1820.] Ferrochyazate of Iron. 219 



of the composition of this acid. The weight of an integrant 

 particle of it seems to be 6'26 or 6'75. I begin to suspect that 

 oxygen enters into its composition. Further experiments are 

 still wanting to throw light on this obscure point. 



I considered these preliminary observations as requisite to 

 enable the reader fully to understand the phenomena which take 

 place when ferrochyazate of iron is exposed to a red heat. To 

 these phenomena I now proceed. 



Ferrochyazate of iron is a tasteless powder, of a very deep and 

 beautiful blue colour. It is partially decomposed by nitric and 

 sulphuric acid, and probably likewise by muriatic acid ; but I 

 did not succeed in obtaining a complete decomposition by diges- 

 tion in these acids, though continued for several days, and 

 assisted by a moderate heat; but all the alkalies, the alkaline 

 earths, and some of the metallic oxides, decompose it with great 

 facility, depriving it of its ferrochyazic acid, and of course 

 destroying the colour. Nothing remains behind, if the experi- 

 ment be properly conducted but peroxide of iron. 



When heated to the temperature of 400°, it catches fire, and 

 burns for sometime without flame, giving out very concentrated 

 fumes of ammonia. Twenty grains of ferrochyazate of iron,, 

 when thus treated, were reduced to 10*9 grs. This residuum 

 effervesced strongly when put into muriatic acid, and dissolved^ 

 leaving I'o gr. of undecomposed ferrochyazate of iron; conse- 

 quently 18-5 grs. of the salt were decomposed by the combus- 

 tion. Now the constituents of these 18"5 grs. were as follows : 



Ferrochyazic acid 9"435 grs. 



Peroxide of iron 6"993 



Water 2-072 



18-500 



The quantity of iron in9"435 grs. of ferrochyazic acid amount* 

 to 2'44(3 grs. which are equivalent to 3- 494 grs. of peroxide. 

 From this it is obvious that part of the iron was volatilized ; for 

 the whole iron in 18*5 grs. of ferrochyazate of iron (supposing it 

 in the state of peroxide) would amount to 10*487 grs. ; whereas- 

 the whole residue amounted orily to 9*4 grs. 



I conceive that during the combustion a portion of the carbon 

 is converted into carbonic acid, which combines with the iron 

 of the ferrochyazic acid, changed at the same time into protox- 

 ide. This accounts fo*- the effervescence which takes place 

 when the residue is thrown into muriatic acid. The evolution of 

 the ammonia' is not easily explicable, unless we suppose that 

 the water of the salt undergoes decomposition at the same time 

 with the ferrochyazic acid. It will be recollected that the pig- 

 ment contains one atom of ferrochyazic acid for every atom of 

 water present. 



Such are the phenomena which take place when theferrochy- 



