PHYSIOLOGICAL CHEMISTRY 



dilute it with 75 c.c. of water and acidify the mixture with 30 c.c. of dilute hydro- 

 chloric acid (i volume of concentrated HC1 to 4 volumes of water). To the cold 

 solution add 20 c.c. of a 5 per cent solution of barium chloride, drop by drop. 1 

 Allow the mixture to stand about one hour, then filter it through a dry filter paper. 2 

 Collect 125 c.c. of the nitrate and boil it gently for at least one-half hour. Cool 

 the solution, filter off the precipitate of BaSO 4 , wash, dry and ignite it according to 

 the directions given on page 546. 



Calculation. The weight of the BaSO 4 precipitate should be multiplied by 

 2 since only one-half (125 c.c.) of the total volume (250 c.c.) of fluid was precipi- 

 tated by the barium chloride. The remaining calculation should be made accord- 

 ing to directions given under Total Sulphates, page 546. 



Calculate the quantity of ethereal sulphates, expressed as SO 3 , in the twenty- 

 four-hour urine specimen. 



Interpretation. The excretion of ethereal sulphates (expressed as 

 SOs) varies ordinarily from o.i to 0.25 gram per day comprising from 

 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. 3 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. 4 of Benedict's sulphur reagent 6 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 



1 See note (3) at the bottom of p. 546. 



2 This precipitate consists of the inorganic sulphates. If it is desired, this BaSC>4 

 precipitate may be collected in a Gooch crucible or on an ordinary quantitative filter 

 paper and a determination of inorganic sulphates made, using the same technic as that 

 suggestedtabove. In this way we are enabled to determine the inorganic and ethereal 

 sulphates in the same sample of urine. 



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



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



6 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. 



