44 
Proceedings of the Royal Society of Edinburgh. [Sess. 
IV. — The Absorption of Light by Inorganic Salts. No. VIII. 
Alcoholic Solutions of Copper, Cobalt, and Nickel Salts in the 
Ultra-Violet. By Alex. R. Brown, M.A., B.Sc., Carnegie Research 
Scholar in the University of Glasgow. Communicated by Dr R. A. 
Houstoun. 
(MS. received October 18, 1912. Read January 6, 1913.) 
The salts experimented on in this research were the chlorides, bromides, 
nitrates, and sulphates of copper, cobalt, and nickel. They were obtained 
from Kahlbaum. Jones and his co-workers * have already investigated 
qualitatively the absorption of alcoholic solutions of some of these salts. 
Also quantitative measurements of the absorption at a few points in the 
visible spectrum have been made by Vaillantf for some of the hydrated 
salts. In the present case solutions of the anhydrous salts were examined. 
The spectrograph and methods used were those adopted by R. A. 
Houstoun and John S. Anderson in a previous research, and described in 
the fourth article of this series.]; 
In the first place it was found necessary to determine the absorption of 
the ethyl alcohol used as a solvent. This has been discussed by Hartley, 
and by Soret and Rilliet. Also in Uhler and Wood’s Atlas of Absorption 
Spectra there is a plate showing the absorption spectrum of ethyl alcohol. 
The latter authors state : “ This liquid transmitted all the strong ultra- 
violet lines, but it absorbed the continuous background from '20//. to about 
•275 jul” The present investigation would tend to show that even beyond 
•275 m there is slight absorption which must be taken into account in quanti- 
tative work with alcoholic solutions. The table on p. 45 gives the value 
of A, the molecular extinction coefficient, for five wave-lengths. Inter- 
mediate wave-lengths have intermediate values of A. 
Of the copper salts, the sulphate is nearly quite insoluble in absolute 
alcohol ; a saturated solution was made for which c, the concentration in 
grm.-mols. per litre of solution, was only *0012. The chloride and bromide 
were easily soluble, and at moderate concentrations gave brownish-green 
and brown solutions respectively. All solutions showed very great absorp- 
tion in the ultra-violet, a photographic plate which was exposed in the 
* Carnegie Institution of Washington, Publication No. 110. 
t Ann. Ghim. Phys. (7), xxviii. p. 213, 1903. 
J Proc. Roy. Soc. Edin ., xxxi. p. 547, 1911. 
