PATENTS.
In Chapter VII. we have described a few of the many artificial bates
which have been proposed, and for which in many cases patents have been
taken out. It would be impossible within the limits of a single chapter
to give an adequate account of all these patents, and therefore it is
not proposed to deal with those which are merely deliming processes,
but solely those in which the use of bacteria and enzymes is directly
applied. We mention, however, one or two of the more interesting
deliming patents.[143]
[143] A most useful source of information is Section XV. (Journal
and Patent Literature) in the Journal of the Society of Chemical
Industry, published fortnightly at Palace Chambers, Westminster.
Abstracts of all patents relating to bates will be found under the
above heading.
*Amend, Otto Paul*, New York (_U.S. Pat._ 763,347, 1904; _Eng. Pat._
18,514 _and_ 18,514A, 1904).--Improved Process for Bating and Puering
Skins, and Improvements relating to the Bating, De-acidifying and
Oxidizing of Hides and Skins.
The skins are treated with a solution of an ammoniacal salt, small
quantities of an acid such as hydrochloric acid being added at
intervals, so as to reform the salts. Pickled skins are de-acidified
and oxidized by treatment in a neutral or slightly alkaline solution of
a nitrite of an alkali or alkaline earth such as sodium nitrite.
*Nowak, O. H.*, Chicago (_French Pat._ 360,854, 1905; _Eng. Pat._
26,771, 1905).--Substance for Treating Hides and Process for Making
same. This is the “dermiforma” described in Chapter VII. Although
bacterial action is used to prepare the bate, the essential action is
an acid one, and, as we have said, resembles the drench.
*Norris, W. M.*, New Jersey (_U.S. Pat._ 840,794, 1907; _Eng. Pat._
29,661, 1906).--Improved Process of Treating Hides and Skins. In this
process the skins are subjected to treatment with a dilute solution
of hyposulphite of soda, which is said to “set” the gelatinous fibres
of the skin. The deliming is completed with hydrochloric acid in the
presence of salt.
*Boehringer Sohn, C. H.* (_Eng. Pat._ 3,140, 1911) Proposes to use in
place of the free organic acid, in this case lactic, the sodium salt,
and then to add slowly the amount of hydrochloric or sulphuric acid
requisite for deliming. The mineral acid combines with the sodium salt,
liberating an equivalent amount of the weaker organic acid, which then
acts upon the lime in the skins. For deliming 100 kilos. of pelt, 0·25
kilo. of sodium lactate (50 per cent.) and 0·56 kilo. hydrochloric acid
(20° Bé.) are used.
The advantage of the method is that a considerable saving is effected
in comparison to the quantity of the free organic acid which would be
required. In the above example 1 kilo. of lactic acid (43 per cent.)
would be required to neutralize a corresponding amount of lime.
In addition to these deliming processes, there are a number of bates in
which various nutritive media are allowed to ferment naturally, without
the addition of any specific bacteria. Among these may be mentioned:--
*Dr. Nördlinger’s Bate*, in which a paste of potatoes is allowed to
ferment at 30°–37° C. for several days; it is then dried at 40°–50° C.,
and used in the same way as dog dung.
*H. E. Simons’, Phosphorbutyralin*, consists of the beetroot residues
in sugar manufacture which have undergone an acid fermentation, and
contain butyrates and phosphates of ammonia.
*Oakes* (_US. Pat._ 798,070, 1905; _Eng. Pat._ 24,488, 1905).--In this
patent an albuminous body, such as casein is allowed to putrefy, at a
temperature of 100° F., for several days; an equal weight of flowers
of sulphur is then added, and the mixture used as a bate or puer. The
sulphur is said to play an essential part in the bate.
A similar process, by the same author (_U.S. Pat._ 798,293), is
described by Dr. Allen Rogers[144] in which 5 per cent. of glucose
syrup and 10 per cent. of sulphur, computed on the weight of the skins,
is fermented with yeast for twenty-four hours, after which it is used
as a bate. From a chemical point of view, it is difficult to express
the reactions taking place.
[144] J.S.C.I. 1906, p. 103.
When the bath is first prepared, it is neutral in reaction, but, after
standing, gradually assumes a slight acid reaction. On introducing the
skins, it becomes alkaline, owing to diffusion of the lime. After a
short time, it becomes neutral again, and remains thus until the skins
are in a perfect condition, when a slight acid reaction is observed.
These changes are caused by the fermentation of the glucose, carbon
dioxide and alcohol being generated. Owing to the presence of sulphur,
a quantity of hydrogen sulphide is produced, which, in its nascent
condition, combines with the alcohol to form mercaptans, which in their
turn are slowly oxidized to thioacids. These mercaptans and thioacids,
being of weak acid character, act in conjunction with any excess of
hydrogen sulphide upon the lime, converting it into soluble compounds,
which are readily removed by diffusion.
*Lederer, L.* (_French Pat. No._ 404,926 _of_ 1909).--Method of
Preparing a Substitute for Animal Excrement (dog dung) in Puering
Skins for Glacé Leather. In this process a mixture of 10 parts finely
powdered bone meal, and 1 part of crushed lupin seeds or beans is
formed into a paste with water and allowed to undergo spontaneous
fermentation from 3–4 weeks. The mixture is said to form a perfect
culture medium for the micro-organisms indispensable in bating. The
removal of the lime is facilitated by the addition of 2 per cent. of
fat, 0·75 per cent. sodium polysulphide and 1-1/2 per cent. common salt
reckoned on the weight of the bone meal.
In this patent the researches of Wood, Andreasch and Eitner are
referred to, and also Benker’s process of bating with Peruvian guano to
which soda has been added.
*Turney, Sir J. and Wood, J. T.*--Coming now to bacterial and enzymatic
bates, the author in conjunction with Sir John Turney applied for a
patent for a new and improved method of bating skins (No. 25,894,
1896), in which cultures of suitable bacteria were to be used in place
of infusions of dog or pigeon dung. It was found however that this
patent had been anticipated by the patent 21,720 of 1895, of Dr. Popp
and Dr. Becker of Frankfort o/M, and the application was therefore not
proceeded with. As has been related in Chapter VII. the late Franz
Kathreiner, who knew of the work which was being done both by Dr. H.
Becker and the author, made us personally acquainted, and most of our
later work was done in conjunction. Like many other new ideas, it was
arrived at quite independently by Dr. H. Becker and the author. (See
Report of Third Conference of I.A.L.T.C., Copenhagen, 1899, Wiss.
Techn. Beilage des Ledermarkt, 1899–1900, p. 8.)
We shall therefore give the original patents in full, and afterwards
the translation of Dr. Otto Röhms’ patent, and the recent patent of Dr.
Eberle, as these cover the whole ground of the bacterial and enzymatic
bates up to the present time.
*Dr. Popp and Dr. Becker’s English Patent* (No. 21,720, 1895).
Improvements in Lyes or Liquors for Preparing Hides for Tanning. An
important role in the process of manufacture of many kinds of leather
is played by the dung liquor or lye, which in particular for calf skins
and skivers constitutes one of the necessary preparatory operations for
the subsequent actual tanning process, and which has for its purpose
to bring the skins or hides, which have been previously swelled by the
liming process, into a condition which allows the easy and thorough
removal of the lime and lime soap as well as the remaining hairs by the
subsequent mechanical treatment, and to obtain a uniform shrinking of
the swelled hides.
The process hitherto employed consists in treating the hides or skins
for some time (such as for 4 or 5 hours) in a vat provided with a reel,
and containing a lye or brine formed of solutions of dog or pigeon or
poultry dung.
Generally speaking, the dog dung acts best in some cases, and pigeon or
poultry dung in other cases, but no satisfactory and sound explanation
has as yet been given as to the nature of the action.
My correspondents have in the first place ascertained that the action
of these lyes or brines is the result of bacteriological processes,
especially of the products created by the action of certain bacteria,
and is certainly not, as it has hitherto been generally assumed, the
result of the action of phosphoric acid or other acids.
The examination of the dog, pigeon and poultry dung in bacteriological
respect, and of the industrial applicability of all the different
results obtained, shows in the first instance that, even after removal
of all other ingredients, which, according to the hitherto ruling
views, enter into reaction, the result of the treatment remains the
same as it had been before the removal. The continued research led to
the second result that a great number of micro-organisms play a role in
the lye, partially an advantageous, and partially a detrimental one.
Generally speaking, the non-peptonizing bacteria act advantageously,
while the peptonizing ones generally have a detrimental effect. In
connexion herewith two methods of utilizing these discoveries have been
found.
One can either, according to the methods of bacteriology (plate
process), remove all the detrimental or even the less useful bacteria,
and effect the treatment of the hide or skins by applying a pure
culture of one or at least a mixture of the different most effective
bacteria; or one can, without employing such a refined process, but
still utilizing the said discoveries, apply the dog dung, and in
particular the white descriptions which are most effective, or, for
certain kinds of leather, the pigeon or poultry dung, subjecting the
said dungs to a certain treatment, which, by the use of a suitable
cultivating bed, will develop the useful bacteria, while on the other
hand, the increase of detrimental bacteria may be prevented or retarded
by the addition of materials hindering the development of the latter.
In every case the employment of the process secures greater rapidity
of execution, and more reliable and better results than the process
heretofore applied.
The leathers obtained are tough and yet softer, and in any case any
discolouring, such as is often unavoidable with dog dung, is avoided.
An advantage not to be underrated with the use of germ cultures, is
that liquors or cakes having a definite percentage of really effective
substance can be prepared, whereas it was heretofore necessary to
proceed by way of trials, the result being subject to great uncertainty.
In addition, the dung liquors are subject to changes overnight
under the influence of atmospheric changes (thunder-storms) in a
most unaccountable manner, owing, as has now been discovered by my
correspondents, to the growth of detrimental bacteria which are mixed
with the effective ones, and which gain the upper hand over the latter
under the change of atmospheric conditions.
The features of the newly discovered useful bacteria are fully
described in the following, and experiments have shown that the
particular kinds designed with 3, 7 and 12 in the table of bacteria,
set forth in the Specification to German Patent No. 86,335 and
hereinafter fully described, are those which are of value for the
purpose in question; in particular No. 12 is the most effective, and 3
the least effective of these three descriptions.
All three are bacteria to be found in the dog dung, and bacteria No.
3 consists of very small rods rounded at the ends and are exceedingly
mobile, while bacteria No. 7, which are similar to the hay bacillus,
are slowly-moving rods, and bacteria No. 12 are medium-sized rods
having rapid motion.
The prick-culture gives with bacteria No. 3 a very good growth in the
depth; from the inoculating prick extend laterally many arms into the
gelatin. At the ends of the arms are formed small knots. On the surface
is formed a thin white covering. The gelatin is not liquefied.
On gelatin plates, the deep-seated colonies consist of pale yellow
round disks, which gradually penetrate to the surface, and there they
form circular disks which show at the centre larger spots. On inclined
agar-agar there is formed a white superstratum.
With bacteria No. 7, the gelatin is strongly liquefied in the
prick-culture. On the surface of the zone of liquefaction there is
formed a white skin.
Along the liquefied prick are formed radiations into the solid gelatin.
On gelatin plates there are formed rapidly liquefying colonies forming
at top a white skin, agar-agar gives a white unequal thin superstratum
with branchings.
Bacteria No. 12 grow with prick-culture equally well along the prick;
the gelatin is not liquefied. On the surface there is formed a thin
shining covering.
On gelatin plates, the deep lying colonies consist of pale yellow
circular disks.
Many colonies have tails similar to the surface colonies of the
Proteus. During the growth of this bacterium on gelatin plates a strong
putrid smell is developed.
On agar-agar this bacterium forms a strong white shining superstratum.
These bacteria grow easily in any decoction of meat, and the flesh
particles from the flesh sides of the hides, which otherwise form a
waste product of little or no value, may be advantageously employed
for this purpose; bran, and other materials known to offer good
culture-beds, may be employed instead.
For this purpose a vessel provided with a cover is charged with equal
parts of waste flesh, such as is obtained in the tannery, and water,
and this is boiled for about half an hour by the direct introduction
of steam, after which concentrated carbonate of soda solution is
introduced until the reaction is slightly alkaline, after which the
decoction is cooled down. As soon as the temperature has sunk to about
35° C. there is added the pure culture obtained by the gelatin plate
process (with dilution), described in the works on bacteriology of
Koch, Fraenkel, Hueppe and others, and also by the further treatment
corresponding to the characteristic peculiarities of the bacteria, and
the whole is allowed to stand covered up for a period of from twelve
hours to five days, depending on the time of year and the temperature.
The hides or skins are then dipped into the concentrated decoction for
a short time, according to the state of development of the bacteria; or
the decoction can be diluted and the hides be then immersed therein for
a greater length of time.
The further treatment is then carried out in exactly the same way as
though the hides or skins had been treated in dog-dung lye, with the
exception that the duration is shorter.
In case the pure culture of the bacteria is to be dispensed with, and
it is only desired to obtain an advantage over the existing methods in
so far as to obtain, on the one hand an artificial increase of the ooze
medium viz. the number of useful bacteria and their products existing
in the dog dung, by providing a suitable culture bed, and on the other
hand to be in a position to limit oneself to the best initial material,
the process can be carried out by starting with a practically proved
dog dung, therefore in particular the white kinds, and the bacteria are
caused to propagate in a decoction such as above described. Afterwards
it is advantageous to effect the killing of the detrimental bacteria
by a small addition of acid, such as 0·5 per cent. of dilute sulphuric
acid or equivalent materials, as in this case the useful bacteria are
also the most enduring.
The more useful bacteria show, in particular in the presence of
alkalis, the same behaviour.
For example, the more useful bacteria arrive at development equally
with the detrimental ones, if to the described culture bed be added 0·5
per cent. of carbonate of soda, while the useful bacteria preponderate
to a considerable extent, and the detrimental ones are practically
unimportant, if the additions of carbonate of soda be raised to about
one per cent.
The pure cultures of the bacteria may be preserved in a suitable liquid
or solid material, and brought on the market in a suitable packing.
In order to obtain a product which shall both be durable, and capable
of being delivered in definite doses, sterilized bran, flour, etc., can
be inoculated with definite quantities of the pure cultures, and the
percentage of water be reduced, by drying, pressing, etc., to under a
certain percentage (10 to 12 per cent.) which will not allow of, or
will retard the evolution of germs.
The bacteria may also, after having been properly developed, especially
after having created a sufficient quantity of their products, be
killed, for instance by heating, and the resulting stuff be brought
on the market in liquid or solid form, as an effectual lye or brine,
it having been found that the liquids containing the said bacteria do
not lose their effect if they are sterilized and the bacteria thereby
killed, provided that a sufficient number of bacteria has been produced.
_Claim._--1. The process for the production of a lye for treating hides
or skins preparatory to tanning, consisting in the propagation of the
bacteria of dung, in particular dog and bird dung, by means of suitable
culture beds substantially as described.
2. As a new article of manufacture a lye containing a pure culture of
one or more of the described bacteria.
3. In the process of producing a lye referred to in the first claim,
the elimination of the detrimental agents substantially as described.
4. In the process referred to in the first claim, the addition of acids
or alkalis for the purpose set forth and substantially as described.
5. The process for the production of a lye for treating hides,
consisting in the separation from the dung of the bacteria herein
designated as 3, 7 and 12, producing pure cultures thereof, and
introducing the same into a decoction preferably freed by boiling from
other bacteria and containing a suitable culture bed, substantially as
described.
6. A process for the production of cakes, for the treatment of hides,
consisting in the inoculation of sterilized bran, flour, etc., with
cultures having a definite percentage of bacteria and the removal of
the proportion of water that is necessary for the development of the
bacteria, substantially as described.
7. As a new article of manufacture sterilized cakes, containing a
certain quantity of the described bacteria, substantially as described.
8. As a new article of manufacture the solid or liquid material
containing the products of the decomposition, as generated by the pure
cultures of the said bacteria, whether such material does or does not
also contain the said bacteria, either in the active condition or
killed by sterilization, substantially as described.
*Wood’s English Patent* (12,549, 1898).--Improvements in and relating
to the means used for the Bating of Hides and Skins. This invention
has reference to improvements in and relating to the means, liquid or
bate, used for the bating or puering of hides and skins previous to the
process of tanning the same.
At the present time skins are usually bated by means of a liquid or
bate prepared from dog or pigeon dung, and although the bating action
or actions have not hitherto been thoroughly understood, it is a well
known fact that fermentations going on in the dung play an essential
part. It was also pointed out in 1885 by H. R. Procter, in his “Text
Book on Tanning,” that the action of the bate was in a great measure
due to bacteria. It is also a known fact to practical tanners that a
dung bate, properly applied, produces the best quality of leather.
Owing, however, to the varying composition of the dung used, the
bate made therefrom possesses varying properties, its bating action
is uncertain, its properties are readily affected by atmospheric
influences, and the skins treated are liable to putrefaction.
As a substitute for dung bate, it has been proposed, as set forth in
the Specification of Patent No. 21,720, A.D. 1895, to use a bate made
from a pure culture of bacteria. Such bate, however, does not possess
all the essential properties of a dung bate; and although bacterial
action is necessary, such action alone is not sufficient, as was
pointed out by the present inventor in 1894 in the “Journal of the
Society of Chemical Industry.”
The present inventor has now discovered that the bating action of a
dung bate is due to the combined action of enzymes or unorganized
ferments, and to certain amine compounds in the dung. These compounds
consist of amines (i.e. ammonia in which one or more atoms of hydrogen
has or have been replaced by alcohol radicles), in combination with
lactic, acetic and other organic acids contained in the dung, the acids
named being the principal ones.
The present inventor has also discovered that the bating action of
the enzymes alone, or the action of the chemical compounds alone, are
inefficient, and that the enzymes exert their bating action in the
presence of the chemical compounds, while these latter in addition have
an independent action.
The object of this invention is the production, according to scientific
methods, of a bate having similar properties to those of a dung bate,
such properties in the improved bate being defined and definite, but
capable of being modified according to the requirements of the skins to
be bated and the leather to be produced.
According to this invention, the liquid or bate is made by producing by
fermentation an enzyme or enzymes of the same character as the enzymes
contained in dog dung or produced from bacteria obtained from dung,
and to the liquid thus obtained there is added an organic acid and an
alkali.
The inventor has discovered that for an efficient bate a pure culture
of bacteria is insufficient, and that no single organism hitherto
isolated will give results equal to dung. He has also discovered that
the production of these enzymes depends more upon the composition of
the nutrient medium in which the bacteria are cultivated than upon the
kind of bacteria, although these latter must be capable of producing
the required enzymes, the production of which appears to be due to a
symbiotic growth of bacteria, at present little understood.
It is desirable that the nutrient medium should be without sugars or
starchy matters, and, although the composition of the nutrient medium
may be varied, good results can be obtained according to ordinary
bacteriological methods by using a medium composed of--
Gelatin 50 parts
Potassium or sodium phosphate 1 do.
Water 2500 do.
This medium is maintained at a temperature of about 37° C. (the most
favourable temperature for the fermentation) until the required
bacterial action is completed, the time necessary being about seven
days, and to each litre of the liquid thus obtained there are added
from 2 to 6 grs. of lactic acid. Acetic or other similar organic acid
may be used instead of the lactic acid, but sulphuric or mineral acids
must not be used. The acid liquid is afterwards neutralized by ammonia,
which is added when the bate is to be used, and there are then formed
certain chemical compounds similar to those found in a dung bate.
The addition of the acid to the nutrient medium will immediately stop
the growth of bacteria, but the acid is not added for that particular
reason, but for the particular purpose set forth.
Instead of the enzymes obtained from the bacteria of dung, other
enzymes of a similar character may be used, such as the enzymes
obtained from the bacteria found on skins during the sweating process.
For bating skins in a practical manner with the improved bate herein
set forth, the method of using the same is preferably varied according
to the skins to be treated and the kind of leather it is required to
produce. Thus for kid skins, skivers and other skins for which dog dung
has hitherto been used, the skins, after the liming process, are first
well washed in water in the usual way to remove the bulk of the lime.
The skins are then placed in a wheel or paddle with the bate prepared
as before described, with the acid exactly neutralized by the ammonia
or so nearly neutralized that the alkaline action of the skins will
complete the neutralization, all skins being alkaline when introduced
into the bate.
The bate is diluted according to the amount of liming the skins have
undergone, and when in the paddle or wheel the skins and bate are
maintained at a temperature of about 37° C., and the skins paddled
until they have “fallen” considerably. The skins are then removed
from the wheel or paddle and scudded preferably on the “grain” side,
after which they are returned to the wheel or paddle and the paddling
continued until the bating action is completed, this being judged in
the usual way by a practical tanner according to the feel of the skins.
The strength of the bate after the scudding process may be varied if
found desirable.
After the bating process is completed the skins are treated in the
usual manner.
When the improved bate is to be used for light hides and similar
skins which have hitherto been treated with pigeon dung, the skins,
after the liming process, are washed in the usual manner, heated to a
temperature of about 37° C., and placed in a wheel or paddle containing
by preference the improved bate in an acid condition, that is before
the ammonia has been added, the bate being previously diluted according
to the amounts of liming the skins have undergone. The skins are then
paddled until the tanner, by the feel, judges that the whole of the
lime has been removed. The acid bate is then neutralized by ammonia,
with or without removing the skins, and the paddling is continued until
the bating process is completed, this being judged of by the feel of
the skins.
The bated skins are then scudded, washed, and treated in the usual
manner.
The strength of the bate, into which the skins are placed for both
methods, is varied according to the amount of liming the skins have
undergone; that is to say, for “high” limed skins, a stronger bate is
required than for skins which have been subjected to a moderate liming.
_Claim._--1. A bate having the essential properties of a natural dung
bate, but prepared according to scientific methods from the means
and in the manner substantially as set forth in the accompanying
specification.
2. The bate described and set forth in the accompanying specification.
*Wood’s American Patent* (638,828, _Dec. 12, 1899_) *Bate.*--This
invention has reference to improvements in and relating to the means,
liquid, or bate, used for the bating or puering of skins previous to
the process of tanning the same.
At the present time, skins are usually bated by means of a liquid
or bate prepared from dog or pigeon dung; and, although the bating
action or actions have not hitherto been thoroughly understood, it is
a well-known fact that fermentations which the dung undergoes play an
essential part. It was also pointed out, by H. E. Procter in 1885, in
his “Text Book of Tanning,” that the action of the bate was in a great
measure due to bacteria. It is also a known fact to practical tanners
that a dung bate properly applied produces the finest and most supple
leather. Owing, however, to the varying compositions of the dung used,
the bate made therefrom possesses varying properties: its bating action
is uncertain, its properties are readily affected by atmospheric
influences, and the skins treated are liable to putrefaction.
As a substitute for a dung bate, it has been proposed, as set forth
in the specification of the British Patent No. 21,720, A.D. 1895, and
the specification of the German Patent No. 86,335, Class 28, to use a
bate made from a pure culture of bacteria. Such bate, however, does
not possess all the essential properties of a dung bate, and, although
bacterial action is necessary, such action alone is not sufficient,
as was pointed out by me in 1894 in the “Journal of the Society of
Chemical Industry.”
I have now discovered that the bating action of a dung bate is due to
the combined action of enzymes, or unorganized ferments, and certain
chemical compounds, which compounds consist principally of amines--i.e.
ammonia in which one or more atoms of hydrogen has or have been
replaced by alcohol radicles--in combination with organic acids usually
found in dung, and of the compounds so formed the lactates and acetates
are the most important. I have also discovered that the bating action
of the enzymes alone, or the action of the above-referred-to chemical
compounds alone, is inefficient, and that the enzymes exert their
bating action in the presence of the chemical compounds, while these
latter, in addition, have an independent action on the limes in the
skins, and on the skin fibre.
The object of this invention is the production, according to scientific
methods, of a bate having similar properties to those of a dung bate,
such properties in the improved bate being modified according to the
requirements of the skins to be bated and the leather to be produced.
According to this invention, the liquid or bate is made by producing by
fermentation, an enzyme or enzymes of the same character as the enzymes
contained in dog dung, or produced from bacteria contained in the dung,
and to the liquid thus obtained there is added an organic acid and an
alkali.
I have discovered that for an efficient bate a pure culture or single
species of bacteria is insufficient, and that no single organism
hitherto isolated will give results equal to dung. I have also
discovered that the production of enzymes of the character above
referred to, depends more upon the composition of the nutrient medium
in which the bacteria are cultivated, than upon the kind of bacteria,
although these latter must be capable of producing the required
enzymes, the production of which appears to be due to a symbiotic
growth of bacteria at present little understood. The bacteria used for
the purpose of this invention may be the bacteria found in dog dung, or
the bacteria obtained from the roots of the hairs of skins during the
sweating process, these latter being used, by preference, on account
of the ease with which they are obtained, compared with the difficulty
of isolating from the dog dung the particular mixture of species most
desirable, there being so many undesirable species present. Of the
bacteria found on the roots of the hair during the sweating process,
and hereinafter referred to as “sweating” bacteria, I have found that
two species predominate, and, so far as I am aware, these have not been
previously isolated. The principal organism, which I call “bacillus
_d_,” in continuation of a series of previous investigations described
in the “Journal of the Society of Chemical Industry,” A.D. 1898, forms
large whitish colonies, with irregular contour spreading on the surface
of the gelatin, the bacilli being very small, mostly occurring in
pairs, but sometimes joined together in thread-like forms. The second
organism, called by me “bacillus _e_,” forms small brownish-yellow
boat-shaped colonies on gelatin plates. The bacteria consist of plump
cells two or three times the size of bacillus _d_, united in pairs and
chains, but the cells vary considerably in size, and are surrounded
by a capsule. I have discovered that the above bacteria, when used
separately as pure cultures, exert little or no action on the skin, but
when used together the action is very remarkable.
The gelatin and gelatin plates referred to in the above description are
the gelatin and gelatin plates used for the cultivation of bacteria,
according to the ordinary bacteriological methods as described in
Günther’s “Bakteriologie,” published by George Thieme, Leipzig, in
1898, and in other text-books.
In the accompanying drawings, made from photographs which are of record
in this case, the bacillus _d_ is shown in Fig. 21, and the bacillus
_e_ in Fig. 22, both photographs showing the bacilli magnified 1000
diameters.
A culture may be prepared from the sweating bacteria by taking the
hair from the skin when it “slips”--that is, when it can be removed by
simply pulling it. The root portion of the hairs are then cut off, and
about 10 grm. carefully digested in 100 c.c. of water at a temperature
of 32° to 35° centigrade for several hours. The liquid portion is then
poured off, and used for inoculating 10,000 c.c. of a nutrient medium
of the character hereinafter described. The inoculated nutrient medium
is then maintained for three days at a temperature of 37° centigrade,
and may then be used for the inoculation of a larger quantity of
nutrient medium.
Theoretically, a single cell of a bacterium is sufficient to inoculate
any quantity of any suitable fluid; but in practice it is found
necessary or expedient to employ 5 or 10 per cent. of inoculating
matter to the volume of the liquid to be inoculated. The inoculation of
the 10,000 c.c. of nutrient medium may be done in a Carlsberg vessel,
as described by Hansen in his “Untersuchungen aus der Praxis der
Gärungsindustrie.”
It is desirable that the nutrient medium should be without sugars
or carbohydrates; and, although its composition may be varied, good
results can be obtained by ordinary bacteriological methods, by using
a medium composed of gelatin, 50 parts or 20 grm.; potassium or sodium
phosphate, 1 part or 0·4 grm.; sodium chloride, 1 part or 0·4 grm.;
water, 2500 parts or 1000 c.c. This medium, after inoculation, is
maintained at a temperature of 37° centigrade, until the required
bacterial action is completed, i.e., until the whole of the nutriment
for the bacteria is exhausted, at which time the maximum quantity of
the required enzymes has been produced. The time required for this
action is not less than three days, nor more than seven days. The
exhaustion of the nutriment may be ascertained scientifically by a
microscopic examination of the liquid, the bacilli at this period
commencing to form spores. To each litre of this liquid there is then
added from 2 to 6 grm. of lactic acid, and the acid liquid is afterward
neutralized by ammonia, which is added when the liquid is to be used as
a bate, the addition of the ammonia forming certain chemical compounds
similar to those found in the dung. Instead of lactic acid, acetic
or other similar organic acid may be used, but sulphuric or mineral
acids must not be used. The addition of the acid to the liquid will
immediately stop the growth of the bacteria; but the acid is not added
for that particular purpose, but for the formation of the chemical
compounds above referred to.
The above-described method is most suitable, when the bate has to be
kept for a time before being used, or when it is desired to concentrate
it for transit or export; but if the bate is to be used immediately,
it may be prepared as follows: 100 parts of gelatin are dissolved in
1000 parts of water, and there is then added 50 parts of commercial
lactic acid. The mixture is then heated, in a closed vessel, to 100°
centigrade, by which operation the gelatin is partially peptonized,
and the subsequent bacterial action is hastened. The acid liquid is
afterward neutralized with ammonia, or other alkali, and the whole
diluted with water to 20,000 parts. The dilution may conveniently take
place in the wheel or paddle in which the bating is to be done, and
to the liquid thus obtained there is added from 5 to 10 per cent. of
the active culture from the Carlsberg vessel, as above described. The
liquid is then allowed to stand for 15 to 20 hours at a temperature of
37° centigrade, and is then ready for use.
For bating skins in a practical manner with the improved bate herein
set forth, the method of using the same is varied, according to the
skins to be treated and the kind of leather it is required to produce,
and the strength of the bate is varied in exactly the same manner as
the strength of a dung bate, and such variation is made according to
the judgment of the tanner, the improved bate acting in the same manner
as a dung bate.
For kid-skins, calf-skins, skivers, and other skins for which dog
dung has hitherto been used, the skins, after the liming process, are
first well washed in water in the usual way, to remove the bulk of the
lime. The skins are then placed in a wheel or paddle, with the bate
prepared, as above described, with the acid exactly neutralized, or so
nearly neutralized, that the alkaline action of the skins will complete
the neutralization, all skins being alkaline when introduced into the
bate. The bate is maintained at a temperature of 37° centigrade, and
the skins are kept in motion until they have “fallen” considerably,
i.e., until the swollen condition of the fibres due to the liming has
disappeared. The skins are then removed from the wheel or paddle and
scudded by hand or machine, preferably on the grain side, and the skins
not sufficiently reduced are returned to the paddle, and the bating
continued until the action is completed, this being judged in the
usual way by the tanner by the feel of the skins. The strength of the
bate, when skins are returned thereto, may be varied from the original
strength, if desired, and after the bating is completed the skins are
treated in the usual manner.
The strength of the bate into which the skins are placed, is varied
according to the amount of liming the skins have undergone--that
is to say, for a high-limed skin a strong bate is required. For
moderately-limed skins the bate may be of such a strength that each
litre as prepared for use contains five grm. of the original gelatin
contained in the nutrient medium, which is equal to one part of liquid
in which the culture has taken place to three parts of water. When
the bate is prepared for immediate use, its strength is varied in
the paddle as required. For very hard skins, such as goat-skins, the
culture may be used as a bate undiluted or it may be diluted with an
equal quantity of water.
For light-dressing hides and similar skins, which have hitherto
been treated with pigeon dung, the skins are washed in the usual
manner after the liming process, heated to 37° C., and placed in a
wheel or paddle containing the improved bate, preferably in an acid
condition--that is, before the ammonia or alkali has been added--the
strength of the bate being equivalent to five grm. of original gelatin
contained in the nutrient medium to each litre of the bate used. When
the lime has been removed from the skins by the bate, which will be
in about one hour, a quantity of the original culture previously
neutralized with ammonia or other alkali and equal to about one-half
of the quantity of the original culture first added is placed in the
wheel and the bating continued until the process is completed, this
being judged by the feel of the skins. If in the above method the
chemical reaction of the bate be examined before the second portion
of culture be added, it will be found neutral, and the action of
the enzymes takes place in a neutral or alkaline solution, as in the
first-described method.
The character of the principal enzyme in dung and in the improved
bate is a proteolytic one; i.e. it resembles the trypsin contained in
pancreatic juice.
Instead of adding an organic acid and neutralizing it by an alkali,
as described with reference to both processes, there may be added an
organic salt of the same character as that formed by the combination of
the acid and the alkali.
_Claim._--1. A bating liquor or bate containing enzymes of the same
character as the enzymes contained in dog dung, an organic acid,
and an alkali, or their chemical equivalent, i.e. an organic salt
substantially as herein set forth.
2. A bating liquor or bate containing enzymes of the same character
as the enzymes contained in dog dung and produced by fermentation an
organic acid and an alkali, or their chemical equivalent substantially
as herein set forth.
3. A bating liquor or bate containing one or more enzymes of the
character of the enzymes contained in dog dung, an organic acid and an
alkali, or their chemical equivalent substantially as herein set forth.
4. A bating liquor or bate containing one or more enzymes of the
character of the enzymes contained in dog dung, or produced from
bacteria obtained from dog dung, an organic acid, and an alkali or
their chemical equivalent substantially as herein set forth.
5. A bating liquor or bate containing enzymes of the same character as
the enzymes contained in dog dung, two to six grm. of an organic acid
to each litre of the liquid and neutralized by an alkali substantially
as herein described.
6. A bating liquor or bate containing enzymes of the same character as
the enzymes contained in dog dung, from two to six grm. of lactic acid
to each litre of liquor and neutralized by ammonia substantially as
herein described.
7. A bating liquor or bate containing enzymes of the same character as
the enzymes contained in dog dung and obtained from bacteria found on
the roots of hairs during the sweating process, from two to six grm.
of lactic acid, and neutralized by ammonia substantially as herein set
forth.
8. A bating liquor or bate containing enzymes produced from bacteria
obtained from dog dung and cultivated in a medium composed of fifty
parts of gelatin, one part of potassium or sodium phosphate, one part
of sodium chloride and two thousand five hundred parts of water, two to
six grm. of lactic acid to each litre of liquor and neutralized by the
addition of ammonia substantially as herein described.
*Oropon* (German Patent 200,519, July 21, 1908).--Process for Bating
Hides. Dr. Otto Röhm, Esslingen a/Neckar. In the present process, a
watery extract of the pancreas in combination with ammonia or alkaline
salts or mixtures of these salts is used as a bate liquor. The object
of the process is to replace the dung bate. From the researches of
Wood[145] also Jettmar[146] it appears that the peculiar behaviour
of the dog dung bate is to be attributed to the action of enzymes in
combination with organic amine compounds and ammonia salts. Starting
from the assumption that other enzymes, known to have an action on hide
substance, might have an analogous action to the dog dung bate, the
author discovered that the trypsin of the pancreas had exactly the same
bating action as the enzymes of dog dung. The action is aided by the
fat-splitting enzyme of the pancreas, steapsin, which saponifies the
fat in the hides.
[145] J.S.C.I. 1898, pp. 1010 to 1013, and 1899, pp. 990 to 993.
[146] An abstract of Wood’s work. 1901, p. 148, section 4, p. 149.
A good bating action is obtained by a watery extract of pancreas, by
the addition of an ammonium salt, which changes the caustic lime (from
the limed pelt) into a soluble lime salt, and gradually reduces the
alkalinity of the bate liquor caused by the lime in the skins, since
the ammonia liberated by the lime escapes to a great extent from the
liquor. The favourable action of the ammonium salt on the skins causes
them to fall and become thinner, nor do they become rough when placed
in clean water after bating, as a strongly alkaline skin will if placed
in water containing calcium carbonate.
For example, the process may be conducted by extracting a pancreas
weighing about 250 grm. with 1 litre of water, and adding 10 c.c.
of such extract to 990 c.c. of a solution containing 0·15 per
cent. ammonium hydrosulphide and 0·3 per cent. sodium chloride.
Such a solution forms a very active bate. In place of the ammonium
hydrosulphide, any other ammonium salt yielding a soluble lime salt
may be used, e.g., ammonium chloride.
The pancreas extract used in the above process must be used in a fresh
condition or preserved from putrefaction by the addition of some
suitable preservative; if putrefied, and consequently acid, it will not
work. The preservation of the pancreas may also be brought about by
drying, and the bate liquor made from the dry material by putting it in
water. No putrefaction occurs during the bating process. The action of
the enzymes is favoured by the alkaline reaction of the hide.
_Claim_.--Process for bating hides, characterized by the use of a
watery extract of the pancreas, with the addition of an ammonium or
alkali salt which forms soluble lime salts, or mixtures of such salts
to the liquid.
In an addition to the above patent, Dr. Röhm proposes to soften the
water used by adding the proper amount of clear lime water to it.
Starch paste can also be used for the same purpose, or a mixture of
lime water and starch paste.
In a further addition, a weak acid mixture, consisting of 0·05 to 0·1
per cent. lactic acid and 0·05 to 0·1 per cent. ammonium chloride, is
proposed in place of the ammonium salt alone, since the evolution of
free ammonia had been found to be detrimental to the skins.
*Eberle’s English Patent* (21,202, 1909).--Improved Process for Bating
Hides. Efforts have been made for years to replace dogs’ excrement
used in many cases in tanning as a bate, by other simpler products
and methods which in particular shall have the advantage of greater
uniformity and thereby act with greater certainty.
Now it has been ascertained that substances which are only solvents of
lime, such as acids of inorganic or organic nature and their salts,
form an incomplete substitute. It has been shown by Eitner, Wood and
others that there are enzymes and bacteria to which dogs’ dung owes its
specific or bating properties. The action of dogs’ dung is explained
as one which liquefies or dissolves the skin substance, such as is
otherwise only done by enzymes and bacteria.
Experiments in the laboratory and in practice have shown that it is
not the dissolving action on the skin substance in the narrow sense
which is desired in bating the derm with dogs’ dung, but in order to
prepare the hide for the manufacture of a soft and elastic leather, the
albuminous intercellular substances and more particularly the layers
of fat lying at the roots of the hair, in the corium and in many cases
also on the epidermis, must be dissolved and thereby the fibrils of the
skin loosened. The highly solvent action of the dung bate on the skin
substance means in very many cases a direct disadvantage by reason of
the loss of leather substance.
Extensive experiments with the separate constituents of dogs’ dung have
shown that with none of them employed alone can a satisfactory action
be obtained. For the experiments, the organic and inorganic salts
contained in dog’s dung were employed. Pure cultures of intestinal
bacteria were also examined and also the intestinal juices, secretions
of the gall bladder, of the pancreatic gland and secretions of the
intestinal mucous membrane. The relatively best bating action was
obtained with the secretion of the gall bladder; only a moderate bating
action could be obtained with the juices of the pancreatic gland and
the secretions of the intestinal mucous membrane. It was therefore
very surprising to find and could not be foreseen that mixtures of
these three secretions of the digestive apparatus alone exerted an
excellent bating action, and that such mixtures not only formed a
perfect substitute for the bate of dogs’ dung, but that they acted far
better than the latter, without it being necessary, as was recommended
elsewhere,[147] to add lime-dissolving salts to the bate, or to take
measures in any other manner for the removal of the lime from the
water.[148]
[147] 1. See German Patent No. 200,519 or British Patent No.
5377^{08} Roehm, Esslingen.
[148] 1. See German Patent of Addition No. 203,889 Roehm, Esslingen.
The explanation of the effective action of such mixtures is evident
from the following statements:--
Pancreatic juice contains three ferments, of which for our purpose
trypsin, which decomposes albumen, and steapsin which decomposes fat,
are the most important. Both ferments are contained as zymogens, that
is to say in an inactive form, in the pancreatic juice. The latter
therefore only gives an incomplete bating action. Gall contains
ferments which have properties which are mainly fat decomposing,
but are also albumen dissolving. Gall also contains the salts of
gallic acids which have the power in a high degree of dissolving and
emulsioning greases or fats, and among others have a great solvent
action on the chloresterin contained in the skin, more particularly in
the roots of the hair. As regards the fat-decomposing and dissolving
action, gall is far superior to pancreatic juice.
The ferments of gall are, however, also capable of energising the
action of the steapsin in the pancreatic juice as a fat-decomposing
ferment, that is to say of imparting to the pancreatic juice, which in
a pure condition has a very slight action on fat, a high capacity for
decomposing fat.[149]
[149] 2. See Abderhalden, “Text-book of Physiological Chemistry,”
1906, page 555 and following.
Finally gall in bating the derms may be of great importance inasmuch
as its acids form easily soluble lime salts. Extensive experiments
have shown that gall, as such, is adapted to dissolve a comparatively
large quantity of lime. In hard water an addition of gall prevents the
precipitation of calcium carbonate, and the roughening of the derm,
which, for instance, has been noticed when pure bacteria cultures are
employed, is prevented by the addition of gall.
The intestinal juice contains in addition to carbonates and alkalis,
enzymes which again exert a slighter bating action on the hide than
those of gall. The intestinal juice alone has a similar action to
pancreatic juice, but if intestinal juice be added to pancreatic
juice, the most powerful enzyme of pancreatic juice, namely the
albumen-decomposing trypsin is energised, and only in this way
does the pancreatic juice fully acquire the property of dissolving
albuminous substances.[150]
[150] 1. See Abderhalden, “Text-book of Physiological Chemistry,”
1906, page 556.
The proportions in which such mixtures best develop their actions, are
those which obtain in animal organisms; the temperature also especially
plays a great part. The maximum temperature lies about 40° C.
From the above statements it is evident that it is possible to
produce various actions with the juices of the pancreas, gall and
the intestines, quite dependent on which are considered the most
important in the bating. Similarly, as the proteolytic action of the
mixture of the three juices may be increased or diminished by using
larger or smaller quantities of intestinal juice and pancreas, the
fat-decomposing and fat-dissolving action of the mixture may also be
increased or diminished by using larger or smaller quantities of gall,
and of gall and pancreas respectively. Finally the quantity of the gall
to be added is decided according to the amount of lime contained in the
water employed in the bating. Experience has shown that a relatively
small addition of gall will act very advantageously.
It must be especially remarked that artificial bates made in this
way are extremely cheap as compared with the natural dogs’ dung, as
gall and intestinal juice may be procured at very low prices and
a considerably smaller quantity of the energised, more expensive,
pancreatic juice is necessary than, for instance, would be necessary if
this juice were employed in a pure condition.
The advantage of this invention also consists in its being possible to
make better bates than that which is made, for instance, from dogs’
dung because, as hereinbefore stated, it is a disadvantage of this
latter bate that it in many cases dissolves too large a quantity of
the albuminous substance. Otherwise, the composition of the improved
bate quite coincides qualitatively with the composition of dogs’ dung,
as the latter actually consists in addition to the unabsorbed portions
of food, of secretions of gall, the pancreatic gland and the mucous
membrane of the intestines. The trypsin and steapsin respectively as
well as being derived from the pancreatic juice, may also be derived
from the vegetable kingdom, for instance, there are considerable
quantities of trypsin in the sap of the fig. Steapsin, in not
inconsiderable quantity, is found in the saps of flax, hemp, maize, etc.
It must also be remarked that the colouring matters in gall are of
quite subordinate importance, and may be disregarded. The view formerly
adopted that the colouring matters in gall stain the leather is
incorrect.
_Example_:--200 c.cm. of gall juice in 1 litre of water are mixed with
the watery extract of 200 grm. of chopped small intestine in 1 litre
of water on the one hand, and 100 grm. of the pancreatic gland in 1
litre of water, on the other hand. This watery solution is added to the
bating bath, according to the bating action desired. It can also, in
order to allow of being more easily handled, be obtained in solid form
by absorption in sawdust or kieselguhr and drying at 30° to 40° C.
_Claim._--A process for bating hides, characterised by the use of
mixtures of gall, the secretion of the pancreatic gland and intestinal
juice, and by the use of mixtures of the active enzymes in these, or
active enzymes derived from the vegetable kingdom, substantially as
described.
*Prof. Dr. H. Becker’s English Patent* (24,982, 1910).--Improvements
in Puering and Bating Hides and Skins.--It has been shown by Wood, of
Nottingham, and by Dr. Popp and Dr. Becker, of Frankfort-on-the-Main,
that the action of a good puer or bate on hides, is connected with the
development of certain species of bacteria.
The preparation of pure cultures of these bacteria (which are derived
from dog dung) has enabled what may be properly termed a safe puer to
be obtained, inasmuch as by its use overpuering the hides is entirely
prevented. Furthermore, the leathers are fuller and do not lose any
excess of hide substance, so that a dozen sheepskins that have been
suitably puered by the bacteriological method, will weigh about 9
ounces more than a dozen skins of the same kind and origin, that have
been treated in exactly the same way in other respects, but puered with
dog dung.
The method of action of the bacterial puer has been elucidated as
follows. The bacteria present in the puer are microscopically small and
pass easily into the skin through the pores of the latter, while on the
surface and in the substance of the skin they produce their metabolic
products and enzymes. These substances are partly proteolytic, partly
fat decomposing, and also diastatic in character, so that the highly
proteid intermediate substance of the skin is degraded. By means of
the ultimately formed ammonia, amine bases and ammonium bases assisted
by the action of organic acids produced by the bacteria, the lime soaps
are decomposed. Lime and fat are partially dissolved, and partially
further decomposed or converted into a form which enables them to be
worked out by mechanical means. At the same time the roots of the hairs
are also loosened so that the hairs also can be readily removed by
mechanical treatment.
Another essential factor is the liberation of gases formed within
the skin by the action of the micro-organisms and exerting a very
gentle pressure on their environment. The structure of the fibres is
loosened, the fibrils are straightened individually without sustaining
any important loss of corporeal matter, and in this way a firm, tough
and yet soft handling leather is obtained. Attempts have been made to
improve this puer by adding, for instance, organic acids and salts to
the bacterial cultures.
Other methods of puering, based on the direct weakening of the skin
fibres from the outside, may also effect the pulling down of the hides,
and moreover, in consequence of that attack on the skin fibres without
straightening the fibrils, an immoderate amount of substance is lost,
and therefore a hard, stiff, thin and light leather is obtained.
To this class belong also the purely digestive puers such as pancreatic
juice, intestinal juice and the like, or purified enzymes. These
enzymes are colloidal and therefore incapable of diffusion, and
consequently they digest the hide mainly from the surface, that is to
say, the grain side and inner side of the hide. The fibres, in-so-far
as they are accessible at all to the action of the colloidal enzymes,
are removed from outside without the fibrils being loosened and
straightened. Hence they are weakened by the digestive puer to such an
extent that the hides seem to be gradually pulled down; but the skin
will by that time have lost too much substance, so that, _inter alia_,
even the grain appears to have been corroded. In this way the leather
is rendered thinner and lighter than that from the dung or bacterial
puer--a defect manifest to every expert.
This danger is particularly great when, by the artificial admixture
of corporeal juices, complications are set up, that intensify the
destructive action of the digestive enzymes on the material, and when
their supplementary action is not suitably controlled.
These animal or digestive enzymes and fat decomposing substances
originate, in-so-far as they are not of vegetable origin, for the
most part in the upper portions of the digestive tract. The use of
these substances effects an imitation of the purely enzymatic and fat
decomposing processes that go on in the upper part of the intestines,
but omits the processes--not less important for digestion and the
formation of excrement--occurring in the large intestine and the
adjoining portions of the digestive tract. Here the bacteria and the
vegetable enzymes secreted thereby, play the chief part. They decompose
not only the food constituents--partly by putrefaction--but also the
albuminoid digestive secretions and the gall, so that only small
quantities thereof are left. Hence when applied to the puering process,
the use of bacteria, together with their specific enzymes and metabolic
products, is equivalent to a restriction of the immoderate digestive
action of the pancreatic and digestive juices, i.e. of the animal
enzymes.
Digestion therefore, with the resulting formation of excrement, is
carried on with the accompaniment of a mutual control, excitation and
restriction on the part of the digestive secretions and the bacterial
phenomena.
These latter form the real basis of the puering of hides in dung
preparations.
This is also evident from the purely practical experience that dog
dung puer, e.g. for glove leather, is essentially improved by leaving
the dung to ferment for several weeks or rather months. During this
process an increase occurs in the micro-organisms present, and also in
their metabolic products and enzymes, but not in the digestive juices
originating in the organs of the animal body--the term “digestive
juices” being restricted to indicate only such juices as are produced
in the course of the digestive tract by the organs and cells of the
animal body, in contradistinction to the juices produced by bacteria.
According to the present invention, the bacterial cultures, together
with their metabolic products or products of digestion and enzymes,
are used in combination with one or more of the substances that are
excreted in the digestive tract by the animal body itself in order
that not only each of these substances may exert its special action on
the skin, but also that the aforesaid mutual influencing, and more
particularly regulating of the action may take place.
On this principle, in preparing an artificial puer for hides, and
in accordance with the nature and preliminary treatment of the raw
material, and the requirements put forward in respect of the finished
product, the bacterial puer, nutrient medium or culture is mixed
with the corresponding digestive juices, or with purified animal or
vegetable enzymes, as well as with fat decomposing media, if necessary,
such as ground castor-oil seeds, hemp seed or the like, or with
extracts of same, or with gall. Where it seems necessary, substances
capable of dissolving lime may also be added, for example, sugar,
molasses, salts of ammonia, organic acids, or the corresponding salts
or the like.
Finally, also, the several operations may be carried out independently
of one another, it being in such case again advisable to adhere to the
processes going on in the intestines.
If, for instance, specially hard goat skins are to be pulled down
strongly by puering, it is advisable to add to the nutrient medium
of the bacteria a little papayotin or papain, either--according as
rendered necessary by the local conditions--in the preparation of the
bacterial puering liquor, or during the propagation of the bacteria.
If the fells are less hard so that less pulling down is required, the
hides are first treated with a weak solution of the digestive ferments,
and then with the bacterial liquor. In this way excessive digestive
action is counteracted in good time.
Sheep and goat skins that are particularly rich in fat are immersed
in a bacterial puering liquor, containing ground castor-oil seed or
castor-oil cake in suspension. The fat-decomposing ferment contained
in this meal then comes into immediate action, and the liberated fatty
acids form readily soluble soaps with the ammonia, originating from the
degradation of the proteid substances, and with the allied bases.
Extensive practical experiments have also shown that, in the case of
very fat skins, the action of the bacterial puer is increased by mixing
a suitable salt of sulpho-ricinoleic acid with the puering liquor, or
by washing the skins with solutions of similar soaps either before they
are immersed in the puering liquor, or subsequently.
Local conditions, and the requirements laid on the finished leather,
must decide which of these methods is specially advisable.
In any event, however, the combinations of the bacterial puer afford
a means of obtaining an increased puering effect in many cases where
puering with the separate auxiliaries mentioned does not produce a
sufficient result.
_Claim._--In the method of puering hides wherein bacterial cultures,
their metabolic products and enzymes are employed, the combined use
with these agents of digestive juices, mixtures of digestive enzymes
or pure digestive enzymes (and, if desired, of fat-decomposing
substances), either simultaneously with said agents or subsequently
thereto.