Improvements in the Preparation and Manufacture of Hydro- sulphurous Acid and Hydrosulphites.
Year: 1894

page_text: Date of Application, 23rd Aug.. 1894-Accepted, 29th Sept., 1894
COMPLETE SPECIFICATION.
Improvements in the Preparation and Manufacture of Hydro-
sulphurous Acid and Hydrosulphites.
I, JACOB GROSSMANN, of Hendham Vale Chemical Works, Manchester, in the
County of Lancaster, 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 :—
The commercial method for the preparation of hydrosulphurous acid is based
upon the action of zinc dust or any other suitable reducing agent on a solution of
bisulphite of soda. But this process as heretofore used yields a very unsatisfactory
proportion of hydrosulphurous acid or hydrosulphites especially if commercial
bisulphite is used. By my invention I am enabled to obtain a much larger
proportion of hydrosulphurous acid or hydrosulphites. It consists in taking a
solution of bisulphite, monosulphite or metasulphite and adding to it a fraction only
of dilute sulphuric acid or any other suitable dilute acid necessary to decompose it
completely; then adding a quantity of zinc dust or any other suitable reducing
agent equivalent or more than equivalent to the quantity of acid added and
agitating until this reducing agent has been oxidised as far as it will oxidize under
the circumstances, and then repeating this process adding successively acid and
zinc dust or other suitable reducing agent in the proper proportions until the
maximum practical yield of hydrosulphurous acid has been obtained.
I will now describe how I make hydrosulphurous acid by my improved method
and for this purpose I will first take the case of the soda salts. The solution
of monosulphite of soda, bisulphite of soda, or metasulphite of soda, or a
mixture of two or three of these compounds in solution is placed into a
suitable vessel which is fitted with an agitator; the strength of the solution being
such as to contain from 15 to 25 per cent. or thereabouts of total sulphurous acid in
the free and combined state or only in the combined state. A pipe going to nearly
the bottom of the vessel enables me to add dilute sulphuric acid containing about
ten per cent. concentrated acid in such a manner that when the sulphuric acid
touches the solution of the sulphurous compound the sulphurous acid which becomes
liberated has to pass a layer of liquid which will absorb it. I now add a small
quantity of acid, say one tenth of the bulk of the sulphurous liquid, agitate and add
quickly a quantity of zinc dust or other suitable reducing agent more than
equivalent to the quantity of acid added; I agitate using the well known precau-
tions for making hydrosulphites as regards temperature, exclusion of air etc.,
until the reducing agent has become oxidized or as much oxidized as the
circumstances will allow, then add the same small quantity of acid as before,
agitate and add again reducing agent as required, and thus I proceed until about
as much acid bas been added as would be equal to half the bulk of the sulphurous
solution. I then go on adding sulphuric acid and reducing agent in smaller
quantities and test each time before adding fresh sulphuric acid so as to find when
the maximum quantity of hydrosulphurous acid has been formed. The test which
may be used for this purpose is Bernthsen's test as modified by Rawson, or a
modification of this test, or any other suitable test. In this manner according to
the apparatus used the best proportions for each of the articles used can be easily
found and adhered to afterwards.
I have in these directions for the sake of simplicity only spoken of the soda
compounds which I take as the type of the soluble compounds; but the method can
be used in like manner in the case of other sulphites even if insoluble or difficultly
soluble, such as bisulphite or sulphite of lime, bisulphite or sulphite of zinc, sodium

page_text: zinc sulphite etc. The only difference in the case of these compounds is that these
compounds if insoluble are mixed with water instead of being dissolved in it. But
the reaction naturally only applies to such insoluble compounds from which a
suitable acid liberates sulphurous acid. It will be obvious that instead of an acid
an acid salt such as bisulphate of soda may be used.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
The production of hydrosulphurous acid and hydrosulphites by the successive
action of small quantities of a suitable acid or acid salt and a reducing agent upon
bisulphites monosulphites and metasulphites of the kind specified above.
August 23rd 1894.
JACOB GROSSMANN,
Hendham Vale Chemical Works, Manchester.
JACOB GROSSMANN,
Hendham Vale Chemical Works, Manchester.