PE0I:ESS0E BUNSEI^ A:ffD DE. H. E. EOSCOE’S mOTO-CHEMICAL EESEAECHES. 911 
In the following Table (XVII.) the numbers calculated by means of this formula are 
compared with the action actually observed : — 
Table XVII. 
No. of the 
experiment. 
Sun’s 
zenith-distance. 
Calculated 
chemical illumination 
in degrees of light. 
Observed 
chemical illumination 
in degrees of light. 
1 
57 35 
67-9 
63-1 
2 
50 51 
85-8 
89-2 
3 
46 8 
96*4 
93-0 
4 
68 34 
33*1 
26-2 
5 
76 30 
9-2 
5-5 
6 
73 49 
16-3 
15-5 
7 
71 37 
24-5 
22-4 
8 
68 34 
33-1 
27-9 
9 
67 30 
36-6 
38-9 
10 
64 42 
47*9 
45-9 
1 11 
60 48 
58-3 
62-6 
! 12 
58 11 
66*2 
67-6 
The probable error of the observations is 
0‘6745/yX = degrees of light. 
This mean en’or must be regarded as extremely small when we consider, — 1st, the 
great difficulty experienced in keeping the mixture of chlorine and hydrogen at the 
maximum degree of sensibility during the whole range of experiments; 2ndly, the 
numeious i eductions by means of which all the disturbing influences must be elimi- 
nated ; and Srdly, the slight alterations in the extinction of the light which local 
changes in the air’s transparency may effect. 
Formula (14.) shows that the sun’s rays before their entrance into the earth’s atmo- 
sphere would effect an illumination of 318'3=L degrees of light. If the rays pro- 
ducing this degree of illumination passed through an infinitely extended atmosphere of 
chlorine and hych-ogen until they were completely extinguished, the absolute height (H) 
of the column of hydrochloric acid, measured at 0° and thus produced in one 
minute, is found from formula (4.), already given on page 888, 
H-X 1 T 
g’l-lO””*' ■ 
In the experiment from which the number 318'3 is obtained, one degree of light 
effected a combination per minute of V=0'00001155 cubic metre of hydrochloric acid 
measured at 0° and 0™’76. According to our former experiments, the coefficient of 
extinction of sunlight for chlorine and hydrogen is a= metre. The internal area 
of the insolation-vessel was y=0’00033 square metre. The internal diameter of the 
same, d=0'0094 metre. The gas in the insolation-vessel was contained, during the 
obsenation, under a pressure of P=0'7551 metre, and at a temperature of 18° C., for 
6 D 2 
