118 
ME. P. V. SEVAN ON THE COMBINATION OF HYDROGEN 
to exist for some time, and are not liable to rapid spontaneous decomjDosition into the 
original molecules HoO and OI3, or into new molecules HCl and HCIO. That this 
complex molecule is to some extent stable apjjears both from the expansion experi¬ 
ments in damp chlorine, and from the fact that pre-insolation of damp chlorine alone 
makes the subsequent combination with hydrogen more rapid (p. 101), for in these 
last experiments the chlorine was darkened while hydrogen was admitted, and this 
operation lasted sometimes for several minutes. Owing, however, to the difficulty of 
ol^taining comparable results with these experiments, all that can be said is that the 
H3O, CI3 molecules can exist at any rate for several minutes. The constants c^, Cj 
cannot at present be more accurately denned, but we may suppose them both to 
depend on the intensity of the light. 
The value for dzjdt, 
Cg - 
Oi C3 
represents the general features of the acceleration jieriod. Originally dz/dt is zero, 
and also and higher coefficients, dhjdfi is always positive, and increases to a 
maximum at a time given by 
Cl C3 
After this time dhjdt^ decreases until dzjdt is constant. 
In fig. 18 the curve representing 1 — (1 — e”"’') is plotted'for the value 
Cg/cj = ' 9 . This expression is proportional to dzjdt, and so the curve in the figure 
should represent the velocity curve of the reaction. The essential features are the 
