418 NOTICES OF THE MEETINGS [March 31, 
to obtain an indication of this by mixing the aqueous solutions of 
two salts, one of which is soluble in alcohol, and the other is 
insoluble, and then pouring them into very strong alcohol, and 
analyzing the salts immediately thrown down. His results are 
tabulated; they are valuable, but to some extent open to objection 
on account of the disturbing influence of the alcohol. Some 
observations of Professor Graham, and others of Professor William- 
son, as yet unpublished, were then spoken of, and the Lecturer 
proceeded to describe his own endeavours to arrive at a knowledge 
of the intimate constitution of a mixture of salts in solution by 
observing their physical properties, especially colour. 
If solutions of one equivalent of nitrate of iron, and a triple equi- 
valent of sulphocyanide of potassium be mixed, a blood-red colour 
results owing to the formation of sulphocyanide of the sesquioxide 
of iron; the question arises—Has all the iron left the nitric acid to 
unite itself with the sulphocyanogen? It has not; for on the 
addition of equivalent after equivalent of sulphocyanide of potassium, 
a deeper red is constantly obtained. The arrangement by which 
this deepening of colour was quantitatively determined was explained, 
and imitated on the lecture table. The result was that even up to 
375 equivalents, a regular increase was observed to take place, more 
rapidly at first than afterwards, which was exhibited to the eye by 
the results being projected as a curve. Again, as in the mixture of 
equal equivalents of the two salts, some iron still remains in combina- 
tion with the nitric acid, a portion of the potassium must still remain 
united to the sulphocyanogen. Accordingly, the addition of more iron 
salt also gives a deeper colour. The curve expressing the results of 
this experiment was a regular continuation of the curve formerly 
mentioned; and neither of them exhibited any of those sudden transi- 
tions which the experiments of Bunsen and Debus present. Dia- 
grams exhibiting curves of the gallate and meconate of iron were 
also exhibited. Various experiments were then performed, showing 
the alteration in the resulting colour upon any change of any of the 
elements in the primary experiment ; for instance, the substitution of 
other acids for the nitric acid, or of other bases for the potash. On 
the addition of a colourless salt to a coloured one, there results a 
diminution of the colour greater than the mere dilution would have 
produced, as was exemplified in the cases of the red sulphocyanide 
of iron mixed with sulphate of potash, and of the scarlet bromide 
of gold mixed with chloride of potassium. The lecturer accord- 
ingly drew the conclusion that when two salts mix without precipi- 
tation or volatilization, the acids and bases frequently, if not uni- 
versally, arrange themselves according to some definite proportion ; 
and that this depends on the relative quantity of the two salts, as 
well as upon the proper affinities of the substances composing them, 
He was unable then to enter upon the influence of heat, or of dilu- 
tion in certain cases, or to add any remarks connected with double 
salts, or with other metals, or upon certain practical applications of 
these views in chemical and physiological science. 
