162 THE URINE. 



Uric acid is comparatively insoluble in water or acids, 

 but dissolves readily in the fixed alkalies, forming salts of 

 uric acid, or urates. In the urine the acid exists in the 

 form of these salts or united with some organic base. It 

 is a dibasic acid like sulphuric acid, having two atoms of 

 hydrogen which can be replaced by metals. It can thus 

 have two series of salts, the acid and the normal, corre- 

 sponding to HKS0 4 and K 2 S0 4 . Of these classes the nor- 

 mal salts are quite soluble in water, but the acid salts do 

 not dissolve so easily. The acid can be set free from its 

 salts by the use of a stronger acid. The solubility of the 

 acid salts is much less in cold water than in warm. Con- 

 sequently they frequently separate from urine which was 

 clear when passed but has stood in a cold room, and they 

 can then be redissolved by warming. 



When it is pure, uric acid exists in the form of color- 

 less crystals. As it is found in the urine, it, as well as its 

 salts, is always colored yellow to brown by the coloring 

 matter which has been carried down from the urine. The 

 simplest form of crystals is tabular with curved sides and 

 pointed ends. These are frequently united at right angles, 

 making a star-shaped form, two of the rays often being 

 smaller than the other two. In urinary sediments many 

 crystals may be united, making a rosette-like form. In 

 strongly-acid urine the crystals sometimes have jagged 

 edges like the teeth of a broken comb. Many different 

 forms may be obtained by precipitating with various 

 strengths of acid. (Plate II, 11.) 



Uric acid and its salts have, in some degree, the power 

 of reducing copper compounds in an alkaline solution and 

 thus give with Fehling's or Trommer's test results which 

 are similar to those obtained with glucose. When the dry 

 substance is warmed with nitric acid it is oxidized, and 



