Chemical Science. 427 



washed several times in water tit 32° F. ; it is then to be strongly 

 pressed in bibulous paper. Without these precautions, the nitrate 

 of urea always retains much colouring matter, which can only be 

 imperifectly removed by animal charcoal. If the urea be ultimately 

 coloured, it is better to form it into a nitrate and proceed as above, 

 than try to change it by animal charcoal. ■ i. , . 



To separate the nitric acid, carbonate of baryta is better than 

 carbonate of potassa, for the nitrate of baryta is much less soluble 

 in alcohol than nitre ; the urea assists, however, the solution of the 

 nitrates, and when the former is to be dissolved out from the nitrates, 

 the alcohol should be used at common temperatures, and not boil- 

 ing ; although a large quantity must be used, the process is safer. 



Jt is said in most chemical works, that a boiling aqueous solution 

 of urea is converted quickly into carbonate of ammoniate; but this 

 is a mistake, occasioned by considering boiling fused urea as a 

 solution. A solution of urea very concentrated has been retained 

 in a boiling state for a long time, without evolving any carbonate 

 of ammonia; but the moment all the water was evaporated, {he 

 temperature rose, and the urea itself boiled and underwent decom- 

 position. Urea fuses at 248° F., and is decomposed at a tempera- 

 ture a little higher than this. During decomposition it boils rapidly; 

 from the carbonate of ammonia evolved, the latter forms a crystal- 

 line crust, and contains no hydrocyanic acid. After a little while, 

 a solid granular substance separates from the urea, which increases 

 in quantity, rendering the urea turbid, and the whole ultimately 

 becomes a dry grey or whitish powder ; after this, the application of 

 heat occasions no further production of carbonate of ammonia. 



This particular residual substance appears to be insoluble in cold 

 water, but dissolves in boiling water, leaving only a little impurity. 

 The filtered solution deposits small white brilliant crystals as it 

 cools, and these are identical with the cyanic acid of M. Serullas, 

 and have precisely the same properties as the latter philosopher has 

 described. It is only, therefore, relative to the quantity of water, 

 and the phenomena occurring during sublimation, that M, Wohler 

 makes any remarks. 



-,ij,M. Serullas does not seem to have observed that the crystals 

 contain much water. If exposed to the air, they lose their transpa- 

 rency, become milky, but retain their form. Being slowly heated, 

 they lose 23.4 per cent, of water, the oxygen in which is equal to 4- 

 pf that which remains in the acid. The experiments were mode with 

 cyanic acid prepared as above, and that prepared according to M. 

 Serullas's process i'rom the chloride of cyanogen. The hydrated acid 

 crystallized in an obHque rhombic prism, and the anhydrous acid 

 in flattened octoedra with square bases. The latter are obtained 

 by dissolving the substance in hot and concentrated muriatic or 

 sulphuric acid. 



When the anhydrous cyanic acid is heated in a little retort, a white 

 partially crystalline powder soon sublimes ; this is uudecomposed 

 cyanic acid ; but it dissolves with difficulty in boiling water, being. 



