Improvements in the Manufacture of Nitric Acid.
Year: 1891

page_text: Date of Application, 29th Sept., 1891
Complete Specification Left, 14th June, 1892-Accepted, 16th July, 1892
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Nitric Acid.
I, ROBERT EDWARD CHATFIELD, of Woodlands, Sewardstone, in the County
of Essex, Manufacturing Chemist, do hereby declare the nature of this invention
to be as follows:-
According to a known process for the manufacture of nitric acid, nitrate of soda
is treated at high temperatures with sulphuric acid, generally in the proportion of
one equivalent of each, the nitric acid distilled off being more or less impure, and
the residue a mixed material difficult to deal with usefully. The object of my
invention is to obtained the nitric acid free from sulphuric acid, and a residue which
can be run off in fluid condition and can be readily utilised for various purposes.
In order to attain these results, I add to the nitrate of soda about two equivalents
of strong, or it may be concentrated, sulphuric acid, taking care that the temperature
at first does not exceed 200° Fahr. and that it does not rise above 450° Fahr. or
about the melting point of tin. After the nitric acid is distilled off in a compara-
tively pure condition and free from sulphuric acid, the residue, consisting mostly of
bisulphate of soda in a fused condition, can be run off and employed for producing
furnace salt cake or for other purposes.
Dated this 29th day of September 1891.
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Nitric Acid.
I, ROBERT EDWARD CHATFIELD, of Woodlands, Sewardstone, in the County
of Essex, Manufacturing 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:—
According to a known process for the manufacture of nitric acid, nitrate of soda
is treated at high temperatures with sulphuric acid, generally in the proportion of
one equivalent of each, the nitric acid distilled off being more or less impure, and
the residue a mixed material difficult to deal with usefully. The object of my
invention is to obtain the nitric acid free from sulphuric acid, and a residue which
cau be run off in fluid condition and can be readily utilised for various purposes.
For this purpose, I treat in vessels of any convenient shape and size which, if of
iron, are protected from the action of the nitric fumes by fire bricks above the
surface of the mixture, one equivalent of nitrate of soda and a large excess of
sulphuric acid, preferably two equivalents; using either brown oil of vitriol or
concentrated oil of vitriol or sulphuric acid of any intermediate strength, according
to the specific gravity of the nitric or nitros (that is to say unrefined) acid
required.
About 75% of the nitric acid distils over under 300° Fah. and the remainder is
got off, save a slight trace, at about the melting point of tin viz. 445° Fah. A
temperature a few degrees higher removes the last traces.
Owing to the comparatively low temperature employed, the distillate is
chemically free from sulphuric acid, thus saving a final distillation in glass or
platinum vessels, when acid free from sulphuric acid is required.
A comparatively small quantity of the lower oxides of nitrogen are contained in
Price 8d.

page_text: the distillate, and these along with the chlorine from the salt in the nitrate of soda
may be driven out by heating in glass retorts.
The resulting residue is liquid and may be run off at any temperature exceeding
350°. It may be used with an equivalent of salt to form muriatic acid and
furnaced salt cake for the manufacture of glass, soda &c. When operating on a
small scale, the residue may be dissolved in water and used with chalk or whiting
to give carbonic acid; the resulting mass when filtered giving a pure solution of
sulphate of soda.
After operating, the vessels should be sufficiently lowered in temperature before
recharging so as not to raise the mixture of sulphuric acid and nitrate of soda
above 200° Fah.
For the manufacture of nitric acid of the highest strength, gradual addition of
the sulphuric acid is to be recommended, in order to avoid a too vigorous action.
The charges of sulphuric acid and nitrate of soda may be worked off very
quickly owing to the easy decomposition and the low temperature required, and to
the nitric acid being condensed with comparative rapidity.
As the produced compound of sulphuric acid and soda has a great power of
retaining water the nitric acid that comes off first in this process is very strong,
and the last portions are comparatively weak.
This weak acid can be collected separately and used for the manufacture of
nitrates &c. Thus the use of such strong acid as oil of vitriol might be avoided
except when all is required to be of the highest possible strength.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
The herein described process for the manufacture of nitric acid, by heating a
mixture of nitrate of soda with large excess of sulphuric acid, preferably two
equivalents of acid to one of nitrate, thus producing a residue in a condition which
runs off liquid at the temperature under which the process is completed.
Dated this 14th day of June 1892.
ABEL & IMRAY,
Agents for the Applicant.