912-13.] The Absorption of Light by Inorganic Salts. 
35 
III. — The Absorption of Light by Inorganic Salts. No. VII.: 
Aqueous Solutions of Iron Salts. By John S. Anderson, 
M.A.^ B.Sc., 1851 Exhibition Research Scholar (Glasgow). Com- 
municated by Dr R. A. Houstoun. 
(MS. received October 18, 1912. Read January 6, 1913.) 
The absorption spectra of aqueous solutions of ferric chloride have been 
examined qualitatively by Jones and Anderson,* and quantitatively by 
Ewan,-f but Ewan’s measurements were confined to very dilute solutions. 
It was thought, therefore, that quantitative measurements might profitably 
be carried out on more concentrated solutions of ferric chloride and on 
solutions of other salts of iron. 
The iron salt which has received most attention from investigators is 
ferric chloride, the chief researches carried out on this salt being mainly 
chemical. The hydrolysis of ferric chloride has engaged the attention of a 
great number of workers. Pean de St Gilles J examined the decomposition 
of ferric salts which is produced when aqueous solutions of the salts are 
heated. Graham § showed how to prepare colloidal ferric hydroxide by 
dialysis. Krecke || studied the amount of hydroxide formed in aqueous 
solutions of ferric chloride of different concentrations and at different 
temperatures. He found that the amount of decomposition increases with 
the temperature and with increase in dilution. Ewanf showed that the 
hydroxide formed in solutions of ferric chloride containing less than ’005 
gramme-molecules per litre contains no chlorine. He found that the absorp- 
tion spectrum of ferric hydroxide obtained by dialysis is not the same as that 
of hydroxide formed when ferric chloride is dissolved in very large 
quantities of water. He explains this fact as being probably due to the 
former hydroxide consisting of larger molecular groups than the latter. 
MalfitanoA using a collodion membrane to dialyse colloidal solutions of 
ferric chloride, found that the membrane, after being stained a deep red 
* Jones and Anderson, “The Absorption Spectra of Solutions,” Carnegie Institution of 
Washington, Publication No. 110, 1909. 
t Ewan, “On the Absorption Spectra of Dilute Solutions,” Proc. Boy. Soc., lvi. p. 286, 
1894 ; lvii. p. 117, 1895. 
f Pean de St Gilles, Ann. Ghim. Phys. (3), xlvi. p. 47, 1856. 
§ Graham, Phil. Trans., p. 209, 1861. 
|| Krecke, Journ. prakt. Ghem. (2), iii. p. 286, 1871. 
% Malfitano, Gompt. rend., cxlii. p. 1277, 1906. 
