The manufacture of gelatine and allied products has received a great
stimulus in this country from the circumstances arising from the
European War. The large restriction of continental--especially French
and Belgian--supplies of gelatine, led to greater demands for the
British-made product, and resulted not merely in a period of greater
prosperity, but in a period in which much greater efforts were made to
supply a high-grade article in larger quantities. Most manufacturers
strove to make high-class gelatine rather than low-grade glue, great
extensions were made, and many new businesses were established. The
development of the leather trades, more particularly in respect of
greater production, caused a bigger supply of raw material for skin
gelatine, and the slaughter of home animals for food caused a more
plentiful supply of bones. At the same time it was realized that greater
production not only reduced working costs, but also that a bigger
turnover in any one factory involved a proportionately less capital
outlay. These facts tend to counterbalance the heavy freight on the raw
materials. Production is thus not only on a larger scale but more
intensive.
One of the greatest difficulties of this industry is to produce a
regular or standard article, for the raw material is so exceedingly
variable in quality; that for skin gelatine tends also to become less
valuable. In such a case, as Rideal has truly remarked, to ensure that
supplies to customers shall be always "up to sample," which is often a
matter of contract--"exact and regular working, strict cleanliness,
observance of temperatures and other physical data, and scientific
supervision", are clearly necessary. "Rule of thumb" is never quite
certain to produce the same article twice. In past years British methods
of manufacture have been far too empirical. As in other industries,
"rule of thumb" must inevitably be replaced by scientific principle. The
advances in colloid chemistry of this last decade or so have, in the
author's opinion, supplied the clue to this line of development. In the
preceding pages emphasis has been laid upon the importance of the
adsorption law, the lyotrope series, and the valency rule. The
manufacturer or supervisor who understands and can apply these
generalizations will find his task vastly easier and his factory more
efficient. Much remains to be learnt, however, and the industry would
certainly benefit by research work, for which there is a fertile field.
There is also considerable room for improvement in the methods of
chemical engineering usually employed. Whilst the heat engineers have
certainly done much to solve the question of evaporation and drying,
there is still great scope in the more economical application of heat in
extraction, and the last word can hardly have been said on the problem
of clarification and decolorization. There is indeed almost as much
scope for research by the chemical engineer as by the colloid chemist.
The industry also exhibits, in common with the leather and many other
trades, the same tendency to save labour, both by careful arrangement of
the factory and by the installing of mechanical labour-saving devices.
Thus, lifts, runways, hoists, and trucks are increasingly used to move the
solids, and pipes and pumps to move the liquors. As ever, there is scope
for the mechanical engineer.
If some of these problems are vigorously tackled during the present
reconstruction period, 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 future.
From what has been said in Section VIII. as to the wide uses of
gelatine and glue, it will be seen that general prosperity in trade is
conducive to better trade conditions in the gelatine and glue industry.
It is similarly true that a general trade slump affects the glue trade
adversely. The severe trade depression which commenced in 1920 has had
this effect, and has made economic production much more difficult as
well as more essential. As often is the case, the larger factories and
firms can better face the difficulties, 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
unite. As in the leather trade, both the War boom and the Peace slump
have caused the gelatine and glue trade to develop along the lines of
the great trusts. It may be reasonably expected, moreover, that these
will be intimately connected with the leather trusts. This fact,
together with the heavy freight charges on the raw material, tends also
to make the skin glue factories gravitate towards the leather centres.
PART VI.--MISCELLANEOUS PROTEINS AND BYE-PRODUCTS
SECTION I.--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 themselves, and all
these are obtained before the tannage proper is commenced. The leather
trades use only the dermis (corium) or true skin for the manufacture of
leather, and as we have noted (Part I., Section II.) this prepared and
purified dermis is called "pelt." The cuttings and trimmings from the
pelt form the most valuable bye-product of the leather trades, and are
the raw material of the gelatine and glue industries (Part V., Section
II.). Many portions of the pelt, indeed, such as ears, noses, and cows'
udders, are quite useless for any other purposes. Other portions, such
as cheeks, faces, and even bellies, may be made either into glue or
leather according to the state of trade. Hardly less important to the
same industry are the cuttings of adipose tissue removed in "fleshing"
the hides and skins. These, though yielding less protein, yield also,
however, the valuable animal greases (Part V., Section II.). To obtain
both these products in a purer condition the removal of "flesh" after
"soaking," but before "liming" (Part I., Section II.), has been favoured
by some, especially in America.
Amongst the epithelial structures of the hides and skins, we have
several protein bye-products which have some commercial value. The
horns of cattle are now almost invariably removed before reaching the
leather manufacturer, but have some little value. This part of the
epidermis is not solid keratin. A "pith" is easily removed after boiling
in water. The outer parts, too, are often coarse and somewhat damaged,
but if removed by scraping reveal often a rather beautiful structure of
varying colour. There is some opening for this product in the
manufacture of small articles of horn, but much of it, together with
hoofs, is roasted and crushed for making fertilizers. The hair of
cattle, goat, etc., has also a commercial value. This is removed after
liming, and needs subsequent purification (Part I., Section II.). The
hair is well washed with water, using either repeated changes or a
continuous supply, the operation being carried out in paddles or similar
machines which stir up the hair in the water. When clean, the hair is
transferred to a centrifugal machine or "spinner," in which much
adhering water is removed. This is a great assistance in drying out,
which is the next and final operation. In drying, the hair is laid upon
steam-heated boxes or pipes, and a current of warmed air passed over or
through it by means of a fan. It is better to have the hair "turned"
occasionally. This ensures quicker as well as more even drying. The
product is made up into large bales and sold for the manufacture of
felts, mattresses, etc. White hair is usually kept separate and commands
a larger price. The power consumed in driving the washing machinery, the
centrifuges and the drying fan, together with the fuel required for the
drying steam, and the labour involved throughout, make it doubtful
whether this bye-product is worth either the capital outlay or the
working costs necessitated. Many manufacturers avoid this treatment
altogether, therefore, and the wet limed hair is sold direct to the
fertilizer factory. A less price is obtained, but much expense is saved.
Especially when the animals have only their short summer coats, this
course is preferred.
In the case of the wool from sheepskins the product is much more
valuable. The wool, indeed, is often the primary consideration.
Unfortunately this sometimes results in the neglect of the pelt. The
removal of wool from sheepskins forms a special industry known as
"fellmongering," which has been previously described (Part II., Section
IV.). Pains are taken to clean the wool even before removal from the
pelt, by the liberal use of water and the "burring machine." There is
much variation in quality, and care is taken to keep the various grades
separate, even during the "pulling" operation. From the fellmonger the
wool passes to the "wool stapler," and forms the basis of one of our
most important mechanical industries, the manufacture of woollen cloths.
Wool is also removed from sheep by the periodic shearing, and in this
case does not reach the fellmonger at all.
Apart from the raw material itself, there are few bye-products of the
leather trades which are of commercial importance. The sludge from the
pits of the limeyard contains, in addition to much lime and chalk, a
certain proportion of protein matter. This is derived partly from the
blood and dung associated with the hide, partly from the solution of the
corium hide substance, partly from the solution of the softer keratins,
and partly also undissolved and loose hair. This bye-product is rather
difficult to deal with, as it will not easily dry. It is indeed
sometimes a problem to dispose of it, except in rural districts, where
the farmers appreciate its manurial value and will usually cart it away
for a nominal fee. Where possible, it is better to let it drain and
settle on land, and pile it up in heaps to dry further. Soak-pit sludge
has a distinctly greater value as manure, on account of the greater
proportion of dung proteins. As some lime is often used in these pits,
the product is a really useful fertilizer.
The only other bye-product of the leather trades is waste leather
itself. For small pieces of leather there is always some little opening
in producing small articles, such as washers for taps, etc., and there
is also the possibility of shredding or pulping and making an artificial
leather. The best leather substitutes, indeed, are made from waste
leather. Nevertheless, there is always a certain amount of waste leather
which only finds an outlet in the fertilizer factory. Such material is
usually steamed or roasted to make it brittle, and then crushed in a
disintegrator. It is then mixed in with other materials, but is
sometimes solubilized by the action of sulphuric acid. Leather seldom
contains less than 30 per cent. protein.
REFERENCES.
"Chemical Fertilizers and Parasiticides," S.H. Collins, M.S.,
F.I.C. (Companion volume in this series on Industrial Chemistry.)
"Wool Wastes," Part II., Section V., p. 75.
"Hoofs, Horns, Leather," Part III., Section II., p. 115.
"Gelatine, Glue, and Allied Products," T. Lambert.
SECTION II.--BYE-PRODUCTS OF THE GELATINE AND GLUE TRADES
From the skin gelatine and glue trades the most valuable bye-product is
the grease, which is obtained from the "fleshings" of the adipose
tissue. These fleshings are themselves a bye-product of the leather
trades. The recovery and purification of this grease has been dealt with
previously (Part V., Section II.). In the skin glue trade the only other
bye-product is the residue from the extraction process (Part V., Section
III.). This residue is known usually as glue "scutch," and is composed
of the proteins of the skin which are insoluble in hot water. These
insoluble portions are obtained from all layers of the skin. There is
much hair often in scutch, the hyaline or glassy layer (grain), and the
elastic fibres of the corium are also insoluble, and a proportion is
derived from the fibres of the adipose tissue on the flesh side. All
these portions are fairly rich in nitrogen, and the scutch has,
therefore, considerable value to makers of fertilizers. It is liable to
contain also a percentage of grease, which is usually removed by
steaming under hydraulic pressure. This process recovers a valuable
bye-product and increases the manurial value of the scutch. There is
always left in scutch some of the gelatinous skin substance which,
strictly speaking, should have been removed during extraction. There is,
however, a practical limit beyond which it does not pay to do this. When
this limit is reached the cost of steam in extracting, and also in
evaporating and drying, together with the loss of time and labour
involved by occupation of the plant, is greater than the value of the
possible product.
From the bone-glue industry, the grease is similarly a valuable
bye-product, but there is also another of equal importance, viz. the
phosphate of lime, which comprises about half the raw material. As
previously described in Part IV., Section II., this is usually
extracted after the grease, by solution in weak hydrochloric acid. The
solution is neutralized in lead-lined vats with milk of lime, a
precipitate of di- and tri-calcium phosphates being obtained. Calcium
chloride is left in solution, and the precipitate should be, therefore,
well washed if it be desired to have dry phosphate. The bone-glue
industry is, generally speaking, much more intimately connected with the
fertilizer trades than the skin-glue trades, indeed the extraction of
the bones for glue is not always advisable, in which case the protein
matter as well as the phosphatic matter of the bones are employed for
making "bone manures." For details of this industry the reader is
referred to a companion volume in this series on "Chemical Fertilizers."
REFERENCES.
"Chemical Fertilizers and Parasiticides," S.H. Collins, M.Sc.
"Bones," Part II., Section V., p. 72.
"Precipitated Bone Phosphate," Part III., Section III., p. 157.
"Bone Manures," Part III., Section V., p. 173.
"Gelatine, Glue, and Allied Products," T. Lambert.
SECTION III.--FOOD PROTEINS
Although there are those who consider that animal proteins are both
undesirable and unnecessary as foods, it is nevertheless true that man
is almost universally a carnivorous animal. The animal world provides
mankind with one of its chief sources of food, and especially of protein
foods. Protein foods are unquestionably essential, and animal protein
foods differ chiefly from those of vegetable origin in the fact that
they contain generally much more protein. Of the proteins noted in our
Introduction, the keratins have no value as foods; the gelatins have
some value as culinary material, but little actual food value; whilst
the albumins comprise practically all the useful animal food proteins.
Whilst the actual flesh of animals is the principal source of food
proteins--both as to quantity and food value--other parts of animals,
_e.g._ kidneys, liver, blood, brains, tongue, are used and relished. The
most important sources of animal food proteins are from fish, fowl,
sheep, cattle, and pigs, the meat from these being roughly in the same
sequence as to digestibility. There are, however, many other animals of
which the flesh is quite edible, but most of the above are specially
farmed and propagated primarily for their food value.
As the animal food proteins are exceedingly putrescible, they are
usually consumed within a short time of the animal being killed. It is
perhaps natural, therefore, that many efforts have been made to discover
means of preserving such foods. These efforts form the basis of some
important industries, and though they can hardly be included as chemical
industries, it will not be out of place in this volume to point out that
these efforts present analogies with, as well as differences from the
methods used for preserving hides and skins (Part I., Section I.). The
curing of hides and skins is a temporary preservation from putrefaction
until the opportunity is convenient for the permanent preservation
(_i.e._ tannage). The preservation of meats is analogous to curing
inasmuch as more drastic treatment might indeed make them
non-putrescible, but would also render them indigestible and unsuitable
for food. Thus drying, salting, drying and salting, pickling and
freezing, are just as suitable for preserving food proteins as for hide
and skin proteins. Hence we have dried meats, salt bacon, pickled beef,
frozen mutton, etc. To a limited extent smoking (fish, bacon, etc.) has
been employed as a cure. When it has been applied to skins it is usually
combined with a fat tannage. There is, however, one method of
preservation of proteins, inapplicable to skins, which has been
eminently successful and useful for food proteins, viz. sterilization by
boiling. The food has been placed in tins, hermetically sealed, and
thoroughly sterilized. Hence have appeared corned beef, tinned tongue,
sardines, etc., which merely illustrate the immense possibilities
involved. A noteworthy advantage of this method of preserving animal
food proteins, is that the food is already cooked and prepared for
immediate consumption.
Another line of effort is the preparation of concentrated foods. Just as
animal foods are on the whole more concentrated in protein than
vegetable foods, so these prepared animal foods are more concentrated
than animal flesh, and generally also more soluble. Such preparations of
animal protein are obviously useful when there is difficulty in
swallowing and when journeys are necessary into regions of poor food
supply. It is a little doubtful, one must say, whether the concentration
is as great in some cases as is claimed.
Yet another industry based upon the animal proteins is the manufacture
of meat-extracts. These are not merely concentrated extracts of animal
flesh, but contain especially the stimulative properties of animal food
proteins. There is now little doubt of the value of these preparations
as stimulants, and it is claimed for them that they not only have food
value, but also that they increase the food value of other foods used
with them. Together with these products may be classed all the
miscellaneous tonic foods, in which proteins are blended with
carbohydrates and often also with drugs. These aim at the cure of
specific disorders, such as nervous debility, sleeplessness, etc. Their
claims are often extravagant. Amongst all the multitude of prepared
foods, there deserve particular mention the partly predigested foods. In
cases where the digestive functions are weak or disordered these
products have been of real service.
One of the most useful and valuable of animal food proteins is obtained
from hen eggs. The "white" of eggs is almost pure albumin, and there is
much protein in the yolk also. Eggs are now produced and imported by the
million, and form a most important item in the country's dietary, the
protein being in a very easily digestible form.
It is also necessary to refer to the importance of cows' milk as a
source of animal food protein. The amount of protein in milk (4-5 per
cent.) is not large, but it is united with fats, carbohydrates, salts,
and vitamines in such proportions, that milk is about the only article
which may reasonably present a claim of being a complete food. Milk,
moreover, forms the staple diet of infants and young children, so that
its protein is certainly of great importance. As an infant food, cows'
milk is not altogether ideal. Even when the proportions of fat,
carbohydrate, and protein have been adjusted to resemble human milk,
there remains the difficulty that some of the proteins of milk
(especially the casein) are too indigestible for young infants. This
difficulty has been only partly surmounted by those industries engaged
in manufacturing infant foods. Some claim to remove the bulk of the
casein; others to have rendered it digestible by treatment with enzymes;
others, again, simply claim to supply concentrated cows' milk. Tinned
milk, generally concentrated to some extent, now forms a useful addition
to animal food products. The casein of milk also finds some outlet for
industrial purposes. When treated with formaldehyde it yields an
artificial horn much used for the preparation of imitation
tortoiseshell. Skim milk is treated with caustic soda or carbonate of
soda, the casein precipitated by acid, pressed, impregnated with
formaldehyde, and dried. The product is termed "galalith." It can be
distinguished from real tortoiseshell by the action of fuming nitric
acid (see _J.C.S.I._, 1909, 101).
The utilization of the blood of animals, which is very rich in protein,
as a foodstuff has long been known, but has met with a good deal of
prejudice in this country. This prejudice has arisen not merely from the
objection to blood as food, but also from the fact that such foods have
been particularly liable to putrefaction and hence to cause poisoning.
The shortage of all foodstuffs occasioned by the European War did much
to overcome this prejudice, and there were considerable developments in
the manufacture of black pudding and similar preparations of animal
blood. The same circumstances made it necessary to consider more
seriously the possibilities of other butchers' offal as human food, and
resulted in new preparations of tinned animal proteins being placed on
the food market.
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 proteins. There is much to be said for this method on every
ground in theory, and it is evidently an increasing success in practice.
Dried milk has been followed by dried eggs, and in view of the success
of the method when applied to fruits and vegetables, there seems a
prospect of better success in respect of dried meats. After all, animal
food proteins are chiefly lyophile colloids, and though desiccation
presents some practical difficulties, the subsequent imbibition
(assisted perhaps by lyotrope influences) seems to be the ideal method
for restoring preserved protein to its original condition.
In conclusion, it will be interesting to note in the subjoined table,
the relative importance of the different sources of supply of both
animal and vegetable food protein. The figures are taken from the report
of a Committee of the Royal Society. They show the average quantities of
food materials (imported and home produced) available for the United
Kingdom during the five years 1909-1913 inclusive, together with the
amounts of protein, fat, and carbohydrate present and the energy value.
This information formed the basis of the Committee's recommendations as
to economy of protein during the war shortage. These recommendations
included the more economical production of meat by slaughtering cattle
younger and the saving of 55,000 metric tons of protein annually by
adopting cheese-making as a general practice in place of butter-making.
| Metric tons. | Energy
+--------------------------------| value,
| Protein. | Fat. | Carbo- |millions of
| | | hydrate | calories.
---------------------------+----------+---------+-----------+-----------
Cereals | 549,000 | 63,000 | 3,628,000 | 17,712,000
Meat | 356,000 | 799,000 | -- | 8,890,000
Poultry, eggs, game, | 42,000 | 31,000 | -- | 461,000
and rabbits | | | |
Fish | 91,000 | 17,000 | -- | 531,000
Dairy produce, including | 199,000 | 686,000 | 258,000 | 8,253,000
lard and margarine | | | |
Fruit | 9,000 | 14,000 | 222,000 | 1,077,000
Vegetables | 120,000 | 10,000 | 1,031,000 | 4,812,000
Sugars (including cocoa, | 5,000 | 18,000 | 1,572,000 | 6,633,000
etc.) | | | |
Other cottage and farm | | | |
produce | 67,000 | 13,000 | 551,000 | 2,655,000
SECTION IV.--MISCELLANEOUS ANIMAL PROTEINS
The excreta of animals include animal proteins of great importance to
agriculture and horticulture, forming the staple supplies of manure. The
manure of animals should contain not only the solid waste material and
undigested food, but also the urine, which contains much nitrogen, and
hence makes considerable difference to the value of the product as a
fertilizer. If the animals are fed on rich foods, the manure obtained is
correspondingly richer, especially in its protein content.
The value of dung manures depends not merely upon the protein content,
but also upon its content of phosphate and potash, as well as other
organic matter. The protein breaks down into simpler nitrogenous
compounds, and eventually, through ammonium carbonate, it becomes
nitrate. Nitrogenous manures darken leaves and increase growth
considerably. Dung manures are deficient in phosphates and potash and
are of value partly as nitrogenous manures producing growth, and partly
as dressings of organic matter for soil. From both points of view it is
desirable that the manure should be well decayed. Fresh dung manures are
both wasteful and injurious to soil, except perhaps to very stiff clays.
They are wasteful inasmuch as much ammonia escapes, and injurious
inasmuch as they cause the "denitrification" of the valuable nitrates
already in the soil. When possible dung manures should be kept under
cover. Free exposure to air and rain will sometimes reduce its value by
one half. It should be stored until "sweet," and until the straw has
rotted and become "short." This takes usually several months. A ton of
well-rotted farmyard manure contains very approximately 10-12 lbs.
nitrogen, about the same amount of potash, and about half that quantity
of phosphates. It is, however, very variable. Horse manure is rather
richer than cow manure, but more liable to loss on storage. Pig manure
is intermediate between them. Sheep manure is distinctly richer in
protein, and has therefore greater value as nitrogenous fertilizers.
Poultry droppings are richer still, perhaps partly because they include
the urinary products. When fresh they contain 18-25 lbs. nitrogen, 12-24
lbs. phosphate, and 6-12 lbs. potash per ton. When dried they have about
double the value. Pigeon manure is even richer, and the pigeon loft
scrapings have a manurial value about double that of dry hen manure, and
eight times that of farmyard manure. Guano is much decayed droppings of
sea birds on the tropical coasts of Africa and America. The supplies are
now quite exhausted, and the market guanos are chiefly artificial
fertilizers.
* * * * *
There is one other animal protein which must be referred to before this
volume is concluded, viz. silk. This is obtained from the cocoon of the
"silkworm," which is the general name given to the larvæ of certain
bombycid moths. These larvæ feed on the leaves of the mulberry, and when
ready to pupate produce a considerable supply of a soft and delicate
thread which is wound round about the larva itself. This is the raw
silk, and it is unwound from the cocoon in a machine called the
"silk-reel," and may then be wound into a thread. Two or more threads
twisted together form "thrown-silk." Silk threads are also woven into
cloth of characteristic texture and appearance. This protein thus forms
the raw material of one of the most important textile industries.
* * * * *
From the fish trade there is much animal protein, which is useless for
food purposes and which, to avoid nuisance, it is necessary to convert
promptly in fertilizers. During the herring season there is the disposal
in this way of the heads, tails, and the guts. Many fish are
incidentally caught which, being valueless as food, are yet useful as
manure. After the extraction of oil from fish livers the residue is
suitable for a similar purpose. These residues are steamed, dried, and
ground up, forming fish manure, rich in nitrogen and often also in
phosphate.
REFERENCES.
"Chemical Fertilizers and Parisiticides," S. H. Collins, M.Sc.
"Organic Nitrogen Fertilizers," Part III., Section II., p. 105.
"Fish Manure," p. 110.
INDEX
Acclimatization in colloid systems, 236
Acid, ellagic, 29
gallic, 29
sulphurous, 227, 243
Acid process for bone gelatine, 243
Acids, for deliming, 23
for pickling, 114
in sour liquors, 29, 44
Adsorption, law of, 43
methods of clarification, 234
nature of, 41
of ions by gelatine, 211
African hides, 15
Albumins, 4, 240, 274, 277
Algarobilla, 32
Alum, 236, 240
American hides, 14
Animal excreta, 279
Arsenic sulphide, 20
Asiatic hides, 14
Astringency of liquors, 44
Bacteria in soaks, 16
limes, 20
bates, 24
tan liquors, 29
Bag leather, 86
Band-knife splitting, 52
Bark, hemlock, 34, 40
mallet, 34
mangrove, 35, 41
mimosa, 33
oak, 34
pine, 34, 41
willow, 32
Basic dyestuffs, 97
Basils, 115
Bating, 24, 94
Belting leather, 65
Blair-Campbell evaporator, 249
Bleaching leather, 62
glue, 241
Block Gambier, 40
Bloom, 29
Boiling process for glue, 223
Bone gelatine, 223
manure, 273
meal, 224
Bones, 223
Bookbinding leather, 104, 106, 117, 120
Boric acid, 23
Bottle tannage, 103
Box calf, 156
Bridle leather, 71
British hides, 8
Brushing leather, 63
Buck leather, 181
Buff leather, 181
Buffing, 52
Burning in, 54
Butt, 22
Bye-products of the gelatine trade, 272
of the leather trades, 268
Calcium sulphydrate, 22
Calf skins, 76, 120, 156
Casein, 276
Cast glue, 257
Catechin, 32
Catechol tans, 32
Caustic soda, 18, 20
Centrifugal fan, 50
Chamois leather, 181
Cheeks, 268
Chemistry of colloids, 201
Chestnut extract, 36
Chlorine bleach for glue, 246
Chrome calf, 156
goat, 163
hide, 170
sheep, 163
Chrome tannage, 127-174
finishing operations, 153
general methods, 139
history of, 127
one bath, 149
special qualities of, 136
theory of, 129
two-bath process, 142
Clarification of gelatine, 234
Coefficient of conductivity, 253
Colloid chemistry, 201
Combination tannages, 191
Concentrated foods, 275
Condenser water, 251
Conductivity coefficient, 253
Continental hides, 14
Crown leather, 178
Cube gambier, 40
Curing hides, drying, 13
dry-salting, 13
freezing, 13
salting, 12
sterilizing, 14
Currying, 49
Cut glue, 257
Decolorization of glue, 238
Deerskins, 92, 181
Degreasing bones, 224, 227
leather, 115
Deliming, 23
Depilation, 19
Divi-divi, 32
Dongola leather, 191
Drenching, 25, 95
Dressing leather, 24, 65-92
Drum stuffing, 53
tanning, 63
Drying gelatine and glue, 255
hides, 13
leather, 50
Dung bates, 24
manures, 279
puers, 94
Dyeing leather, 96
Ears, 220, 268
Eggs, 276
Elastic fibres, 6, 272
Ellagic acid, 29
Enamelled leather, 123
Enzymes, 24, 25, 94, 95
Erodin, 94
Evaporation, 37, 248
Evaporators, Blair Campbell, 249
Kestner, 249
Yaryan, 249
Evolution of gelatine industry, 265
of leather industry, 194
Extraction of gelatine and glue, 230-233
of grease, 115, 224, 227
of phosphate, 224
of tannin, 35
Extracts of meat, 275
of tanning material, 37-41
Faces, 220, 268
Fan drying gelatine, 257
leather, 50
Fat liquoring, 154
tannages, 178
Federation of Tanners, 108
Fellmongering, 113
Fermentation in bates and puers, 24, 94
in drenches, 25
in limes, 20, 21
Fertilizers, 269, 279
Filter press, 238
Finger test, 218
Finishing chrome leather, 153
heavy leather, 49
light leather, 96
Fish glue, 228
manure, 280
Fleshing, 22
Flocculation, 237
Food proteins, 274
Foods, concentrated, 275
dried, 277
Formaldehyde tannage, 185
Fractional extraction of glue, 230
Galalith, 277
Gallic acid, 29
Galls, 32
Gambier, 40
Gelatine, bleaching, 241
clarification of, 234
decolorization, 234
drying of, 255
evaporation of, 248
extraction of, 230
properties of, 200
raw material for, 220
uses of, 260
Glacé calf, 156
goat and sheep, 163
Glazing, 97, 155
Glove leather, 174
Glue (_see_ GELATINE)
difference from gelatine, 241
Goatskins, 99, 163
Graining, 97
Grease in bones and scutch, 224, 227
in skins, 115
Guano, 278
Hair, removal of, 22
Handlers, 47
Hard-grain morocco, 117
Harness leather, 71, 170
Heavy leather, 7-92
chrome leather, 170
Helvetia leather, 179
Hemlock bark, 34
Hides, American, 14
African, 15
Asiatic, 14
British, 8
Continental, 14
dried, 13
dry-salted, 13
fresh, 8
frozen, 13
salted, 12
Hoofs, 268
Horns, 268
Hyaline layer, 272
Hydrophile colloids, 240
Hydrophobe colloids, 240
Hydrosulphite of soda, 245
Hypo bath, 128, 147
Imitation box calf, 159
glacé kid, 163
Imperial aspect of leather trade, 198
Increase in strength of tan liquor, 44
Incrustation, 254
Influence of Lyotrope series, 206-209
Intensive production, 194, 265
Interfibrillar substance, 24
Iron and logwood, 75, 83, 109
Jacking leather, 51
Japanned leather, 123
Jelly, 203, 258
Keratins, 4
of epidermis, 272
Kestner evaporator, 249
Kid skins, 163, 174
Kips, 8, 76, 159
Lactic acid, 23
Lambskins, 110, 163, 174
Larch bark extract, 41
Layaways, 47
Layer, hyaline or glassy, 272
Layers, 47
Leaching, 35
Leather, definition of, 27
Legging leather, 76
Levant grain, 109
Lime, function of, in depilation, 20
Liming for chrome leather, 127
glue pieces, 220
hides, 18
leather, 83
skins, 92
Liquor, chrome 127, 129, 143-153
lime, 18-22
tan, 35
Logwood, 75, 83, 109
Lyophile colloids, 201
Lyophobe colloids, 201
Lyotrope series colloids, 206-209
Machine fleshing, 23
scudding, 23
shaving, 52, 82
Mallet bark, 34
Mangrove bark extract, 41
Mean temperature difference, 252
Meat extracts, 275
Mellow lime liquors, 18-21
tan liquors, 44
Memel butts, 83
Milk, 276
Mimosa bark, 33
Miscellaneous proteins, 266, 279
tannages, 174
Mixed tannage of sole leather, 55
Mordants, 96
Morocco leather, calf, 120
goat, 99
seal, 106
sheep, 110
Motor butts, 170
Multiple-effect evaporation, 249
Myrabolans, 30
Nature of chrome leather, 127
of leather, 27
Nett adsorption, 215
Neutralization, 153
Nitrogen in proteins, 1
value of manures, 280
Noses, 268
Oak bark, 34
Oakwood extract, 37
Offal for sole leather, 63
Oil tannage, 181
One-bath chrome tannage, 149
One-pit system of liming, 19
Open-vat system of extraction, 231
Oxidation method of bleaching, 245
Paddles for washing, puering, dyeing, and tanning, 17, 94, 96, 103
Parker, on valonia, 31
Pelt, preparation of, 16, 92, 139
Peroxides for bleaching, 246
Phlobaphenes, 33
Phosphate of lime, 223, 225, 273
Picking band butts, 90
Pickling foods, 275
skins, 114
Pigskins, 92
Pine bark, 34
Plumping, 19, 44
Precipitation, 236
Predigested foods, 276
Preparation of pelt, 16, 92, 139
Press leach, 35
Principles of chrome tannage, 139
clarification of gelatine, 234
liming, 92
vegetable tannage, 41
Procter, definition of leather, 27
glucose chrome liquor, 152
on gelatine swelling, 217
on pickling, 115
Properties of chrome leather, 127
gelatine and glue, 200
Protective colloid, 237
Proteins, classification, 3
composition of, 1-3
food, 274
miscellaneous, 266, 279
of dermis, 271
of epidermis, 272
Puering, 94
Purification of grease, 227
Putrid soaks, 18
Pyrogallol tans, 28
Qualities of chrome leather, 127
gelatine and glue, 200
Quebracho extract, 38
_Quercus ægilops_, 30
_robur_, 34
Quick processes of evaporating, 248
of tanning, etc., 194
Rabbit skins, 221
Raw material for gelatine, 220
heavy leather, 7
light leather, 92
Reds, 33
Reduction bleaching of glue, 243
Refrigerator, 258
Roans, 117
Rockers, 46
Roller leather, 118
Rolling leather, 51
Round of pits, 19, 46
Rounding pelt, 22
Salted food proteins, 275
hides, 12
Samming, 50
Satin leather, 76
Schultz chrome tannage, 128
Scouring, 51
Scudding, 22
Scutch, 271
Sealskins, 106
Seasoning, 97
Semi-chrome, 191
Sharp limes, 19
Shaving, 51
Shearlings, 114
Shedwork on gelatine, 257
on leather, 50
Sheepskins, 110, 163, 174, 181
Short processes, 47, 194
Silk, 280
Skins, 92
Skivers, 116
Sludge from lime pits, 270
Smoked foods, 275
Soaking hides, 16
Soda, 18, 20
Sodium sulphide, 18, 20
Sole leather, 55
Sour tan liquors, 44
Split fleshes, 76, 181
hides, 86
Splitting, 52
Staking, 155
Stocks, 18
Stoning, 51
Stove drying, 105, 109, 125
Strap butts, 65
Striking leather, 51
Stuffing leather, 49, 53
Substance, interfibrillar, 24
Sulphide of arsenic, 20
soda, 18, 20
Sulphurous acid, 227, 243
Sumach, 31
use in dyeing, 104, 117
use in finishing, 62, 84
use in tanning, 102
Suspenders, 46
Sweating, 113
Swelling of gelatine, 201-220
of pelt, 19
Syntans, 188
Synthetic tanning materials, 187
Tannage, alum, 174
bag, 103
bottle, 103
chrome, 127, 139
combination, 191
drum, 47
fat, 178
formalin, 185
oil, 181
with synthetic materials, 187
of bag leather, 86
of bridle leather, 71
of belting leather, 65
of harness leather, 71
of bookbinding leather, 99, 110, 120
of morocco leather, 99, 106, 110, 120
of picking band leather, 90
of sole leather, 55
of upper leather, 76
of roller leather, 118
Tannage, chrome, of calf, 156
of goat and sheep, 163
of hides, 170
Tannage, vegetable, heavy hides, 55-90
skins, 92-123
Tanning, theory of, 41
chrome, theory of, 129
Tannins, catechol, 32
classification of, 28
properties of, 27
pyrogallol, 28
Three-paddle system of tanning skins, 103
Three-pit system of liming, 19
Tissue, adipose, 271
Two-bath chrome tannage, 142
Udders, 220
Unhairing, 22, 23
Upper leather, 76, 115, 120, 123
Vacuum on condenser, 250
pan, 248
Valency rule, 131, 236
Valonia, 30
Vatting sole leather, 62
Vegetable tannage, 41
of hides, 55-90
skins, 92-123
tanning materials, 28
Velocity effect on heat transference, 253
War, effect on methods, 194, 265
on supplies, 11-13, 33, 277
Warble fly, 10
Waste leather, 270
Wattle or mimosa bark, 33
Waxed leathers, 76-86
Weather drying, 49
Willow bark, 32
calf, 156
Wood, J. T., action of puer, 94
Wool, 110, 269
Yaryan evaporator, 249
Zones of compressed water, 202-205