,610 PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHOnCAL EESEAECHES. 
amount of colouring matter contained in the unit quantity of water, and I the fraction 
of the unit amount of light transmitted through the unit length of the several cylinders. 
Series of Expeiiments 
Exp. 1. 
Exp. 2. 
Exp. 3. 
lo 
7*41 
8-13 
8-22 
I 
4-28 
4-73 
4-87 
h 
0-578 
0-582 
0-592 
h 
11-8 mm. 
27*4 mm. 
83-8 mm. 
e 
1-000 
0-4306 
0-1408 
1 
0-04895 
0-02123 
0-00707 
€ 
I 
0-204 
0-203 
0-200 
From the closely approximating values of y we may conclude, that with the chemical 
rays the amount of transmitted light varies proportionally with the density of the 
coloured medium. 
Havmg determined these preliminary points, we may now return to the question 
originally proposed, viz. : — 
In the combmation effected by the light between the particles of chlorine and hydro- 
gen, are the chemical rays expended in a relation proportional to the quantity of hydro- 
chloric acid formed In order to solve this question, it was necessary to determine 
experimentally the coefficient of extinction of pure chlorine for a flame of coal-gas. 
The chlorine used in the following experiments, prepared from bichromate of potash 
and hydrochloric acid, carefully washed and diied, was led through the transparent 
cylinders until all atmospheric an was expelled. Each of the measuroments contained 
in the following Table is reduced from three series of obsen ations, the first of which 
was made without interposed chlorine-cylinder, the second with chlorine-cyhnder, and 
the third again without the cylinder. The mean of the fii’st and thu'd series gives lo, or 
the mtensity of the chemical rays before transmission through the chlorine-cylinder, 
whilst the second series gave I, or the intensity after transmission ; li signifies the length 
of the interposed column of chlorine, P the pressure, and t the temperature on filling 
the cylinders with chlorme. 
Series of Experiments VIII. 
Exp. 1. 
Exp. 2. 
Exp. 3. 
Exp. 4. 
lo 
13-51 
10-86 
11-12 
11-40 
I 
3-79 
3-25 
3-23 
6-39 
h 
83-8 mm. 
83-8 
83-8 
27-4 
P 
0-7437 m. 
0-7528 
0-7528 
0-7528 / 
t 
l6°-0 C. 
14-3 
14-3 
14-3 
The amount of light I^ is not that which enters the column of chlorine. This 
