43 
1912-13.] The Absorption of Light by Inorganic Salts. 
The values of pe/m calculated from the formula * 
pe _ , 317OA 0 (X 1 - A 0 ) 
m A 0 2 
are given below in Table III. jp represents the number of electrons or ions 
per molecule of salt causing the absorption band considered, e being the 
charge on the electron or ion, and m being its mass. A 0 is the value of A 
at the maximum of the band, A 0 is the position of the maximum, and A x is 
the wave-length for which A = A 0 /2. 
Table III. — Values of pejm. 
Salt. 
c. 
A 0 . 
A 0 . 
V- 
pejm. 
Fe 2 Cl 6 .12H 2 0 . 
1-0 
•24 
•880^ 
1*300,4 
4T 
10 2 
T 
•50 
•800 
1T50 
8*7 
10 2 
Fe 2 Br 6 .... 
1-0 
4-9 
1-050 
1-350 
4-2 
10 3 
•5 
27 
■970 
1-500 
4*8 
10 3 
T 
1-3 
•920 
1-600 
33 
10 3 
Fe 2 (N0 3 ) 6 .18H 2 0 . . 
1*0 
•34 
•810 
1-200 
6-4 
10 2 
•1 
•51 
•800 
1-300 
1-3 
10 3 
Fe 2 (S0 4 ) 3 .... 
1-0 
•51 
•840 
1-300 
IT 
10 3 
T 
•64 
•840 
1-300 
1-3 
10 3 
Fe01 2 .... 
4-0 
1T7 
1-020 
•570 
1-6 
10 3 
1-0 
1 07 
1-010 
•570 
1-5 
10 3 
FeS0 4 .7H 2 0 . 
1-0 
1-65 
1-020 
•570 
2-3 
10 3 
If m is the mass of the iron atom, e/m should be about 178. 
Further researches on the iron salts require to be undertaken before a 
more exact knowledge of their structure can be obtained. The study of 
the iron salts is somewhat complicated from the point of view of absorption 
spectra by the hydrolytic action which takes place, more especially in the 
more dilute solutions. The systematic study of freshly made-up aqueous 
and other solutions may, however, shed light on the complex question of 
molecular structure. 
The main part of the work connected with this paper was carried out 
in the Natural Philosophy Department of the University of Glasgow when 
I was the holder of a Carnegie Research Scholarship. I beg to express my 
thanks to Dr R A. Houstoun, at whose instigation the work was entered 
upon, and to Professor Zsigmondy, Gottingen, Germany, to whom I am 
indebted for my present knowledge of colloidal chemistry. 
* R. A. Houstoun, “ On the Mechanism of the Absorption Spectra of Solutions,” Proc. 
Roy. Soc.j lxxxii. A, p. 606, 1909. 
(. Issued separately February 13, 1913.) 
