1910-11.] Absorption of Light by Inorganic Salts. No. III. 545 
The values obtained with the thermopile for ’684// and *720 /ul are not 
given by the curves, as, owing to the smallness of the deflections, together 
with the great absorption in that region, they are not accurate. 
The striking feature brought out by the above curves is the great 
increase in absorption in the violet in the case of the chloride and bromide 
produced by increase of concentration and by heating. Yet we have never 
been accustomed to associate nickel chloride and bromide solutions with 
colour changes as we do the corresponding cobalt salts. This is principally 
due to the changes in the cobalt salts being greater, but partly to our eyes 
not being sensitive to violet light. 
In order to study this change further, I made up a set of solutions of 
nickel chloride of gradually increasing concentration and determined A 
as a function of c for the wave-length X = 434 / u / u. The results are given in 
the following table, and illustrated by fig. 5. 
c. 
A. 
4*09 
2-65 
3’07 
1-64 
2-27 
1-27 
2*05 
1-17 
•76 
103 
•34 
•96 
•17 
•94 
•085 
1*04 ? 
VOL. XXXI. 
35 
