AND CHLORINE UNDER THE INFLUENCE OF LIGHT. 
91 
with regard to damp chloriiie. The light from a Welsbach Imrner was allowed to 
fall on the bulb already described, and the rise in temperature and expansion were 
observed. The expansion was proportional to the rise in temperature as far as the 
accuracy of the method admits. 
The following table gives the expansion, the rise in temperature, and the expansion 
for ’01° C. obtained in a series of experiments of this kind. 
Expansion. 
Rise in temperature. 
Expansion for •OF G. 
48 
°C. 
•068 
7-05 
50 
•053 
9-4 
50 
•060 
8-3 
73 
•092 
7-9 
85 
•113 
7-5 
The mean of the numbers in the last column is 8'03. From the dimensions of the 
bulb and capillary tube a rise of temperature of •01° C. should produce an expansion 
of 8’2 scale divisions. It thus appears that the expansion observed is accounted for 
by the rise in temperature of the gas. To test whether the slight wnrming of the 
apparatus affected the expansion, by liberating some of the chlorine dissolved in the 
water in the bulb, the rise in temperature of the chlorine was observed and the 
exj)ansion due to the warming of the room during the course of the day. This 
expansion was very slow and was 9 scale divisions for a rise of temperature of '01° C. 
The amount of chlorine, therefore, evolved is so small that it can be neglected. 
2. The Final Contraction. 
On cutting off the light after insolation has been proceeding, an increase in the 
rate of contraction is first observed. For example, the mixture of hydrogen and 
chlorine was exposed to light, and a continuous supply of fresh gas was kept running 
into the insolation bulb, to keep the index on the scale. After the maximum rate of 
action was reached—observed by stopping the supply of fresh gas for a short time — 
the light was cut off and the time of contraction through various lengths of the index 
scale noted. Fig. 8 represents the course of the contraction. The maximum action, 
when the light was on the mixture, was about 100 scale divisions in 4 seconds. It 
will be noticed that the initial rate of contraction, after the light was cut off, was 
about 100 scale divisions in 2 seconds. The behaviour on darkening before the 
maximum rate of action is reached is shown in the curves in fig. 9. In each case the 
phenomena are essentially similar to the case when the action, before light is cut off, 
has reached its maximum value. The rate of contraction is, on cutting off the light, 
greater at first than before the darkening, and gradually diminishes until the index 
comes to rest. 
N 2 
