ON THE MANUFACTURE OF SULPHURIC ACID. 291 
into a hydrated acid, forms under these circumstances, on 
the one hand nitrous acid, and on the other sulphuric acid 
as my experiments have shown. 
In a leaden chamber in operation, the sulphurous acid 
therefore reduces the nitric to nitrous acid without the for- 
mation of crystals, the quantity of water being too large for 
the compound (SO 3 NO 3 -{-SO 3 HO) to be produced, and too 
small for the nitrous acid to be decomposed into nitric oxide 
and nitric acid. 
When the latter case occurs, which happens sometimes 
under circumstances that must be regarded as accidental, 
the product is impurified with larger or smaller amounts of 
nitric acid, from which it is freed by passing sulphurous acid 
through it. This operation can never fail to succeed, be- 
cause such an acid contains sufficient water for the nitrous 
acid to be decomposed into nitric oxide, which escapes, and 
into nitric acid, which is again destroyed by the influence 
of the oxidizing agent. 
In the opposite case, when the sulphuric acid is too con- 
centrated, the nitrous acid undergoes no further decompo- 
sition from the sulphurous acid : nor is it possible, by means 
of this acid, to free the commercial sulphuric acid at the 
ordinary temperature from nitric acid, but perfectly well 
from nitrous acid. The first of these acids is decomposed 
during the concentration into oxygen and nitrous acid, as 
I have shown, by allowing hydrochloric acid gas to act on 
the monohydrated sulphuric acid which had been employed 
for concentrating commercial nitric acid. No chlorine was 
disengaged, and thence follows, contrary to the opinion of 
M. Peligot, that the concentrated sulphuric acid contains 
neither nitric nor hyponitric acid. Nor can there be any- 
nitric oxide contained in it, this not being perceptibly solu- 
ble in this acid ; but it may contain nitrous acid, the pre- 
sence of which may be readily proved, on the one hand by 
means of hydrochloric acid, and on the other by means of 
the protosulphate of iron and metallic copper. — Chem. Gaz 
from Poggcndorff's Jlnnalen. 
