10 



UEEA. 



the few analyses which have been published by other 

 chemists, it would appear that these numbers represent the 

 usual proportion of water. 



The urine of pigs contains much more water than that of 

 horses and oxen. In one case Van Settin found that 1000 

 parts of urine contained 990*28 of water, and in two other 

 analyses by Von Bibra, the water amounted to 981*96 and 

 982-57 in 1000 parts of urine. 



Urea is the most important of all the constituents of the 

 urine, and one of the most important products of the waste 

 of the tissues. Urea has the composition of C 2 H 4 N 2 2 . 

 When pure, it crystallizes from watery solutions in trans- 

 parent quadratic prisms, with rectangular terminal planes. 

 Urea is colourless, readily soluble in water and spirit, but is 

 insoluble in ether. It has a cooling saline taste, not at all 

 unlike that of nitre. (Fig. 155.) 



Fig. 155. (LEHMANN.) Crystals of Pure Urea. 



Urea is one of those substances which modern chemistry 

 has enabled us to build up from its elements; it is very 

 readily decomposed. When heated a little above the tern. 



