8 
In a paper read before the Physical and Mathematical 
Section, April 13th, 1880, I referred to some experiments I 
had made to obtain a soluble black, and showed the advan- 
tages of such a solution in photometry, also its application 
to the determination of the law of absorption of light. The 
mixture used consisted of nickel, cobalt, and copper sul- 
phates in acidulated water. In a paper read before the 
Chemical Society, May 19th, 1881, Mr. Thomas Bayley gives 
the results of some similar investigations. He also finds a 
mixture of nickel, cobalt, and copper sulphate suitable. 
The proportions of the metals in his solutions are : 
Co. Ni. Cu. 
1 1-48 2-16 
The quantities of the salts used in the preparation of the 
fluid referred to in my paper give the following ratios be- 
tween the metals : 
Co. Ni. Cu. 
1 1-49 2-46 
