191 2—1 3.] The Absorption of Light by Inorganic Salts, No. IX. 143 
than when they are dissolved in water. The absorption in alcohol and 
acetone varies very greatly from one salt to another of the same base, and 
seems to depend more on the bonds connecting the base to the acid radical. 
An attempt was next made to apply the law of mass action to some 
of the colour changes. The case of cobalt chloride in alcohol has already 
been dealt with in the sixth article. Only three of the other salts used 
here seemed suitable for investigation in this respect, namely, copper 
chloride, copper bromide, and cobalt bromide. 
Three solutions of copper chloride in alcohol were prepared of con- 
centrations ‘600, '300, and '150 respectively, and the change in A at the 
point A = 470 jujui caused by the addition of water was examined. This point 
was selected as being the farthest into the violet for comfortable observa- 
tion. The changes in A are shown by the curves in fig. 3. The abscissae^ 
give the concentration of the water present in the solution in gm.-mols. 
per litre. 
The solution gradually changed from olive-green to pale green ; and 
when a certain concentration of water was reached, it became blue and 
began to throw down a colloidal precipitate which could not be removed 
by filtration. Moreover, the curves show a peculiar behaviour on the 
first addition of water, the absorption first rising and then falling asympto- 
tically to the aqueous value. Conditions thus seemed too complex for 
mathematical investigation. 
Copper bromide also gave trouble owing to the absorption varying 
much too rapidly on the addition of water, a single drop of water added 
to 8 c.cs. alcoholic solution bringing A down almost to its value for water. 
The solutions of copper chloride and copper bromide in acetone decomposed 
slightly on the addition of water. 
