THE ACTION OF CHEMICAL AFFINITY. 
205 
The gradual diminution of power of the chloride of potassium added is exhibited by 
the curve in Plate IX. fig. 6. 
It was found that bromide of gold was reduced in colour by very small quantities 
of hydrochloric acid, or even of the common yellow crystals of the chloride of gold, 
which are, as is well known, the hydrochlorate of that salt. Bromide of gold, as 
might have been anticipated, was not affected in colour by admixture with neutral 
chloride of gold. 
These gold salts then have afforded a good example of the influence of mass in 
gradually counterbalancing and overcoming a strong affinity. 
Platinum salts. 
Neutral bichloride of platinum and different amounts of iodide of potassium were 
mixed in a series of vessels, diluted to an equality of bulk, and allowed to stand some 
hours for the colour to develope itself properly — a precaution which in this instance 
was necessary. The following were the appearances noted : — 
Bichloride Iodide of 
of platinum, potassium. 
Character of mixture. 
1 equiv.+ 0'5 equiv. 
Very pale brown solution. 
1 equiv. + 1 equiv. 
Reddish brown, and opalescent. 
1 equiv. + 2 equivs. 
The same, but deeper. 
1 equiv. + 3 equivs. 
The same ; some biniodide of platinum deposited on the glass. 
1 equiv. + 4 equivs. 
Red ; opalescence slight ; biniodide of platinum deposited. 
1 equiv. + 6 equivs. 
Bright red ; scarcely any opalescence or deposit. 
1 equiv. + 8 equivs. 
Brighter red ; no opalescence or deposit. 
1 equiv. + 10 equivs. 
Still brighter red. 
1 equiv.+ 15 equivs. 
Still brighter. 
The formation of the insoluble iodide of platinum renders some of these cases less 
distinct in their testimony than the instances previously considered. The opalescence 
too was doubtless owing to a minute trace of solid matter. This, however, is per- 
fectly clear, that the two salts, though they have mutually decomposed each other, 
have not done so in the atomic proportions ; not according to the schemes 
Pt Ck+2Kl=Pt I 2 -I- 2 KCI 
and Pt Ck+3Kl=PtI„ KI-1-2KC1. 
It has required, in fact, about four equivalents of iodide of potassium to produce the 
maximum amount of the platinic iodide ; and the latter terms of the series exhibit a 
still increasing amount of the intensely red double iodide of platinum and potassium. 
It may be expected that the double chloride is one of the salts produced in such a 
mixture*. Successive additions of a strong solution of chloride of potassium to a 
mixture of one equivalent of bichloride of platinum with two of iodide of potassium, 
were found to reduce the colour greatly, making it browner. 
* See Note C. 
2 F 2 
