708 URINE. 



in the dissociation on the addition of strong acids, uric acid is soluble 

 with difficulty in the presence of mineral acids. It is soluble in a warm 

 solution of sodium diphosphate, and in the presence of an excess of uric 

 acid, monophosphate and acid urate are produced. It is ordinarily 

 assumed that sodium diphosphate forms a solvent for the uric acid in 

 the urine, while according to GUDZENT this is not dissolved by the mono- 

 phosphate. RUDEL * believes that urea is an important solvent, but 

 this view has not been confirmed by the observations of His and PAUL. 

 Uric acid is not only dissolved by alkalies and alkali carbonates, but also 

 by several organic bases, such as ethylamine and propylamine, piperidine 

 and piperazine. Uric acid can form supersaturated solutions with alkalies 

 and these, according to SCHADE and BoDEN 2 contain colloidal uric acid 

 and they may gelatinize on cooling as well as under other conditions. 

 Uric acid dissolves, without decomposing, in concentrated sulphuric 

 acid. It is completely precipitated from the urine by picric acid (JAFFE S ). 

 Uric acid gives a chocolate-brown precipitate with phosphotungstic 

 acid in the presence of hydrochloric acid. 4 



Uric acid is dibasic and consequently forms two series of salts, neu- 

 tral and acid. Of the alkali urates the lithium salts are the most soluble 

 and the acid ammonium salt is the most insoluble. The acid alkali 

 urates are very insoluble and separate as a sediment (sedimentum later- 

 itium) from concentrated urine on cooling. According to GUDZENT 

 1 liter of water at 18 C. dissolves (as primary salts) 1.5313 grams 

 potassium, 0.8328 gram sodium, and 0.4141 gram ammonium urate, 

 and at 37 C. 2.7002, 1.5043 and 0.7413 grams of the respective urates. 5 

 The salts of the alkaline earths are soluble with great difficulty. The 

 above solubilities apply only, in GuDZENT's 6 experience, to the freshly 

 prepared solution, as the solubility to a certain limit gradually dimin- 

 ishes, due to intramolecular transposition (change of the uric acid from 

 the lactam-form into the lactim-f orm) . 



Besides the mono- and diurates also " quadriurates " have been described 

 and these occur in the excrement of snakes and birds and in the sedimentum 



1 His, Jr., and Paul, Zeitschr. f. physiol. Chem., 31; Smale, Centralbl. f. physiol., 

 9; Riidel, Arch. f. exp. Path. u. Pharm., 30; Gudzent, Zeitschr. f. physiol. Chem., 

 60 and 63. 



2 Zeitschr. f. physiol. Chem., 83. 

 a Ibid., 10. 



4 In regard to the combinations of formaldehyde and uric acid, see Nicolaier, 

 Deutsch. Arch. f. klin. Med., 89 (1906). 



6 Determinations of the solubility of the monourates in serum have been made by 

 Gudzent, Zeitschr. f. physiol. Chem., 63. See also Bechhold and Ziegler, Bioch. Zeitschr., 

 20. 



6 Zeitschr. f. physiol. Chem., 56 and 60. 



