A Process for Testing or Estimating the Strength of Solutions of Tannin.
Year: 1887

page_text: Date of Application, 15th Nov., 1887
Complete Specification Left, 15th Aug., 1888
Complete Specification Accepted, 21st Sept., 1888
PROVISIONAL SPECIFICATION.
A Process for Testing or Estimating the Strength of Solutions of
Tannin.
We BENJAMIN NICHOLSON of The Torrs South Norwood in the County of Surrey
Gentleman and THOMAS PALMER of Ashbrooke, Sevenoaks in the County of Kent,
Bachelor of Sciences and Fellow of the Chemical Society do hereby declare the
nature of this Invention which has been communicated to us from abroad by Charles
Collin of 15 Rue Quincamcoix, Paris in the Republic of France Merchant and
Lucien Benoist of the Montsouris Observatory, Paris aforesaid Micographic
Assistant to be as follows:-
This Invention has for its object to provide a simple ready and exact process or
means for testing and estimating the strength of solutions of Tannin. This Invention
is based on the facts that Gelatine in solution is precipitated by tannic acid and that
anilines have an affinity for animal matter.
According to this Invention gelatine coloured with aniline colour is submitted to
the action of a suitable salt (such for example as acetate of lime) at a temperature
favourable to the precipitation of tannin and by reason of the coagulation of the
gelatine the colouring matter separates from the solution in which it was dissolved.
The following is a mode of proceeding according to this Invention.
A solution of clarified gelatine is made and also a solution of tannic acid and a
solution of acetate of lime. These two solutions are say 5% solutions. There is also
provided a solution of blue methylene or other suitable aniline colouring matter. A
test glass is filled with gelatine solution and to it is added the solution of aniline and
the solution of acetate of lime and then distilled water is added and the temperature
is raised to from say 130° to 140° Fahrenheit. There is then added thereto from a
graduated container a certain quantity of the solution of tannin when a coloured
precipitate is formed. The test glass is then stoppered and the contents well shaken to
Insure a perfect state of combination. It is then allowed to stand when the precipitate
which carries with it a portion of the colouring matter rises rapidly to the surface.
Del
.

page_text: The titration is continued by adding the solution of tannin in less and less quantities
(shaking well after each addition) until the whole of the colouring matter in the test
glass is discharged and the liquor becomes colourless when the gelatine is all pre-
cipitated. In this way the strength of any solution of tannic acid or tannin can be
ascertained by reference to the effect on a standard solution.
Dated this 15th day of November 1887.
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C..
Agents.
COMPLETE SPECIFICATION.
A Process for Testing or Estimating the Strength of Solutions of
Tannin.
We BENJAMIN NICHOLSON of The Torrs South Norwood in the County of Surrey
Gentleman and THOMAS PALMER of Ashbrooke Sevenoaks in the County of Kent
Bachelor of Sciences and Fellow of the Chemical Society do hereby declare the
nature of this Invention which has been communicated to us from abroad by Charles
Collin of Paris in the Republic of France Merchant and Lucien Benoist of the
Montsouris Observatory Paris aforesaid Micrographic Assistant and in what manner
the same is to be performed to be particularly described and ascertained in and by
the following statement :-
Our Invention has for its object a process enabling the amount of tannic acid
present in solutions employed for tanning and other purposes to be readily and accurately
ascertained.
This is accomplished according to our Invention by measuring the quantity or pro-
portion of the acid solution that is required to precipitate the gelatine in a solution
containing a certain quantity of coloured gelatine as hereinafter explained.
This Invention is of great utility in all manufactures in which tannin is employed
but the most important application is for tanning purposes as it enables the strength
of the tanning liquors to be readily and accurately tested from time to time and gives

page_text: an indication of the quantity of tannin absorbed by the hides at any period of the
tanning process. Juices and extracts containing tannin and tan yard liquors in
particular are liable to continual and considerable changes especially when they have
not been sterilised and the present invention enables the exact amount of tannin
contained in any solution or tan liquor to be ascertained with ease and precision.
Tannic acid is the only known substance that is capable of precipitating gelatine
from a solution under all conditions of strength and we take advantage of this peculiar
property of tannin for the purposes of our invention. Aniline colours possess great
affinity for substances of animal origin and colored gelatine in the presence of certain
salts being subjected to a temperature which favours its precipitation on the addition of
tannin will by reason of the coagulation resulting from the action of that substance
on the gelatine separate the aniline colouring matter from a liquid containing the said
colouring matter in a state of solution.
The new and accurate process of estimation by means of decolorisation is based on
these properties of the materials we employ for the purposes of our invention.
In carrying on this invention in practice we employ the following materials viz. :-
1) A solution composed of 5 per cent of gelatine in water the said gelatine being
clarified and preferably sterilised.
2) A solution composed of 5 per cent of methylene blue in water.
3) A solution composed of 5 per cent of acetate of lime or other suitable salt in
water.
4) A tannin solution containing a known quantity say 5 per cent of tannin herein-
after referred to as the standard solution.
0.5 cubic centimetres for example of the gelatine solution is placed in a test glass
and two drops of the methylene blue solution are added with 5 cubic centimetres of
the acetate of lime solution after which the total amount of liquid in the test glass is
increased to 80 cubic centimetres by the addition of distilled water at a temperature
of from about 55 to 66 centigrade (130 to 140 Fahrenheit).
By means of a suitable vessel such as a graduated burette or measuring glass
provided with a stop cock a few drops of the tannin solution are slowly added to the
gelatine solution and immediately form a coloured precipitate. The test glass is then
closed and its contents well shaken after it the precipitate is allowed to stand and the
precipitate rapidly rises to the surface. If the liquid still appears coloured the
addition of tannin solution is repeated as often as necessary (shaking the test glass
after each addition) until the blue colour entirely disappears the whole of the gelatine
being separated or precipitated. The quantity of the tannin solution employed is then
carefully noted. Assuming for example that 0-5 cubic centimetres of gelatine
consume or combine with 2-7 cubic centimetres of the tannin solution at 5 per 1000
the result is as follows viz. :-0.5 = 2.7 x 0.005 = 0.0135 of tannin.
=
Having thus ascertained the exact quantity of the standard solution required to
decolourize a known quantity of the coloured gelatine solution it becomes easy to
ascertain the amount of tannin contained in any other tannin solution by simply
measuring the quantity of the solution that is required to precipitate a corresponding
quantity or proportion of the gelatine solution. For example let A represent the
standard value and a the quantity requisite to decolourise à fresh measure of the
solution à 0.0135 a 0.0135:: 1000: .c = {grammes of tannin per litre.
The
proportions given in the foregoing are mentioned merely by way of example to illustrate
the practical application of our invention and may evidently be varied or modified
according to circumstances without departing from the principle of the invention.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed we declare that what
we claim is :-
1. Ascertaining the quantity of tannin in solutions containing that substance by
causing a measured quantity of the solution to act upon a testing solution containing
coloured gelatine in the presence of acetate of lime or other suitable salt substantially
as hereinbefore described.

page_text: 2. Ascertaining the quantity of a standard solution or a solution containing a known
quantity of tannic acid required to precipitate or coagulate the gelatine in a given
gelatine solution as set forth and employing this gelatine solution for the purpose of
ascertaining the quantity of tannic acid in a solution or liquid containing an unknown
quantity of this acid substantially as herein before described.
3. The improved process for testing or estimating the strength of solutions of tannin
substantially as herein before described.