IMPROVEMENTS IN THE MANUFACTURE OF CARBONATES OF SODA AND POTASH
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Alexander Melville Clark at the Office
of the Commissioners of Patents on the 20th April 1881. A communication
from abroad by Jean Baptiste Marie Prosper Closson, of 29, Avenue Trudaine,
Paris, France.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of
Middlesex, Patent Agent. "IMPROVEMENTS IN THE MANUFACTURE OF CARBONATES
OF SODA AND POTASH." [A communication from abroad by Jean Baptiste Marie
Prosper Closson, of 29, Avenue Trudaine, Paris, France.]
The processes of manufacturing soda are very numerous. Besides the manu-
facture from cryolite only two processes are employed commercially, viz., the
Leblanc process and the so called ammonia process, in both of which chloride of
sodium is treated, the first named passing by the intermediate stage of sulphate of
soda, whilst in the second sea salt is treated directly. Potash is extracted in
considerable quantity from chloride of potassium. In France a process has been
employed, and is so still on a certain scale, which consists in first converting
chloride of potassium into sulphate of potash, and then decomposing this sulphate
in solution in water by means of carbonate of baryta in the presence of carbonic
acid in excess, care being taken to avoid the formation of bicarbonate of potash at
the end of the operation.
The Leblanc process is employed on a large scale in Germany, the principal
source of chloride of potassium being at Strasfurt.
It is generally acknowledged that this process presents considerable difficulties,
there being always considerable quantities of soluble sulphides and cyanides formed,
and it is difficult to obtain a saleable potash without several calcinations and
successive dissolutions.
It has also been attempted in Germany to apply the ammonia process to the
manufacture of potash (carbonate of potash). The great loss of chlorides, which
is not worth considering in the case of sea salt, is a serious impediment to
commercial success when chloride of potassium is used.
This Invention consists in the process hereafter described of manufacturing
carbonate of potash or carbonate of soda from sulphate of potash or sulphate of
soda and saccharate of lime.

page_text: I convert chloride of potassium into sulphate of potash in one of the known
ways. I make a suitable solution of saccharate of lime, and by treating this
saccharate in the proper way and in proper proportions with a solution of sulphate
of potash I obtain sulphate of lime, which precipitates, and saccharate of potash,
which remains in solution. The sulphate of lime is allowed to precipitate, or is
separated by filtration or otherwise, and the liquid containing the saccharate of
potash is collected, and is treated by passing through it a current of carbonic acid,
whereupon bi-carbonate of potash is formed and precipitates, the sugar being set
free and capable of use again in another operation.
This
As regards the small quantity of sulphate of lime which is dissolved, it forms
with the carbonate of potash sulphate of potash and carbonate of lime.
carbonate of lime might be allowed to deposit in the first instance, but this is not
necessary, the carbonic acid forming with it bi-carbonate of lime, which remains in
solution. The precipitates of sulphate of lime and bi-carbonate of potash are
washed to recover saccharate of potash from the first, and sugar from the second.
This process is very economical, as (apart from the loss of sugar which is very
small if one operates with care, especially as the whole operation is performed in
the midst of the same liquid) in making potash from sulphate of potash lime only
is consumed equivalent for equivalent, or theoretically, 28 of lime for 69 of
carbonate of potash. There are however certain precautions to be taken in
practice.
I reserve the right to vary the degree of concentration of the liquors and the
strengths of the saccharates employed. Good results are obtained by using for
100 of sulphate of potash 220 of monobasic saccharate. With these proportions a
little sulphate of potash remains undecomposed, but is found again in the liquor at
a subsequent operation. Similarly with the portion of the carbonate of potash which
does not precipitate. When an excess of saccharate of lime is used there is a little
carbonate of lime which may however be easily got rid of. The precipitate of
bicarbonate of potash washed and calcined yields carbonate of potash and carbonic
acid.
The process of manufacturing soda or carbonate of soda from sulphate of soda is
similar to that above described for potash.