438 Professor Berzelius on [June, 



ammoniacal salt pure, because the prussian blue of commerce 

 affords it much mixed with other substances, and during evapo- 

 ration with them, it constantly decomposes. 1, therefore, 

 prepared some cyanuret of iron and lead, which I decomposed 

 by caustic ammonia. The solution was evaporated in vacuo, 

 and having powdered the salt, I again dried it in vacuo to separate 

 all the water mechanically mixed with it. 



In order to determine whether this salt contains any water, I 

 heated it in a small retort made with the lamp, and received the 

 products of the distillation in a long tube, that by the difference 

 of their volatility they might be deposited at difterent distances 

 from the heated part. The first effect produced by the heat is 

 that of rendering the salt green at the bottom of the retort, and 

 the smell of hydrocyanate of ammonia is perceived at the open 

 end of the tube. The greenish colour was soon succeeded by a 

 greyish-yellow, considerably resembling that of the pulverized 

 salt before it is heated. The yellowish stratum increased in 

 thickness, and at the same time a very minute greenish stratum 

 which separated it from the unchanged salt gradually rose 

 towards the surface, where it at last disappeared, leaving the 

 salt completely converted into a yellowish-grey mass. During 

 this decomposition, water continued forming and depositing in 

 small drops in those parts of the tube which were near the 

 retort. A great quantity of hydrocyanate of ammonia was at 

 the same time disengaged, and when the salt had driven the 

 atmospheric air out of the apparatus, it began to crystalHze at 

 some distance from the water, so that the interior of the tube 

 was entirely lined with its crystals. Tlie centre, which was at 

 first limpid, became gradually yellowish, and afterwards brown- 

 ish nearer the crystallized ammoniacal salt ; this arose from the 

 spontaneous decomposition which hydrocyanate of ammonia 

 suffers. This salt did not contain any water chemically combined ; 

 for it was crystaUized in the form of httle rectangular tables and 

 prisms, which are the usual forms of this salt when it is 

 prepared with ammoniacal gas and hydrocyanic acid free from 

 water. The yellowish mass contained in the retort was cyanuret 

 of iron, the lower part of which had begun to decompose before 

 the upper part was entirely deprived of water and hydrocyanate 

 of ammonia. By continuing the heat, the cyanuret of iron 

 became of a deeper colour ; first, brown ; and at last, black, and 

 disengaged azotic gas. 



In order to satisfy myself that the decomposition was com- 

 plete, I placed the small retort in a charcoal tire to make it red- 

 not, when, to my great surprise, the coaly mass burned vividly, 

 as if oxygen gas had been present in the retort. A small quan- 

 tity of undecomposed cyanuret of iron disengaged azotic gas 

 with so much rapidity, that a part of the mass was thrown into 

 the neck of the retort. When the retort was cold, it was found 

 to contain a black pulverulent mass, weighing 25*25 per cent. 



