1910-11.] Absorption of Light by Inorganic Salts. No. II. 533 
Afterwards more concentrated solutions of the salts were experimented 
on. On account of the greater concentration it was necessary to use a 
thinner layer of solution. At first an attempt was made to make cells of 
a suitable thickness by taking two rectangular plates of mirror-glass 4 cm. 
by 3 cm., placing a U-shaped sheet of mica between them and cementing 
the glasses and mica together with seccotine. By using different sheets of 
mica the thickness of the cell could thus be varied at will. But the 
solutions seemed to make the seccotine swell, the solutions were sometimes 
affected by the seccotine and the cells sometimes leaked. So this method 
was abandoned. 
More satisfactory results were obtained by using the same method as in 
the infra-red and placing rectangular blocks of glass in the cells so as to 
diminish the thickness of the layer of solution. The thickness of the block 
was obtained by the screw-gauge, the thickness of the cell with a micro- 
scope, and hence the thickness of the layer was determined. 
The results tabulated below are, in the case of the sulphate and nitrate, 
the mean of three sets of readings. In the other cases only one set of 
readings was made : — 
Values of A for more Concentrated Solutions. 
A. 
c = 3-10. 
Chloride. 
c = 2-79. 
Bromide. 
c = 2’96. 
Iodide. 
c==l *78. 
Nitrate. 
c=l-83. 
Sulphate. 
434 nn 
2-89 
1*56 
1-09 
•73 
444 
1*69 
1-17 
453 
3-76 
3*22 
2*45 
1-75 
463 
3-45 
2-45 
475 
6-22 
5-23 
4*26 
2-86 
486 
5-02 
3 22 
499 
8-95 
7-08 
13 6 
5-62 
3-78 
514 
6-06 
4-02 
529 
8-63 
6*50 
9-53 
4-94 
311 
547 
2-64 
1-72 
563 
3-47 
2-02 
3 83 
1-41 
•87 
582 
•67 
•39 
602 
1-38 
•61 
1*44 
•44 
•26 
625 
•39 
•21 
653 
159 
•45 
•57 
•29 
•18 
687 
•23 
•11 
717 
1-28 
•40 
13 
•15 
•11 
An attempt was then made to study the effect of heating. The diffi- 
culties here are evaporation, slow chemical changes, loosening of the cement, 
and cracking of the glass of the cells. We at first used a method which 
was a development of that formerly used by one of us.* The figure 
* “ Untersuchungen liber den Einfluss der Temperatur auf die Absorption des Lichtes 
in isotropen Korpern,” Ann. d. Phys. (4), xxi. p. 535, 1906. 
