PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EEREAECHES. 383 
The first action was observed in Experiment 4 after 6 minutes ; in Experiment 2 after 
4 minutes ; in Experiment 1 after 3 minutes ; and in Experiments 5 and 6 a considerable 
action occurred duiing the first minute. The maximum action was obtained in Experi- 
ments 5 and 6 after 15 minutes, in Experiment 1 after 11 minutes, and in Experiments 
3 and 4 after 9 minutes. 
From these experiments we may conclude, that the time which elapses from the first 
insolation until the first traces of the photo-chemical induction become visible, and until 
the maximum action is attained, is according to circumstances extremely difierent. 
One of the chief conditions modifying the induction relates to the volume of the gas 
exposed to the light. The influence of the mass of the gas on the induction is easily 
shown by exposing the chlorine and hydrogen mixture in cylinders of equal surface, but 
unequal length, to the same amount of light under precisely similar conditions. For this 
purpose we employed the glass cylinders ah*eady described in our former communication, 
and represented by fig. 1, Part I. The relative lengths of the cyhnders No. 1, No. 2, and 
No. 3 were respectively 2 ‘6, 1*5 and 1-0. 
The experiments were conducted in the following manner : — Having proved by various 
experiments, which we here omit, that the gas could be preserved in these cylinders for 
twenty-four hours by exclusion of light without undergoing any appreciable change, we 
connected the cylinders together by caoutchouc* joinings, as represented in fig. 1, Part I., 
and at the end of the system we placed the tube r of known capacity. After the dried 
electrolytic gas entering at the tube c had passed through the system for a considerable 
time in the dark, all the caoutchouc joinings were closed by suitable screw-clamps, any 
alteration of temperature during the closing being carefully avoided, and the temperature 
T and the barometric pressure P were noted. In order to be convinced that the gas 
was pure, we analysed the contents of the tube r according to the iodometric method. 
If the amount of chlorine found from the formula given in Part I., 
773 Cl / , , X 
C = — ) 
si 
CP 
agreed with the amount calculated according to the formula = +o-oo366 T) x 0*76 
the capacity of the tube, we could rely on the purity of the gas in the cylinders. The 
cylinders thus filled were employed in the following experiments. 
Experiment I. — Cylinders I, 2, and 3 were placed close together and exposed in 
exactly the same position for two hours to the diffuse light from a cloudless sky. The 
temperature on closing the cylinder was T=I2°‘9 C., and the atmospheric pressure 
P=0-7533 ; the capacity C of the tube r, fig. 1, was 34-81 cub. cent. ; of cylinder 1, 190-24 
cub. cent. ; of cylinder 2, 113-03 cub. cent.; and of cylinder 3, 73-42 cub. cent. Analysis 
gave,— 
* Eor these joinings common sheet caoutchouc must he employed, the chloride of sulphur formed from 
the vulcanized tubing rendering the surface of the glass plates dim. 
