UREA. 75 



and of magnesia, have been examined by Braconnot. They crys- 

 tallize and do not absorb moisture from the atmosphere. 



It would be an object of some consequence to examine this 

 acid more in detail. It is probably analogous to the compound 

 acid described in the Chemistry of Vegetable Bodies, p. 168. 



CLASS II. 



OF ANIMAL BASES. 



THESE bodies have been hitherto but imperfectly examined 

 The number of animal bodies which are known to combine and 

 neutralize acids does not exceed eleven, and, if we except urea, 

 not one of them has hitherto been subjected to an ultimate ana- 

 lysis. It is true, indeed, that ammonia is obtained from the ani- 

 mal kingdoms, and that it is a very decided base. But, for reasons 

 too obvious to require being stated here, that alkali was described 

 while treating of the chemistry of inorganic bodies. Here, there- 

 fore, we shall simply give a list of the principal combinations in- 

 to which it enters. 



CHAPTER II. 



OF UREA. 



THE substance now known by the name of urea was discover- 

 ed by Rouelle Junr., during his researches on urine, which were 

 published in the Journal de Medecine for 1773 and 1777. He 

 obtained it by evaporating recent urine to dryness and digesting 

 the residue in alcohol. The urea, which he distinguished by the 

 name of soapy matter, was dissolved. By proper evaporation it 

 was obtained in crystals. He mentions that it is difficult to ob- 

 tain it in a dry state, and that it absorbs moisture from the at- 

 mosphere. When heated, it yielded, he says, much more than 

 half its weight of carbonate of ammonia.* In 1808 a new set of 

 experiments was made upon it by Fourcroy and Vauquelin.f 



* Macquer's Dictionnaire de Chimie (second edition), ii. 645. 

 t Ann. de Mus. d'Hist. Naturelle, ii. 226. 



