386 PEOFESSOE BENSEN A]ST) EE. H. E. EOSCOE’S PHOTO-CHIEnCAX EESEAECHES. 
of action in the cylinder 83 millims. long was not perceptible, whilst Exj-eriment 2 of the 
same series showed that in the cylinder 32-0 milhms.long, the action amormtedto 73 per 
cent. The full explanation of this singular phenomenon will be given in experiments which 
we shall communicate at the end of this, and in the next Part of this research. We shall 
there show that the action of hght rapidly decreases "uith the depth of the insolated gas, 
and that the combining power of the chlorine and hydrogen mixture diminishes in the 
dark, or on exposure to a smaller amount of light. If the particles of the induced gas are 
brought by diffusion to a depth in which the mtensity of the hght is much decreased, 
they must therefore lose a portion of their combining power. On this account the layer 
of insolated gas employed for experiments on photo-chemical iuduction should be as thin 
as possible. For this purpose we have employed the insolation-vessel represented in 
Plate XVII. fig. 2.- This flattened vessel was made by pressing a bulb blown before 
the blowpipe, whilst still red-hot, between two wet pieces of wood, so that the thickness 
of insolated gas did not exceed 3 milhms., and all differences in the insolation in the 
various depths could be disregarded. 
The relation which the intensity of the light stands to the induction next engaged oru 
attention. The source of light employed for the experiments on this subject was the 
flame from the annular burner previously described. The rays horn the flame passed 
first through a large plano-convex lens by which they were concentrated, and afteiwards 
through a screen of water 63-0 milhms. in thickness, contamed between two parahel 
plates of glass, by which, as preliminary experiment showed, all distuihing action of heat 
was perfectly excluded. The lens was furnished wuth an arrangement of screens, by 
means of which any desired segment of the lens could be left open, and the amomit of 
light thus regulated. 
The following experiments made with a chlorine and hydrogen mixture wliich had 
attained the constant maximum action, show the influence of the intensity of the light 
on the photo-chemical mduction. 
Series of Experiments IV. 
Experiment 1. 
Experiment 2. 
Experiment 3. 
Experiment 4. 
Amount of light = 
1 - 0 . 
Amount of li 
ght = l-78. 
Amount of li 
2:ht = 2'45. 
Amount of light = 4-] 
7 . 
Time in 
Action 
Time in 
Action 
Time in 
Action 
Time in 
Action 
minutes. 
in 1 minute. 
minutes. 
in 
L minute. 
minutes. 
in 
1 minute. 
minutes. 
in 1 minute. 
a. 
h. 
c. 
d. 
a. 
i. 
c. 
d. 
a. 
b. 
c. 
d. 
a. 
b. 
0 
0 
0 
0 
1 
0-0 
0-0 
O'O 
1 
4-2 
2-1 
3*1 
1 
? 
5*2 
2-6 
1 
65*6 
2 
0-0 
0-0 
0-0 
2 
7*3 
10*8 
9*0 
2 
36-5 
65*6 
51-0 
2 
122*1 
3 
0-0 
0-0 
0-0 
3 
44-8 
33-1 
38*9 
3 
71*4 
80*1 
75*7 
3 
128-0 
4 
0‘0 
0-0 
0-0 
4 
51*0 
53-7 
52-3 
4 
76-4 
78-0 
77*2 
5 
0*0 
0-0 
0-0 
5 
54*3 
56*2 
55-2 
6 
2*1 
2-2 
2*2 
7 
14-6 
3-1 
8-9 
8 
29-2 
21-8 
25*5 
9 
31-4 
29-2 
30-3 
10 
30-1 
32-7 
31-4 
