184 Proceedings of the Royal Irish Academy. 



peroxide of iron) was produced ; these changes being accompanied by 

 the evolution of more or less of ammonia, and by the mixture, which 

 was at first quite neutral, acquiring a strong alkaline reaction. The 

 solution being filtered, and concentrated by evaporation, was found to 

 yield small prismatic crystals of a colourless or very light yellow salt, 

 which appears to be a double cyanide of potassium and mercury. 



Considering that the principal feature of interest in the reaction of 

 the fulminate on the ferrocyanide was the formation of the purple 

 compound, my attention was chiefly directed to its investigation. But 

 I soon ascertained that this compound was a substance of a very 

 unstable character, and that it presented great difiiculties in the way 

 of its separation from the matters with which it was associated, as 

 procured in the reaction referred to ; and not being able to obtain it in 

 a pure or suitable state to submit it to actual analysis, I was for a 

 considerable time unable to obtain any clue as to its real nature, fur- 

 ther than it was some organic compound of iron, in which cyanogen, 

 or at least its elements, were constituents. 



At last it occurred to me, that the coloration observed might 

 be in some measure connected with the formation of the fulminate 

 of iron ; and on making some of that salt, and comparing its reac- 

 tions with those of the compound referred to, many points of agree- 

 ment between them were at once perceptible. I may observe that 

 the fulminate of iron is readily obtained by the action of metallic 

 iron on the fulminate of mercury, suspended in water. Thus if about 

 equal bulks of the fulminate and of fine iron filings are placed in 

 a small stoppered bottle, which is then filled with distilled water, 

 and being closed is occasionally agitated, the liquid in a short time 

 acquires a yellowish tint, which gradually deepens in colour, whilst 

 the filings become tarnished, and more or less of mercury, in the 

 form of minute globules, make their appearance. After a few hours 

 the decomposition of the fulminate of mercury will be more or less 

 complete, and on filtering the mixture, a dull yellow liquid is obtained, 

 wliich holds the fulminate of iron in solution. This fulminate, as so 

 obtained, was described by my late father, amongst several other com- 

 pounds of fulminic acid, which he was, I believe, the first to discover, 

 during his elaborate researches on that acid. This salt was observed 

 by him to produce, when treated with diluted acids, a fine red or purple 

 colour, which disappeared after some time, evolving hydi-ocyanic acid 

 amongst other products. He also found that a somewhat similar 

 colour, rapidly changing to a bluish black, with a precipitate of that 

 colour, was developed on heating this fulminate. 



But this development of colour only occurs in the case of the freshly 

 prepared fulminate of iron, for the salt, being one of very great insta- 

 bility, commences almost immediately after its formation to undergo 

 spontaneous changes, which are attended by the separation of a dark 

 brown substance, even when the solution is kept excluded from the 

 air in a well-stoppered bottle ; and after such changes have taken place, 

 it ceases to develop, either by the action of acids or by heat, the colo- 



