176 URIC ACID. 



a dry filter paper. Measure off 15 c.c. of the filtrate 

 (=10 c.c. of urine) into a small beaker, add the standard 

 nitrate of mercury solution from a burette or other 

 graduated vessel until a drop of the mixture when 

 added to a drop of carbonate of soda solution on the 

 glass plate produces a distinct yellow colour in two 

 seconds. When this colour appears read off the 

 number of cubic centimetres used ; each cubic centi- 

 metre required indicates 1 centigramme of urea in the 

 10 c.c. of urine. Thus, if 25 c.c. of mercury solution 

 were used there would be 25 centigrammes or 0*25 

 grin, in 10 c.c. or 25 grm. in the litre. 



Uric acid, C 5 H 4 N 4 3 . 1. Obtain from human urine 

 by adding to it -^ hydrochloric acid, let stand in a 

 warm place at first, afterwards in the cold, and collect 

 the precipitate of crystallised coloured acid. Purify as 

 described in 2. 



2. Obtain from excrements of serpents by dissolving 

 them in hot caustic soda ley, boiling to expel am- 

 monia, precipitating urate by a current of carbonic 

 acid, dissolving the urate in caustic soda, and pouring 

 this solution in hot dilute hydrochloric acid. White 

 uric acid in crystals is deposited. 



3. Observe its forms of crystallisation under the 

 microscope, and make yourself acquainted with the 

 principal typical forms (rhombic prisms and plates) 

 which the acid assumes, particularly when it is depo- 

 sited spontaneously in the urinary passages or in the 

 urine after emission. 



