424, Dr. Gladstone on the Effect of Heat 
Bichloride of platinum, while it becomes more intense in colour, 
assumes also a redder tint. . 
Protochloride of platinum, held in solution by hydrochloric 
acid, changes also in the same way. 
Bichloride of palladium acts precisely as the platinum salt 
does under the influence of heat. 
Ferrideyanide of potassium gives a greenish solution, which, 
when heated, alters in colour, and if not too dilute, assumes a 
distinctly red appearance. 
Polysulphide of potassium passes from yellow to a most in- 
tense red. 
Sesquichloride of iron passes from orange to a deep and 
almost pure red. y 
Chloride of nickel passes from a bluish to a yellowish green. 
Iodide of nickel, when dissolved in a little water, gives a clear 
green solution, which, on the application of heat, becomes of a 
nondescript shade, that appears distinctly red by gas-light. 
Chloride of copper gives a green saturated solution, which on 
the addition of more water becomes blue. If this blue solution 
be heated (unless too dilute), the green colour is restored. On 
cooling, it again becomes blue. 
Bromide of copper behaves in every respect like the chloride. 
Sulphocyanide of cobalt in a minimum of water, gives a mag- 
nificent bluish purple colour, but on dilution it changes to the 
ordinary pink tint of cobalt salts in solution. If this be heated, 
provided it is not too dilute, it will reassume the purple hue. 
Chloride of cobalt dissolves in water always ef a pink, and in 
absolute alcohol always of a blue colour, while in mixtures of al- 
cohol and water it will assume an immediate tint. By arranging 
properly the proportions of the two solvents, a liquid may be 
obtained which will show all the changes of an aqueous solution of 
the sulphocyanide, passing from pink through purple to blue when 
it is heated, and conversely, from blue to pink when it is cooled. 
In all these cases it is to be understood that the change of 
colour lasts only as long as the heat continues. No permanent 
chemical change is effected; and the original colour of the solu- 
tion returns in every instance as it cools. 
A glance at the above observations will suffice to show that 
where the colour is not materially altered in character, it in- 
variably becomes more intense when heated, that is to say, 
fewer rays are transmitted ; and when the light is analysed by a 
prism, it is found that not in these only, but in every one of the 
instances, rays are absorbed by the hot solution which were 
vansmitted by the same solution when cold. 
Yet a distinction must be made between two classes of action, 
both of which influence the above observations, and influence 
