Improvements in the Process of Depilating Hides or Skins.
Year: 1897

page_text: Date of Application, 16th Nov., 1897-Accepted, 18th Dec., 1897
COMPLETE SPECIFICATION.
Improvements in the Process of Depilating Hides or Skins.
I, HENRY HOLMES, a citizen of the United States, residing at No. 923 North
Fourth Street, in the City of Philadelphia, in the County of Philadelphia, and
State of Pennsylvania, Manufacturer, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement:-
My invention has relation to a process, whereby hides or skins may be depilated,
in from eighteen to twenty-four hours, and thoroughly prepared for the subsequent
operations of fleshing and tanning.
99
Hitherto the usual mode, whereby hides and skins were successfully and com-
pletely depilated, and prepared for fleshing or tanning, was that known as the
* liming" process or method, wherein the hides or skins were covered with a
paint or layer of lime applied to both the flesh and the hair sides, and subjected
ic the caustic action of the lime for a period ranging from ten to fourteen days.
My present invention is designed to accomplish the same end as the "liming"
process above referred to, and to thoroughly and completely depilate the hide or
skin in a materially less time, to-wit:-in from eighteen to twenty-four hours.
In the carrying out of my invention, I first subject the hide or skin to the action of
a bath, consisting of a strong solution of sulphide of sodium, the strength of the
solution varying with the nature of the hide or skin to be treated, in an open vessel
which will permit of the escape of noxious and destructive gases, then the hide
or skin and solution are agitated by means of a paddle or paddles, after which the
hide or skin is permitted to remain at rest in the solution for about ten or twelve
hours, when the strength of the solution is gradually diluted, whilst the hide or
skin remains therein, the caustic strength of the solution being thereby gradually
weakened, until the hide or skin remains in a bath of pure or substantially pure
water. The result of this process is a hide or skin which is pulpy, porous, soft
and well adapted to undergo the subsequent operations of fleshing and tanning.
The nature and scope of my invention will be more fully understood from the
following description taken in connection with the accompanying drawings form-
ing part hereof, in which
Figure 1, is a transverse sectional view of an apparatus designed to carry the
depilating process of my invention into effect; and
Fig: 2, is a longitudinal sectional view of said apparatus.
The
Referring to the drawings, A, represents a vat or tank which is preferably
cylindriform having an opening extending longitudinally across the upper end. On
the open upper end is mounted a shaft b, carrying a series of paddles B, and adapted
tr be revolved or rotated by a belt 2, and pulley B', as illustrated in fig: 2.
shaft b, is eccentrically. located so that the paddles will dip into the upper portion
of a liquid introduced into the vat and to one side of the vertical center of the
vat. The rotation of the shaft b, and paddles B, by reason of the position of the
paddles, will cause a circulation of the liquid as indicated by the arrows in fig: 1.
In the vat A, is introduced sulphide of sodium in solution of required strength,
and the hides or skins to be treated are submerged in this solution and agitated

page_text: by the revolution of the paddles B. The hides travel in the liquid from the
bottom of the vat along its sides to the top of the vat when they are pushed down
by the paddles and along the sides of the vat to the bottom" thereof. By this
action of the paddles the hides or skins are thoroughly washed in the solution.
At the side of the vat A, is arranged a pipe d, controlled by a cock or valve d
and adapted to discharge into the vat at or near its upper end, a stream of fresh
water and at the sides of the vat are arranged a series of valve controlled outlets c
adapted to permit of the discharge of the solution in the vat. When the valve di
is open and the outlets c, are also open, a quantity or current of water enters the
vat and mixes with the solution of sodium sulphide therein and gradually dilutes
it, the diluted mixture flowing through the outlet c, thereby permitting of a still
further dilution of the solution upon the entrance of more fresh water from the
pipe d.
The operation of the apparatus hereinbefore described is as follows:-The
solution of sodium sulphide and the hides or skins are introduced into the vat
and subjected to agitation by the paddles for a period of about half an hour. The
hides or skins are then permitted to remain at rest in the solution over night or
for a period ranging from ten to twelve hours, when the hides or skins and the
solution are preferably again agitated by the paddles for a period of about two
hours. During this second agitation the valve d, is opened to permit of the
constant flow of water through the pipe d, and hence the addition of fresh water
to the solution of sodium sulphide for the purpose of gradually diluting said solu-
tion and at the same time the outlets c, of approximately the same area as that
of the pipe d, are also opened to permit of the escape of the solution. During the
entire operation, the upper end of the vat being open, all noxious and destructive
gases are permitted to escape from the vat. The constant inflow of water and
constant outflow of solution is so proportioned to the bulk of solution in the vat,
that it requires approximately two hours to replace the solution in the vat with
fresh water. Thus if the vat contains say 480 gallons, the inflow and outflow
should be approximately 4 gallons per minute.
From the description of the operation above set forth, it will be understood that
my depilating process consists in certain well defined steps, which may be sum-
marized as follows:-
First: The placing of the hides or skins in a bath of sulphide of sodium of a
required strength of solution.
Second: The agitation of the hides or skins and the bath for a comparatively
short period of time.
Third: The subjection of the hides or skins to the action of the solution for
from 10 to 12 hours, more or less, without agitation.
Fourth The second agitation of the hides or skins and the solution; and
Fifth The gradual weakening of the strength of the solution by dilution
during the second agitation, until the bath in which the hides or skins are
immersed, becomes free or substantially free of caustic matter.
Of all these steps the fifth appears to be the most important, for by it the hides
or skins are subjected to a washing by a solution of gradually decreasing strength,
which solution washes out whatever caustic matter remaining in the substance of
the hides or skins and washes out or removes the dissolved hair and certain fibrous
matters and breaks up the gristle of the hides or skins, thus leaving the same
pulpy, porous, soft and well adapted to undergo the fleshing, tanning and other
subsequent operations to bring to a state or condition for use.
As far as I am enabled at present to understand, the chemical action of my
process upon the hide or skin is as follows:-
The solution of sulphide of sodium of normal strength burns out and dissolves
the nitrogenous and hairy matters and swells the hide or skin, rendering it pulpy
and porous, but fills the pores with caustic matter in a more or less undissolved
state and in chemical combination with the substance of the hide or skin. If
this caustic material were permitted to remain in the hide or skin, it would

page_text: speedily eat up those matters which give to the finished leather its life or vitality
and would render the hide or skin brittle, liable to split or break and imperfectly
susceptible to the tanning operation. By agitating the hide or skin a second
time, in the solution which is gradually weakened by dilution, I am enabled to
wash out this caustic matter and at the same time the diluted solution appears to
penetrate the body or substance of the hide or skin and acts upon the gristly
matter which it breaks up and renders porous. The caustic matter I believe is
dissolved by the weakened solution and is thus carried off as the solution escapes
from the vat. The original solution should be of a strength varying from two to
six degrees Baume test according to the nature of the hide or skin to be treated
as well as the uses to which the skin or its hair is to be put.
Having now particularly described and ascertained the nature and objects of
my invention and in what manner the same is to be performed, I declare that
what I claim is:-
:-
1. The herein described process of depilating hides or skins, which consists in
subjecting the hide or skin to a bath consisting of a solution of sulphide of
sodium of required strength, then agitating the hide or skin and the solution for
a relatively short interval of time, then subjecting the hide or skin to the action
of the solution for a comparatively long period of time and without agitation,
then re-agitating the hide or skin and the solution, and finally gradually weakening
the strength of the solution by dilution during this re-agitation, substantially as
and for the purposes described.
2. The herein described process of depilating hides or skins, which consists in
subjecting the hide or skin to a bath, consisting of a solution of sulphide of
sodium of required strength, then agitating the hide or skin and the solution,
then again subjecting the hide or skin to the action of the solution, but without
agitation, then re-agitating the hide or skin and the solution and at the same
time gradually weakening the strength of said solution and finally permitting
during the entire operation the free escape of gases generated in the solution,
substantially as and for the purposes described.
Dated at I maderpnia, La., uns 20th day of October A.D. 1991.
HENRY HOLMES.
Per James G. Lorrain,
Norfolk House, Victoria Embankment, London, W.C.
Chartered Patent Agent.