100 
MR. P. V. SEVAN ON THE COMBINATION OF HYDROGEN 
uninsolated gas can easily be introduced into the insolation vessel while the action is 
progressing. If this he done, a large decrease in the rate of action is at once noticed, 
and the combination may cease altogether if sufficient quantity of gas be introduced. 
Then an induction period sets in as in the case of a fresh gas mixture. But the 
attainment of the original maximum is only performed gradually compared with the 
case of the fresh gases. This will be made clear by the experiments represented in 
fig. 14. At first the gas was illuminated and, after a period of inertness of about 
20 minutes, the acceleration period represented in curve I, fig. 14, took place. After 
the maximum action had been reached, a quantity of uninsolated gas, occupying 
about 400 millims. of the index tube, was introduced while the light was still on the 
mixture. The index came to rest and an inert period of about 1 minute occurred. 
The acceleration period then set in, hut was very much longer than in the case of the 
original gas; in fact, the rate of action was increasing slowly for as long as the index 
could be followed, and the maximum action was not attained. This is shoum by the 
curve II, fig. 14, being very much flatter than curve I, 
If the mixture be left in the dark for some time before illuminating, aftei' fresh gas 
has been added, this retarding effect passes off to some extent, and the attainment of 
the maximum action is not so gradual. Curve III, fig. 14, represents the occurrences 
when the same gas as for curves II and I had again about 400 millims. of fresh 
uninsolated gas added, and was then darkened for 5 minutes. The action is seen to 
0 
Fig. 15o Aljscisspe, time iii minutes from l)egiuiiing of action. 
Ordinates, velocity of action. 
