250 
Urea may be obtained by the evaporation of 
human urine, till it is of the consistence of a syrup ; 
and the action of alcohol on the crystalline sub- 
stance, 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 by 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 distinguishes it from all other animal 
substances. 
According to Fourcroy and Vauquelin, 100 parts 
of urea, when distilled, yield 
92.0^7 parts of carbonate of ammonia. 
4.608 carburetted hydrogene gas. 
8.22 5 of charcoal. 
Urea, particularly when mixed with albumen or 
gelatine, readily undergoes putrefaction. 
Uric acid , as has been shown 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. 
