mineral Constituents ; Determination of Mineral Materials in Mineral Tanned Leathers of Knapp and Heinzerling ; Examination of the cutting surface of leather, as a criterion ; Behavior of Tanned Leather toward boiling water as a test . . . . . . . . " . 85

Determination of means used to increase the weight of Leather ; Detection of Adulterations, such as Glucose, added for this purpose ; Physical methods of testing Leather ........ 86

I. Change in volume and ability for resisting water ; Table of Dr. Heinzerling in regard to the comparative resisting qualities of Tanned Leather and Heinzerling' s Mineral Tanned Leather . . . .87

Results shown by the Table ; IL Testing the strength of Leather ;

AVeiner's Apparatus . ... . . . . . 89>'

Tables showing the strength of a Skin in different places ... 91

Part II. Chapter Y

ANIMAL SKIN.

The Raw Products with which the Tanner has to deal — 1. Hides and Skins. 2. Tanning Materials ; the construction of Animal Skin ; the Ejjidermis and its Composition ........ 93

The Epidermis does not combine with Tannin, and is, therefore, useless to the Tanner ; the Corium or Leather Skin ; the Quality of the Leather dependent upon the thickness, flexibility, and strength of the Corium ; Coriin ; Illustration showing an enlarged Transverse Section of the Skin 94

Chemical Process in the production of Glue ; Skin slowly and completely dried in the air can be kept for a long time ; Decomposition of Moist Skins ; Preservation of Skins with Salt, . or Immersed in Strong Brine ; the Chemical and Morphological Constitution of Skins as shown by RoUet and Reimer ......... 96

Modes of Preparing Coriin ; to obtain perfectly pure Coriin free from an admixture of Cell Elements . . . . . . .97

Behavior of Coriin toward different Substances ; Liming contliuied too long gives poor weight ; Composition of Coriin ; Connective Tissue Substance and the Intercellular Substance, the difference between . 98

Xll CONTENTS.

PAGE

To prepare Connective Tissue Substance ; Behavior of Connective Tissue Substance towards various other Substances .... 99 The Swelling Property of Skin Fibre 100

CHAPTER VT.

VEGETABLE TANNING MATERIALS.

Section I. Tannix or Tannic Acid ; Tannin or Tannic Acid ; Great variety of Plants in which Tannic Acid occurs . . . .100

The different varieties of Tannin, their Chemical and Physical behavior, and whence derived .......... 101

Classification of Tannic Acids by E. Wagner into physiological and pathological Tannic Acids ; -whence these Tannic Acids are derived ; Wagner's views on the Subject of Leather Tanned with the respective Tannic Acids ; our knowledge of the different Tannic Acids still incomplete ; Principal obstacles to a determination of the Nature of Tannic Acids 102

Gallotannic Acid — Tannin of the Xut-gall ; Discovered by Lewis in the Eighteenth Century; Pelouze's Process for its Examination; Apparatus of Robiquet and Boutron . . . . . . . . lOo

Process of Mohr for the Exhaustion of Gall-nuts . . . . .104

Appearance and Qualities of the Tannin ; Domine's Process for the exhaustion of Gall-nuts ; Separation of the Tannic Acid by the Aqueous Solutions of Sulphuric and Hydrochloric Acids, etc. ; Melting and decomposition of Tannin ......... lOS

Behavior of Tannin under various conditions ; Tannin considered by

Sti'ecker a Glucoside . . . . . . . , .106

More recent Experiments prove Tannin not to be a Glucoside ; Experiments of Rochleder and Kawalier ; Liebig on the Transformation of Tannin into Gallic Acid by means of Potash and thence into Carbonic and Pyrogallic Acids ; Behavior of Tannin toward various Substances 107

Jmpure Tannin Substances modify themselves when kept in contact with the Air ; Constituticni of Gallotannic Acid ; Experiments of Strecker and Schriff ; Conclusions of SchrifF; Schriff's formula of Tannin . 108

The new formula of Tannin confirmed ; Tannomelanic Acid ; how obtained ; Tannopinic Acid . . . . . . . . .109

Tannoxylic or Ptufitannic Acid ; Quercotannic Acid ; Properties and Behavior of Quercotannic Acid. . . . . . . .110

Quercus Red ; Quercus Bitter or Quercin . . . . . .111

Querphlobaphene ; Phloroglucin ; Protocatechuic Acid ; Pyrocatechin ; the property in Tannic Acid of forming insoluble combinations with Alkaline Salt ; loss of Tannic Acid in using Hard Water ; Fermentation of Tannic Acid by Fungi - and P'erments ; Filtering of Water through exhausted Tan ; Researches of Sclmlze in regard to the Tannic Acid yielded by Oaks of different ages . . . . .112

CONTENTS. Xlll

PAGK

Tannic Acid generally present in the Roots, Barks, and Branches of Trees ; Tannic Acid a Brimary product of Vegetable Life ; Action of the different Tannic Acids toward the Corium or Leather Skin ; Tannic Acid which when heated forms Byrogallic Acid, furnishes Leather less capable of resisting Water than Tannic Acid yielding Pyrocatechin ; Influence of Extractive Substances upon the value of a Tannic Acid; Influence of Resins, Pectine Substances, etc. . .113

Spxtion IL Vegetable Tanning Materials .... 113

Rutea ; Kino ; African Kino, Malabar or East Indian Kino ; Kino very rich in Tannic Acid ; Garabier, its percentage of Tannin high ; Catechu or Terra Japonica ; its Constituents, Qualities, and Adulterations; the Leather produced from Catechu ; Gall-nuts — the richest in Tanning of all Tanning materials, their formation and qualities . .114

Green Galls ; European Galls ; Chinese Gall-nuts ; the countries in which Gall-nuts are produced ; Rove or Bassora Gall-nut . . .115

Sumach ; different varieties of Sumach found in Commerce — Sicilian, Italian, Spanish, Tyrol, French, and American Sumachs . . .116

Swedish Sumach ; the Tannic Acid contained in the Sicilian Sumach according to Stenhouse identical with Gallotannic Acid ; Tannic Acid of Old Sumach ; Leather prepared with Sumach possesses but little capacity of resisting Water ; Valonia ; Qualities of Leather prepared with Valonia ; Divi-divi ; Qualities of Leathers Tanned with divi-divi ; Tannic Acid of divi-divi ; Myrobalans . . . . . .117

Bublah ; Logwood ; Fustic ; Weld ; Larch Bark ; Fir Bark ; Hemlock

Bark; Qualities of Hemlock Bark . . . . . . .118

American Hemlock Extract; Oak Barks; Walnut Bark; Lombardy Poplar Bark; Elm Bark 119

Horse-chestnut Bark ; jEsculotannic Acid ; qualities, constitution, and behavior of ^li^sculotannic Acid ; Horse-chestnut Extract ; AVillow Bark 120

Alder Bark ; Beach Bark ; Protaceae Barks ; Snouba Bark ; Scorza Rosa; Ratanhy Root 121

Avens Root ; Tormentil Root ; Sassafras Root ; Live Oak Wood ; Quebracho ; Mimosa . . . . . . . . . . 122

Table showing the percentage of Tannin contained In the various Tanningmaterials determined according to different methods . . . .123

Results of more recent examinations of various substances containing Tannin, according to Fraas . . . . . . . .124

Tanning materials used in most countries only such as are there produced in great abundance ; the Tanning materials used in principal countries ; Practical experiments show that there is a considerable difference in the quiintity of the various Tannins absorbed by the Skin; Table of the quantities of Tannin required, according to Anthon, for the conversion of each one pound of Skin into Leather .... 125

XIV CONTENTS.

PAGE

Table of Experiments ; Experiments by Kester showing the increased weight of Hides after Tanning ........ 126

Tables of Experiments of Prof. Miintz and Dr. Schon regarding the absorption of different Tannins by the Skin, and of the removal of resinous extractive substances in Leather Tanned with different Tannins ; Conclusions of Miintz and Schon regarding the value of Leather . 127

Tables showing the results of the experiments of Miintz and Schon on the percentages of Skin and Tannin in various kinds of Leather, as well as of Glue, Tannin, and Nitrogen in Leather perfectly dry and free from all soluble substances . . . . . . . . 1 28

Table of the number of pounds of Leather free from Resin obtained from <

220 pounds of Dry Skin ; Results to be deduced from these Experiments as to the quantities of different Tannins absorbed by Skins . 129

CHAPTER YII.

MINERAL AND ARTIFICIALLY PREPARED TANNING SUBSTANCES.

Section I. Mineral Tanning Materials ; Use of Mineral Tanning materials in very early times ; Principal Mineral Substances to be considered — 1. Alum, Aluminium Sulphate, and Aluminium Acetate. 2. Chromates and Chromic Oxides. 3. Ferric Salts. 4. Common Salt ; Aluminium Sulphate; Preparation, qualities, and characteristics . 130

Aluminium Sulphate in Tanning ; Alum ; Preparation, qualities, and characteristics . . . . . . . . . . .131

Iron Alum ; Manganese Alum ; Chromium Alum ; Alum in Tanning ; Aluminium Acetate ; Preparation, (jualities, and characteristics . 132

Chromium Salts ; Potassium Bichromate in Tanning ; Preparation,

qualities, and characteristics ........ 133

Sodium Bichromate ; Calcium Bichromate ; Strontium and Barium ; the Neutral Alkaline Chromates; Chromium Alum, its use in Tanning ; Chromic Sulphate . . . . . . . . . .134

Ferric Salts ; Recommendation of Ferric Salts for Tanning by D' Arcet in the last century; Patent of Bordier in 1842 ; Experiments of Professor Knapp on Tanning with Ferric Salts; Knapp's L-on Soap; Common Salt, its use in Tanning . , . . . . .135

Section II. Artificially Prepared Tanning Substances; Jennings's Artificial Tanning Material . . . , . . .136

Sky's Tanning Material; Lees's Artificial Tannin; an Artificial Tannin formed by heating a solution of Resins and Camphor with Sulphuric Acid 137

The Classes to which the different Artificial Tannins belong . . . 138

CONTENTS. XV

CHAPTER VIII.

CHEMICAL EXAMINATION OP VEGETABLE TANNING MATERIALS.

PAGE

Method of determining the Tannic Acid ; Substances found by Gerber in a solution of the inner layer of Oak Bark ; Davy's Volumetric method of analysis .......... 139

Miintz and Rampercher's Apparatus for Filtering Tanning Liquor under pressure ............ 140

Fleck and Wolf's Method; Persoz's Method 141

Wildenstein's Colorimetric Method ; Fehling's Method modified by G.

Muller 142

Satisfactory results secured from the last-named method according to Gauhe and Hallwachs ; Lippowitz employs Isinglass in place of White Glue for precipitation of the Tannic Acid in the Felling-Miiller Method; Carpene-Barbieri's Method ...... 143

Gerland's Method ; Jeans's Method ; Hammer's Method . . . 144 Table of the relation between the Specific Gravity and the Percentage of Tannic Acid, intended to facilitate calculations when Hammer's Method is employed; Franz Schulze's modification of Hammer's Method . 145 Salzer on Schulze's modification ; Observations on the manner of executing Hammer's Method ......... 146

Special Areometers which can be used to advantage with Hammer's

Method; Mittenzwei and Terreil's Method 147

Manner of executing this method . -, . . . . . . 148

Hallwachs states that the results of this method are too high ; Grassi's

Method 150

Wagner's Method 151

Biichner's Remarks on Wagner's Method . . . . . .152

Neubauer's Criticisms on Wagner's Method ; Clark's modification of Wagner's Method . . . . . . . . . .153

Loewenthal's Method modified by Neubauer ; Details of the execution of this method . . . . . . . . . . .154

Making the Titre . .156

Loewenthal's modification of his method; Kathreiner on the manner of executing Loewenthal's Method ....... 157

Results of experiments by Kathreiner on the Tannic Acid in Tanning materials ............ 158

Recommendations of Kathreiner ; Examination of Oak Bark . . 159

Practice of Neubauer and Kathreiner . . . . . . .160

Results obtained by Cech and Neubauer . . . . . .162

Comprehensive comparison of the results obtained by the above-described methods . . . . . . . . . . . .163

Table by Hallwachs showing the difTcrence in the percentage of Tannic Acid determined according to the methods of Fehling, Muller, Loewenthal, Hammer, Fleck, and Mittenzwei . . . . ... 164

XVI CONTENTS.

CHAPTER IX.

WATER.

PAGE

Section I. General Remarks Concerning Water . . .165 Determination of the qualities of Water for Tanning purposes . . 1(36 The effects of Hard and Soft Watei's when used for Soaking, Cleansing, and Washing the Hides ; Eitner's Experiments regarding the effects of inorganic constituents of Water upon the depilated Skin ; Comparative effects of Hard and Soft Waters in Swelling or Plumping Hides ; temperature of Water for Preparing Hides . . . . . .167

Importance of a Uniform Temperature in the Water used in a Tannery ;

Supply of Water to a Tannery . . . . . . . .168

Section II. Methods for Determining the Constituents of Water; Qualitative Examination of Water ..... 169

Clark's Process of Determining the Hardness of Water by Soap Solution ; Mode of Execution of Clark's Process according to Faisst and Knauss . . . . . . . . . . . .170

Determination of total Hardness . . . . . . . ^ . 1 ? 1

Determination of permanent Hardness . . . . . . .173

PART HI.

CHAPTER X.

BARK — THE NATURE OF BARK — TOOLS USED IN BARKING — ROSSING BARK — LIST OP AMERICAN PATENTS FOR BARK-ROSSING MACHINES

PREPARING BARK FOR TRANSPORTATION LIST OF AMERICAN

PATENTS FOR PREPARING BARK FOR TRANSPORTATION.

The Nature of Bark ; the Epidermis . . . . . . .174

Davy's Examination of the Epidermis of the Bamboo, the Sugar Cane, etc. ; the Parenchyma ; the Epiphloeum ; the Mesophlceum ; the Lieber or Endophloeum ; the Cortical Layers ; the Alburnum or Sap-wood . 1 75 Peeling the Bark and the most convenient time for it . . . .176