Royal Institution. 373 



other influences. Several reactions, however, were mentioned 

 as tending to show that there is some truth in the law : — for 

 instance, the solution of gold in hydrochloric acid upon the addition 

 of nitrate of potash. The experiments of Bunsen on mixtures of 

 carbonic oxide and hydrogen, exploded with a quantity of oxygen 

 insufficient for complete combustion ; and those of Debus on the 

 precipitation of mixed hydrates of lime and baryta by carbonic acid 

 were explained ; as also the remarkable fact noticed by both, that 

 the resulting products were always in certain atomic proportions to 

 one another. But in both these cases the first products of the 

 chemical action are removed at once from the field : it is quite 

 another case when they remain free to act and react on one another. 

 Supposing they all remain in solution, the requisite is fulfilled ; but 

 how are we to know what has then taken place .'' Malaguti thought 

 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 son, as yet unpublished, were then spoken of, and the Lecturer 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 sulj)hocyanide 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 trans- 

 itions 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 tlie 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 



