THE JOURNAL OF PHARMACOLOGY. 159 



In normal urine, uric acid is always found in combination with bases 

 (sodium, potassium, ammonium, etc.), either as an acid or a neutral salt. 

 It is quite insoluble in hot or cold alcohol, and in ether. Glycerin dis- 

 solves it sparingly, as do solutions of salts (borax, carbonates, phosphates 

 and acetates of alkalies, lithium salts, etc.). Acid urine upon standing 

 often deposits a sediment of urates, which in consequence of their different 

 degree of solubility nearly always consists of the acid variety. When a 

 strong acid is added to urine containing an excess of soluble (neutral) 

 urates, a fine granular precipitate results, rendering the mixture opaque. 

 The reason for this change is as follows : The acid unites with a part of 

 the base thus causing acid urates to form, which on account of their 

 feeble solubility are precipitated. This change often leads to errors in 

 the application of the nitric acid test for albumin. Uric acid, as such, may 

 be deposited from very acid urine, or from urine which has undergone 

 acid fermentation. It is never safe to assume the presence of excessive 

 amounts of uric acid from the mere fact that a precipitate has formed in 

 the urine upon standing. It is possible that such may be the case, co- 

 incident with a positive deficiency in uric acid, as for instance in urine pos- 

 sessing a high degree of acidity. Acid potassium or sodium urate are 

 often found forming a deposit in the urine of rheumatic patients, in febrile 

 conditions, or in any condition in which the quantity of urine is much di- 

 minished. Such sediments are usually high-colored (brick dust deposit), 

 from the presence of certain pigments (uroerythrin, etc.). Sometimes they 

 are yellow and in rarer cases nearly white. Under the microscope they 

 are seen to consist of small amorphous granules, arranged in groups. At 

 times they occur in spherical or biscuit form. Such a sediment consisting 

 of acid urates, dissolves upon the application of heat, but upon cooling it 

 again deposits. Acid ammonium urate is found as a deposit in alkaline 

 urine. It is usually yellow in color, and consists of spherical masses, 

 which are often studded with small spicules, hence the name "thorn 

 apple " crystals. This salt is often a component part of various kinds of 



calculi. 



Qualitative Determination, 



I. The sediment or residue is moistened with nitric acid, or chlorine 

 water, or a few crystals of potassium chlorate and several drops of hydro- 

 chloric acid may be used, evaporated to dryness in a porcelain capsule, 

 and the residue allowed to cool. It is then held over another dish contain- 

 ing ammonia water, when a purple red color will become apparent 

 (murexid test). Upon addition of solution of sodium or potassium hydrate 

 the color changes to violet. When warmed the color rapidly disappears 

 (difference from xanthin bases). The purple red color is due to the for- 

 mation of purpura te of ammonium (murexid), and the violet color to the 

 formation of purpura te "of sodium or potassium. 



