AND STATICS UNDER THE INFLUENCE OF LIGHT. 
347 
vessel (M). The tap (30) was again shut and the india-rubber tube removed from 
the tajD (31). After opening tap (29) and carefully allowing air to pass into (M), the 
vessel (M) was detached from the rest of the apparatus at (32), where the ground 
tube (N) perfectly fitted into the neck of (M). The chlorine was then removed from 
(M) by blowing through a tube introduced into it through its neck ; (M) was now 
replaced on the tube (N) and evacuated. Chlorine was aspirated into (M) and blown 
out until a pretty high vacuum was obtained in all the apparatus. Air was then 
allowed to pass into the vessels which contained the chlorine and the whole again 
evacuated directly by the Fleuss pump, and finally to a high vacuum by the Topler 
pump, in the ordinary way. Chlorine can now be again prepared from the copper 
chloride in (7). 
Experience has shown that the only and perfectly reliable way of getting pure 
gases free from any contamination with air is to remove, before each experiment, the 
chlorine and carbon monoxide (though they are apparently perfectly pure) from all 
the heated vessels as completely as possible, and to immediately prepare perfectly 
fresh chlorine and carbon monoxide. As soon as they are prepared they are sealed 
up in the quartz vessel (or the glass bulb used instead of it) as quickly as possible. 
The Preparation of Pure Gases. 
A. Preparation of Pure Chlorine. (See (7) and (8) in fig. 1, Table I.) 
In order to get chlorine free from any admixture of air and water vapour, which 
prove to be most fatal to the gas mixture, and also of any other gas, the ordinary 
simple methods could not be employed. It was therefore prepared either from 
platinous chloride or cupric chloride in a vacuum. Cupric chloride, suggested by 
Dr. Ludwig Mond, has great advantages in comparison with platinous chloride; it is 
very much cheaper, water can be easily removed from it, and there is no danger that 
oxygen or hydrogen from the air will be absorbed by the residue, as is the case with 
platinum. Besides this, occluded gases cannot be completely removed from the 
platinum unless by exhaustion at a temperature higher than that at which platinous 
chloride gives off chlorine. Cupric chloride, so called “ purissima,” always contains 
hydrochloric acid. This, it was found, cannot be completely removed. The cupric 
chloride was, therefore, prepared from precipitated copper and chlorine, taking all 
precautions to avoid conditions which might contaminate the product with hydro¬ 
chloric acid. Finely divided copper, precipitated from a solution of copper sulphate 
by means of zinc, was placed in a long combustion tube drawn out at both ends. 
The hydrogen current, first washed and dried, was passed over the copper (heated to 
a dull red heat) for several hours to remove the film of oxide. The tube was next 
sealed at one end and exhausted, and air was then allowed to pass into the tube, 
which was again exhausted and heated. The hydrogen was thus completely removed. 
2 Y 2 
