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sides sulphur, sulphide of zinc, and the undissolved metal. 
As regards the reaction under 8, Iam perfectly aware that 
sulphur under ordinary conditions does not unite with 
sulphurous acid, but if separated in the fluids containing it, 
its more active state may very likely favor such combin- 
ation; the reaction under 4 is a fact as it is a method for 
the preparation of S;Os. . 
This fluid does not contain tetra- or penta-thionie acid, for 
on saturating it with caustic potassa and dissolving by an 
excess of alkali the first precipitated oxide of zinc, no sulphur. 
separated to form sulphide of potassium on boiling. Both of 
these acids are decomposed, by boiling with alkalies, into 
sulphur and trithionic acid; this latter being decomposed in 
its turn again, but very much slower, into sulphurous and 
hyposulphurous acids. 
‘ Upon treating now sulphurous acid with metallic zine in 
the presence of hydrochloric acid, we obtain a milky liquid, 
and the odor of sulphuretted hydrogen becomes more or less 
perceptible. The reaction here is more rapid and compli- 
eated. Zinc and hydrochloric acid generate hydrogen, as is 
well known, and the question may arise whether the 
hydrogen, being in the nascent’ state, will directly reduce 
sulphurous acid to water and sulphuretted hydrogen gas. 
Many metals decompose water, oxide of the metal being 
formed, while hydrogen is set free. On filling a little flask 
with sulphurous acid solution, inverting it and letting its 
mouth dip under sulphurous acid, contained in a porcelain 
dish, and introducing into the flask a piece of sodium, a 
vivid: separation of hydrogen took place, while the sulphur- 
ous acid remained clear, and no trace of hydrosulphuric acid 
could be detected in the escaping gas. The same was ob- 
served when a piece of aluminium was substituted, in which 
case the fluid had to be heated to accelerate decomposition. 
The nascent hydrogen here was therefore without action upon 
the sulphurous acid, and it is not likely that in the case of 
zine and hydrochloric acid the hydrogen should reduce sul- 
phurous acid to water and sulphuretted hydrogen gas. 
However, another experiment was tried, the result of which 
