SULPHURIC ACID FOR WATER. 381 
I will now advert to the manufacture of sul- 
phuric acid, and make such reviews of the che- 
mical actions which take place in it, as are required 
to enable me to show in what respect the improve- 
ment I have alluded to is to be made. 
It is, I think, universally admitted, that dry 
nitrous acid gas has not the property of changing 
dry sulphurous acid gas into sulphuric acid; and 
that it only has that property when water inter- 
venes. The theory of the production of sul- 
phuric acid being, that nitrous acid gas, sul- 
phurous acid gas, and a little water or aqueous 
vapour meeting together, a mutual action takes 
place between the three bodies, and a crystalline 
substance is formed: this crystalline substance 
is permanent until brought into contact with more 
water, either in the liquid or vaporous state : 
when it has had an opportunity of acquiring suf- 
ficient water, it is resolved into sulphuric acid and 
nitrous gas: the latter, immediately taking to 
itself more oxygen from the atmospheric air in the 
interior of the chambers, is reconverted into 
nitrous acid gas; and this, mingling itself with 
sulphurous acid gas and water, causes a repetition 
of the operation just mentioned. In this contin- 
uous manner the ordinary process of the manu- 
facture of sulphuric acid is conducted. 
