Davy — On Properties possessed hij Salts of Fulminic Acid. 187 



passes into that of a reddish shade, and if a portion of the mixture in 

 this early stage of reaction be treated with a cbop or two of any dilute 

 acid, or is heated, the deep pui'ple coloration which results when the 

 double fulminate is similarly acted on will at once be developed. I 

 shall now briefly notice some of the more characteristic properties of 

 the acid fulminate of ii'on as obtained by the action of the f errocyanide 

 of potassium on the fulminate of mercury, most of my experiments 

 having been made on that salt as so procured. When that compound 

 is dissolved in water, it appears to possess, at the ordinary temperatui'c, 

 considerable stability, for it has been exposed to the air and even light 

 in an open vessel for several weeks, without its appearing to undergo 

 any change of colour ; but when the solution is allowed even sponta- 

 neously to evaporate to dryness, the dark purple residue very soon 

 passes to a brown colour, from the decomposition of this salt, and the 

 separation of its ii^on in the form of peroxide ; and this proneness to 

 decompose in the dry condition may account for the residue not ex- 

 ploding on the application of a strong heat, the salt having quietly 

 decomposed before reaching the temperatui'e necessary to explode it, 

 or other fulminates ; and I may further observe, that even in aqueous 

 solution it soon decomposes if the temperature is raised to the boiling 

 point, its decomposition being attended with the separation of per- 

 oxide of iron and ammonia. 



It does not appear to be soluble in ether, ^chloroform, bisulphide of 

 carbon, or in benzole, though it is readily dissolved by alcohol. 



It is quickly decomposed by strong acids, with the evolution of 

 hydi-ocyanic acid and the development of Prussian blue, and even in 

 their diluted condition the same occurs, but more slowly. 



The caustic alkalies, at the ordinary temperature, slowly discolo- 

 rize its solution ; with the assistance, however, of heat that effect is 

 quickly produced. 



It appears to possess but little, if any disposition to assume a crys- 

 talline form, for as yet all my attempts to obtain it separately in such 

 a condition have been unsuccessful. 



Several experiments were made as to the effects of different metal- 

 lic salts on this compound, but no very characteristic results were ob- 

 servable, except in the case of the nitrate of silver, which produced a 

 dull bluish precipitate, leaving the liquid colourless, if sufficient of the 

 silver salt be added. This precipitate, however, is one of great insta- 

 bility, for it veiy soon loses its blue colour (even when lying at the 

 bottom of the stratum of liquid from wliich it has been precipitated), 

 and becomes of a white or yellowish-white appearance. 



If, however, while it still retains its blue colour, it is treated with 

 diluted hydrochloric acid, or with an alkaline chloride, the solution 

 regains its original purple colour, whilst the chloride of silver precipi- 

 tates ; but if the addition of the acid or chloride be delayed till after 

 the precipitate has become white, then both fail to reproduce tlie 

 purple coloration, owing to the previous decomposition of the silver 

 compound. 



