and Observations on Iodine. 
505 
2. I thought it probable from the rapid action of tin on iodine, 
that tin foil would burn in the vapour of iodine, but on intro- 
ducing it into the violet coloured gas in a small retort made 
very hot, though the combination was instantaneous, yet no 
light was apparent. 
I thought it possible that the acid properties of the com- 
pound of tin and iodine, which I have described in my last 
communication to the Society, might depend upon the decom- 
position of water and upon the formation of hydroionic acid. 
On this idea I distilled the solution of it in water, hoping if 
hydroionic acid were formed, that I should obtain some in this 
process; but the fluid that came over was merely water 
coloured by a minute quantity of iodine, and the orange 
coloured substance which remained when dissolved in water, 
exhibited the same acid properties as before, and combined 
with ammonia without affording any oxide. 
The compound of iodine and iron when dissolved in water 
exhibited acid properties, but when the solution was distilled 
it yielded hydroionic acid and deposited oxide of iron, and the 
entire solution acted on by ammonia, afforded an olive coloured 
precipitate in great abundance. 
On the action of some compound gases on Iodine. 
1. I heated some iodine in a dry glass globe filled with 
sulphuretted hydrogene ; there was a considerable absorption 
of gas, no sulphur was deposited, and a reddish brown fluid 
was formed, which when thrown into water rendered it . 
strongly acid and deposited much sulphur ; the water passed 
through a filter exhibited the properties of hydroionic acid. 
3 T 2 
