672 URINE . 



angles of the rhombic plate. The whetstones are generally connected , 

 two or more crossing each other. Besides these forms, rosettes of pris- 

 matic crystals, irregular crosses, brown-colored rough masses of broken-up 

 crystals and prisms occur, as well as other forms. 



Uric acid is insoluble in alcohol and ether; it is rather easily soluble 

 in boiling glycerin, but very insoluble in cold water, in 39480 parts 

 at 18 C. (His and PAUL), and in 15505 parts at 37 (GUDZENT). At 

 this temperature, according to His and PAUL, 9.5 per cent of the uric 

 acid is dissociated in the saturated solution. Because of the reduction 

 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, but SMALE claims that the monophosphate has only a slight 

 solvent action. RUDEL 1 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 car- 

 bonates, but also by several organic bases, such as ethylamine and propyl- 

 amine, piperidine and piperazine. Uric acid dissolves, without decom- 

 posing, in concentrated sulphuric acid. It is completely precipitated 

 from the urine by picric acid (JAFFE 2 ). Uric acid gives a chocolate- 

 brown precipitate with phosphotungstic acid in the presence of hydro- 

 chloric acid. 3 



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

 neutral 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 

 lateritium) 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 grams sodium, and 0.4141 grams ammonium urate, 

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

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

 above solubilities apply only, in GUDZENT'S 4 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-foim). 



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. 



2 Zeitschr. f. pyhsiol. Chem., 10. 



3 In regard to the combinations of formaldehyde and uric acid, see Nicolaier, Deutsch. 

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



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



