IM- PROVEMENTS IN THE PRODUCTION OF SULPHIDE OF SODIUM AND IN THE TREATMENT THEREOF FOR THE MANUFACTURE OF SODA
Year: 1866

page_text: PROVISIONAL SPECIFICATION left by Walter Weldon at the Office of
the Commissioners of Patents, with his Petition, on the 11th May
1866.
I, WALTER WELDON, of Park Villa, West Hill, Highgate, in the County
of Middlesex, do hereby declare the nature of the said Invention for "IM-
PROVEMENTS IN THE PRODUCTION OF SULPHIDE OF SODIUM AND IN THE TREATMENT
THEREOF FOR THE MANUFACTURE OF SODA," to be as follows :-
The improvements which constitute my present Invention consist, firstly, in
a new method of obtaining sulphide of sodium; and, secondly, in a combina-
tion of processes, which constitute collectively a new method of manufacturing
commercial soda by way of the intermediate production of the compound just
mentioned, in which new method of manufacturing soda the more costly of
the re-agents employed are continually recovered for use over again.
The new method of obtaining sulphide of sodium, which constitutes the first
part of my present Invention, consists in heating in admixture together (in
any proportions) chloride of sodium, or common salt, sulphate of magnesium
having associated with it at least one equivalent of water, and coal, coke, or
other convenient form of carbon. The chloride of sodium is decomposed by
the sulphate of magnesium, and the one equivalent of water essential to be
present also undergoes decomposition, the products formed being sulphate of
sodium, oxide of magnesium, and hydrochloric acid, which last flies off as
vapour and must be condensed in the usual way. The sulphate of sodium
formed as thus described is deoxidized by the carbon into sulphide, so that

page_text: what finally remains is a mixture of sulphide of sodium and oxide of magne-
sium or magnesia. If preferred, free sulphuric acid or certain metallic
sulphates other than the one mentioned (such, for example, as the sulphate
of aluminium) may be used in this process, instead of sulphate of magnesium;
but the use of the latter sulphate will usually be the most advantageous.
The combination of processes which constitutes the second part of my
Invention has for its object, firstly, the decomposition of sulphide of sodium,
with production of either caustic soda or carbonate of sodium; and, secondly,
the continual reproduction both of the re-agent, whereby this decomposition is
effected, and of the compound by means of which, when manufacturing soda by
the combination of processes in question the sulphide of sodium is produced,
whether by one operation, by the new process which forms the first part of
my present Invention, or by first obtaining sulphate of sodium by means of
sulphate of magnesium, and making the deoxidation thereof a second and
distinct operation. I attain these two objects by causing to react upon the
sulphide of sodium the oxide or carbonate of some heavy metal, a sulphide of
which can be obtained by treating sulphide of sodium with its oxide or car-
bonate in presence of water by ebullition or otherwise, and which heavy metal
is further characterized by its sulphide being convertible into soluble sulphate,
either by roasting or by mere exposure to the atmosphere; by then converting
the sulphide of heavy metal so obtained into soluble sulphate by the means
indicated, and by finally decomposing this sulphate in solution by means of
magnesia, thereby producing, on the one hand, sulphate of magnesium, which
I use for the decomposition of a fresh portion of salt, in order to the pro-
duction of a fresh portion of sulphide of sodium, at the same time re-obtaining
magnesia, wherewith to again decompose sulphate of the heavy metal when again
formed, and, on the other hand, hydrated oxide of heavy metal, by means of
which the said fresh portion of sulphide of sodium may be decomposed. If I
wish to obtain carbonate of heavy metal instead of oxide (whether because I
desire to obtain carbonate of sodium instead of caustic soda, or because the
carbonate of the heavy metal I am using affords a denser precipitate, and one
Jess retentive of liquid than its precipitated oxide, as I find to be the case,
for example, with manganese, which is one of the metals which may be advan-
tageously used in this new process of manufacturing soda); I pass carbonic
acid into the vessel in which the solution of sulphate of heavy metal is being
treated with magnesia, and so convert into carbonate the oxide liberated by
that treatment. The carbonic acid used for this purpose may be obtained
from any ordinary source thereof, or may be that which is produced by the
reaction upon the sulphate of sodium of the carbon which deoxidises it into

page_text: sulphide. I prefer, though this is not always essential, that this process of
obtaining sulphate of magnesium and carbonate of heavy metal by means of
sulphate of heavy metal, oxide of magnesium and carbonic acid, should be
performed in a closed vessel into which carbonic acid is forced under pressure.
The combination of the several processes just described with the new
process, which forms the first part of my present Invention, constitutes a new
method of manufacturing soda possessing most important advantages as
regards economy over the method at present generally practised, inasmuch
as it enables soda, either in the form of caustic soda, or in that of carbonate
of sodium, as may be preferred, to be obtained by two operations only, and
then by two further operations each, very simple and inexpensive, reproduces
all the materials required for the manufacture of soda by this process, except
salt and coal.