AND STATICS UNDER THE INFLUENCE OF LIGHT. 
339 
answer could be afforded to the question whether the velocity of reaction is a function 
of the varying masses or concentrations of the combining substances or not, unless 
the hj^drochloric acid formed is as rapidly removed as it is formed during the reaction. 
A secondary reaction would thus take place which would complicate the principal 
reaction. For these and similar reasons* Davy’s reaction (CO + CL = COCL) was 
chosen for study. The reaction occurs only in light, the gases can he used in a dry 
state, and the volume of the mixed gases changes, two volumes of the original 
mixture producing one volume of the compound. 
Since highly dried gases combine very slowly, it was obvious that an artificial 
source of light must be employed, which should be at the same time of great actinic 
power and susceptible of being maintained constant in its intensity for long periods. 
At the suggestion of Dr. Ludwig Mond the acetylene light was finally decided on, 
as it is rich in actinic rays and its spectrum closely resembles that of sunlight. 
Apparatus was devised for producing a flame constant in intensity and composition. 
Arrangements were made for measuring the intensity of the light with an accuracy 
to OT per cent., and suitable methods chosen for the preparation of pure chlorine and 
carbon monoxide. A preliminary study extending over two and a half years was 
made of the conditions under which the experiments must be conducted so as to give 
not only concordant but accurate results, i. e ., results free from constant errors. The 
general arrangement of an experiment was as follows :—- 
Pure, dry chlorine and carbon monoxide were freshly prepared in the dark, and 
there introduced into a reaction vessel, connected with a manometer to indicate the 
variation of pressure during the reaction. The reaction vessel was placed behind a 
quartz window, in a water bath kept at a constant temperature, and exposed to a 
powerful acetylene light. The acetylene light was kept of constant intensity and 
free from smoke by means of a special generator, balance governor, regulating tap, 
purifier and burner. The intensity of the acetylene light was measured by means of 
a Rubens’ thermopile and the deflections of a galvanometer, and the observed values 
standardized by means of a Clark cell and manganin resistances. The variations of 
the pressure in the reaction vessel were read on the scale of the manometer by 
means of a cathetometer. After applying corrections for the variation of 
temperature of the bath, atmospheric pressure, &c., the experimental results 
representing the rate of formation of carbonyl chloride from chlorine and carbon 
monoxide were subjected to a theoretical investigation. 
* See Mellor, ‘Journal of the Chemical Society,’ 1901, p. 227. 
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