98 
MR. P. V. SEVAN ON THE COMBINATION OF HYDROGEN 
the increase of intensity of the light, and in a greater ratio than the increase of light, 
and that the tiine of exposure t('» reach the niaxinuim action decreases with increase 
Fig. 13. Abscissfe, time in minutes from beginning of insolation. 
Ordinates, HCl formed. 
Curve I, fresh gas. Curve H, after 22 hours dark. Curve HI, after | hour dark. 
Curve lY, after 5 minutes dark. 
of light, but in a less ratio than the increase of the light. These conclusions were 
confirmed, but as they were so well established by Bynsex and Boscoe, there is no 
need to give the results of any of the experiments on these points. 
§ 3. The Effect of Impurities. 
One of the most remarkable facts connected with the action under consideration is 
the large effect on the rate of combination produced by a small quantity of impurity. 
Bunsen and Eoscoe showed that the addition of paiTs of oxygen reduced the 
maximum action from 100 to 9‘7. It is extremely difiicult to prepare the gas 
mixture with a definite quantity ol impurity in it, and as yet no experiments have 
been performed which are sufficiently comparable to determine the relation between 
tire quantity of the impurity and the rate of the action. To quote the words of 
Bunsen and PtOSCOE : “ It is perfectly useless to collect the electrolytic gas in a large 
vessel, then mix it with the impurity, and afterwards to allow the mixture to pass 
through the apparatus, for there is no possible means of collecting this pure mixture 
of hydrogen and chlorine in large masses, and again forcing it out in a given 
