396 PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 
is best observed when gas has been led through the apparatus until the traces of gaseous 
admixture (only to be estimated as millionths of the whole mass) have become so small 
that their absence would not diminish the resistance to combination of the induced 
gas. In order to estabhsh this fact we have made many experiments, one of which we 
subjoin; the insolation-vessel contained only about 3 cub. cent, of gas, and many litres 
of the chlorine and hydrogen mixture had passed for two days through the apparatus. 
The first horizontal division of the follovsdng Table contains the number of the experi- 
ments according to the order in which they were made ; the second division contains the 
times during which the newly-evolved gases stood in the dark previous to insolation ; 
and the third division gives the length of time which the gas was led through the instru- 
ment between each set of observations. The numbers in the corresponding vertical 
columns represent the photo-chemical action for the times found in the first vertical 
column. 
Series of Experiments XI. 
No. 1. 
No. 2. 
No. 3. 
No. 4. 
No. 5. 
No. 6. 
No. 7. 
No. 8. 
No. 9. 
No. 10. 
0 ' 
30 ' 
0 ' 
30 ' 
0 ' 
30 ' 
0 ' 
30 ' 
0 ' 
40 ' 
t' 4 ' 
' 20 ' t 2 
1 
.' 4 
/ 
1 
? 
2-1 
3-1 
6-2 
4-3 
1*0 
10-0 
2-1 
6-3 
2-1 
2 
6*3 
9-4 
8-3 
15'6 
16-7 
21-9 
19-3 
21-8 
20*8 
12-2 
3 
7-3 
20-8 
10*4 
22-9 
19-8 
28 - 1 * 
22-9 
27 - 0 # 
21-9 
21-9 
4 
10-4 
21-9 
11-5 
23*3 
21-9 
27-8 
25-5 
27-3 
25-0 
24-3 
5 
12-6 
24-0 
15-6 
25-3 
23-9 
28-3 
26 - 1 * 
27-3 
28 - 5 * 
26 - 7 * 
6 
14-6 
26 - 3 * 
17-7 
27 - 3 * 
26 - 3 * 
29-4 
26*8 
29-3 
28-3 
25-8 
7 
? 
27-3 
19-8 
26*9 
25-3 
28-8 
26-8 
28-0 
26*3 
8 
19*2 
26-3 
22-3 
27-0 
27*3 
28-0 
9 
23*3 
27-9 
26 - 3 » 
29-8 
10 
24-3 
26-3 
11 
24-3 
26-9 
12 
28 - 0 * 
13 
28-0 
14 
28-0 
1 
These figures show, — 
(1) That the resistance to combination effected by the slightly impm'e gas diminishes 
when the gas is allowed to stand in the dark. 
(2) That the diminution of the resistance ensuing spontaneously in the dark becomes 
less as the purity of the gas increases by longer saturation. 
(3) That this diminution of the resistance is observed after the gas is so nemly pme 
that on further saturation no increased maximum induction is perceptible. 
The experiments give the following maxima of induction arranged in the order in 
which the observations were made : — 
t Evolution-vessel changed, and gas led through for some time. 
