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elements were constituents. At last it occurred to him that the 

 coloration obseiTeci might be in some measure connected with the 

 foiTQation of the Pulminate of Iron, and on making some of that salt 

 and comparing its reactions with those of the compound referred to, 

 many points of agreement between them were at once perceptible. 

 That Fulminate, which is easily obtained by the action of iron filings on 

 the Fulminate of Mercury suspended in water, as shown by its dis- 

 coverer the late Professor Davy, developes, when treated with diluted 

 acids, a fine red colour ; and the author has fiu'ther observed that the 

 salt which remains after the action of caustic alkalies on that Fulmi- 

 nate, and the separation of the resulting oxide, gives rise to the same 

 coloration on the addition of diluted acids ; and that the red-coloured 

 matter so produced resembles in all its properties that developed in 

 the more complex reaction of the Fulminate of mercury on the 

 Ferrocyanide of Potassium already noticed. The author further stated 

 that (as far as he was aware) no explanation had yet been, given for 

 the development of the red coloui' on treating the Fulminate of Iron 

 with diluted acids ; and the one he would suggest was capable of 

 accounting for its production, not only in that case, but also in the 

 new reactions he had himself observed. 



Fulminic Acid, the empirical formula of which was !!<,__, CiN^ Oz, is 

 generally regarded as a bibasic acid which is capable of forming two 

 classes of salts, viz., the neutral and the acid salts, according as the 

 hydi'ogen of the acid is either in whole or in part replaced by m^etals ; 

 and he conceived that the red-coloured compound which was de- 

 veloped from the neutral Fulmiaate of Iron by the action of acids, 

 was an acid Fulminate of that metal — a hitherto undescribed salt, the 

 formation of which was expltuneci by the following reaction : 



2 Fe, CJs\Oo, +ir,SO, = FeH. {C,N^O^y + Fe SO,. 



Again, when the neutral Fulminate of Iron was acted on by a dilute 

 solution of an alkali, such as Potash, a double neutral Fulminate of 

 Iron and Potassium — another undescribed salt — was formed, as shown 

 in the following equation : 



2Fe a.N'^O^ + 2 KHO = FeK,{ C\N^O.)' + Fe + S.O; 



and this double fulminate developes the red acid fulminate on beiug 

 heated with acids, as the following formulse indicate : 



FeK, {cumo.y + ^2'S'o, = Fern {aK,o,y + ir.so. 



