14 Prof. Berzeliiis on the Composition of Prussiates. [July, 



deposits a green powder, the quantity of which increases during 

 evaporation ; and by long exposure to the atmosphere, we pro- 

 cure at last crystals of the common cyanuret. 



The best method of getting rid of this modification of cyano- 

 gen is to heat the anhydrous mass in a well-covered crucible 

 until it begins to fuse. The crucible is then to be removed from 

 the fire, the mass is to be suffered to cool, and then dissolved in 

 water. Some charcoal and carburet of iron remain undissolved. 

 The solution contains cyanuret of iron and potassium, hydrocy- 

 anate of potash, and carbonate of potash. Acetic acid is to be 

 added to decompose these two last salts with base of potash, the 

 liquid is concentrated, and the cyanuret of iron and potash pre- 

 cipitated by alcohol. It is to be afterwards crystallized, and it 

 is then obtained of a constant light-yellow colour, and finer than 

 in any other manner. In the common way it is always procured 

 of a variable shade of colour. 



If prussian blue be treated with sulphuric acid, or still better 

 with muriatic, this modification of cyanogen is for the greater 

 part avoided. 



Hydrate of barytes also produces a green compound with 

 prussian blue. The liquid loses its green colour ; but it is 

 restored by evaporation to dryness, and if the salt mixed with 

 alcohol is exposed to the sun's rays in a stopped bottle. When 

 mixed with a solution of deutoxide of iron, it gives prussian blue, 

 exactly like the green cyanuret of iron and potassium. I exa- 

 mined this substance but very superficially. 



Hydrate of lime gives scarcely any trace of similar combina- 

 tion ; but it decomposes prussian blue very imperfectly ; an 

 insoluble mass of a light ochre colour is obtained, which suffers 

 no further change by an excess of hydrate of lime, and which is 

 a subhydrocyanate of lime and oxide of iron. Acids decompose 

 it, combining with the lime, and separating the prussian blue. 

 It is probable that the green modification remains insoluble in 

 the subsalt. 



Ammonia gives the green modification in great abundance ; 

 frequently nothing else is obtained. It crystallizes in the form 

 of small green needles. Alcohol precipitates it of a green 

 colour, but of the consistence of a syrup. The aqueous solution 

 deposits a green powder during evaporation; it is sometimes 

 possible to obtain some crystals of common hydrocyanate of 

 ammonia and iron ; but the greatest part decomposes by long 

 exposure to the air, and gives a green powder. 



Hydrocyanate of ammonia without iron suffers decomposition 

 even in close vessels, and when surrounded by its own gas, it 

 gives rise; to a brown substance, which often preserves the out- 

 line of the crystals. After this decomposition, ammonia is 

 obtained, which precipitates the salts of deutoxide of iron of a 

 green colour. The brown mass does not possess this property. 



The green powder which is obtained in all these expeinatiils 

 is the modification of the hydrocyanate of protoxide and deutox- 



