An Improved Process of Tanning.
Year: 1899

page_text: Date of Application, 18th July, 1899-Accepted, 18th Nov., 1899
COMPLETE SPECIFICATION.
An Improved Process of Tanning.
We, CHARLES SUMNER DOLLEY, Biologist, of 118, Farragut Terrace, and
ALBERT FILMORE CRANK, Chemist, of 683, Bource Building, both in Philadelphia,
in the County of Philadelphia and State of Pennsylvania, do hereby declare the
nature of this invention and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
―
This invention relates to certain new and useful improvements in processes
for treating hides, skins and leather, and the objects of the invention are to
provide a process by means of which a superior leather can be produced either
from raw hides or skins, or from such hides or skins as have been previously
tawed, or from such as have been partly but imperfectly tanned and which do
not meet the various tests which are commonly employed to determine perfectly
tanned leather and which are therefore susceptible to improvement.
Certain varieties of skins (as is the case with E. I. kips and goat skins, basils
and white leather) are for convenience of shipment or for other reasons placed
upon the market in a tawed or an imperfectly tanned condition. Such skins in
many cases, do not respond favorably to the usual tests for perfect leather, hence
require subsequent treatment.
Certain methods of tanning throw upon the market a considerable amount of
imperfect leather, which is susceptible to improvements, (as for instance that
treated with cutch or terra japonica, divi-divi, etc.) which if properly tanned
would command higher prices.
It is one of the objects of the present invention to take such tawed and poorly
tanned leather and by proper treatment to convert the same into nearly perfect
leather, thus greatly enhancing its value.
The invention has for a further object, to fix in the skins or hides such sub-
stances (for example, extractives, coloring-matter, fillers, natural and artificial
tannins, etc.), as may be employed with the purpose of feeding the leather and of
providing it with certain desired physical characters, such as plumpness, weight,
color, softness, impermeability to moisture, etc.
Our invention consists essentially of two steps, the first of which is concerned
with the introduction into the hide or skin, of some material or materials, which will
render the skins sensitive to the fixing or tanning agent employed in the second
step, by overcoming the agglutinating action of the interfibrillar ground-substance
(mucin, coriin, etc.), and effect a splitting up of the connective tissue fibre-
bundles with an accompanying swelling and separation of the fibres and fibrils,
producing thereby a fulling or plumping effect, clearing the grain and at the
same time feeding the leather, that is to say impregnating the skin with materials,
the presence of which is desirable for the production of the physical qualities
noted above. This first step has the same purpose as that commonly attained by
the employment of old and sour liquors and weak solutions of extractives, and
which precedes the actual tanning process.
The second step of the process consists in treating the hide or skin to the action
of formicaldehyd, (CHO), a material possessing the property of fixing the

page_text: connective tissue-fibres and fibrils in the swelled and plumped, tawed or partially
tanned condition produced by the first treatment and at the same time of fixing
in, upon or between the fibres and fibrils of the connective tissues, materials
which have been supplied by the first step of the process to contribute special
physical qualities, such as body, color, suppleness, weight, etc., essential to a
solid well nourished leather. The use of the formicaldehyd in this second step
is not a mere aggregation of elements or materials as it is in its nature and
effects entirely different from the materials employed in the first step, and could
not be substituted for them to produce the effects of the first step, while it
possesses distinctive and positive characters, by which it acts upon both the skin
and the materials with which it has been impregnated by the first step, in a
manner peculiar to itself, as will be hereinafter more fully set forth.
In carrying out our invention, we take advantage of the property possessed
by various tawing and tanning agents (such as alum, salt, argol, eggs, flour,
vegetable extractives, gambier and cutch, and the artificial and natural tannins,
used in making leather, many of which have none or only feeble tanning proper-
ties), of causing a swelling up or separation of the fibres and fibrils of the skin
connective tissue, and the deposition in, upon and between the same, of materials
which prevent them from again becoming agglutinated, thereby allowing the
interlacing fibres to move readily upon each other, and which at the same time
add material to the skin which is of advantage in respect to weight, body, color,
etc., whereby a plump, soft, pliable, tough and elastic leather may be produced.
Owing to the manifold qualities and varieties of leather required in the various
industries, it is impossible for us to specify any one of the agents, such as alum,
salt, eggs, flour, extractives, reds, gambier, tannins, etc., as being capable of meet-
ing all requirements, and in the first step of our process we hold ourselves free to
use any or all materials which will produce the effect or effects desired, that is
to say, the separation and swelling of the fibres and fibrils and the clearing and
raising the grain, together with the plumping, filling coloring, weighting and
rendering supple the skin; in short, its preparation for the subsequent fixing
action of formicaldehyd as employed in our second step, an action in some re-
spects analogous to that ordinarily secured by means of those tannins which are
capable of rendering gelatin insoluble, but in many respects peculiar to itself.
The ultimate object of the invention in using the materials designed in the
first step of our process is to secure desirable states and qualities in the hides or
skins treated which may be fixed or supplemented therein by the action of formi-
caldehyd subsequently applied in the second step, as hereinafter described. The
following particular case will serve to illustrate the steps involved in our process:
Commercial sheep or goat skins or hides, having been previously prepared
for treatment by softening, unhairing or other necessary and ordinary steps,
usually referred to as beam house treatment," are placed in a drum or reel,
in which they may be agitated by the revolving of the receptacle, by paddles,
or by any other suitable means, the particular method or mechanism employed,
constituting no part of the present invention. We hold ourselves to employ any
form of receptacle or method of agitation whatsoever..
"
Together with the hides or skins in the receptacle is placed a solution of
gambier extract diluted to present the extract to the entire mass of the skins,
containing approximately four pounds of gambier to each one-hundred pounds
of wet hides or skins, the exact amount of gambier being based upon the weight
of the skins or hides to be treated, also upon their acidity or alkalinity, according
to well known gambier tanning processes.
The skins or hides are then agitated in the gambier-bath until they are per-
meated through and through by the solution forming the bath, the time required
depending somewhat upon the nature of the particular skins or hides, the size
of the receptacle, the number of volume of skins and the rapidity with which
the receptacle is revolved, or its contents agitated, factors which do not concern
the principle involved in the process,

page_text: When the gambier has struck through or thoroughly permeated the skins,
(which may be ascertained by cutting into the thickest edge and examining the
exposed interior) the skins are rinsed in clean water, but this washing or
rinsing may if preferred, be dispensed with, and the second step proceeded with
at once, and we do not wish to be held to washing the skins as a feature essential
to our process.
We wish it clearly understood, that the object of the first step of our process
is, as has been previously stated, to bring the skins into a desired physical con-
dition, characterized by such a separation and swelling of the tissue fibres and
fibrils and such plumpness, weight, color and suppleness as will, when fixed by
the chemical action of formicaldehyd, constitute a superior leather of the par-
ticular character desired. Thus we are able to develop the desired physical
characters by means of alum, salt, argol, eggs, flour, the tannins, gambier and
other vegetable extracts.
In the first step therefore, it is not so much a question of the materials em-
ployed, as there is a wide choice in this respect, but rather the securing of
physical qualities in the skin, which we proceed to supplement, fix and render
permanent by the second step. The use of saline liquors serves to swell the
tissues and fibres of the skin and to render it more readily affected by the tan-
ning or fixing agent subsequently employed, while the vegetable extractives or
their equivalents add color, weight, etc.
The second step of our process consists in subjecting the skins or hides to the
action of formicaldehyd, preferably in solution although it may be employed in
the state of gas, either in the same receptacle in which they were given the pre-
liminary treatment, or if desired, in a special receptacle.
The amount of the solution employed varies somewhat, but is based upon the
weight of the skins or hides to be treated and we have found in practice, that
three pounds of commercial, forty-per cent. (40%), formicaldehyd solution to each
one-hundred pounds of wet-hides or skins, is sufficient for ordinary sheep or goat
skins.
The amount of water with which the formicaldehyd is diluted, is based upon
the bulk of skins, being just sufficient to keep them well wetted and to present
the formicaldehyd to the entire mass of the skins, but not so much as to prevent
the pounding action of the skins when revolved in the drum.
The skins or hides are subjected to the action of formicaldehyd until permeated
through and through, and until they respond to the usual tests for good leather
In the particular case which is cited herein as an illustration, namely sheep or
goat skins, we have found that the time required is approximately three hours.
The time however, depends to a very considerable extent, as in the treatment by
the first step of our process, upon the number of skins in the receptacle and the
rate and mode of agitation to which they have been subjected. It is advisable
to maintain the bath in the second step, at a temperature of not less than 80° Fh.,
and not above 120° Fh., in order to secure the greatest efficiency from the formi-
caldehyd, which has greater penetration and less liability to polymerize than at
low temperatures. After the skins are found to have been thoroughly fixed by
the formicaldehyd, they are washed and are then ready for the usual treatment
employed in finishing.
In case the formicaldehyd is employed in the state of a gas, we prefer the
following method:
The skins having been brought to the desired state by the first step, as herein-
before described, an amount of commercial formicaldehyd, (40%), solution
representing approximately three pounds to each one-hundred pounds of wet
hides or skins to be treated, is placed in a suitable generator, a variety of which
are upon the market, and the gas generated is allowed to pass by suitable con-
nections into the chamber containing the skins. The temperature of this chamber
is preferably maintained at from 110° Fh. to 120° F., and the atmosphere of
the chamber should also be kept moist, both of which conditions are readily

page_text: secured by the admission from time to time of a small quantity of warm aqueous
vapor, by means of a suitable steam connection. The chamber employed should
be a closed one and no larger than necessary to allow the skins to be fully
exposed to the action of the gas. If desired, the gas may be admitted to the
drum in which the preliminary treatment took place, or into a similar drum,
and the skins agitated therein, or the skins may be stretched on suitable frames
and enclosed within a stationary chamber, in either case being exposed to the
action of the gas until they respond to the usual tests for good leather, say for
a period of six hours, the time depending however, on the thickness and char-
acter of the skins under treatment.
The market supplies certain tawed or imperfectly tanned skins and hides,
which have been already subjected to the action of salt and alum, flour, eggs,
vegetable extractives, gambier, cuteh, tanning or other materials, and which
do not constitute high grade leather, but which are susceptible of improvement.
The effect produced on these skins are analogous to those produced by the first
step of our process, and we find it both possible and advantageous to take such
skins and after softening them in water, proceed to treat them as described in
the example cited for treating raw-skins, whereby we are able to secure the
results of the first step with less time and material than would be required in
treating green or raw hides or skins, and in certain cases where the tawed or
imperfectly tanned skins or hides have the plumpness, color, weight, etc., desired,
and which we would have secured by means of our first step, we may proceed at
once to the second step of the process, which consists essentially in the fixation
of the natural or added constituents of the skin, substantially as described.
We have found by a large number of practical tests that the actual tanning
effect of the natural tannins as introduced into the skin by the first step of our
process, may be greatly hastened and augmented by the employment of formi-
caldehyd in conjunction therewith, as accomplished by the second step of our
process. Thus with the pyrogallol tanning a considerable proportion of which
possesses little or no tanning power, a compound is formed, whereby all the
tannin is rendered available and consequently a greater action secured from a
given amount of extract, a matter of importance in point of economy.
2
Again we find that by means of formicaldehyd used in conjunction with, but
subsequent to the use of those natural (catechol) tannins, containing phlobo-
phanes or "reds," as introduced into the hides by the first step of our process,
these substances, which in many instances are insoluble and not directly avail-
able for tanning, can be fixed in the leather, and again with other, (pyrogallol)
tanning, the deposit of "whites" or "bloom is prevented, the ellagic acid or
catchin being in some way altered and indissolubly bound in combination with
the skin substances, as are also certain extractives (e. g. gambier) by the action
of the formicaldehyd upon the impregnated collagen of the skin, whereby an
occlusion of the introduced material is brought about, also by its direct action
upon the catechus themselves, whereby they are rendered insoluble and pre-
cipitated as a filling and coloring material upon and between the fibres and fibrils
of the skin connective tissue, thus effecting which is technically known as feeding
the leather. A special advantage afforded by our process, is that it overcomes
the obstacles hitherto encountered in the use of materials like divi-divi, which
add to the leather substances extremely susceptible to fermentation, and which
leads to loss of leather in damp weather. The superior bactericidal and anti-
fermentative properties of formicaldehyd prevents this fermentation and the
consequent softening of the leather; it also prevents moulding during the
drying of the unfinished leather.
Formicaldehyd has the property of fixing the collagen and other gelatigenous
constituents of the skin in the condition in which they are when subjected to its
action, and we have found that it is highly advantageous in using formicaldehyd
in the manufacture of leather, to prepare the skins or hides by some preliminary
treatment, as by our first step, whereby the fibres and fibrils of the connective

page_text: tissue are properly separated and swelled or plumped, colored or filled, as seems
desirable in the particular case in hand, when they together with the other gela-
tigenous constituents of the skin, may be fixed in the particular state desired,
by the use of formicaldehyd, as has been previously described, and which con-
stitutes the second step of our process.
Our invention therefore proposes the application of formicaldehyd to hides
and skins, the collagen of which is either not at all, or but partially combined
into insoluble compounds either:
-
1st. From a lack of suitable quality in the agents used in the preliminary
treatment, such agents being for example salt, eggs, flour, alum, argol, vegetable
extractives, gambier, cutch, and such other tannin-containing materials as possess
little or no tanning properties, or-
2nd. From lack of sufficient combination with an agent, such as oak or hem-
lock tannin, which is potentially capable of saturating the collagen and forming
therewith an insoluble and imputrescible compound, but which in the skins we
propose to treat, has de facto not fully saturated the collagen.
In other words we propose to apply formicaldehyd to hides or skins containing
a soluble collagen compound, or unsaturated collagen. We therefore employ
formicaldehyd to fix the collagen of the skins after the skins have been prepared
by such processes as produce the qualities peculiar to ordinary salt and alum
tawed skins, chamois leather, oil-tawed leather, wash-leather, Knapp's-leather,
etc., or the peculiar leather resulting from the employment of gambier and similar
vegetable extracts, or where the fixation of the tissue constituents has been imper-
fectly accomplished by the ordinary tanning processes. The skins may be
specially prepared or tawed skins, chamois leather etc., may be taken ready pre-
pared, and submitted to the fixing action of formicaldehyd.
Much of the leather commonly regarded as well tanned, is open to great im-
provement, and our invention proposes the employment of the ordinary processes
of tanning as our first step, or the taking of commercial leather already prepared
by others, and submitting it to the fixing and supplemental action of formical-
dehyd as a second or final step in the production of perfectly tanned leather.
Our invention therefore involves the use of formicaldehyd subsequent to the
use of tawing or tanning materials, and inasmuch as these materials give varying
degrees of plumpness, weight, density and color to hides and skins, our invention
necessarily involves the use of formicaldehyd in conjunction with all materials
producing these effects, in accordance with our process as hereinbefore described.
We do not confine ourselves to the use of any one tawing or tanning, plumping
feeding or coloring material in conjunction with formicaldehyd, as our process
is nor limited to the production of any kind of leather but is applicable to the
production of either light or heavy leather, white or colored, as desired, in fact
to all varieties of leather, and its employment as herein described results in a
very material saving in time, labor and materials.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is:
1. The process for the production of leather, which consists in plumping, feed.
ing, weighting or coloring skins or hides with tawing or tanning materials, and
then submitting them to the action of formicaldehyd.
2. The process for the production of leather, which consists in subjecting
skins or hides to the action of tannin-containing extractives, whereby they are
plumped, fed, weighted or colored, and then subjecting them to the fixing and
tanning action of formicaldehyd.
3. The process for the production of leather, which consists in submitting such
skins and hides as have been previously plumped, fed, weighted or colored, by
the use of tanning agents, but which are imperfectly tanned, to the tanning
and fixing action of formicaldehyd.

page_text: 4. The process for the production of leather, which consists in treating hides
or skins with a tanning-containing extractive capable of forming a combination
with formicaldehyd (e. g. gambier) and then submitting the impregnated skins
to the action of formicaldehyd, whereby the material with which the skins have
been fed, weighted and colored is fixed and occluded in the skin-tissue.
5. The process for the production of leather, which consists in securing a
plumping, feeding, weighting or coloring action on skins or hides, by means of
such tanning materials as are liable to fermentation (e. g. divi-divi), and then
subjecting them to the tanning and preservative action of formicaldehyd.
6. The process for the production of leather, which consists in securing the
plumping, feeding, weighting and coloring effect to be had by subjecting skins
or hides to the action of a bath made from tan-bark or tannin-containing extracts,
containing phlibophanes or reds," and subsequently submitting the impreg-
nated skins or hides to the fixing and tanning action of formicaldehyd.
6
7. The process for the production of leather, which consists in securing the
plumping and coloring effect and the action on the grain to be had by subjecting
skins or hides to a bath of sour or weak liquors and then submitting them to
the tanning and fixing action of formicaldehyd.
8. The process for the production of leather, which consists first, in plumping,
feeding, weighting coloring or raising and clearing the grain of skins or hides,
by treating them in a bath of such agents and to such steps as are commonly
employed for this purpose, and subsequently fixing the skins or hides in the
state thus secured and tanning the same by treating them in a bath of formi-
caldehyd.
9. The process for producing leather, which consists in treating skins or hides
with such tanning as possess little or no tanning action, but which may be used
for their plumping, feeding, weighting or coloring effects, and then subjecting
them to the tanning action of formicaldehyd.
Dated this 18th day of July 1899.
BOULT & WADE,
Agents for the Applicants.