1818.] Proximate Principles of the Urine, 353 



in alcohol, which takes up the urea alone, leaving the saline 

 bodies, or other extraneous matters ; and from the alcoholic 

 solution, the urea may be obtained pure and in the crystallized 

 state, although it is often necessary to repeat the crystallization 

 from the alcohol two or three times. 



The properties of pure urea are then detailed by the author. 

 Its crystals assume the form of a four-sided prism ; they are 

 transparent and colourless, and have a slight pearly lustre. It 

 has a peculiar, but not urinous odour ; it does not affect litmus 

 or turmeric papers ; it undergoes no change from the atmosphere, 

 except a slight deliquescence in very damp weather. In a strong 

 heat it melts, and is partly decomposed, and partly sublimed 

 without change ; the specific gravity of the crystals is about 

 1-35. It is very soluble in water; alcohol at the ordinary tem- 

 perature of the atmosphere dissolves about 20 per cent., when 

 boiling considerably more than its own weight, from which the 

 urea separates, on cooling, in its crystalline form. The fixed 

 alkalies and alkaline earths decompose it ; it unites with most of 

 the metallic oxides, and forms crystalline compounds with the 

 nitric and oxalic acids. 



In the analysis of organized substances the method generally 

 adopted is to employ some body which may afford a quantity of 

 oxygen, and thus convert their elements into various oxides, the 

 composition of which being known, may enable us to estimate 

 the quantity of the elements. The oxymuriate of potash has 

 been used for this purpose, and serves veiy well for the analysis 

 of vegetables ; but for animal substances it is less useful, because 

 it combines in variable proportions with the azote which enters 

 into their composition. On this account Dr. Prout employed 

 the black oxide of copper, and found it to answer completely, as 

 at a- moderate temperature it parts with its oxygen to hydrogen 

 and carbon, but not to azote. The substance under examina- 

 tion was heated with the oxide of copper in an apparatus so con- 

 trived, that the amount of water and carbonic acid formed might 

 be accurately ascertained, and the carbon and hydrogen thus 

 estimated, while the azote remained uncombined. When four 

 grains of urea were employed, the product was, 



Water 2-45 grains. 



Carbonic acid 6- 3 cubic inches. 



Azote 6-3 ditto. 



Hence it was estimated to consist of 



Hydrogen 0-266 



Carbon 0-799 



Azote 1-866 



2-933 

 Oxygen 1-066 



4-000 

 Vol. XL N° V. Z 



