434 PEACTICAL PHYSIOLOGY 



Place 50 c.c. urine in a round bottom litre flask A (Fig. 248), add 20 grm. 

 sodium chloride to prevent decomposition and 50 c.c. methyl alcohol to reduce 

 the boiling point of the mixture. In flask B place 50 c.c. or less JV/IO acid and 

 in C 10 c.c. N/10 acid, diluted in both cases with a little water. The flasks may 

 be tilted obliquely, and should be large enough to prevent loss of acid by spraying 

 during the violent commotion which is set up by the rapid passage of steam. If 

 such loss should occur, the acid may be recovered by rinsing out the flask D. 

 When the apparatus is ready, 1 grm. of dry sodium carbonate is added to the 

 liquid in the flask A, the stopper is rapidly inserted and the suction started. 

 The pump will quickly reduce the pressure to about 30 mm., and the liquid in A, 

 which is warmed up to about 40 C. in a water-bath, will begin to boil. The 

 temperature of the bath must be maintained and should not be allowed to rise 

 above 50 C. for fear of decomposing urea. When the boiling has continued for 

 fifteen minutes, all the ammonia will have been given oft 7 and the operation is 

 stopped by slowly letting in air by the stop-cock a. The acid in B and C is 

 titrated, after a few drops of a 1 per cent, solution of Alizarin red have been added 

 as the indicator. 



CHAPTER XIX. 



THE INORGANIC ACID RADICLES OF URINE. 

 URINARY DEPOSITS. 



Chloride. 



EXPERIMENT I. Add to urine a few drops of nitric acid, and then 

 silver nitrate solution. A white precipitate of silver chloride forms, 

 which is soluble in ammonia. The nitric acid prevents the precipitation 

 of other silver salts such as phosphate. 



Estimation of Chloride. Volhard's Method. The chloride is 

 precipitated by the addition of a known excess of silver nitrate in 

 the presence of nitric acid, and the excess of silver nitrate deter- 

 mined by titrating a known part of the filtered solution with 

 potassium sulphocyanide solution, which precipitates the silver, using 

 ferric alum to indicate when the sulphocyanide has been added in 

 slight excess. 



Into a 100 c.c. graduated flask measure with a pipette 10 

 c.c. urine free from albumin. Add 5 c.c. pure nitric acid and 



N 

 30 c.c. y~r silver nitrate solution (17 grm. per litre) measured with 



a pipette. Add distilled water up to the 100 c.c. mark and rinse 

 thoroughly. Filter the liquid through a dry chloride free filter into 

 a dry clean beaker. Measure 50 c.c. of the filtrate with a pipette 

 into an evaporating dish. Add 10 to 20 c.c. 10 per cent, ferric alum 



N 

 solution, and run in from a burette potassium sulphocyanide 



