356 PHYSIOLOGICAL CHEMISTRY. 



and then add sufficient ammonium chloride to dissolve the precipitate and 

 lastly dilute to 1 litre. 3. SODIUM- SULPHIDE SOLUTION. Dissolve 10 grms. 

 caustic soda which is free from nitric and nitrous acids in 1 litre of water. 

 One half of this solution is completely saturated with hydrogen sulphide and 

 then mixed with the other half. 



The solutions are such that 10 c. c. of each is sufficient for 100 

 c. c. of the urine. 



100-200 c. c., according to concentration, of the filtered urine 

 freed from albumin (by boiling after the addition of a few drops of 

 acetic acid) are poured into a beaker. In another vessel mix 10-20 

 c. c. of the silver solution with 10-20 c. c. of the magnesium mix- 

 ture, and add ammonia, and when necessary also some ammonium 

 chloride, until the mixture is clear. This solution is added to the 

 urine while stirring, and the mixture allowed to stand quietly for 

 J- hour. The precipitate is collected on a filter, washed with am- 

 moniacal water, and then returned to the same beaker by the aid 

 of a glass rod and a spirit-bottle without destroying the filter. Now 

 heat to boiling-point 10-20 c. c. of the alkaline sulphide solution, 

 which has previously been diluted with an equal amount of water, 

 and allow this solution to flow through the above filter into the 

 beaker containing the silver precipitate, wash with boiling water, 

 and warm the contents of the beaker on the water-bath for a time, 

 stirring constantly. After cooling filter into a porcelain dish, wash 

 with boiling water, acidify the filtrate with hydrochloric acid, evap- 

 orate to about 15 c. c., add a few drops more of hydrochloric acid, 

 and allow it to stand for 24 hours. The uric acid which has crys- 

 tallized is collected on a small weighed filter, washed with water, 

 alcohol, ether, and carbon disulphide, dried at 100-110 C., and 

 weighed. For each 10 c. c. of the watery filtrate we must add 

 0.00048 grm. uric acid to the amount found directly. Instead of 

 the weighed filter-paper a glass tube filled with glass wool may be 

 substituted. This tube was constructed by LUDWIG, and is' de- 

 scribed in other hand books. 



HAYCRAFT'S METHOD: 25 c. c. of the urine are first treated 

 with 1 grm. bicarbonate, then made strongly alkaline by ammonia, 

 and lastly precipitated by an ammoniacal silver solution. The 

 carefully washed precipitate is dissolved in 20-30$ nitric acid and 



n 

 this solution titrated with a j^ sulphocyanide solution according 



to VOLHARD'S method. Each c. c. of this solution corresponds to 

 0.00168 grm. uric acid. This method has been modified by CZA- 

 PEK. After the addition of a known amount of silver solution of 

 known strength, the amount of silver salts remaining in the urine 

 after all the uric acid has been precipitated is titrated with alkali 

 sulphide. The advantage of HAYCRAFT'S method is the ease and 

 rapidity with which it can be performed, and it is therefore recom- 



