26 Mr. H. A. Smith on the Chemistry of 



to doubt this from various circumstances. In the first place, 

 they seemed to differ from the chamber crystals in form, these 

 partaking more of the needle-shaped form of the crystals of 

 sulphuric acid ; and also, when exposed to the air, they remained 

 a long time (several days in fact) without change. This shows 

 they are not the same as the chamber crystals. Again, when 

 they were brought into contact with water, they dissolved 

 without the evolution of nitrous fumes, from which we may 

 fairly conclude that they were crystals of sulphuric anhydride. 



I had long been inclined to take a different view of the 

 cause of this action from that generally accepted. It seemed to 

 me, in all its phases, to resemble the action of a small piece 

 of leaven in a loaf of unleavened bread, or the action of a 

 minute crystal dropped into a supersaturated solution of a 

 salt, which immediately causes the solidification of the whole 

 liquid. The action only requires to be commenced, and it 

 then continues till the whole of the attainable oxygen has 

 been made use of. This action, if quickened at all, is only 

 slightly so, by the further addition of steam. 



Exp. II. If, again, instead of inserting a drop of water into 

 the vessel in which the gases are confined, it be surrounded 

 with a coating of ice, the same effect takes place, a much 

 longer time, however, being required. 



Exp. III. The same end can also be attained by the sudden 

 application of heat. 



These results then led me to judge of the action as I have 

 said, showing that the sulphurous acid is able to deprive the 

 nitric acid of some of its oxygen without the intervention of 

 steam, a medium which has hitherto been considered neces- 

 sary. 



It has been shown that a very small amount of water can 

 cause the action to commence. The next experiment tried was 

 to find what effect water present in a large quantity had upon 

 the formation of the acid. 



Exp. IV. A mixture of two volumes of steam to one of the 

 mixed gases was put into a glass vessel and allowed to stand 

 twenty-four hours (the gases being mixed in requisite propor- 

 tion). The same amount 



(Exp. V.) of the mixed gases was passed into a similar vessel, 

 but into which no air was allowed to enter, to see if any 

 action could take place in its absence ; and the water was pre- 

 sented to the gases in the liquid condition on a platinum 

 wire, and allowed to stand the same length of time. At the 

 end of the time the results were : — 



