Improvements in or relating to Tanning by Electricity.
Year: 1892

page_text: Date of Application, 29th Jan., 1892
Complete Specification Left, 28th Oct., 1892-Accepted, 17th Dec.. 1892
PROVISIONAL SPECIFICATION.
Improvements in or relating to Tanning by Electricity.
1, RAFFAELE PINNA of No. 2 Rue Bogino, Turin, in the Kingdom of Italy,
Engineer, do hereby declare the nature of this invention to be as follows:-
Electricity was first utilized in tanning hides in 1860 and the experiment has
been a great many times repeated since. None of the methods tried, however,
have given results of any real, technical or economical value in practice. Most
tanners have therefore to the old methods which takes from 6 to 24 months,
and upwards, to carry out according to the nature of the hides or skins to be
treated and to the quality of leather to be obtained. Various means, not involving
the use of electricity have indeed been suggested with a view to accelerating
the tanning operation, such as the employment of very strong tannic extracts
and astringents. But these means have proved futile as, apart from considera-
tions of expense, and while shortening to a certain extent the time taken up by
the tanning, they produce leather liable to crack and fulfilling none of the
desirable conditions of dynamometrical strength and durability. The reason of
this is very simple. The rich tannic extract energetically acts upon the surface
of the skin and thereby prevents the diffusion of the acid solution in the derma.
Now the advantage of employing electricity precisely lies in the fact, that it
powerfully assists the penetration and diffusion of the tannic extract in the skin,
in consequence of the physiological action electricity naturally exercises upon
the cellular tissue of the skin. If, however, continuous currents were used for
the purpose, electrolytic action might set in, producing dangerous or undesirable
effects, which would place the advantages derived from increased rapidity
entirely in the background; for, owing to the transformation undergone by the
tannic acid, the solution is deteriorated and impoverished in an excessive degree
so that from the economical point of view at all events, the employment of
continuous currents does not entirely commend itself to appreciation by the trade.
My improved process consists in causing weak alternate currents, with a slight
difference of potential, to pass through the hides or skins steeped in the tanning
bath, however it may be prepared. In this process the usual rotary motion,
imparted to the skins by means of drums or otherwise, is preferably dispensed with,
whereby not only the cost of the plant and of its operation is saved, but also the
inconvenience is avoided which arises from the fact that the bath becomes heated
by the rotation and apt to impair the good quality of the skins.
This process may be carried out with great facility and at very little expense, as
it requires no special apparatus of expensive construction, and may be employed in
conjunction with any suitable tanning material.
The hides are first treated in the ordinary manner for removing the hair. They
are then immersed in the usual pit, in the lower portion of which there has been
previously arranged an electrode of copper, brass, lead, or other suitable metal,
nsoluble in tannin. This electrical conductor should be equal in size to the surface
of the hides or skins to be tanned, which are placed one upon the other, the whole
pile resting upon the said conductor or electrode. The tanning solution is then
poured over the skins until it rises to a level above the uppermost skin. The second
electrode is so arranged in a wooden frame as to be maintained above the liquid.
This electrode may be either solid or open (reticulated) but must be equal in size
o the lower electrode. Its surface may thus vary in shape to suit the required
lensity of current, which should be from 04 to 1 ampère per square decimetre,
ccording as the skins treated are light or heavy.
The current generated by an alternate battery should be so transformed (or.
:

page_text: produced directly) as to be of small tension (50 volts) and variable by means of a
rheostat, so that the intensity of the current corresponds with the limits of the
given electrical density, care, being taken that the temperature of the bath does not
exceed 35° C. through excessive intensity. I have before stated that the difference
of potential should be slight, miz. not over 50 volts, but a higher tension may be
arrived at if necessary, so long as the intensity of the current does not exceed the
predetermined limit. 50 volts, however, is the tension which, for purely electro-
technical considerations, I would rather not exceed under normal circumstances.
The frequency of the intermittent currents should preferably not be less than
5000 pulsations per minute, though this but very slightly affects the result.
The arrangement herein described does not require tanners to make any alteration
in the shape and size of the tanning pits, with the exception of the additional
arrangement of the electrodes.
I may, however, describe an arrangement specially devised for tanning hides by
my process, which enables each skin to be readily and conveniently inspected and a
number of different skins to be tanned in the same apparatus. It consists of a
watertight tank about 2 or 3 metres deep and square or rectangular in section with
sides measuring from 2 to 2 metres each, in the former, and from 1 to 2 metres
in the latter case. The skins are suspended side by side in a parallel position and
well stretched by means of weights attached to their lower part.
Each tank may contain from 20 to 25 skins or more. The electrodes are parallel
to the skins, being arranged along the two opposite walls of the tank, and insulated
from these walls. Between the first and last skin and their respective electrodes a
space of at least 10 cm. is left free. The electrodes equal the largest of the skins
in superficial size. One electrode is solid, and the other open, consisting of a
number of small, flat rods movable upon a fixed frame so that while its size at the
ends remains constant, the shape of the surface may be varied or adjusted at will,
to ensure under all circumstances a constant intensity of current.
I will point out in conclusion that any of the usual tanning agents may be
employed in connection with the above described process, and the bath need not be
very rich in astringent substances. Simple extract from the bark of oak showing
a weight of about 14 to 24° (on the tannin weight or meter) may be used with a
current of ampère, with a slight difference of potential and will produce very fine
leather answering all requirements of economy and durability. By my process the
whole tanning operation is completed in from 100 to 400 hours according to the
quality of the skins to be treated. Light calf or sheepskins for example, will take
about 100 hours, heavy calf from 150 to 200, horse and light cow hides from 250 to
300 and ox hides from 350 to 400 hours.
Dated this 29th day of January 1892.
W. P. THOMPSON & BOULT,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in or relating to Tanning by Electricity.
I, RAFFAELE PINNA of Via Bogino 2, Turin, in the Kingdom of Italy,
Engineer, 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:
Electricity was first utilized in tanning hides in 1860 and the experiment has
been a great many times repeated since. None of the methods tried however have
given results of any real, technical or economical value in practice. Most tanners
have therefore adhered to the old methods which takes from 6 to 24 months and
upwards to carry out according to the nature of the hides or skins to be treated
and to the quality of leather to be obtained. Various means, not involving the use
of electricity have indeed been suggested with a view to accelerating 'the tanning

page_text: operation, such as the employment of very strong tannic extracts and astringents.
But these means have proved futile, as, apart from considerations of expense, and
while shortening to a certain extent the. time taken up by the tanning, they
produced leather liable to crack and fulfilling none of the desirable conditions of
dynamometrical strength and durability. The reason of this is very simple. The
rich tannic extract energetically acts upon the surface of the skin and thereby
prevents the diffusion of the acid solution in the derma.
Now the advantage of employing electricity precisely lies in the fact that it
powerfully assists the penetration and diffusion of the tannic extract in the skin in
consequence of the physiological action electricity naturally exercises upon the
cellular tissue of the skin. If however continuous currents were used for the
purpose electrolytic action might set in, producing dangerous or undesirable effects,
which would place the advantages derived from increased rapidity entirely in the
back-ground; for owing to the transformation undergone by the tannic acid the
solution is deteriorated and impoverished in an excessive degree so that from
the economical point of view at all events, the employment of continuous currents
does not entirely commend itself to appreciation by the trade.
My improved process consists in causing weak alternate currents, with a
slight difference of potential to pass through the hides or skins steeped in the
tanning bath however it may be prepared. In this process the usual rotary motion
imparted to the skins by means of drums or otherwise, is preferably dispensed with
whereby not only the cost of the plant and of its operation is saved, but also the
inconvenience is avoided which arises from the fact that the bath becomes heated
by the rotation and apt to impair the good quality of the skins.
This process may be carried out with great facility and at very little expense
as it requires no special apparatus of expensive construction and may be employed
in conjunction with any suitable tanning material.
The hides are first treated in the ordinary manner for removing the hair. They
are then immersed in the usual pit, in the lower portion of which there has been
previously arranged an electrode of copper, brass, lead, or other suitable metal,
insoluble in tannin. This electrical conductor should be equal in size to the surface
of the hides or skins to be tanned, which are placed one upon the other, the whole
pile resting upon the said conductor or electrode. The tanning solution is then
poured over the skins until it rises to a level above the uppermost skin. The second
electrode is so arranged in a wooden frame as to be maintained above the liquid.
This electrode may be either solid or open (reticulated) but must be equal in size
to the lower electrode. Its surface may thus vary in shape to suit the required
density of current, which should be from 0.04 to 0-10 ampere per square decimetre,
according as the skins treated are light or heavy.
The current generated by an alternate battery should be so transformed (or
produced directly) as to be of small tension (50 volts) and variable by means of a
rheostat, so that the intensity of the current corresponds with the limits of the
given electrical density, care being taken that the temperature of the bath does not
exceed 35° C. through excessive intensity. I have before stated that the difference
of potential should be slight viz. not over 50 volts, but a higher tension may be
arrived at if necessary, so long as the intensity of the current does not exceed the
predetermined limit. 50 volts however is the tension which for purely electro-
technical considerations, I would rather not exceed under normal circumstance.
The frequency of the currents should not be less than 5000 alternations per
minute though this but very slightly affects the result.
The arrangement herein described does not require tanners to make any alteration
n the shape and size of the tanning pits with the exception of the additional
rrangement of the electrodes.
I may however describe an arrangement specially devised for tanning hides by
ay process which enables each skin to be readily and conveniently inspected and a
umber of different skins to be tanned in the same apparatus. It consists of a
ater-tight tank about 2 or 3 metres deep and square or rectangular in section with

page_text: sides measuring from 2 to 2 metres each, in the former, and from 1 to 2 metres
in the latter case. The skins are suspended in the tank side by side in a parallel
position.
Each tank may contain from 30 to 35 skins or more. The electrodes are parallel
to the.skins being arranged along the two opposite walls of the tank and insulated
from these walls. Between the first and last skin and their respective electrodes
a space of at least 10 cm. is left free. The electrodes equal the largest of the skins
in superficial size. One electrode is solid, and the other may be open, consisting
of a number of small flat rods movable upon a fixed frame so that while its size
at the ends remains constant the shape of the surface may be varied or adjusted
at will to ensure under all circumstances a constant intensity of current.
I will point out in conclusion that any of the usual tanning agents may be
employed in connection with the above described process and the bath need not
be very rich in astringent substances. Simple extract from the bark of oak
showing a weight of about 15 to 35° (on the tannin-weight or meter) may be used
with a current of 15 ampere with a slight difference of potential and will produce
very fine leather answering all requirements of economy and durability. By my
process the whole tanning operation is completed in from 100 to 400 hours according
to the quality of the skins to be treated. Light calf or sheep skins for example
will take about 100 hours heavy calf from 150 to 200, horse and light cow hides
from 250 to 300 and ox-hides from 350 to 400 hours.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is,-
The tanning process mainly characterized by the employment of alternate
electrical currents normally traversing the skins or hides without the assistance of
any fulling operation.
Dated this 28th day of October 1892
..
W. P. THOMPSON & BOULT,
Agents for the Applicant.