354 PHYSIOLOGICAL CHEMISTRY. 



form is the whetstone shape formed by the rounding off of the 

 obtuse angles of the rhombic plate. The whetstones are numerous, 

 connected together, two or more crossing each other. Besides these 

 forms, rosettes of prismatic crystals, irregular crosses, brown-colored 

 rough masses of crystals which assume the shape of needles and 

 prisms occur, also other different forms. 



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

 dissolved in boiling glycerin, very difficultly soluble in cold water 

 (14,000-15,000 parts); and difficultly soluble in boiling water (in 

 1800-1900 parts), it is soluble in a warm solution of sodium 

 diphosphate, and in the presence of an excess of uric acid mono- 

 phosphate and acid urate are produced. Sodium phosphate is 

 considered as a solvent for the uric acid in the urine. Uric acid is 

 dissolved without decomposing in concentrated sulphuric acid. It 

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



Uric acid forms with bases two series of salts, neutral and acid. 

 Of the alkali urates the neutral potassium and lithium salts dis- 

 solve the most easily, and the ammonium salt dissolves with the 

 most difficulty. The acid-alkali urates are very insoluble and 

 separate as a sediment (sedimentum lateritium) from concentrated 

 urine on cooling. The salts with alkaline earths are very insoluble. 



If a little uric acid in substance is treated with a few drops of 

 nitric acid, the uric acid dissolves on warming with a strong 

 development of gas, and after thoroughly drying on the water-bath 

 a beautiful red residue is obtained, which turns a purple-red (pur- 

 purate of ammonium) on the addition of a little ammonia. If, 

 instead of the ammonia, we add a little caustic soda (after cooling), 

 the color becomes more blue or bluish violet. This color disappears 

 quickly on warming, differing from certain xanthin bodies. This 

 reaction is called the murexide test. 



Uric acid does not reduce an alkaline solution of bismuth, but 

 does, on the contrary, an alkaline copper-hydroxide solution. In 

 the presence of only a little copper salt we obtain a white precip- 

 itate consisting of copper urate. In the presence of more copper 

 salt red suboxide separates. 



If a drop of uric acid dissolved in sodium carbonate is placed 

 on a piece of filter-paper which has been previously treated with 

 silver-nitrate solution, a reduction of silver oxide occurs producing 



