VOLUMETRIC ANALYSIS FOR UREA. 95 



the Indicator. 1 cc. of the SS. (Mercuric Nitrate) = -01 gramme 

 urea. 



(a.) Collect the urine of the twenty -four hours, and 

 measure the quantity. 



(b.) If albumin be present separate it by acidification, 

 boiling, and filtration. 



(c.) Mix 40 cc. of urine with 20 cc. i.e., half its volume 

 of a solution of barium nitrate, and barium hydrate (com- 

 posed of one volume of solution of barium nitrate and two 

 volumes of barium hydrate both saturated in the cold). This 

 precipitates the phosphates, sulphates, and carbonates. 



(d.) Filter through a dry filter to get rid of the above 

 salts. While filtration is going on, fill the burette with 

 the standard solution (SS.) of mercuric nitrate up to the 

 mark on the burette. See that there are no air-bubbles, 

 and that the outflow tube is also filled. 



(e.} With a pipette take 15 cc. of the clear filtrate and 

 place it in a beaker. N.B. This corresponds to 10 cc. of 

 urine. Place a few drops of the sodic carbonate solution 

 (the indicator) on a piece of glass resting on a black back- 

 ground. 



(/.) Note the height of the fluid in the burette. Bun in 

 the SS. of mercuric nitrate from the burette into the 15 cc. 

 of the mixture, in small quantities at a time, until the preci- 

 pitate ceases. Stir and mix thoroughly with a glass rod. 

 After each addition, with the glass rod lift out a drop of the 

 mixture and place it on one of the drops of sodic carbonate 

 until a pale yellow colour is obtained. This indicates that 

 all the urea has been precipitated, and that there is an 

 excess of mercuric nitrate. Read off the number of cc. of 

 the SS. used. 



(g.) Repeat the experiment with a fresh 15 cc. of the 

 filtrate, but run in the greater part of the requisite SS. at 

 once before testing with sodic carbonate. 



Read off the number of cc. of the SS. used, and deduct 2 cc.; 

 multiply by *01, which gives the amount (in grammes) of urea in 

 10 cc. of urine. 



