TRANSACTIONS OF SECTION B. 529 
5. On Active Chlorine. By C. H. Burcess and D. L. Cuapman. 
The theory which postulates the formation of an unstable additive compound 
in the preliminary stages of chemical change has of late received considerable 
attention and support. It is claimed for this theory that it readily accounts 
for the remarkable influence of water vapour on the rate of chemical change, and 
also for the initial inert period which can be observed when a mixture such as 
hydrogen and chlorine is exposed to light. The theory in question cannot, in the 
opinion of the authors, be accepted as a complete explanation of the latter 
phenomenon, the chief objection to it being grounded upon certain quantitative 
results connected with the induction period with mixtures of carbon monoxide 
and chlorine and hydrogen and chlorine. In addition to carrying out work which 
has led to the above-mentioned conclusion, the authors have discovered several 
new facts of practical importance connected with the subject, which are briefly 
described below. 
It is well known that hydrogen and chlorine inclosed in a Bunsen and Roscoe’s 
actinometer over water do not immediately combine at their maximum rate when 
exposed to light. 
In repeating this experiment of Bunsen and Roscoe it was found that, even 
after the maximum rate of combination had been reached, a fresh period of 
induction resulted on shaking the contents of the actinometer bulb. The period 
of induction produced in this way was not so long as the first period with the 
fresh gases. On again shaking the actinometer another induction period was 
observed still shorter than the second. By constantly repeating this operation 
and re-exposing to light, the contents of the actinometer were at last brought into 
such a condition that no fresh induction period resulted on shaking. 
The experiment shows clearly enough that not only does a fresh mixture of 
hydrogen and chlorine on exposure to light change its condition in such a manner 
as to be ready to enter into combination, but that the aqueous solution of 
chlorine also alters, and ultimately becomes incapable of absorbing the activity 
of the mixed gases. Since the aqueous solution contains a considerable quantity 
of chlorine and very little hydrogen, it seemed probable that the change is mainly 
in the moist chlorine. 
This was made the subject of a series of experiments. At first we were able 
to observe only a slight difference, somewhat similar to that noticed by Bevan in 
the behaviour of the insolated and uninsolated chlorine when mixed with hydrogen 
and exposed to light ; but it was afterwards shown that, if proper precautions are 
taken to keep the chlorine in its active condition during admixture with hydrogen, 
combination occurs promptly on exposure to light. In accounting for the in- 
duction period the main fact to be taken into consideration is, therefore, the 
condition of the chlorine. 
Our attention was next turned towards the discovery of all the possible 
methods of rendering chlorine gas and also its aqueous solution active. It was 
shown that chlorine gas becomes active when heated to 100° C. and then cooled, 
and also when it is acted upon by the silent discharge. An aqueous solution of 
chlorine can be rendered active, ¢.e., incapable of absorbing the activity from 
active oxy-hydrogen gas, (1) by the action of light, (2) by contact with active 
chlorine gas, (3) by heating at a temperature of 100° C., and then allowing to cool. 
The ability to remove the activity from chlorine is possessed in a much more 
marked degree by saline solutions and by acids than by pure water. 
A solution of chlorine which has once been rendered active does not become 
inactive when the chlorine is removed in a vacuum. It can, however, be rendered 
inactive by dissolving in it certain salts such as crystallised barium chloride and 
fused calcium chloride. The foregoing observation suggested the possibility of 
preparing crystallised barium chloride both in an active and an inactive condition, 
and the following experiment showed that this could be done. An aqueous solu- 
tion of barium chloride was rendered active by constantly shaking with chlorine 
in daylight ; the chlorine was then removed in a vacuum, and the water distilled 
off in vacuo. The crystals thus obtained were dissolved in water which had 
been made active by contact with active chlorine. Another solution was made 
1904, MM 
