IM- PROVEMENTS IN THE MANUFACTURE OF CARBONATE OF SODA
Year: 1860

page_text: PROVISIONAL SPECIFICATION left by Alexander Robertson Arrott at the
Office of the Commissioners of Patents, with his Petition, on the 19th
'June 1860.
I, ALEXANDER ROBERTSON ARROTT, of Saint Helen's, in the County of Lan-
caster, Chemist, do hereby declare the nature of the said Invention for "IM-
PROVEMENTS IN THE MANUFACTURE OF CARBONATE OF SODA," to be as follows:-
The object of my Invention is to produce crude soda or black ash from salt
cake or sulphate of soda, by using a smaller proportion of limestone or chalk
than is generally used for this purpose, by which a saving of limestone or chalk
is effected, and the "waste" remaining after the extraction of the carbonate
of soda from the black ash by lixiviation is of such a composition that on
adding to it hydrochloric acid, sulphuretted hydrogen is evolved in a suffi-
ciently pure state for burning for the production of sulphuric acid in the
leaden chambers used for this purpose; the combustion of sulphuretted hydro-
gen for this purpose produced from ordinary "waste" has hitherto been un-
successful, owing to the large quantity of carbonic acid evolved along with the
sulphuretted hydrogen, and also because the hydrochloric acid produced in
the manufacture of the quantity of salt cake or sulphate of soda converted
into carbonate of soda or black ash is insufficient to decompose the whole of
the "waste" produced, owing to the excess of limestone or chalk used in the
production of the black ash.

page_text: In the ordinary process for making black ash, one-and-a-half to two equi-
valents of limestone or chalk, or seventy-five to one hundred parts, are
mixed with one equivalent or seventy-two parts of salt cake or sulphate of
soda, and a certain quantity of coal, generally about three-fourths of the weight
of the salt cake used, and the mixture is then fused in a reverberatory furnace,
it being supposed that the excess of limestone, or the quantity beyond one
equivalent, formed an insoluble compound with the sulphuret of calcium
formed in the fusion, and that thus the sulphuret of calcium remained inso-
luble when the fused mass or black ash was lixiviated to extract the carbonate
of soda.
Now I have discovereed that an economical decomposition of salt cake or
sulphate of soda, and production of black asb, or crude carbonate of soda, may
be effected by using only one equivalent of limestone or chalk with one equi-
valent of salt cake or sulphate of soda, or fifty parts of the former and seventy-
two of the latter, and a proper quantity of coal by using a certain method of
producing the decomposition, and the method I propose is as follows:-
I fuse together in a reverberatory furnace, one equivalent of limestone, and
an equivalent of salt cake or sulphate of soda, or about fifty parts of the
former to seventy-two parts of the latter, and these when fused form a thin oily
liquid, which on cooling solidifies into a crystalline mass. While this mixture
is in a state of fusion, it is to be mixed with a quantity of small coal equal
to about three-fourths of the salt cake or sulphate of soda used, and the whole
then finished as in the production of ordinary black ash; in place of mixing
the coal with the fused materials, the fused mixture may be withdrawn
from the furnace, and granulated by being allowed to fall from a height, or it
may be crushed and then mixed with coal, and worked in the same manner
as common black ash; in either case the whole of the salt cake or sulphate of
soda will be converted into carbonate of soda with the exception of a small
but variable portion of undecomposed sulphate of soda, and a quantity of
sulphuret of sodium equal to from one to one and a half per cent. on the
carbonate of soda produced.
When the black ash thus produced is is acted on by water in vats, the car-
bonate of soda dissolves along with the undecomposed sulphate of soda the
sulphuret of sodium, and the small portion of common salt usually existing in
common salt cake, and a mixture remains consisting of coke and sulphuret of
calcium; to this I add hydrochloric acid, which evolves sulphuretted hydrogen
in a nearly pure state, and this I propose to burn for the production of sul-
phuric acid.

page_text: When a supply of pure carbonic acid is of importance, it can be obtained
from the fusion of the limestone and salt cake by fusing them in a close fur-
nace, and slightly increasing the temperature; the whole or a portion of the
carbonic acid goes off with effervescence, but the evolution of the carbonic
acid must not be carried too far, as the mixture becomes very infusible.
A decomposition of salt cake, but by no means so complete, may be made
with one equivalent of limestone by grinding them together, and decomposing
in mixture with coal, but from the fineness required in the grinding, and the
imperfect decomposition obtained, I prefer to fuse the salt cake and limestone
together before adding the coal.
I have mentioned a reverberatory furnace as the means of producing this
decomposition, but I do not confine myself to the use of this form of
apparatus.