PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAU EESEAECIIES. 395 
ments verify this supposition. The determinations were so conducted that a small quan- 
tity of uninsolated gas, measured on the scale, was allowed to mix with the insolated 
gas, which had been brought to the induction-maximum, and the time observed which 
elapsed before the maximum action was again reached. 
Series of Experiments X. 
Time of obser- 
vation in minutes. 
Induced gas. 
Ditto, with -5-?- 
1000 
non-insolated gas. 
Ditto, with 
1000 
non-insolated gas. 
0-5 
7 ' 5 * 
4-0 
4-0 
1-0 
6*5 
4-0 
6-0 
1-5 
7-0 
4-5 
6-0 
2-0 
8-0 
3-0 
5-0 
2-5 
7-0 
5-0 
8 - 0 * 
3-0 
7 - 0 * 
7-5 
3-5 
7*5 
7*5 
4-0 
7-5 
8-0 
4*5 
7-5 
7*5 
5-0 
7*5 
These experiments show that the non-insolated gas acts upon the insolated in the 
same manner as a contact-substance, an addition of 0'6 per cent, of the first producing 
a diminution of the maximum from 100 to 55‘6*. 
The curves, Plate XXI. fig. V., represent the relation in which the induction of the 
chlorine and hydrogen stands to the mass and nature of the foreign admixtures. The 
abscissae express the volumes of the foreign gas to 1000 volumes of the normal mixture, 
and the ordinates the action effected by equal amounts of light under the influence of 
these admixtures. 
If the effect produced by the expansion of the gas from the addition of the foreign 
body were ehminated, and if the action were reduced to the unit of intensity of light, 
we might construct curves of the values thus found, which must express the relation 
existing between the catalytic action and the substance and mass of the contact-body. 
Our experiments are, however, as yet not extended enough to enable us here to enter 
more fully into this new field of research. 
Our experiments have led us to another very singular relation, which is of great in- 
terest as playing an important part in the whole of the phenomena of photo-chemical 
induction. The normal gas from which all light has been excluded, needs, as we have 
shown, a certain length of exposure before the maximum action is attained. The 
length of exposure is not altered when the pure gas is allowed to stand for some time in 
the dark before insolation. If, however, the gas contains such minute traces of impuri- 
ties that the maximum action is not thereby lessened, we still find evidences of the pre- 
sence of these admixtures in the fact, that on standing in the dark the time required for 
the attainment of the maximum induction is considerably shortened. This phenomenon 
* The mean of the second vertical column =100. 
3 F 2 
