THE ACTION OF CHEMICAL AFFINITY. 
213 
when equivalent portions of sulphocyanide of potassium and ferric citrate are mixed, 
or of chloride of gold and bromide of potassium. But it makes all the difference 
whether there be a small, though inappreciable, quantity of the other salt formed at 
the same time, or whether the decomposition be absolute ; and a consideration of the 
whole series of experiments, and of the influence of mass in these very instances, will 
leave, I think, a strong conviction on the mind that such cases differ from the others 
only in degree, and that if we possessed the means of observing minuter differences 
of colour we should find evidence of traces of the original salts still remaining. But 
of this each reader will form his independent judgment. Atnong those instances 
where evidently four salts were produced by the mixture of two, the following sub- 
stances took part in the reaction : — 
Iron (in both basic conditions), gold, platinum, mercury, copper, zinc, lead, molyb- 
denum, manganese, baryta, lime, potash, soda, ammonia, hydrogen, ethyl, quinine, 
gesculine (?), base in stramonium (?). 
Sulphuric, nitric, phosphoric, hydrochloric, hydrobromic, hydriodic, hydrofluoric, 
hydrosulphocyanic, hydroferrocyanic, acetic, oxalic, citric, tartaric, gallic, meconic, 
pyromeconic, and comenamic acids. 
It must be borne in mind, that when, in studying the mutual action of AB and 
CD, we have determined the laws according to which A and D combine, we have 
equally ascertained them in reference to C andB ; that is to say, to take a particular 
instance, if we find, on mixing ferric nitrate and sulphocyanide of potassium, that 
ferric sulphocyanide is formed in certain proportions according to the relative force ot 
affinity and mass, we have determined this also in respect to the nitric acid and the 
potash. We know indeed that for every portion of ferric sulphocyanide produced, an 
exactly equivalent portion of nitrate of potash must be formed, so that in fact the long 
curve in Plate VII. fig. 1 will express the amount of nitrate of potash in the experiment 
equally well with that which it primarily represents. And not only this, but in any 
such mixture, where we know the original amounts of the two salts, and the amount 
of any one of the four into which they are resolved, we have the data for determining 
the amounts of the other three likewise. This may be illustrated from the reaction 
just alluded to. Suppose (which is about the truth) that one equivalent of ferric 
nitrate mixed with three equivalents of sulphocyanide of potassium produce one-fifth 
of an equivalent of ferric sulphocyanide, the following is the only formula which can 
represent the reaction. The amounts are multiplied by five to avoid decimals : 
5(Fe, O 3 , 3 N 03 ) + 15KS,Cy=Fe„3S, Cy-i- 12 KS,Cy+ 4 (Fe 3 O 3 , 3 N 03 )+ 3 (KO, NO 3 ), 
or more simply, 
5AB-1-5CD=AD-F4AB + 4CD-1-CB. 
Of course this method of reckoning is inapplicable where polybasic acids are con- 
cerned. 
2 G 2 
