102 PHYSIOLOGICAL A^D PATHOLOGICAL CHEMISTRY. 



of reduced silver appear at once. These are yellow-brown 

 to deep black according to the quantity of the dissolved 

 uric acid. 



4. If we add to the sodium carbonate solution of uric 

 acid some magnesia mixture (solution of magnesium hydrox- 

 ide in ammonia and ammonium chloride) and then add silver 

 nitrate solution, a double compound, silver magnesium urate, 

 separates in the form of a gelatinous precipitate. 



5. Dissolve some uric acid in water and caustic soda, add 

 some Fehling's solution and heat: white cuprous urate pre- 

 cipitates, or, when the quantity of the copper relative to the 

 uric acid is sufficiently large, red cuprous oxide is formed. 

 This reaction is important, as it shows that, when making 

 the Trommer's test with normal urine, the reducing action 

 of the uric acid always present must be taken into account. 



Of the reactions the precipitation of the magnesium silver 

 urate is especially important for the isolation of uric acid, 

 the murexide test for its detection. Uric acid is not always 

 deposited from urine on the addition of hydrochloric acid; 

 it is then necessary to use the precipitation of the magnesium 

 silver c mpound to show its presence. 



V. DETECTION OF CREATININE, C 4 H 7 N 3 0. 



Make 240 cc. of urine faintly alkaline by cautiously adding 

 milk of lime and precipitate exactly with a solution of cal- 

 cium chloride; dilute with water to 300 cc., mix thoroughly, 

 and after fifteen minutes filter through a dry filter. Measure 

 off 250 cc. of the filtrate, which must have a faintly alkaline 

 reaction, and after neutralizing with acetic acid evaporate 

 to about 20 cc., at first over a free flame and then on the 

 water-bath. Mix this with the same volume of absolute 

 alcohol, transfer the mixture to a 100-cc. measuring-flask, 

 rinsing with absolute alcohol, and finally fill the flask up to 



