REFRACTIVE INDEX OF GASES ON TEMPERATURE. 445 
The results on 14th and 17th March are quite anomalous and beyond ordinary 
error of observation, and my inference is that more impure gas had come off at the 
highest temperature. I therefore refilled with fresh COg, keeping the tubes at about 
80° C. while filling. 
The following table gives the results obtained on the new gas. 
New Carbon Dioxide, put in 18th March, 1902. 
j 
Date. 
Temperature 
tubes. 
Temperature 
of 
manometer. 
Ratio. 
Corrected 
ratio. 
Multiplied l)y 
1 + -00375;:. 
1+-00380t 
1+ -00385t 
1 
C. 
° C. 
i 9th March 
10-5 
17-3 
9-673 
9-700 
10-080 
10-085 
10-090 
1 19th „ 
10-5 
17-4 
9-659 
9-685 
10-075 
10-070 
10-075 
20 th ,, 
74-8 
17-3 
7-832 
7-845 
10-045 
10-075 
10-105 
! 20 th „ 
74-9 
17-4 
7-833 
7-845 
10-045 
10-075 
10-105 
21 st 
21-7 
16-7 
9-259 
9-285 
10-040 
10-050 
10-060 
21 st 
21-7 
17-0 
9-276 
9-300 
10-055 
10-065 
10-075 
24 th „ 
31 -55 
14-4 
8-955 
8-975 
10-035 
10-050 
10-065 
24th „ 
31-45 
14-4 
8-984 
9-000 
10-060 
10-075 
10-090 
Mean 
10-055 
10-070 
10-085 
Greatest variation . 
+ -025 
+ -015 
+ -020 
- -020 
- -020 
- -025 
No alteration appears to have taken place in the gas during the experiments. The 
results are also in very close agreement witli the results on the former gas. Both 
sets are shown on the curve for CO 3 . 
We may take the ratio as 
10-070 ± -01 
1 -f t (-00380 ± -00003) 
and the refractive index for CO 3 is 
P — f "T 
-0004510 ± -0000005 p 
{1 + t (-00380 ± -00003)1 76‘ 
Hydrogen. 
The gas was prepared from zinc and moderately diluted hydrochloric acid. The 
apparatus was exhausted and filled about seven or eight times at the temperature of 
the room. The gas was dried by phosphoric pentoxide. 
Observations for a week at about 10° C. indicated a gradual increase in the 
refractive index, which I attribute to carbon dioxide comina; off the walls. When 
this effect had ceased, the apparatus was exhausted and kept exhausted for a few 
