GLYCINE. 153 



4 parts of concentrated hydrochloric acid, it becomes decomposed 

 into glycine and benzoic acid ; on the addition of water to the boiled 

 fluid, a great part of the benzoic acid separates and must be 

 removed by nitration ; the clear fluid is then evaporated nearly to 

 dryness, and the residue (hydrochlorate of glycine) decomposed with 

 caustic ammonia ; finally the glycine is precipitated by, and washed 

 with, absolute alcohol. 



Tests. When the substance suspected to be glycine is separated 

 as much as possible from all other matters, the most striking of the 

 properties by which it may be distinguished are its relation towards 

 a hot solution of potash, its difficult solubility in alcohol, and the 

 blue solution which it yields with caustic potash and sulphate of 

 copper, without any separation of the suboxide; and if, further, 

 we study its power of combining with acids as well as with baryta, 

 oxide of copper, oxide of lead, &c., and forming crystallisable bodies, 

 there can hardly remain any doubt regarding its nature. It may 

 easily be distinguished from leucine by the form of its crystals and 

 by its becoming decomposed on exposure to heat. 



According to Horsford the quantities of urea and uric acid in 

 the urine are increased after the ingestion of glycine, but no 

 unchanged glycine is found in the urine. 



UREA. C 2 H 4 N 2 O 2 . 

 Chemical Relations. 



Properties. Urea crystallises, when it separates rapidly, in 

 white, silky, glistening needles; but when the crystallisation is 

 effected slowly, in flat, colourless, four-sided prisms full of cavities 

 and appearing to be formed of numerous parallel crystalline lamellae: 

 at the ends the prism is terminated by one or two oblique surfaces. 

 According to C. Schmidt*, these forms do not pertain to the mono- 

 clinometric system, but rather to a hemihedral form belonging to 

 the rhombic system, and bounded by parallel surfaces. These 

 crystals contain no water. Urea is devoid of smell, of a saltish, 

 cooling taste, and is unaffected by exposure to the atmosphere; 

 it dissolves readily in its own weight of water, giving rise to a 

 marked evolution of heat ; in hot water it dissolves in every 

 proportion ; it is also soluble in 4 or 5 parts of cold and in 

 2 parts of warm alcohol ; it is insoluble in ether, if anhy- 

 drous and devoid of alcohol, and in etherial oil, and exerts no 



* Entwurf u. s. w. S. 41. 



