URINE 565 



5 to 15 per cent of the total sulphur excretion. The absolute amount 

 of ethereal sulphate increases with increase in the protein of the diet and 

 particularly with increase of putrefactive processes in the intestine or 

 elsewhere. The amount excreted cannot however be taken as an 

 index of the extent of intestinal putrefaction. 



4. Total Sulphur. Benedict's Method. 1 Principle. The urine 

 is evaporated and ignited with a solution of copper nitrate and 

 potassium chlorate. Organic matter is thus destroyed and all un- 

 oxidized sulphur is oxidized to the sulphate form and can be readily 

 precipitated with barium chloride in the usual manner. The method 

 is very convenient and accurate. 



Ten c.c. of urine are measured into a small (7-8 cm.) porcelain evaporating dish 

 and 5 c.c. 2 of Benedict's sulphur reagent 3 added. The contents of the dish are 

 evaporated over a free flame which is regulated to keep the solution just below the 

 boiling-point, so that there can be no loss through spattering. When dryness is 

 reached the flame is raised slightly until the entire residue has blackened. The 

 flame is then turned up in two stages to the full heat of the bunsen burner and the 

 contents of the dish thus heated to redness for ten minutes after the black residue 

 (which first fuses) has become dry. This heating is to decompose the last traces 

 of nitrate (and chlorate) . The flame is then removed and the dish allowed to cool 

 more or less completely. Ten to 20 c.c. of dilute (i : 4) hydrochloric acid is then 

 added to the residue in the dish, which is then warmed gently until the contents 

 have completely dissolved and a perfectly clear, sparkling solution is obtained. 

 This dissolving of the residue requires scarcely two minutes. With the aid of a 

 stirring rod the solution is washed into 4 a small Erlenmeyer flask, diluted with 

 cold, distilled water to 100-150 c.c., 10 c.c. of 10 per cent barium chloride solution 

 added drop by drop, and the solution allowed to stand for about an hour. It is 

 then shaken up and filtered as usual through a weighted Gooch crucible. Controls 

 should be run on the oxidizing mixture. 



Calculation. Make the calculation according to directions given under Total 

 Sulphates, page 563. Calculate the quantity of sulphur expressed as SO a or S, 

 present in the twenty-four-hour urine specimen. 



Interpretation. The total sulphur (S0 3 ) excretion averages about 2.5 

 grams per day. It runs more or less parallel with the decomposition 



1 Benedict: Journal of Biological Chemistry, 6, 363, 1909. 



2 If the urine is concentrated the quantity should be slightly increased. 



1 Crystallized copper nitrate, sulphur-free or of known sulphur content 200 grams. 



Sodium or potassium chlorate 50 grams. 



Distilled water to 1000 c.c. 



Denis has suggested the use of the following solution: 



Copper nitrate 25 grams. 



Sodium chloride. 25 grams. 



Ammonium nitrate 10 grams. 



Water to make 100 c.c. 



The procedure is the same as the above except that 25 c.c. of urine and 5 c.c. of reagent 

 are taken. It gives accurate results. 



4 Sometimes the porcelain glaze cracks during heating, in which case the solution should 

 be filtered into the flask. 



