1821.] the Composition of Prussiaies. 439 



of the hydrocyanate employed. This substance, when heated 

 in the flame of a lamp, took fire, and continued to burn like 

 amadou, but without either smoke or smell, and it left a residue 

 of oxide of iron, the weight of which was precisely equal to that 

 of the mass before combustion. 



In another experiment, I heated the hydrocyanate by a spirit 

 lamp, taking care not to heat it enough to occasion the deflagra- 

 tion which occurred in the former case ; but the heat was con- 

 tinued as long at; the disengagement of gas was perceptible, and 

 the products of the distillation were passed through a tube 

 containing muriate of lime, and the gases received over 

 mercury. The coaly residuum weighed 26*3, and gave by com- 

 bustion in an open vessel exactly 26'*3 of red oxide of iron. It 

 burned as before, but without the deflagration abovementioned 

 occurring at the temperature required to inflame it. The muriate 

 of lime gained 9*7 per cent, of the weight of hydrocyanate. When 

 heated, it gave out at first much hydrocyanate of ammonia, 

 afterwards ammoniacal gas, and lastly Vv^ater much impregnated 

 with ammonia. In this experiment, the quantity of water could not 

 be determined, but it proves nevertheless that the salt cannot con- 

 tain more water than is requisite to convertthecyanuretof iron into 

 hydrocyanate : for otherwise the muriate of lime ought to have 

 gained much more. The gases produced contained no trace of 

 carbonic acid. I introduced some lime-water which absorbed a 

 great quantity without becoming turbid. The liquid contained 

 much hydrocyanate of ammonia, and the unabsorbed gas was 

 azote. The explanation of these phenomena is very simple : the 

 hydrocyanate of iron and ammonia is decomposed by heat, and 

 gives hydrocyanate of ammonia, cyanuret of iron, and water. 

 The green colour which appears during the decomposition 

 appears to be owing to the formation of a small quantity of 

 Prussian blue, which always begins the decomposition of this 

 salt, even when in solution. When the heat is increased, the 

 cyanuret of iron is decomposed, azote is disengaged, and the 

 carbon remains combined with the iron. As cyanuret of iron 

 contains four atoms of carbon to one of iron, the same propor- 

 tions ought to be found in the carburet which results frorn its 

 decomposition. Then in comparing the weight of four atoms of 

 carbon with that of three atoms of oxygen, the first is found to 

 be 301'66, and the last 300; so that when the quadricarburet of 

 iron is converted into red oxide of the metal, its weight should 

 not alter more than 1-lOOOth, which is too small to be ascertained 

 in experiments made upon so minute a scale as mine. As to the 

 deflagration, I shall hereafter have occasion to mention it. 



I tried several times to expose the hydrocyanate of iron and 

 ammonia to temperatures very gradually raised in order to see 

 whether it would not be possible to separate the water, and 

 preserve the hydrocyanate ; that is to say, to reduce this salt to 

 the composition supposed in the first case; but I have not 



