344 PHYSIOLOGICAL CHEMISTRY 



pipette 10 c.c. urine and 20 c.c. standard silver nitrate solution. 

 Add about 4 c.c. cone, nitric acid and about 5 c.c. iron alum 

 solution. Add distilled 'water up to the 100 c.c. mark, stopper 

 and mix thoroughly. Filter through a dry filter into a dry 

 vessel. The above process will have precipitated all chlorides 

 as AgCl, and an excess of silver nitrate will be left over. 



Accurately measure 50 c.c. of the filtrate into an Erlenmeyer 

 or beaker and titrate the excess of silver with standard thio- 

 cyanate to a permanent faint pink or reddish-brown. The 

 amount of thiocyanate used corresponds to the excess of silver 

 remaining in the solution. 



One c.c. thiocyanate corresponds to 1 c.c. of the standard sil- 

 ver nitrate. 



One c.c. standard silver nitrate corresponds to 0.01 g NaCl. 

 Since only half the liquid was titrated, multiply the titration 

 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. 



43. 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: 



