356 ANALYSIS OF URINE. [CH. XIII. 



416. The estimation of inorganic sulphates by Folin's method. 



Place 25 cc. of urine and 100 cc. of water in a 250 cc. Erlenmeyer 

 flask. Acidify with 10 cc. of hydrochloric acid (i volume of con- 

 centrated HC1 to 4 volumes of water). Add 10 cc. of 5 per cent, 

 barium chloride, drop by drop, as in the previous exercise, and 

 proceed as there directed. 



Calculation. The same as for total sulphates. 



Ethereal Sulphates. 



This can be found by difference. Total sulphates less inorganic 

 sulphates = ethereal sulphates. 



417. The estimation of total sulphur by Benedict's method.* 



Place 10 cc. of urine in a small (7-8 cm.) porcelain or silica 

 crucible and add 5 cc. of Benedict's sulphur reagent. Evaporate 

 over a free flame, keeping the solution just below the boiling point, 

 to prevent loss by spattering. When dry, raise the flame slightly 

 until the entire residue has blackened. Raise the flame still more 

 and heat to redness for ten minutes after the black residue (which 

 first fuses) has become dry. Allow the dish to cool. Add 10 to 20 

 cc. of i in 4 hydrochloric acid, and heat again till the residue has 

 completely dissolved to a clear solution. Wash the contents 

 quantitatively into an Erlenmeyer flask, and dilute with cold water 

 to 100 to 150 cc. Add 10 cc. of 10 per cent, barium chloride, drop 

 by drop, and allow to stand for about an hour. Shake thoroughly 

 and proceed as in Ex. 415. 



Calculation. Weight of BaSO 4 from 10 cc. of urine multiplied by 3*413 

 = SO 8 per cent. 



NOTE. Benedict's sulphur reagent is : 



Crystallised copper nitrate, 200 grams. 

 Potassium chlorate, 50 grams. 

 Distilled water to i litre. 



Neutral Sulphur. 



This can be found by difference. Total sulphates less total 

 sulphur = neutral sulphur. 



* Journ. Biol. Chem., vi., p. 363. 



