390 
DR. MEYER WILDERMAN ON CHEMICAL DYNAMICS 
that, starting with a system such as chlorine and carbon monoxide, at first it seems 
for some time that no combination takes place at all. Combination, however, becomes 
gradually more and more apparent, the velocity becomes greater and greater, till a 
constant value for K is obtained. This is a peculiar phenomenon, which Buxsex 
and Pv-OSCOE first observed in the case of chlorine and hydrogen, and which they 
appropriately called the “ induction period. If now, after the velocity constant has 
been observed for some time, the light is removed from the system, the reaction at 
once becomes very slow and soon stops. If the system is, after a time, again exposed 
to light, we find at first an “ induction period,” after which the same velocity 
constant is obtained. This shows that as the light is removed from the system the 
reacting molecules lose the properties which they had acquired in the light, gradually 
returning to their old state; and that when the system is again exposed to the light 
the molecules and atoms each time gradually acquire the same new properties. 
Besides the “ induction period” we thus have to deal also with a “ deduction period.” 
The “ induction period” is evidently not due-to the absence of some product of the 
reaction, but is a period during which the molecules and atoms of the systems 
continuously change their state of energy from that in the dark to that in the light; 
and the “deduction period” is a period during which the molecules and atoms 
gradually return from their state of energy in the light to the state of energy they 
possess in the dark. The properties of the “induction” and “deduction” periods 
require, however, still further consideration. On removing the light from the system, 
that state of energy of the atoms and molecules which makes them capable of 
entering into reaction rapidly passes away, with the energy stored in the molecules 
and atoms under the action of light, and is transformed partly into heat and partly 
in chemical action as long as this goes on after the removal of the light. 
The curves given above show, however, that while chemical action ceases, or 
apparently ceases, after a short time, it takes a considerable time before the atoms 
and molecules again completely acquire the properties which they previously had 
in the dark. Thus, between the first curve and the second (between 7 and 8) the 
light was removed for 16 hours and 48 minutes, between the third and fourth 
(between 47 and 48) for 17 hours, between the fourth and fifth (63 and 64) the light 
was interrupted only for 5 minutes, and the rest of the time (39 minutes) it was 
again exposed to the light. We nevertheless find that, after 17 hours, the “induction 
period ” of the second curve did not again become as slow as it was in the first 
curve; after the third interruption of the light, for about the same 17 hours, the 
“induction period” was almost quite the same—starting with almost the same 
values of K ; again, during the fourth interruption of the light for only a few 
minutes, the chlorine and carbon monoxide of the system returned only so little 
to the properties which they had at first in the dark that no marked variation 
in the value of the velocity constant K could be established. Thus we find a 
remarkable analogy (though not a reversible identity) between the period of “ deduc- 
