1912-13.] The Absorption of Light by Inorganic Salts, No. X. 147 
XIII. — The Absorption of Light by Inorganic Salts. No. X. By 
R. A. Houstoun, M.A., Ph.D., D.Sc., and Chas. Cochrane, 
Thomson Experimental Scholar in the University of Glasgow. 
(MS. received February 10, 1913. Read March. 3, 1913.) 
This article describes work done with the spectrophotometer with the 
view of clearing up four different points arising out of the earlier articles. 
At the time it was commenced, the hope of finding a mathematical 
connection between absorption spectra and molecular structure had been 
given up, at least so far as aqueous solutions were concerned, and attention 
was being concentrated on some chemical questions arising out of the 
work. The spectrophotometer and methods were the same as had been 
used in Nos. II., III., VI., VII., and VIII. of the series. 
The first point investigated was in connection with the acetates of 
cobalt, nickel, and copper. Ewan * had stated that the molecular extinction 
coefficient of copper acetate varied with the wave-length in the same way 
as the molecular extinction coefficients of the other salts of copper, but 
that its value was always roughly two and a half times as great as the 
values of the latter. He worked with solutions the concentrations of 
which were of the order *004 gm.-mol. per litre. 
Our results are tabulated on p. 148 : c is the concentration in 
gm.-mols. per litre, A the molecular extinction coefficient, and X the 
wave-length. In the graphs the heavy curves are for the acetates, 
the dotted ones are for the corresponding sulphates. The values for 
the cobalt and nickel sulphates are taken from Nos. II. and III. 
respectively of this series, those for copper sulphate from a paper by 
Griinbaum.-)* 
The difference in the behaviour of copper acetate from the other 
acetates is possibly to be found in a different chemical constitution. It 
has recently been shown that ferric acetate is not so simple as was formerly 
thought.^ 
* Proc. Roy. Soc., 56, p. 286 (1894) ; ibid., 57, p. 117 (1895). 
+ Ann. d. Phys. (4), 12, p. 1004 (1903). 
X R. F. Weiuland and E. Gussmann, Zs. f. an. Chem ., 66, p. 157 (1910), 67, p. 250 
(1910). 
