URIC ACID. 53 



Hydrochlorate of urea has been formed by the direct combi- 

 nation of dry urea with hydrochloric acid gas. It is a veiy 

 unstable compound, and Avhen exposed to the air dissolves into 

 a very acid liquid, from which hydrochloric acid is disengaged. 



Lactate, hippurate, ayid urate of urea have been described 

 by Cap and Henry ; who in fact assert that in human urine the 

 urea exists as a lactate. Pelouze has, however, disproved the 

 existence of all these compounds. 



Prout has examined certain compounds of silver and lead, in 

 which the urea seems to combine with the oxides of those metals 

 as bases. They are of no importance in a practical point of \dew. 



The presence of urea modifies the solubility and crystalline 

 form of certain salts ; it causes common salt to crystallize in 

 octohedra, instead of in cubes ; but it has been observed that if 

 these octohedra are dissolved in pure water they recrystallize in 

 cubes. This peculiarity affords a common microscopic test for 

 the presence of urea. 



Diagnosis of urea. Urea is distinguished by its solubility in 

 water and in alcohol, and by its behaviour with nitric and 

 oxalic acids. 



13, Uric acid. 



Uric acid is a constituent of the urinary secretion in appa- 

 rently all classes of animals ; it is found in man and the car- 

 nivora, in graminivora (Fownes),' in birds, amphibia, serpents, 

 insects, and mollusca. It is the most common ingredient (in 

 combination with a base) of urinary calculi and gouty concre- 

 tions; it has been detected in the saliva (Wright), in sweat 

 (Wolf)," and on the surface of ulcers in arthritic persons 

 (Schonlein.) 



Uric acid may be obtained in a state of purity, by the fol- 

 lowing process, from the excrement of the boa constrictor,3 



' London and Edinburgh Phil. Mag. xxi, p. 139. 



2 Dissertatio sist. casum Calculositatis ; Tul)ing. 1817. 



■^ The excrements of the boa constrictor have been found by Prout to jield more 

 than 90g of uric acid. (Annals of Philosophy, t. v, p. 413.) The excrements of the 

 rattlesnake have been examined by Simon. He found in 100 parts of the dried 

 residue — free uric acid, with a httle fat and extractive matters, 56-4 ; urate of am- 

 monia, 31-1 ; urate of soda, with some chloride of sodium, 9-8 ; urate of lime, 1-4 ; 

 phosphate of lime, 1-3. Although we have retained the term "excrements" in ac- 

 cordance with popular usage, the substance is in reality the mine of the serpent. 



