. 



Urea may be obtained by the evaporation of hu- 

 man urine, till it is of the consistence of a syrup; and 

 the action of alcohol on the crystalline substance which 

 forms when the evaporated matter cools. In this 

 way a solution of urea in alcohol is procured, and the 

 alcohol may be separated from the urea fry heat. 

 Urea is very soluble in water, and is precipitated 

 from water by diluted nitric acid in the form of 

 bright pearl-coloured crystals; this property distin- 

 guishes it from all other animal substances. 



According to Fourcroy and Vauquelin, 100 parts 

 of urea when distilled yield. 



92.027 parts of carbonate of ammonia. 

 4.608 carburetted hydrogene gas. 

 3.225 of charcoal. 



Urea, particularly when mixed with albumen of 

 gelatine, readily undergoes putrefaction. 



Uric add^ as has been shewn by Dr. Egan, 

 may be obtained from human urine by pouring an 

 acid into it; and it often falls down from urine in 

 the form of brick-coloured crystals. It consists of 

 carbon, hydrogene, oxygene and azote; but their 

 proportions have not yet been determined. Uric 

 acid is one of the animal substances least liable to 

 undergo the process of putrefaction. 



According to the different proportions of these 

 principles in animal compounds, so are the changes 

 they undergo different. When there is much saline 

 or earthy matter mixed or combined with them, the 

 progress of their decomposition is less rapid than when 

 they are principally composed of fibrine, albumen, 

 gelatine, or urea. 



