An Improved Process of Continuous Tanning.
Year: 1899

page_text: Date of Application, 31st July, 1899
Complete Specification Left, 20th Apr., 1900-Accepted, 21st July, 1900
[Communicated from abroad by GERBEREI GESELLSCHAFT MIT BESCHRÄNKTER
HAFTUNG, of 64, Herderstr., in the City of Hamburg, in the Empire of
Germany, Manufacturers].
An Improved Process of Continuous Tanning.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton, Buildings, in the County of Middlesex, do hereby declare the
nature of this invention to be as follows:-
This invention relates to an improved process of continuous tanning in rotary
drums and the object of this invention is to enable the hides or skins, which have
been depilated and bated, to extensively and quickly receive the oxides of the
tannic acid, the so-called anhydrous tannic acids.
Hitherto the absorption of the tannic-acid anhydrides (oxides) by the skins
could only be effected by pit-tanning as only in this manner owing to the
exceedingly lengthy duration of tanning the anhydrides gradually, after being
in contact with water for months, dissolved sufficiently to enable the skins to
absorb them.
The various methods heretofore known for quick tanning do not provide for
this hydrating process in the preparation of the tanning liquor simply because
the time allowed is insufficient and this accounts for the better quality of pit
tanned hides.
It has been found, however, that the anhydrides can be caused to penetrate
the skins even in an undissolved condition or state by enabling the tannic acid
to form anhydrides in the soaked skins at the moment it enters the pores thereof
and according to the degree of swelling the skins have undergone. The fact
ascertained by observation that the anhydrides are capable of penetrating more
or less the fibres of the skins according to the degree of their swollen condition,
has served as the basis of this improved process and it is all the more important
to know that the formation of anhydrides in insufficiently swollen skins interferes
to a great extent with the favourable completion of the process of tanning.
Now the improved process consists broadly in that the tanning liquor enter-
ing the skins is supplied with appropriate means for promoting the formation
of anhydrides but regulated in such a manner as to gradually reduce this forma-
tion of anhydrides in the proportion as the astringent action of the tanning liquor
reduces the original swelling of the skins, until finally the formation of anhy-
drides is entirely stopped. For the more the action of the tanning liquor re-
duces the original swelling of the skins by causing the fibres thereof to shrink
closer together, the less opening there will be for the passage of the anhydrides
and therefore the formation of anhydrides requires to be reduced in corre-
sponding proportions. If this is not attended to the result would be accumu-
lation of anhydrides between the outermost layers of fibres in the skins and the
formation thereby of a crust so to speak which prevents the further entrance

page_text: of tanning liquor and thus acts disadvantageously to the advance of the tanning-
process.
The oxygen required for the formation of oxides may be introduced as a gas
free from other mixtures or it may be mixed with indifferent gases, the cheapest
form being atmospheric air rich in oxygen. The vessel for the carrying out of the
tanning process must therefore be supplied with the tanning liquor and the skins
and also with the gaseous oxidizing medium into which the wet skins are intro-
duced by suitable means.
In order to enable the oxidation to be regulated in accordance with the dis-
appearance or decrease of the swelling in the skins, as herein before intimated,
it has been found advantageous to close the tanning vessel and only partly fill
it with tanning liquor and skins and leave the remaining portion to the oxidiz-
ing agent thus exposing the wet skins in the liquor to the constant action of only
the one volume of air enclosed in the vessel. Thus in the same proportion as
the tanning-process advances and the swelling of the skins disappears or de-
creases in consequence of the astringent effect of the steadily increasing con-
centration of the tannic-acid solution, the oxidizing agent is rendered continu-
ously weaker owing to the loss in oxygen during the previous oxidation.
In order to render the process more effective arrangements should be made io
bring the swollen skins at first into contact with very weak tanning liquor so
as to produce a slow action and to enable the oxides to penetrate as deeply as
possible into the skins. With the advance of the process the tanning liquor must
be rendered more and more concentrated so as to quicken the absorbing action
of the skins. Thus the improved process is preferably carried out by using
liquor with a constantly increasing concentration.
A convenient construction of apparatus for carrying out the improved pro-
cess, consists of a number of vessels, say four rotary drums to each of which is
firmly connected a toothed wheel adapted to be driven by toothed pinions upon
a shaft revolved by belting or other convenient means. The drums being
rotatably mounted in suitable standards receive a slow rotary motion and are
supplied with liquor from a tank by means of a main pipe with branch pipes,
inlet connections and nozzles, while the discharge takes place through other
nozzles and outlet connections into a common outlet pipe. By this means the
drums can only be half filled with liquor while the upper space thereof is
filled with air having a greater or less percentage of oxygen in a definite pro-
portion to the weight of the skins.
The wooden walls of the cylindrical drums are furnished with
during the rotation of the drums repeatedly lift the skins out of the liquor and
pegs, which
thus temporarily expose these skins soaked with liquor to the action of the
oxygen of the air and finally allow them to drop back into the liquor.
4
While proceeding to describe the manner of working with the apparatus for
carrying out the process it may be stated that one of the four drums is being
discharged and then re-fitted during the time the others are at work.
supposed the drums to be designated 1st 2nd 3rd and 4th and that the 2nd 3rd
It may be
and 4th drums to be operating and the 1st drum to be kept stationary for the
reason just stated. Of the said three drums, the drum 2nd is the most advanced, the
3rd is the next and the 4th is the one last charged. The introduction of con-
centrated liquor is effected by closing the inlet valves to the 1st 3rd and 4th
drum and opening the valve of the 2nd drum and also the valve of the tank,
the liquor from the tank then flows through the main pipe into the 2nd drum. 5
From the latter drum the liquor after having been deprived of tannin so as to be
now of a mean concentration, runs off through the outlet nozzle and through the
connection pipes and valve into the 3rd drum in a continuous stream, and finally
leaves the said drum in form of a weak liquor passing through the connection into
the 4th drum and after being then fully deprived of its tannin it escapes through 5
the nozzle and pipe connections into the exhaust pipe and may then be used for
other purposes. In this manner within the 4th drum containing very weak

page_text: liquor and skins not yet reduced, that is to say, skins which have not yet lost
the capability of swelling, the formation of oxides of the tannic acid is favoured
by the influence of the air rich in oxygen. In the 3rd drum the skins have con-
tracted to a certain degree by the moderately or semi-concentrated liquor, and
the air, previously deprived of much of its oxygen by the formation of anhydrides,
has less power to form anhydrides while in the 2nd drum the fresh and concen-
trated liquor causes the fibres in the skins to contract so as to lay tightly against
each other and the formation of now injuriously acting anhydrides is entirely
suppressed.
When it is found that the skins in the 2nd drum are thoroughly tanned this
drum is stopped for discharging while the 1st drum newly charged is put into
service and the strongest liquor from the tank is then caused to pass through
the main pipe and connections into the 3rd drum from which it flows in a
medium concentrated condition through the outlet connections into the 4th drum
and thence through proper connections into the return pipe through the open
valves therein, pipe connections and valve nozzle into the 1st drum. After the
liquor becomes exhausted it is discharged through the outlet nozzle and con-
nections into the waste or discharge pipe thus at that moment the 1st drum
charged with the newest skins receives the weakest liquor and the air richest
in oxygen.
When it is desired to drive out the liquor from any one drum compressed air
from an air inlet pipe is allowed to enter the main pipe opening the valve in
said pipe and thus permitting the air to pass into such drum and there force out
the liquor by pressure upon its upper surface.
The improved process enables leather to be produced which in toughness and
quality far surpasses any of that produced by the quick processes heretofore
employed as well as that produced by the lengthy pit-tanning.
11: 511 1
T
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C,
Agents for the Applicant
An Improved Process of Continuous Tanning.
1, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, 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:-
-
My invention relates to a process for tanning hides, whereby the tanning
solution, in conjunction with oxygen or air is caused to act upon the bated and
depilated hides, thereby effecting a more rapid process and better leather.
I have found that tannins in the presence of oxygen split up and form pro-
ducts whose exact chemical composition is not known; but which I have called
in my Provisional Specification "tannic-acid anhydrides' and which have a
most beneficial and rapid tanning action on the hides, especially in the early
stages of the process, when they penetrate the hides with the greatest ease.
The hides or skins are raised or swelled previous to my tanning process, which
can be done in accordance with any of the methods usually employed, such as
by means of water acidulated with sulphuric acid, or similar solutions. This
swelling or raising, loosens all the fibres of the corium and allows the products

page_text: due to the action of the oxygen on the tan liquor to penetrate into the hide or
skin.
If this swelling or raising were not done, the aforesaid tannin products would
not penetrate the hide or skin, but form a crust on or in the outer fibres and
prevent any further penetration or absorption.
As the tan liquor or ooze is in contact with the hides during the tanning process
and has an astringent or shrinking action on the fibres, it is best, in order to
effect a thorough penetration of the said split products or products of decom-
position, to treat the depilated and bated hides first with a weak solution of tan
liquor in conjunction with a gas rich in oxygen, such as air enriched in oxygen
or ozone, that is to say air containing from about two to about three times the
normal proportion of oxygen or ozone, so as to cause, at this stage, the most active
formation of decomposition products of the tannin, before the fibres of the
hide or skin have shrunk or contracted too much, which would be the case if a
strong solution of tannin were used at this time, thereby preventing the forma-
tion of an impermeable deposit or crust on the surface of the hides.
Inasmuch as the astringent action of the tanning liquor upon the hides de-
pends upon the degree of concentration of such liquor, and in order to avoid
too great a contraction of the hides in the start, and at the same time promote
the formation of the split products referred to, and enable them to more readily
penetrate into the raised or swelled green hides, I use in the start a weak tanning
solution and a gas or air rich in oxygen or ozone, as above set forth.
The green hides are kept in motion in a confined space in a revoluble drum
half filled with tan liquor and hides, the other half of the drum being filled with
air rich in oxygen or ozone. The great amount of oxygen or ozone acting upon
the constantly agitated tan liquor in contact with the hides, oxidizes the former,
split products in large quantities being formed, which readily penetrate the
hides. After the hides have been exposed to the action of these split products,
say for from about four to about ten hours, according to texture and weight of
the hides, the tan liquor is removed, and fresh and more concentrated liquor is
introduced into the drum in such a manner as not to allow the air therein to
escape. Inasmuch as the air has given up about one-half of its oxygen in the
first stage, the oxidizing action of the air on the tan liquor is correspondingly
reduced, while the action of the stronger tan liquor on the hides is correspond-
ingly increased, resulting in a further contraction or shrinking of the hides or
skins with a reduction in the proportion of split products. After the hides have
been exposed to the action of the stronger liquor and to the action of the split pro-
ducts formed for a sufficient length of time, say for from about four to about ten
hours, the tan liquor is again removed and a stronger liquor supplied to the drum.
During the second stage the air will have been deprived of about two-thirds to
three quarters of its oxygen or ozone, so that the formation of split products during
the third stage is still further reduced, while the action of the still stronger
tanning solution on the hides or skins is correspondingly increased, the opera-
tion of tanning being completed during this third stage after the hides or skins
have been exposed to the action of the tan liquor and split products for a suitable
length of time, say for from about four hours to about ten hours, when it will
be found that the air has been deprived of substantially the whole of its oxygen
or ozone. It will thus be seen that the action of the tanning agent upon the
hides is successively increased while the formation of split products is successively
reduced.
The strength of the tanning liquor at each of the above described stages of
my process will naturally vary in accordance with the texture and weight of the
hides or skins to be tanned. Thus, for instance, in tanning hides or skins of
finer texture and of moderate weight, the tanning liquor used in the first stage
may have a strength of 1° B., more concentrated liquor being used for the second
and third stages, such as liquors of from 20 to 4° B., while about sixty gallons
of air rich in oxygen or ozone to every square foot of hide or skin is required.

page_text: In view of the peculiar mode of carrying out my invention the process 18
readily applicable to a continuous operation, as will hereinafter appear.
In order that the nature of the invention with reference to a continuous opera-
tion may be more fully understood, I will now describe the same in detail,
reference being had to the accompanying drawing, which illustrates in section
the preferred form of apparatus for the purpose.
Similar letters of reference refer to like parts.
The apparatus consists of a series of vessels, say four drums, A, B, C, D, to
each of which is secured a gear wheel, K K K³ K, respectively, adapted to be
driven by pinions on a belt-driven line-shaft or other convenient means, not.
shown.
The drums receive a slow rotary motion, and are supplied from a suitable
tank M by means of a main feed pipe E having branch pipes el e² e³ e, inlet
connections d d² dd, and central nozzles a¹ a² a³ a³, while the tanks discharge
through similar nozzles b¹ 62 63 64 and outlet connections g¹ g³ g³ g' into a common
outlet pipe L.
By this means the drums can be only half-filled with tan liquor, while the re-
maining space is filled with air having a greater or less percentage of oxygen
according to the weight and size of the skins, or hides.
The wooden walls of the cylindrical drums are furnished with pegs z¹2
respectively, which during the rotation of the drums repeatedly lift the soaked
skins out of the liquor and expose them to the action of the oxygen of the air
contained in the drums, and finally allow them to drop back into the tan liquor
In order to start the apparatus all the valves are closed and the drums A B
CD rotatably mounted in suitable standards H¹ J¹, H² J², H³ J3, H4 J, charged
with the hides to be tanned. A weak ooze of about 1° B. (ooze No. 1) is then
allowed to flow from the tank M through the valve Z, conduit E e¹, valve Q',
conduit and inlet nozzle a into the drum A until the latter is half-filled.
After this the oxidising agent, air enriched in oxygen, is introduced into the
drum A, whereupon the latter is hermetically closed and set in slow rotary
motion. In some cases the percentage of oxygen already in the atmospheric
air will be sufficient and an enrichment of the air in oxygen may therefore be
dispensed with. In such cases it suffices to simply close the drum after the
charging of the same with hides and ooze. As the week ooze has none or only
a very small astringent effect upon the fibres the formation of splitting products
must be promoted at this very time i.c. in the beginning of the tanning process
in order to enable the tannin to easily penetrate between the fibres, and in
reality an intensive formation of splitting products of the tannin takes place
in the drum A by the influence of the oxygen of the oxidizing agent. After
the ooze No. I has acted upon the hides in the drum A for from about four hours
te about ten hours, the air-like oxidizing agent has lost about half of its oxygen;
a stronger ooze of about 210 B (ooze No. II) is then allowed to flow from the
tank M, by the same way as above described, into the drum A, whilst at the same
time by opening the valve R² the weakened ooze of the drum A, which by the
commingling and mixing with a portion of the entering ooze No. II has regained
about its original strength, runs off practically as ooze No. I through outlet
nozzle, connecting pipes g h and inlet nozzle 2 into the drum B, wherein
the same process takes place as that above described with reference to the
drum A, that is to say, the fresh hides in the drum B also set in rotation are
subjected to the action of a weak ooze (ooze No. I) and under the influence of
the oxidising agent still rich in oxygen a copious formation of splitting pro-
ducts takes place. In the drum A the stronger ooze (ooze No. II) effects a
greater astringing of the fibres of the skins. According to this astringment
or decrease of swelling the formation of splitting products must be reduced.
and this is really the case, because the oxidizing agent in the drum A, in conse
quence of the prior formation of splitting products casued by the co-operation
of the ooze No. I with the said oxidising agent, has become poorer in oxygen and

page_text: at
a
is therefore in lesser degree enabled to produce splitting products
of the tannin. After the drums A and B have been in operation
for a further period of from about four hours to about ten hours,
which time about two-thirds to three-quarters of the percentage
of oxygen of the oxidizing agent have been consumed or absorbed
the valves R and Sare opened and a still stronger coze of about 4° B. (ooze
No. III) is allowed to flow from the tank M into the drum A, whereby the
weakened oozes in the drum B and A are caused to run off into the drums C
and B respectively the ooze of drum B taking its way through the pipe con-
nection 1² 9² 13 №³. During this running off of the oozes the ooze No. I of
the drum B mixes with a portion of the ooze No. II of the drum A and the latter
with a portion of the ooze No. III coming from the tank M, so that both the
said oozes weakened before by the delivery of tannin, are somewhat refreshed
and regain about their original strength when entering the drum C and B
respectively. In the revolving drum C comes to pass the same process as above
described in connection with the drum B, and in the latter the same process is
repeated which took place in the drum A when ooze No. II was acting therein.
In the drum A the relatively strongest ooze, ooze No. III, effects a still greater
astringing or contraction of the fibres, whilst the oxidizing agent becoming more
and more poorer in oxygen is able to produce but a very small formation of
splitting products. After the drum C has been set in operation the feed of the
ooze No. III to the apparatus may be allowed to be a continuous one, so that the
ooze taking its way seriatim through the drums A, B, C and being weakened
thereby or depleted of its tannin gradually, flows off finally as exhausted ooze
or liquor through the pipe connections b³ ³ m³ and exhaust pipe L, being now
too poor in tannin for further use in this process.
and
The drums A, B, C, through which the ooze flows continuously as above de-
scribed, remain in operation (for from about four hours to about ten hours).
until the skins in the drum A are thoroughly tanned. When the tanning of
the skins in the drum A is performed it is stopped for discharging
and recharging respectively (the necessary valves of the pipe-conduit must
of course be closed for this purpose), while the drum D, previously and properly
charged, is put into service, so that the drums B, C, D), are now in operation.
Of these drums the drum B contains hides in the last stage or third period of
the tanning process and an oxidising agent being depleted of about three parts
of its oxygen, the drum Chides in the middle stage or second period of the
tanning process and an oxidising agent having lost one half of its oxygen,
the drum D hides in the first stage or period of the tanning process i.c. fresh
hides and an oxidising agent having the full percentage of oxygen. The supply
of the ooze (ooze No. III) which shall be used or employed in the tanning pro-
cess, has been effected by closing the valves Q R2 S2 and opening the valves Q²
R T. The ooze or liquor from the tank then flows continuously through the
valve, main pipe E. branch pipe 2, into drum B, where a strong solution of
tan liquor flows into said drum, which, in the last stage of the process is exhausted
of the greatest part of the oxygen therein, thus allowing mostly tannin itself
rather than its decomposition products, to act on the hides contained therein.
From this drum B the weakened liquor, say of mean concentration runs off
through the outlet nozzle 2, connecting pipes valve R³ pipe d and nozzle a
into the drum C in a continuous stream, where is a liquor of mean concentration,
an oxidizing agent or atmosphere say of from mean to still lesser concentration
in oxygen, and hides in the middle stage or second period of the tanning process.
The liquor leaves the tank C through outlet pivot connections and
valve R4, pipe 4, inlet nozzle and enters the drum 1) a weak liquor where it
comes in contact with hides just raised or swollen and an atmosphere rich in
oxygen. The liquor leaves this tank by nozzle, pipe valve T and pipe m*
into the exhaust pipe L, and may then be used for other purposes, but is too
poor in tannin for further use in this process.

page_text: When the skins in the drum B are tanned, it is stopped for discharging, while
the drum A which has just been charged is put into service and the strong
liquor from tank M is caused to pass through the main pipe E, branch pipe
valve connecting pipe d³ and hollow pivot a³ into the drum C, from which
it flows mediumly concentrated as above described, into drum D, and thence
through nozzle 6 pipe g* return pipe U through the open valves W and V therein,
pipe valve R₁ pipe d' and nozzle a¹ into drum A, a weak liquor, and after
exhaustion it is discharged through the nozzle b' pipe gl valve s and pipe m¹
into the discharge pipe L.
When it is desired to discharge the liquor from any one drum, compressed air
from an air pipe G is allowed to enter the main pipe E by opening the valve N
and thus permit the air to pass to such drum and force out the liquor.
My improved process enables me to produce a leather tougher and of a better
quality than that produced by the quick processes now in use, and even better
than that produced by the lengthy pit tanning.
Having now particularly described and ascertained the nature of the said in-
vention and in what manner the same is to be performed, as communicated to
me by my foreign correspondents, I declare that what I claim is:--
1. In the art of tanning, the process which consists in subjecting bated and
depilated skins to the action of a tan liquor of increasing strength and to an
oxidising agent, atmosphere and the like, decreasing in its content of oxygen,
substantially as described.
2. In the art of tanning, the process which consists in subjecting bated and
depilated skins to the action of a weak tan liquor and an atmosphere strong in
oxygen, concentrating the liquor during the tanning and decreasing the amount
of oxygen, substantially as set forth.
3. In the art of tanning, the process which, consists in subjecting the skins
to the action of a weak tan liquor and to the action of an atmosphere rich in
oxygen, then subjecting said skins successively to the action of tan liquors of
correspondingly increasing strength and to the action of an atmosphere corre-
spondingly poorer in oxygen said skins being exposed to the action of the tan
liquor and to that of the oxygen alternately during said operation, substantially
as set forth.
4. In the art of tanning, the process which consists in subjecting bated and
depilated hides to the simultaneous action of a tanning liquor of gradually in-
creasing strength and an atmosphere containing oxygen, the proportion of oxygen
in the atmosphere diminishes as the strength of the tan liquor increases, sub-
stantially as set forth.
That his 2011.
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.