474 Rev. P. J. Kirkbv on the Unioi 



oj 



lowering of the catatytic temperature, although considerable, 

 was, nevertheless, limited. 



Thus, in the case of the pure platinum wire (see Table I.), 

 the reaction began in the mixed gas at pressure 9' 6 mm., 

 when the resistance of the platinum reached 5*13 ohms and 

 its temperature 279° C. The quantity of water formed was 

 small, for the pressure only diminished by about 2 per cent. 

 The platinum wire w T as then heated by a series of gradually 

 diminishing currents to a series of gradually diminishing 

 temperatures. Each of these currents was passed through 

 the wire for about a minute ; and, after each was stopped, the 

 formation of water v^as detected so long as the resistance of 

 the wire exceeded 4*73 ohms, that is, so long as its temperature 

 exceeded 236°. The whole amount of waiter formed during 

 these observations was small and only reduced the pressure 

 by about 5 per cent. The gas was then left for about two 

 hours, after which the catalytic temperature had risen to 

 268°, as recorded in Table I. This observation was confirmed 

 on the following day and was again confirmed eleven days 

 later, the gas meanwhile having been left drying. On 

 account of the slight discrepancy between this result and the 

 temperature 279°, obtained at the pressure 9*6 mm., the gas was 

 then replaced by fresh gas at the pressure 8'6 mm., and 

 fresh observations were taken. The result once more sup- 

 ported the smaller temperature, giving 265° as the catalytic 

 temperature. 



The same phenomenon was observed with the impure plati- 

 num wire (see Table II.). The chemical action at the pressure 

 31*2 mm. did not begin until the wire's resistance reached 

 7*37 ohms. The pressure was then immediately reduced to 

 4'4 mm._, at which the reaction was renewed with a resistance 

 of 6*98 ohms. Next day no combination was recorded until 

 the resistance again reached 7*37 ohms. Thus, the setting- 

 up of the chemical reaction was followed by a lowering of the 

 catalytic temperature from about 238° to about 195°, but only 

 for a time. The effect soon passed off. But there is no reason 

 to suppose that the catalytic temperature might not be further 

 reduced, at least temporarily, by first raising the wire to a 

 higher temperature than was done in the present case, or by 

 other means. 



These observations prove that the starting of the chemical 

 reaction is bound up with some circumstance which facilitates 

 the renewal of the reaction. 



It is difficult to think that this phenomenon is due to the 

 presence in the mixed gas of the water-vapour which is pro- 

 duced by the reaction. For this water-vapour was formed 



