DECOMPOSITION OF WATER BY HEAT. 319 



was brought to a full ignition by the battery, and kept ignited 

 for a few seconds ; connection was then broken and the lamp 

 removed, so that the water gradually ascended. A bubble of 

 the size of a large mustard-seed Fi 



was left in the extremity of the 

 tube, and I was much gratified at 

 finding that when this was caught 

 by a lighted match at the surface 

 of the water trough it detonated. 

 The experiment was then repeated, 

 continuing the ignition for a longer 

 time, but the gas could not be in- 

 creased beyond a very limited quantity ; indeed it was not 

 to have been expected, as, supposing it to be mixed gas, 

 re-combination of the excess would have taken place, and 

 the fact of any uncombined gas existing when exposed to 

 incandescent platinum will doubtless surprise those who hear 

 it for the first time. 



The experiment was repeated as at first and the bubble 

 transferred to another tube ; the wire was then again ignited 

 in vapour, another bubble was instantly formed and trans- 

 ferred, and so on, until after about ten hours' work sufficient 

 gas was collected for analysis ; this gas was now placed in an 

 eudiometer, it detonated and contracted to 0*35 of its original 

 volume ; the residue being nitrogen. The experiment was 

 repeated several times with the same general results, the residue 

 sometimes containing a trace of oxygen. 



Here electrolysis was out of the question ; the wire was 

 ignited in (if I may use the expression) dry steam, the upper 

 part of the tube being far above the boiling-point, and of 

 course perfectly transparent ; if not an effect of heat it must 

 have been a new function of the electric current, at least one 

 hitherto unknown, 



As the voltaic arc and electric spark afford heat of the 

 greatest intensity, I tried a succession of electric sparks from 

 platinum wires through steam in the apparatus fig. 8, the water, 

 as in all my experiments, having been previously purged of 

 air (to save circumlocution I will in future call it prepared 

 water). The sparks were taken from the hydro-electric 



