394 PEOFESSOE BIIXSEJs AXD DE. H. E. EOSCOE’S PHOTO-CTEE^nCAL EESEAECHES. 
employed. For although the hydrochloric acid formed is absorbed very quickly by the 
water, still a certain amount must always be mixed with the normal gas duimg expo- 
sure to light, and this amount must vary with the size and shape of the insolation-vessel. 
Fortunately, however, the catalytic action of the hydrochloric acid upon the mixture of 
chlorine and hydrogen is, as the foUowmg experiments show, so small, that it may he 
entirely disregarded. 
The experiments were carried out as follows : — In the first place, the insolation-vessel 
was filled with pure water and the maximum action obsen ed ; hydrochloric acid of spec, 
grav. 1T48 was then placed instead of the water, and the observations not made use of 
until, after repeated saturation, the maximum action was attained. In order to deter- 
mine the amount of hydrochloric acid contained in the gaseous mixture at the tempera- 
ture I6°-4 of the experiment, a litre of air was slowly led, first, thi’ough a small quantity 
of hydrochloric acid of the above strength, and next through a bulb apparatus containing 
an alkaline solution free from chlorine. The solution of alkah acidified with nitric acid 
and precipitated by a salt of silver gave 0‘0086 grm. chloride of silver, which is equiva- 
lent to 1*3 cub. cent, hydrochloric acid gas in one litre of gas at 16°'4 and 0™-7516. The 
normal gaseous mixture contained therefore 1‘3 pro 1000 hydrochloric acid. The photo- 
chemical measurements with this mixture gave the follo'vvmg results : — 
Series of Experiments IX. 
Time of 
observation, 
in minutes. 
Gas with pure 
water. 
Ditto, saturated 
again. 
Gas with , 
1-3 pro niille 
hydrochloric acid.; 
1 
0 
i 
1 
10-4* 
10-4* 
2 
12-0 
9-9 
12'5^ 
3 
12-0 
11-0 
13-0 
4 
12‘5 
10-4 
9-4 
5 
11-5 
11-5 
8-3 
6 
8-3 
11-5 
9-4 
7 
10-3 
9-4 
8 
10*1 
12-3 
9 
12-1 
10 
12-1 
11 
10-1 
12 
IM 
The mean of the fii'st series of observations is 10-9, of the second 10-8, and of the third 
10'9. This exact agreement, which was verified by other experiments, shows — 
(1) That an amount of 0T3 per cent, of hydrochloric acid contained in the normal gas 
exerts no perceptible action on the induction. 
The complicated law which, as we have seen, regulates the increase of the induction 
of the chlorine and hydrogen mixture mider the influence of light, renders it possible 
that the presence of uninsolated gas may have precisely the same action on the insolated 
gaseous mixture as the foreign gases have been shown to exert. The following experi- 
