1910-11.] Absorption of Light by Inorganic Salts. No. I. 527 
by something between F04 and 0*96 to make them correct. The changes 
produced by concentration are, however, in many cases much greater than 
4 per cent. The following table gives the results : — 
Values of A for more Concentrated Solutions. 
Scale 
Reading. 
A. 
<7 = 1 mm. 
d = 5 mm. 
c = 3T0. 
Chloride. 
c = 2-78. 
Bromide. 
c = 2-96. 
Iodide. 
c = 3*66. 
Nitrate. 
c = 2-00. 
Sulphate. 
50 10 
•684/* 
2*00 
•67 
•41 
•20 
T17 
49 58 
•720 
0-41 
•37 
TO 
TO 
•078 
49 49 
•750 
•37 
•23 
T2 
•09 
•057 
49 40 
*794 
T6 
T6 
T2 
•073 
49 31 
•850 
T8 
•23 
•20 
T6 
T36 
49 22 
•910 
•29 
T5 
T7 
T14 
49 13 
•980 
•38 
•26 
•23 
•31 
•211 
49 4 
1-07 
•74 
•70 
•74 
•66 
•60 
48 55 
1*17 
1-43 
1-52 
1-37 
1*20 
I'll 
48 46 
1-27 
1-92 
2-00 
1-64 
1-54 
1-47 
48 37 
| 
1-38 
1-67 
1-64 
1-26 
1*19 
These results are the mean of two independent determinations in the case of 
the chloride, nitrate, and sulphate. One determination only was made in the 
case of the bromide and iodide. One cell with a piece of glass in it held the 
solution, another, with a similar piece of glass in it, the water ; for the second 
determination, if two were made, the solution was put in the other cell. 
The fluoride is not given here, as the solution used for the last table was 
a saturated one. The solutions of the chloride and sulphate were saturated 
solutions prepared by leaving the water in contact with an excess of salt 
for days. For each wave-length the effective width of the thermopile and 
the width of the slit were the same as for the former concentration. The 
thinner layer of water has enabled us to gain an additional point in the 
infra-red, and it is seen that the end absorption has reached a maximum 
and is beginning to decrease. This conclusion is supported by results for 
the weaker solutions for the same wave-lengths, which were not given in 
the table on account of their uncertainty. It may be stated that two cobalt 
glasses examined gave an absorption band in the infra-red with a maximum 
at about IT 5/ul. Abney and Festing * also find one band in the infra-red 
for cobalt glass, but they place it at 1'32/x. 
It will be noticed that increased concentration always produces the same 
effect except in the case of the sulphate, namely, A increases at both ends of 
* “Absorption-spectra Thermograms,” Proc. Boy. Soc., xxxviii. p. 77 (1885). 
