224 
Selected Articles. 
Chim. t. 85, p. 206) the red sulphate of manganese, as the best 
reagent that that can be employed, to recognise if a body is 
capable of oxidizing. This salt, which some regard as a sul- 
phate of the sesquioxide of manganese; others as a sulphate of 
the bioxide, and some as a sulphate of the bioxide mixed with 
hypermanganesic acid, is obtained, by digesting peroxide of 
manganese, reduced to an impalpable powder, in concentrated 
sulphuric acid for a few days ; a beautiful red, and very acid li- 
quid results, which is the salt in question. All the combustible 
bodies greedy of oxygen, organic substances, the slightly oxy- 
genated acids, as the sulphurous, phosphorous, &c, cause a 
loss of its beautiful colour, by reducing it to the state of a salt of 
the peroxide. It may therefore be employed to ascertain the pre- 
sence of sulphurous acid in the hydrochloric acid of commerce, 
as a few drops of this red liquor, on being added to the latter 
acid will speedily become colourless, if any traces of the former 
be present. But the use of this reagent in this case is not attend- 
ed with all the advantages that might have been supposed. 
First, this salt, like all the red salts of manganese is not sta- 
ble; it loses its colour by long exposure to the air, and is im- 
mediately changed on the addition of water; but above all it 
is as readily acted upon by nitrous as by sulphurous acid, and 
hence it happens that a hydrochloric acid containing the for- 
mer, which is often the case, will act on this reagent as if it 
contained the latter, thus giving rise to mistakes. 
Being constantly consulted by manufacturers of Rouen on 
the purity of hydrochloric acids, and consuming a large 
quantity myself, in the manufacture of artificial mineral wa- 
ters, I endeavoured to discover a simple, prompt and infallible 
method of discovering the least traces of sulphurous acid in 
these acids. The following appears to unite all these condi- 
tions, and has never failed. 
It is formed on the action of the protrochloride of tin on 
sulphurous acid. Pelletier, Senr. long since taught us (Ann. 
de Chim. 12, p. 231. — 1792) that when placed in contact with 
this latter, it becomes deoxigenated, and gives rise to a preci- 
pitate of a beautiful yellow colour, consisting of sulphur and 
peroxide of tin. 
