298 PHYSIOLOGICAL CHEMISTRY 



figure by two. This gives the excess of silver nitrate remain- 

 ing. 



Subtract the excess of silver solution from the total amount 

 added. This will give the amount of silver solution required 

 to precipitate the chlorides present. Since each cubic centimeter 

 of silver nitrate will precipitate the chloride from 0.01 grams 

 of sodium chloride, the sodium chloride in 10 c.c. of urine 

 may be calculated. From this, calculate the sodium chloride in 

 the 24 hour sample. 



14. Sulphates. 



The most accurate and satisfactory methods for estimating 

 sulphates are gravimetric. (See Folin's methods.) The sul- 

 phates are precipitated by adding barium chloride, the precipi- 

 tate collected and weighed. Inorganic sulphates are estimated 

 directly. Inorganic + ethereal, after the splitting of ethereal 

 sulphates by boiling with hydrochloric acid. Total sulphur is 

 estimated by fusing the urine with an oxidizing agent and 

 determining the sulphates as above. 



Neubauer has suggested the following approximate volu- 

 metric method which serves for most clinical purposes: 

 Measure 50 c.c. of urine into a flask, add 3 c.c. pure HC1 and 

 boil gently for 15 minutes to decompose the ethereal sul- 

 phates. From a burette run in standard barium chloride solu- 

 tion (1 c.c. = 0.01 gm. SO 3 ) as long as a precipitate forms, 

 the mixture being kept hot. After running in the first 3-4 

 c.c. of barium chloride, allow the precipitate to settle and 

 with a glass rod remove a drop of the liquid. Place it on a 

 watch glass over a black surface and add a few drops of the 

 BaCl 2 solution. If there is a precipitate, return the whole 

 to the flask, rinsing in the last traces with water, and add 

 more BaCl 2 . Again allow to settle and test as before. Pro- 

 ceed until no more BaS0 4 is precipitated. Excess of BaCl 2 

 must be avoided. When the minimal excess has been added, 

 a drop of the clear fluid removed from the flask will give only 

 a cloudiness with a drop of dilute H 2 S0 4 . If more than a 



