1911-12.] Absorption of Light by Inorganic Salts. No. VI. 51 
The width of the spectroscope slit was less than in the previous deter- 
minations of the absorption of concentrated solutions of cobalt chloride, and 
independent readings could consequently be taken more closely together in 
the spectrum. The following table gives the effect of heating a solution of 
strength c = 3T0. Each value for the cold solution is the mean of two 
determinations ; each value for the hot solution is the mean of three except 
in the case of the last three wave-lengths, when only one determination was 
made. 
Values of A. 
c = 3'10 ; d = - 046 cm. 
A. 
Temp. 
Cold solution. 
Temp. 
Hot solution. 
434 w 
16° 
2-40 
84° 
2*49 
444 
3 37 
375 
453 
4-24 
4-52 
463 
6T1 
6T4 
475 
6-84 
7-75 
486 
8*10 
9-95 
499 
9*11 
12-0 
514 
9-49 
130 
529 
8-82 
14-0 
547 
5-58 
12-2 
563 
3-74 
101 
582 
1-82 
9-91 
602 
1-44 
18-7 
625 
1-58 
76-8° 
17-4 
653 
1-62 
70° 
170 
687 
1-96 
61-5° 
13-2 
797 
1*77 
The increase in the value of A found on heating the solution to a 
temperature over 80° is by this method shown to be less than appeared 
from the method of heating the cell in hot water to about 90°, removing it, 
and allowing it to cool before the slit. This difference can be easily 
explained. 
In the first place, A increases decidedly more rapidly in value between 
80° and 90° than between 70° and 80°, and two values of A at 85° and 75* 
respectively obtained by the previous method, as the cell cooled from 90° 
to 70°, which it did in 3 minutes, would not give as their average the 
correct value of A for 80°. But there is an additional cause of the 
difference. In heating by the method described in the preceding pages I 
noticed that for some minutes after the solution had reached a steady 
temperature of about 84° the value of A continued to increase. This 
indicates that the change in absorption lagged behind the change in 
