AND CHLORINE UNDER THE INFLUENCE OF LIGHT. 
117 
when the steady state is reached; dijjdt and dxjdt, both are zero, whence 
dz/dt = Cg, X = ^ , y — , 
C3 c-^ 
where x, y are the final values of x and y. 
Integrating equations (1) we obtain 
a: = ^ (1 — e ^*0, 
Co 
using the condition that x, y, and z are initially zero. 
For the velocity of formation of the hydrochloric acid we have 
dz _ 
dt ~ 
and for the acceleration 
-cf ’’ 
With regard to the constants c^, C3, Cg; Cg is the final rate of formation of hydro¬ 
chloric acid, and this was found to be proportional to the intensity of the light by 
Bunsen and Boscoe. Cg is also a measure of the rate of formation of the chlorine- 
water additive molecules, and, as we have seen in the description of the cloud 
experiments on p. 106 , the more intense the light the more rapid is the formation of 
the cloud producing nuclei. For the other two constants we have seen that the 
water-chlorine molecules are produced some time before any hydrochloric acid is 
formed, so that- the last two stages of the action do not take place so rapidly that 
the first intermediate compound has a very short existence. Both and Co are, 
therefore, not very large. Further, Bunsen and Boscoe showed that there was a 
definite absorption of light associated with the combination—more than was absorbed 
by an equal quantity of damp chlorine. One, therefore, or both of the constants c^, 
C3 depends on the light intensity. This also appears from the fact that the efiect of 
insolation persists for some time after the mixture is darkened. If Cj and were 
both independent of the intensity of the fight, we should expect that in a short time 
the HjO, CI2 molecules would all be used up, and that the gas would very soon 
return to its normal condition. But the effect of previous insolation can persist for 
several hours. This is explained if we suppose that the HgO, CI3 molecules are able 
