1821.] the Composition of Prussiates, 43T 



with a certain tension, which varies with the temperature. It 

 appears, therefore, that the salt in question contains water ready 

 formed, and not hydrocyanic acid, and oxidated bases ; for it is 

 not very hkely that the base and the acid should be decomposed 

 and recomposed, in proportion as the tension of the water varies, 

 according to the temperature and the quantity of aqueous vapour 

 in the surrounding atmosphere. In this case, we must consider 

 the crystalhzed ferruginous prussiate of potash, as a double 

 cyanuret of iron and potassium, combined with water of crystal- 

 lization, after the manner of salts, all the external characters of 

 which it possesses even in its efflorescent state. 



III. On the Hydrocyanate of Iron and Ammonia. 



In order to learn the nature of the ferruginous hydrocyanates 

 with more certainty, I also examined the composition of the- 

 ammoniacal one. It appeared to me at first probable that it 

 might throw hght upon the true nature of ammonia. If, for 

 example, this salt were reducible to cyanuret of iron and the 

 metallic substance which amalgamates with mercury, when 

 ammonia is decomposed by the electric pile, and if it were pos- 

 sible to obtain this salt free from water, or, what is the same^ 

 without oxygen, it is evident that, in this case, it would be a. 

 double cyanuret, and it would be easy to d(;termine whether the 

 metallic radical of ammonia is composed of an atom of azote 

 and of six atoms of hydrogen, as appears to result from the 

 experiments of MM. Tlienard and Gay-Lussac, or whether it 

 consists of an atom of nitricum and six atoms of hydrogen,, 

 according to the conjecture which I have hazarded. In the 

 first case, this salt would appear to be composed of cyanuret of 

 iron and hydrocyanate of ammonia ; and the hydrogen assigned 

 to the hydrocyanic acid would in fact be the additional atom of 

 hydrogen required to metallize the ammonia. In the second 

 case, on the contrary, there w^ould be no other hydrogen than, 

 that which is a constituent part of the ammonia. But there is 

 still a third case : it is that this combination might consist of 

 hydrocyanate of protoxide of iron and hydrocyanate of ammonia^ 

 and which would not part with the oxygen and hydrogen neces- 

 sary to the existence of the hydrocyanate, without being at the 

 same time totally decomposed ; and unfortunately this is the 

 actual state of the case. 



The experiments necessary to determine which of these cases 

 happens, are neither difficult, nor subject to give ambiguous 

 results. The hydrocyanate must contain four atoms of ammonia 

 and one atom of iron : since the oxygen presupposed in this 

 alkali must be double that which iron absorbs in becoming 

 protoxide. Consequently, in the first case, the salt decomposed 

 by heat ought to leave 27-53 per cent, of its weight of red oxide 

 of iron ; in the second, 31*18; and on the third, 25*9. The 

 greatest difficulty in this experiment was that of obtaining thft 



