Read Ebook: The Principles of Leather Manufacture by Procter H R Henry Richardson

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Ebook has 742 lines and 117007 words, and 15 pages

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

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

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

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

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

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

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

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

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

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

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

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

Methods of removing lime and reducing swelling -- Use of acids -- Lactic, acetic and formic acids -- Boral -- Sodium bisulphate -- Boric 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

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

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

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

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

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

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

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

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

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

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 -- D?gras 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

Primitive use of oil in leather manufacture -- Chamoising and the production of washleather -- Manufacture of Moellon, or D?gras -- 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

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

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

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

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

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

Metrical weights and measures -- Centigrade thermometer PAGE 481

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

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.

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 palaeolithic 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.

See also Gen. iii. 21.

"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 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.

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.

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 some special manufactures we are surpassed by the Continent and by America. In making comparisons of this kind, it must, however, be remembered that, especially in sole-leather tannage, the most rapid progress has been made during the last few years in those countries which were more backward, and that therefore our superiority is much less pronounced than formerly, and in a few years will probably cease to exist unless marked improvements are introduced in the methods of production.

In the sketch of the development of leather manufacture which has just been given, it has been implied that its object is to convert the putrescible animal skin into a material which is permanent, and not readily subject to decay, while retaining sufficient softness or flexibility for the purposes for which it is intended. As these range from boot-soles to kid-gloves, there are wide divergences, not only in the processes employed, but also in the materials used and in the principles of their application.

The most important method of producing leather is by the use of vegetable tanning materials, and this is perhaps the only one which is really entitled to be called "tanning," though the distinction is not very strictly adhered to. It includes the whole range--from sole leather, through strap, harness and dressing leather, to calf and goat skins, and the various sumach tannages which yield morocco and its imitations. All of these products but the first and the last undergo, after tanning, the further processes of "currying," of which the most important operation consists in "stuffing" with oily and fatty matters, both to increase the flexibility and to confer a certain amount of resistance to water. Sumach-tanned skins are not strictly "curried" but usually receive a certain amount of oil in the process of "finishing."

Next in importance to the vegetable tannages are the "tawed" leathers produced by the agency of alum and salt, including the "white leathers" for belt laces and aprons, and calf- and glove-kid. A connecting link between tanning and tawing is found in the "green leather," "Dongola," and "combination" tannages, in which alum and salt are employed in conjunction with vegetable tanning materials, and especially with gambier.

Salts of several of the metals, and particularly those of aluminium, iron, and chromium, have the power of converting skin into leather; and processes in which salts of chromium are used have recently attained very considerable commercial importance.

In the production of calf- and glove-kid, in addition to alum and salt, albuminous and fatty matters, such as egg-yolk, olive oil and the gluten of flour, play a considerable part, and are thus linked both to the primitive methods in use by the Indians and Kalmucks, and to those by which "crown" and "Helvetia" leather, and many other forms of belt- and lace-leathers are now produced by treatment with fats and albumens.

In an attempt to view all these complex processes from the scientific standpoint, the reader should constantly realise that the present methods of leather manufacture are the results of tens of centuries of experience, and of innumerable forgotten failures, and must not therefore expect that they can be easily superseded. Science must follow before it can lead, and its first duty is to try to understand the reasons and principles of our present practice, for we can only build the new on the foundation of what has been already learned. Another fact, which is scarcely understood by the practical man in his demands on science, is that in leather manufacture every question which is raised seems to rest on the most recondite problems of chemistry and physics; the chemistry of some of the most complex of organic compounds, and the physics of solution, of osmose, and of the structure of colloid bodies--problems which are yet far from completely conquered by the highest science of the day.

After what has just been said, it may be well to emphasise the great importance of practical knowledge and experience to the leather manufacturer. Even in trades which have reached the highest scientific development, such, for instance, as the manufacture of the coal-tar colours, the small experiments of the laboratory are not transformed into manufacturing operations without experience and sometimes even failure; and this must still more often be the case in a trade like that of leather-making, where our knowledge of the actual changes involved is still so incomplete. On the other hand, the cost of experiments on a manufacturing scale is usually so heavy that the least scientific must admit the advantage of learning all which the laboratory can teach before venturing on anything more; while even our present imperfect knowledge of the chemical changes involved will often warn us off hopeless experiments, and give us hints of the directions in which success may be attained. A knowledge of chemistry will probably prove at least as important to the future of our trade as that of mechanics has been in the past.

The object of tanning has been stated to be the rendering of animal skin imputrescible and pliable, but as we now rarely require leather with the hair on, preliminary processes are needed to remove it, and to fit the skin for tanning, and the nature of these processes has great influence on the subsequent character of the leather produced.

The first step is usually a washing of the skin to remove blood and dirt; while, where it has been salted or dried, a more thorough soaking is needed to remove the salt, and to restore the skin to its original soft and permeable condition.

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