Process for Utilizing Nitre-cake and other Acid Sulphates.
Year: 1895

page_text: Date of Application, 25th June, 1895-Accepted, 31st Aug., 1895
COMPLETE SPECIFICATION.
Process for Utilizing Nitre-cake and other Acid Sulphates.
J, JAMES DOUGLAS DARLING, residing at 4826 Greenway Avenue, in the
City of Philadelphia, State of Pennsylvania, United States of America,
Electrician and Chemist, 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 :-
The following is a Specification of my said invention, reference being had to the
accompanying drawing.
In the commercial manufacture of nitric acid, and also of sulphuric acid, when
nitrate of soda is employed to furnish the nitrogen compounds required, the
resulting by-product has approximately the composition of bisulphate of soda,
although there is usually an excess of sulphuric acid present, even beyond the
amount which would be due to the formula NaHSO,. This by-product, termed
"nitre-cake," is of trifling commercial value, and various methods have been
attempted to utilize it, but so far as I am aware, all of such methods are relatively
costly and the commercial results therefrom have been neither satisfactory nor
profitable.
My process is principally addressed to the economical and efficient treatment of
nitre-cake for the derivation of two by-products, viz.: neutral sulphate of soda
(Na,SO) and chlorine gas. It may, however, be applied to the utilization of
other acid sulphates, with corresponding results.
To this end my process consists in electrically decomposing a solution which
contains a base similar to that of the acid sulphate, and causing such base to travel
(by electrical action) towards, and combine with, the acid sulphate, until the
desired neutralization thereof has been effected. The other derivation of the
electrolytic decomposition is conducted away under proper control, and recovered
as a distinct by-product.
For convenience of nomenclature, I term the solution which is to be thus
decomposed, (in order to furnish an additional quantity of base to the acid
sulphate), the base-supplying electrolyte, and I term the transfer of the base from
the region of its decomposition to the region of recombination, the electrolytic
travel thereof.
In the accompanying drawing I have represented in vertical section a typical
apparatus adapted to the conduct of my process, but I do not limit myself to the
employment of this, or of any particular form of apparatus.
I will now proceed to describe the process of treating nitre-cake by means of
the devices shown in said drawing.
A, represents a tank of wood or slate, divided into three compartments by means
of the transverse partitions, B, B. These partitions should be in whole or in
part porous, to an extent sufficient to allow the electrolytic travel, unaccompanied
by any excessive increase in electrical resistance.
In the central compartment (which is the decomposing cell) is placed a carbon
electrode, D, which constitutes the positive pole, and in each of the other
compartments is placed an electrode, E, which may be of sheet lead, constituting
negative poles. The central or positive compartment is provided with a close
fitting cover, F, having an outlet, G, and a feed orifice, H.
The central compartment is filled with the base-supplying electrolyte, which is a.
saturated solution of sodium chloride, and the two adjacent compartments are

page_text: filled to the same level with a solution of nitre-cake. The physical intermingling
of the two solutions, as snch, is practically prevented by the partitions, B, but on
passing a suitable current of electricity from the positive to the negative pole of
the apparatus, the sodium chloride solution in the central compartment is
decomposed and the sodium is caused to travel through the porous partition to the
region of the nitre-cake solution, where it combines with the surplus sulphuric acid
and forms neutral sulphate of soda; whilst the liberated chlorine passes off
through the outlet pipe, G, to any convenient receptacle, where it may be absorbed
by lime, or condensed into liquid form directly, or utilized in any desired
manner.
As the process proceeds, chloride of sodium may be supplied through the feed
orifice, H, in the cover, F, and the process may be thus continued until the entire
charge of acid sulphate contained in the negative compartment has been neutralized
and the desired product obtained. The solution of neutral sulphate is then drawn
off and after filtering to free it from precipitated iron and other impurities, is
allowed to crystallize.
The mother liquor, with the addition of a proper amount of water, may be
again used to dissolve a fresh quantity of nitre-cake and the process repeated as
before.
For practical purposes, I deem it important to maintain a physical separation
between the two solutions, since if they are allowed to commingle freely,
decomposition to a certain extent of the sulphuric acid takes place and oxygen is
liberated at the positive pole, which action tends to disintegrate the carbon
electrode. There is also the further liability to a physical intermingling of the
two solutions, so that at the close of the process the neutral sulphate would contain
more or less of the sodium chloride diffused through it.
These objections are, however, not vital, and hence I do not limit my claim to
the employment of the specified type of apparatus.
I do not limit myself to the employment of this process in connection with nitre-
cake, as it may be applied to the treatment of other acid sulphates for the
production of neutral salts. It is of course necessary that the base-supplying
electrolyte should in such case be of a character to correspond to the salt to be
neutralized.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
1. The herein before described process for the treatment of acid sulphates, which
consists in electrically decomposing an electrolyte containing a similar base to that
of the sulphate, and transferring said base to the sulphate by electrolytic travel,
substantially as described.
2. The hereinbefore described process for the treatment of acid sulphates, which
consists in electrically decomposing an electrolyte containing a similar base to that
of the sulphate, transferring said base to the sulphate by electrolytic travel, and
recovering the gaseous product of said decomposition of the base-supplying
electrolyte, substantially as described.
Dated this 23rd day of May 1895
CARPMAEL & Co.,
Agents for the Applicant.