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LEATHER ***




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Transcriber’s Notes

Text _between underscores_ represents text printed in italics, text
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subscript D. Small capitals have been transcribed as ALL CAPITALS.

More Transcriber’s Notes may be found at the end of this text.




THE PRINCIPLES
OF
LEATHER MANUFACTURE


[Illustration: _Frontispiece._

PLATE I.

SECTION OF CALF-SKIN. (For key, see Fig. 9.)]




THE PRINCIPLES
OF
LEATHER MANUFACTURE

BY

H. R. PROCTER, F.I.C. F.C.S.

PROFESSOR OF LEATHER INDUSTRIES AT THE YORKSHIRE COLLEGE, LEEDS;
PAST PRESIDENT OF THE INTERNATIONAL ASSOCIATION
OF LEATHER TRADES CHEMISTS

[Illustration]

=London:=
E. & F. N. SPON, LIMITED, 125 STRAND

=New York:=
SPON & CHAMBERLAIN, 123 LIBERTY STREET

1903




=Dedicated to=

PROFESSOR F. L. KNAPP

GEHEIMEN HOFRATH, DR. PHIL. AND DR. ING.

THE PIONEER OF SCIENTIFIC RESEARCH
IN LEATHER MANUFACTURE




PREFACE.


The origin of the present work was an attempt to prepare a second
edition of the little Text-Book of Tanning which the Author published in
1885, and which has been long out of print. Though persevered in for
years, the work was never brought to completion, partly owing to the
constant pressure of other duties, but still more to the rapid advances
which have been made in our knowledge of the subject, and in the
scientific thought which has been devoted to it. For his share in the
initiation of this work, much credit is due to Wilhelm Eitner, Director
of the Imperial Royal Research Institute for Leather Industries in
Vienna, but the advance he began has been energetically carried forward
not only in Vienna, but in the Tanning Schools and Research Institutes
of Freiberg, Leeds, London, Liège, Copenhagen, Berlin and elsewhere, and
to a less extent in private laboratories.

Under the pressure of this rapid growth, as it was impossible to
complete the work as a whole, the Author published an instalment dealing
with the purely chemical side of the subject in 1898, under the title of
the ‘Leather Industries Laboratory Book’; which has been translated into
German, French and Italian, and of which the English edition is rapidly
approaching exhaustion.

The present work, which should by right have preceded the Laboratory
Book (and which frequently refers to it as “L.I.L.B.”), attempts to deal
with the general scientific principles of the industry, without
describing in detail its practical methods (though incidentally many
practical points are discussed). To complete the subject, a third volume
ought to be written, giving working details of the various methods of
manufacture; but apart from the difficulty of the subject, and the
weariness of “making many books,” the methods of trade are so
fluctuating, and dependent on temporary conditions that they have not
the same permanent value as the record of scientific advance.

As the present volume is intended to appeal both to the chemist and to
the practical tanner, it must to a certain extent fail in both, since
many matters are included which are already familiar to the former, and
it is to be feared, some, which may prove difficult to the latter. For
these and other imperfections the Author claims the indulgence of his
Readers.

The Author must here acknowledge his indebtedness to Dr. TOM GUTHRIE and
to Mr. A. B. SEARLE for assistance in writing several of the chapters;
to Dr. A. TURNBULL and Mr. F. A. BLOCKEY for much help in reading proofs
and preparing the MS. for the press; and to the many gentlemen who have
furnished or allowed him to use their blocks and drawings in
illustration.

THE YORKSHIRE COLLEGE,
LEEDS.




CONTENTS.


CHAPTER I.

_INTRODUCTORY AND HISTORICAL._

Primitive methods of leather manufacture - Use of leather by the
ancients - Progress of leather manufacture in England - Methods of
production of leather - Vegetable tannages - Combination tannages -
Use of aluminium, iron and chromium - Oil- and fat-leathers -
Difficulties of scientific treatment PAGE 1


CHAPTER II.

_INTRODUCTORY SKETCH OF LEATHER MANUFACTURE._

The object of tanning - Washing and soaking - Removal of hair by
liming - Unhairing by putrefaction - Unhairing and fleshing -
Deliming - Bating, puering and drenching - The vegetable tanning
process - Currying - Alum, chrome and chamois leathers PAGE 7


CHAPTER III.

_THE LIVING CELL._

The structure of cells - White blood-corpuscles - The yeast-cell -
Epidermis cells - The building up of plants PAGE 10


CHAPTER IV.

_PUTREFACTION AND FERMENTATION._

The nature of ferments - Organised and unorganised ferments -
Classification of organised ferments - General properties of ferments
- The alcoholic fermentation - The action of enzymes or unorganised
ferments - The destruction of ferments by heat and antiseptics - The
products of fermentation - The fermentations of the tannery -
Fermentation in bating and puering - Fermentation in the tanning
liquors - Moulds and mildews - Control of fermentation PAGE 15


CHAPTER V.

_ANTISEPTICS AND DISINFECTANTS._

Distinction of antiseptics and disinfectants - Lime - Sulphur
dioxide - Manufacture of sulphuric acid - Bisulphites and
metabisulphites - Boric acid and borates - Mercuric chloride -
Mercuric iodide - Copper sulphate - Zinc salts - Arsenic -
Fluorides - Phenol - Use of carbolic acid - Eudermin - Creasote -
Creolin - Salicylic acid - Benzoic acid - Cresotinic acid -
Anticalcium - “C.T.” bate - Naphthalene sulphonic acid - Naphthols
- Hydronaphthol - Oxynaphthoic acid - Carbon disulphide -
Formaldehyde - Triformol - Camphor and essential oils PAGE 21


CHAPTER VI.

_THE ORIGIN AND CURING OF HIDES AND SKINS._

Marking of hides - Fellmongering of sheep-skins - The use of salt -
Salting of packer hides - Brining - Dry-salting - Indian plaster
cures - Analysis of salt-earths - Salt- and iron-stains - Drying of
hides and skins - Damage by insects - The warble-fly - Damage by
branding - Cockle PAGE 33


CHAPTER VII.

_STRUCTURE AND GROWTH OF SKIN._

Similarity of Mammalian skins - Development of skin - Structure of
calf-skin - The epidermis - The structure of hair - The sebaceous
glands - The development of hair - The hair-sheath - The
hair-muscle - The hyaline layer - The corium - Connective tissue -
Fat cells - Striped muscle - Elastic fibres - The unhairing process
- The sweating process PAGE 46


CHAPTER VIII.

_THE CHEMICAL CONSTITUENTS OF SKIN._

The keratin tissues - Production of gelatine from connective tissue
- Analyses of hide and gelatine - Constitution of gelatine -
Analysis and Reactions of gelatine - Decomposition of gelatine -
Reactions of gelatine - Chondrin - Coriin - Hide-albumin - “Acid”
and “alkali” albumins - Egg-albumin - Vitellin - Casein - Keratins
- Elastic fibres - Analytical methods - Kjeldahl process PAGE 56


CHAPTER IX.

_THE PHYSICAL CHEMISTRY OF THE HIDE-FIBRE._

Causes of swelling and contraction - The essentials of the tanning
process - The constitution of matter - The nature of molecules -
Vapour-pressure - Surface-tension - Solution-pressures - Jellies -
Crystals - Osmotic pressure - Electrolytic dissociation -
Electrolysis - Reactions of ions - Absorption of water by gelatine
- Dehydration by alcohol - Action of acids, alkalies and salts on
gelatinous fibre - Physical explanation of swelling - Action of
acids on gelatine - Action of alkalies on gelatine - Effect of salt
- The pickling process PAGE 73


CHAPTER X.

_WATER AS USED IN THE TANNERY._

Impurities of natural water - Hardness - Soap test - Temporary
hardness - Clark’s softening process - Archbutt and Deeley’s
softening apparatus - Other appliances - Effect of temporary
hardness in tanning and dyeing - Permanent hardness - Boiler scale
- Mud - Iron - Alumina - Soda - Copper, lead, etc. - Sulphuric
acid - Nitrates and Nitrites - Chlorine - Carbonic acid - Silicic
acid - Effect of hardness on plumping - Peaty waters PAGE 93


CHAPTER XI.

_SOAKING AND SOFTENING OF HIDES AND SKINS._

Washing of fresh hides - Danger of putrefaction - Soaking of salted
hides and skins - Soaking and softening of dry and dry-salted hides
- American wash-wheel - Chemical methods - Difficulty of softening
hides dried at high temperature PAGE 108


CHAPTER XII.

_DEPILATION._

Methods of depilation - Sweating process - Liming - Sources of lime
- Quicklime - Slaking of lime - Solubility of lime in water -
Analysis of lime - “Available” lime - Action of lime on hide -
Liming in pits - Suspension limes - Effect of warming limes -
Quantity of lime required - The Buffalo method - Action of old limes
- Solution of hide substance by limes - Sodium and potassium
hydrates - Payne and Pullman’s process - Alkaline carbonates -
Alkaline sulphides - Sodium sulphide - Calcium Sulphydrate -
Gas-lime - Tank-waste - Lufkin’s liming preparation - Barium
sulphydrate - Realgar, or red sulphide of arsenic - “Inoffensive”
unhairing solution - Earp’s patent - Unhairing on the beam -
Unhairing machines - Vaughn machine - Leidgen machine - Unhairing
in stocks and wash-wheel - Jones machine - Fleshing - Vaughn
fleshing machine - Rounding PAGE 119


CHAPTER XIII.

_DELIMING, BATING, PUERING AND DRENCHING._

Methods of removing lime and reducing swelling - Use of acids -
Lactic, acetic and formic acids - Boral - Sodium bisulphate -
Boric (boracic) acid - Borax - “Pulling down” process - Use of
ammonium chloride and sulphate - Pickling solutions - Drenching with
lactic acid - Metabisulphite of soda - Washing out lime, French
process - Nesbitt’s process - Use of carbonic acid - Carbolic acid
- Cresotinic acid - Oxynaphthoic acid - “Anticalcium” - “Acrilene
bating acid” - “C.T. Bate” - Use of sulphides and polysulphides -
Babool pods - Bran-drenching - Bating and puering - Causes of
bating effect - Pepsin - Trypsin, or Pancreatin - Wood’s researches
- Erodin - Palmer’s experiments - Other artificial bates -
Relative effect of dog- and pigeon-dung bates - Analysis of dungs -
“Scudding,” or “fine hairing” - Preservation and use of dung PAGE 152


CHAPTER XIV.

_ALUM TANNAGE, OR TAWING._

Nature of leather - Mineral tanning substances - Salts of aluminium
- Alums - Aluminium sulphate - Effect of salt in tawing - Basic
alumina solutions - Tawing of skins for rugs - Calf-kid manufacture
- Glove-kid - Green leather and other combination tannages PAGE 184


CHAPTER XV.

_IRON AND CHROME TANNAGES._

Iron tannages - Chrome tannages - Chemistry of chromium compounds -
Knapp’s method of chrome tannage - Cavallin - Swan - Heinzerling -
Hummel’s improvement - Schultz’s method - Theory of the two-bath
process - Practical management of the two-bath process - Dennis’s
chrome tanning liquor - Procter’s liquors - Theory of basic process
- Practical use of basic liquors - Washing and neutralisation -
Effect of sulphur on chrome leather - Bluebacking - Fat-liquoring -
Dyeing of chrome leather - Glazing and finishing PAGE 198


CHAPTER XVI.

_PRINCIPLES OF THE VEGETABLE TANNING PROCESSES._

Methods of sole-leather tanning - Finishing of sole-leather - Theory
of vegetable tannage - Deliming of sole-leather - “Mellowness” of
liquors - Penetration of tannage - Drying of sole-leather - Tanning
of dressing leathers - Preparation for tannage - Avoidance of
“bloom” - Tannage of moroccos and other skins PAGE 220


CHAPTER XVII.

_COMBINATION OF VEGETABLE AND MINERAL TANNAGES._

Early combination tannages - Respective effect of mineral and
vegetable tannages - Use of fat-liquor - Action of mineral and
vegetable tanning materials on each other - Danish and Swedish glove
leathers - Green leathers - Making of fat-liquors - Chrome
combinations PAGE 236


CHAPTER XVIII.

_VEGETABLE TANNING MATERIALS._

Distribution of tannin in plants - Structure of barks - Botanical
list of important tanning materials PAGE 242


CHAPTER XIX.

_THE CHEMISTRY OF THE TANNINS._

Sources of tannins - General qualities of tannins - Chemical
constitution - Catechol- and pyrogallol tannins - Catechins -
Tendency of Catechol tannins to darken with light - “Physiological”
and “pathological” tannins - Presence of mordant colouring matters
PAGE 294


CHAPTER XX.

_THE SAMPLING AND ANALYSIS OF TANNING MATERIALS._

The International Association of Leather Trades Chemists - The
American Official Association of Agricultural Chemists - The sampling
of material - Preparation of solution for analysis - Extraction of
solid materials - Total soluble matter - Evaporations of solutions
- The weighing of residues - The determination of non-tannins - The
hide-powder filter method - The hide-powder shake method -
Determination of moisture - Colour-measurement PAGE 300


CHAPTER XXI.

_THE GRINDING OF TANNING MATERIALS._

Primitive methods of grinding - The bell mill or coffee mill - Disc
mills - Disintegrators - Carr’s disintegrator - Carter’s
disintegrator - Adjustment of disintegrators - The Williams
pulveriser - Myrobalans and Valonia crushers - Sawing mills -
Shaving mills - Dyewood cutting machines - Screening of ground
materials - Hatching of bark - Disintegrators and fire insurance -
Dust from disintegrators - Chain conveyors - Belt conveyors -
Vibrating conveyors PAGE 316


CHAPTER XXII.

_THE EXTRACTION OF TANNING MATERIALS, AND THE MAKING OF EXTRACTS._

Leaching - Early forms of leaches - The press-leach system -
Handling of liquors - Distributing troughs and valves - Construction
of leaches - Influence of temperature - Use of silent boiling jet -
Closed extractors - Sprinkling leaches - Manufacture of extracts -
Decolorisation of extracts - Soluble extracts - Concentration of
extracts - Yaryan evaporator - Multiple effects - The use of
extracts in the tannery - Effect of temperature on extraction and
colour PAGE 328


CHAPTER XXIII.

_FATS, SOAPS, OILS AND WAXES._

Characteristics of fats and oils - Chemical constitution - Nature
and production of soaps - Insoluble soaps - Distillation of fats -
Solvents of oils - Drying oils - Saturated fatty acids - Non-drying
liquid fatty acids - Less-saturated liquid fatty acids - Castor oil
- Tallow - Neatsfoot oil - Wool fat - Holden fat - Distilled wool
grease - Distilled stearine - Olive oil - Castor oil - Turkey-red
oil - Linseed oil - Boiled oils - Japan for leather - Cottonseed
oil - Sesame oil - Cod oil - Shark liver oil - Whale oil - Seal
oil - Menhaden oil - Fish oils - Fish tallow - Dégras and Sod oil
- Waxes - Sperm oil - Beeswax - Carnauba wax - Japan wax -
Volatile or essential oils - Birch oil - Wintergreen oil - Mineral
oils and waxes - Vaseline and vaseline oil - Paraffin wax -
Ozokerit - Resin oils - Resin PAGE 350


CHAPTER XXIV.

_OIL TANNAGES, AND THE USE OF OILS AND FATS IN CURRYING._

Primitive use of oil in leather manufacture - Chamoising and the
production of washleather - Manufacture of Moellon, or Dégras - Sod
oil - Formaldehyde leathers - “Crown” and “Helvetia” leathers -
Theory of oil leathers - Processes of currying - Theory of the
stuffing process - Hand-stuffing - Drum-stuffing - Stuffing of dry
leather - “Spueing” and its causes - Fat-liquoring PAGE 378


CHAPTER XXV.

_DYES AND DYEING._

Coal-tar colours - Acid and basic colours - Theories of dyeing -
Fixation of colours on leather - Mordants and mordant colours -
Curriers’ inks - Glazes and finishes - “Assistants” in dyeing -
Bronzing - Fading of colours - Practical methods of leather dyeing
- Use of dyewoods - Iron “strikers” - Tannin blacks - Staining -
Theory of colour-mixtures - Finishing dyed leathers - Testing of
dyes - Injurious effects of metals in dyeing PAGE 394


CHAPTER XXVI.

_EVAPORATION, HEATING AND DRYING._

Theory of evaporation - Boiling point and vapour-pressure -
Consumption of heat in evaporation - Heat-units - Mechanical energy
of heat - Evaporation by “multiple effect” - Vapour-pressure of
atmospheric moisture - Wet and dry bulb thermometers - Heat and air
required in leather-drying - Loss of heat by buildings - Quantity of
heat given by steam and hot-water pipes - Screw-fans for drying -
Centrifugal fans - “Turret” dryer - Downward ventilation -
Arrangement of steam-pipes - Hot water pipes PAGE 420


CHAPTER XXVII.

_CONSTRUCTION AND MAINTENANCE OF TANNERIES._

Selection of site - Arrangement of buildings - Fire insurance -
Automatic sprinklers - Possibility of extension - Production and
distribution of power - Electric motors - Shafts, pulleys and
belting - Balancing of machinery - Fire-risk from bark mills -
Chain-conveyors - Lubricating oils - Construction of pits -
Underground pipes and overhead troughs - Pumps and pumping appliances
PAGE 444


CHAPTER XXVIII.

_WASTE PRODUCTS AND THEIR DISPOSAL._

Hair - Fleshings and glue-stuff - Fat - Bate-shavings - Horns -
Spent tan - Tan-furnaces - Sewage and other waste liquids -
Chemical purification of sewage - Settling tanks - Filter-presses -
Bacterial purification of sewage - Tannery waste-liquors PAGE 460


APPENDIX A.

_METHOD OF THE INTERNATIONAL ASSOCIATION OF LEATHER-TRADES CHEMISTS
FOR THE ANALYSIS OF TANNING MATERIALS: Corrected to 1901._

Sampling from bulk - Preparation for analysis - Preparation of
infusion - Determination of tanning matters and non-tannins -
Colour-measurement - Analysis of used liquors PAGE 475


APPENDIX B.

_THE DECIMAL SYSTEM._

Metrical weights and measures - Centigrade thermometer PAGE 481


APPENDIX C.

_METHOD OF ANALYSIS OF TANNING MATERIALS OF THE AMERICAN ASSOCIATION
OF OFFICIAL AGRICULTURAL CHEMISTS: Corrected to 1901._

Preparation of sample - Quantity of material - Moisture - Total
solids - Soluble solids - Non-tannins - Tannins - Testing of
hide-powder - Testing non-tannin filtrate PAGE 482


APPENDIX D.

_LISTS OF COAL-TAR DYES SUITABLE FOR DYEING AND STAINING LEATHER,
furnished by Mr. M. C. LAMB._

Colours for staining leather - Colours for dyeing vegetable-tanned
leather - Dyeing and finishing chrome-leather - List of colours
suitable for chrome-leather PAGE 485


INDEX PAGE 499




PRINCIPLES
OF
LEATHER MANUFACTURE.

[Illustration]




CHAPTER I.

_INTRODUCTORY AND HISTORICAL._


The origin of leather manufacture dates far back in the prehistoric
ages, and was probably one of the earliest arts practised by mankind.
The relics which have come down to us from palæolithic times, and the
experience of the modern explorer, alike tell us that agriculture is a
later and a higher stage of development than the life of the hunter; and
since, in the colder regions, clothing of some kind must always have
been a necessity, we may conclude that it was first furnished by the
skins of animals.[1]

[1] See also Gen. iii. 21.

While wet skins putrefy and decay, dry ones are hard and horny; and
nothing could be more natural to the hunter than to try to remedy this
by rubbing the drying skin with the fat of the animal, of which he must
have noticed the softening effect on his own skin. By this means a soft
and durable leather may be produced, and this process of rubbing and
kneading with greasy and albuminous matters, such as fat, brains, milk,
butter and egg-yolks, is in use to this day, alike by the Tartars on
Asiatic steppes and the Indians on American prairies; and not only so,
but we ourselves still use the same principle in the dressing of our
finest furs, and in the manufacture of chamois, and many sorts of lace-
and belt-leathers.

Such a process is described in the _Iliad_ (xvii. 389-393) in the
account of the struggle over the body of Patroclus:

“As when a man
A huge ox-hide drunken with slippery lard
Gives to be stretched, his servants all around
Disposed, just intervals between, the task
Ply strenuous, and while many straining hard
Extend it equal on all sides, it sweats
The moisture out and drinks the unction in.”

It must also have been early noticed that wood smoke, which in those
days was inseparable from the use of fire, had an antiseptic and
preservative effect on skins which were dried in it, and smoked leathers
are still made in America, both by the Indians and by more civilised
leather manufacturers. To this method the Psalmist refers[2] when he
says, “I am become like a bottle in the smoke;” and such bottles, made
of the entire skin of the goat, are still familiar to travellers in the
East.

[2] Ps. cxix. 83.

The use of vegetable tanning materials, though prehistoric, is probably
less ancient than the methods I have described, and may possibly have
been discovered in early attempts at dyeing; an art which perhaps had
its origin even before the use of clothing! The tannins are very widely
distributed in the vegetable kingdom, and most barks, and many fruits,
are capable of making leather.

The employment of alum and salt in tanning was probably of still later
introduction, and must have originated in countries where alum is found
as a natural product. The art was lost or unknown in Europe till
introduced into Spain by the Moors.

Leather manufacture reached considerable perfection in ancient Egypt. A
granite carving, probably at least 4000 years old, is preserved in the
Berlin Museum, in which leather-dressers are represented. One is taking
a tiger-skin from a tub or pit, a second is employed at another tub,
while a third is working a skin upon a table. Embossed and gilt leather
straps have been found on a mummy of the ninth century B.C., and an
Egyptian boat-cover of embossed goat leather, as well as shoes of dyed
and painted morocco, are still in comparatively good preservation. The
art is of very early date in China, and was well understood by the
Greeks and Romans. In the Grosvenor Museum at Chester is the sole of a
Roman _caliga_, studded with bronze nails, which is yet pretty flexible.
After the fall of the Roman empire many arts were lost to Europe, and
it was not until the Moorish invasion of Spain that the art of dyeing
and finishing the finer kinds of leather was reintroduced.

England was very backward in this manufacture up to the end of the last
century, owing to the fossilising influence of much paternal
legislation, and of certain excise-duties, which were only repealed in
1830. Since this time the art has made rapid strides, especially in the
use of labour-saving machinery, and England may at the present moment be
considered fairly abreast of any other country as a whole; though in



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