PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 3-57 
chloric acid contained in the liquid electrolyte does not diminish below a certain amount. 
The composition of the absorbed gaseous mixture varies with every change of tempera- 
ture, whereas the composition of the free gas remains the same for all temperatures, pro- 
vided that the statical equilibrium is not disturbed by alteration of the temperature and 
pressure during the evolution of the gas. 
After the statical equilibrium has been established, the gas invariably contains one 
volume of chlorine to one of hydrogen. This important fact, which is strictly conform- 
able to the laws of gas absorption, is deduced from the following analyses made with 
electrolytic chlorine and hydrogen evolved both from carbon and platinum poles of dif- 
ferent dimensions, by cm-rents of various degrees of intensity. In order accurately to 
measure the volume of gas required for analysis, we allowed the dried electrolytic gas to 
pass through the glass cylinders represented in Plate XVII. fig. I. These cylinders, of 
the same diameter, but of various lengths, are closed by surfaces of plate glass pressed 
upon the ground ends of the cylinders by means of the screws aaa^ and the joint 
rendered perfectly au’-tight by a thin roll of white wax squeezed flat between the two 
surfaces of glass. Each cylinder is furnished with a delivery- and exit-tube ground into 
the glass, and firmly fastened by cements of gutta-percha and gypsum. The gases passed 
through the cylinders until the whole of the atmospheric air was displaced ; and after 
the height of the barometer and the temperature (which was kept constant during the 
experiment) had been observed, the caoutchouc joinings were closed by screw-clamps, and 
one of them du’ectly opened under a solution of iodide of potassium. The solution rose 
immediately into the vessel and liberated a quantity of iodine exactly equivalent to tire 
amount of contained chlorine. A volumetric analysis* of this liberated iodine gave us 
the amount of the chlorine contained in the gas. This amount, subtracted from the 
total volume of gas contained m the vessel, gave the volume of hydrogen. 
If a signify the amount of iodine in grammes contained in one division of the burette, 
n the number of measures of sulphurous acid required for complete decolorization of 
the iodine liquid, t the number of di\isions of the burette which represents one measure 
of sulphiu’ous acid, and t' the number of divisions which must be added to the liquid to 
which n measm’es of sulphurous acid have been added until the blue colouring appears ; 
and if the atomic weight of chlorine Cl=221’87, and that of iodine 1 = 794-37, and the 
specific grawty of chlorine gas s=2-45307, the volume of chlorine contained in the 
vessel in cubic centimetres is equal to 
( 1 .) 
If the heights of the barometer and thermometer on closing the vessel were respectively 
P and T, and if the capacity of the vessel expressed in cubic centimetres is equal to C, 
the total volume of gas present, reduced to 0°C. and 0'"-760 expressed in cub. cent., is 
found from the equation 
r_ CP 
(1+0-00366 T) X 0-76 
* Ann . Cfe. Pham. Lsxxvi. p. 265, and Quart. Journ. Chem. Soc. viii. p. 219. 
