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On the Purification of Oil of Vitriol from Nitric Acid. 355 
common salt, that this might afford me an indirect mode of ascer- 
taining whether the whole of the nitric acid had been removed. 
A quantity of oil of vitriol, previously boiled with sugar as de- 
scribed, was diluted with water, and caused to act on purified com- 
mon salt, as directed by Professor Gregory in his process for pre- 
paring pure hydrochloric acid, but it was found that the acid ob- 
tained had a yellow colour, and when mixed with protosulphate of 
iron, it became nearly black, which does not occur when hydrochloric 
acid free from nitric is used. I explain the fact that nitric acid re- 
mained in a liquid containing much sulphurous acid, in the following 
way: Sulphurous acid, when boiled with oil of vitriol, does not de- 
stroy the nitric acid entirely, or nearly so ; but if the oil of vitriol be 
diluted with water, the sulphurous acid then decomposes the nitric 
acid. 
The second method is one recommended a few years ago by 
M. Pelouze, and consists in boiling the impure oil of vitriol with the 
addition of sulphate of ammonia, which it appears first changes into 
nitrate of ammonia, and subsequently is decomposed into nitrous 
oxide and water. I have tried this method, and find that when 
a considerable quantity of the sulphate is added, the whole of the 
nitrous compounds are removed ; but it is exceedingly difficult, if 
not impossible, to add the exact quantity requisite to decompose the 
whole of the nitric acid, without the risk of leaving some ammonia 
in the liquid. 
The first experiment I made, was with the view of learning 
whether carbonic oxide in the nascent state, might not decompose 
the nitric acid contained in strong oil of vitriol. About four fluid 
ounces of the acid were heated in a flask, and successive quantities of 
oxalic acid added, but on testing, it was found the nitric acid had 
“not been removed. 
Having frequently observed, on diluting large quantities of oil of 
vitriol with water, that red vapours were disengaged, I made seve- 
val experiments, by mixing various proportions of these two liquids, 
and afterwards boiling them so as to favour the expulsion of the va- 
pours, but although a part of the nitrous compound was removed, 
enough remained to render the liquid dark-coloured on adding sul- 
phate of iron. 
After the trial of a great many other bodies, including sulphuretted 
hydrogen, in various ways, I found that the only substance likely to 
answer the purpose, was sulphurous acid. The experiments made 
with this substance led to the result that, if the oil of vitriol be di- 
luted to the specific gravity of 1°715, or thereabouts, and a stream 
of sulphurous acid passed through it, the whole of the nitric, nitrous, 
or hyponitrous acid will be reduced to binoxide of nitrogen, which, 
along with the excess of sulphurous acid, may be totally removed by 
boiling. 
