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

page_text: Date of Application, 23rd Aug., 1894-Accepted, 13th Oct., 1894
וש ט שם
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 :-
Hydrosulphurous acid and hydrosulphites are commercially prepared from
bisulphite of soda or from sulphurous acid by the reduction of these substances by
means of zinc or other suitable reducing agents. These reducing agents do not
act on monosulphites or metasulphites and up to the present these compounds have
therefore not. been used for the preparation of hydrosulphurous acid or hydro-
sulphites. By my invention I am enabled to utilize these compounds for the
purpose of making hydrosulphurous acid and hydrosulphites. It consists of mixing
a solution of monosulphite or metasulphite with a quantity of dilute sulphuric
acid or any other suitable acid sufficient to liberate from one half to the whole of the
sulphurous acid contained in it in such manner that most of the sulphurous acid
remains dissolved in the liquid, and subsequently treating the liquid with a suitable
reducing agent.
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 or metasulphite of soda, or a mixture 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. A pipe going to nearly the bottom of the vessel enables me to
add dilute sulphuric acid containing about ten per cent. of 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 carefully and not too much at once as much acid
as will liberate from one half to nearly the whole of the sulphurous acid present
and agitate gently so as to dissolve the liberated sulphurous acid in the liquid,
taking care that the total bulk of the mixture is at least ten to fifteen times
greater by weight than the weight of the liberated sulphurous acid and keeping
the temperature as low as practicable. When the reaction is completed I add
gradually the necessary quantity of zinc or other suitable reducing agent and
agitate, proceeding in such manner as is known to produce hydrosulphurous acid,
and which can ultimately be converted into a hydrosulphite if required. In order
to ascertain which proportion of the sulphurous compound and sulphuric acid give
ultimately the best yield of hydrosulphite it is necessary to make a series of
batches in which the proportions of the sulphuric acid are varied, and to test the
final hydrosulphite by means of Bernthsen's test as modified by Rawson, or by a
modification of this test or by any other suitable test. In this manner according
to the apparatus used the best proportions 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 this method
can be used in like manner in the case of other monosulphites or metasulphites
even if insoluble or difficultly soluble, such as sulphite of lime, sulphite of zinc,
sodium 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

page_text: which a suitable acid liberates sulphurous acid. It is obvious that instead of an
acid an acid salt such as bisulphate of soda can be used. The method is also
applicable to bisulphites either alone or mixed with monosulphites or meta-
sulphites.
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 from monosulphites
and metasulphites of the kind specified above, or from a mixture of these, or from a
mixture of either of these or of both with bisulphites, or from bisulphites, by the
intermediate action of a suitable quantity of a suitable acid, or acid salt previous
to the addition of the reducing agent.
001004
JACOB GROSSMANN,
Hendham Vale Chemical Works, Manchester.