UREA. 77 



pure urea than that of Berzelius, with which, indeed, he was un- 

 acquainted. He described the properties of pure urea and sub- 

 jected it to an accurate ultimate analysis. An analysis had been 

 previously made by Berard and another by Prevost and Dumas ; 

 both of which approached very near the results obtained by Prout, 

 except in the hydrogen, of which they obtained a great excess, be- 

 cause their urea had not been freed from water. More lately 

 Wohler made the curious discovery, that urea may be made ar- 

 tificially by uniting together cyanic acid and ammonia* He 

 described also the phenomena which take place when urea is ex- 

 posed to a high temperature, f He showed likewise thaf urea is 

 obtained when uric acid is distilled. } Berzelius, in the seventh 

 volume of the French translation of his Traite de Chimie, gives 

 a new process for obtaining urea. It seems merely a modifica- 

 tion of that of Prout. 



The process of Dr Prout is the following : Evaporate by a 

 gentle heat a quantity of fresh urine to the consistence of a syrup. 

 Allow it to cool, and add by degrees pure concentrated nitric 

 acid till the whole assumes the form of a crystallized mass, hav- 

 ing a deep brown colour. Let this mass be washed with a little 

 cold water, and left to drain, then pour upon it slowly a pretty 

 concentrated solution of carbonate of potash or soda till it is com- 

 pletely neutralized. Concentrate the liquid by a cautious eva- 

 poration, and set it aside till the nitre formed is deposited in crys- 

 tals. Separate the liquid portion from these crystals, and add to 

 it enough of animal charcoal to reduce the whole to the state of 

 a thin paste. Let the mixture remain at least for some hours, 

 and then pour upon it a sufficient quantity of cold water to se- 

 parate the urea. Evaporate the colourless liquor to dryness by 

 a gentle heat and then boil the residue in very strong alcohol, 

 which will dissolve the urea, but leave the nitre and most other 

 saline substances behind it. By evaporating the alcoholic solu- 

 tions we obtain the urea in crystals, and two or three solutions in 

 alcohol and crystallizations are sufficient to bring it to a state 

 of purity. 



The process of Berzelius is as follows : Evaporate the urine 

 to the consistency of a syrup, and then dry it over the steam-bath 



* Poggendorf's Annalen, xii. 253. 



f Jour, de Pharmacie, xvi. 298, or Poggendorf's Annalen, xv. 619. 



\ Poggendorf, ibid. p. 529. 



