DECOMPOSITION OF WATER BY HEAT. 311 



detailed. I at one time thought that the contraction might 

 be due to a slight oxidation of the wire, but it never went 

 beyond a very limited point ; nor was the wire altered in size 

 or weight, though it was kept ignited for many hours. 



Chlorine over water gave dense white fumes ; a greyish 

 yellow insoluble powder accumulated on the sides of the tube 

 near the platinum wire, which appeared of the same nature as 

 the vapours ; the deposit was insoluble in cold nitric, sul- 

 phuric, or muriatic acid, but dissolved by the last when boiled. 

 The fumes did not, as far as I could judge, affect litmus- 

 paper ; a barely perceptible tinge of red was indeed communi- 

 cated to it, but this, I had every reason to believe, was attri- 

 butable to a slight portion of muriatic acid not absorbed by 

 the water. I have not yet worked out this result, as it is 

 probable, considering the number of experiments that have 

 been made on heated chlorine, that it is a known product, 

 though I cannot find, in several books to which I have 

 referred, any substance answering to it in description, and the 

 field opened by voltaic ignition is so new that each result 

 demands a separate and prolonged examination ; if I find 

 that this is an unknown compound I shall probably resume 

 its investigation. * 



Cyanogen gave, though in very minute quantities, a some- 

 what similar deposit, but at its then very high temperature it 

 began to act rapidly on the mercury, and I was obliged to 

 give up the experiment after an hour's ignition. Both these 

 gases require peculiar and novel apparatus for examination by 

 voltaic ignition. It will presently be seen that my whole 

 attention and disposable time were necessarily occupied with 

 certain phenomena to which this class of experiments ulti- 

 mately led me. 



Hydrogen gave a very notable contraction, amounting in 

 some cases to one-tenth of its volume. This was an unex- 

 pected result, and I examined it with care. It took place both 

 over water and over mercury ; rather more with the former 

 than with the latter. It obtained equally with hydrogen pro- 

 cured by electrolysis from carefully distilled water and pure 



* See Supplemental Paper, p. 20. 



