552 PHYSIOLOGICAL CHEMISTRY 



carefully over a small flame till the contents are black, and then heat to redness for 

 only two minutes. Cool, add 2 c.c. of hydrochloric acid (1:4) and warm. Neutralize 

 the clear solution with NaOH (10 per cent) and again acidify with i drop of HC1 

 (i 14). Add 25 c.c. of a solution of benzidine hydrochloride 1 with stirring. Let 

 stand 15 minutes and then filter off on an asbestos filter. Transfer the precipitate 

 to the filter by means of the filtrate and wash with 5 c.c. of cold water, drop by drop. 

 Put the filter into a 500 c.c. Erlenmeyer flask, add i c.c. of NaOH (10 per cent) and 

 200 c.c. of water. Boil the suspension for five minutes and then cool to room tem- 

 perature. Add 20 c.c. concentrated sulphuric acid and titrate the warm solution at 

 once with N/io potassium permanganate solution till a distinct pink coloration is 

 obtained, which should last 20 seconds. In titrating at first add only about 0.5 c.c. 

 at a time and toward the end only 2 drops at a time, waiting till the color disappears 

 before further addition of permanganate solution. As the titration progresses it. 

 will be noticed that the yellow color gradually disappears, the solution turning prac- 

 tically colorless. It is at this stage of the titration that care should be taken in add- 

 ing only 2 drops of permanganate at a time. 



Calculation. One c.c. of N/io potassium permanganate is equivalent to 0.099 

 mg. of sulphur. Multiply the number of cubic centimeters of permanganate used 

 by 0.099 an d divide by 2 in order to obtain the weight of sulphur in i c.c. of urine. 

 Calculate the day's sulphur output. 



Interpretation. See page 549. 



Phosphorus 



i. Total Phosphates. Uranium Acetate Method. Principle 

 Standard uranium acetate is run into a measured quantity of urine 

 until all of the phosphate has been precipitated as insoluble uranium 

 phosphate. An excess of uranium is indicated by a reddish coloration 

 with potassium ferrocyanide. This method is accurate and gives 

 practically the total phosphorus of urine inasmuch as the latter exists 

 generally almost entirely as phosphates. 



Procedure. To 50 c.c. of urine in a small beaker or Erlenmeyer flask add 

 5 c.c. of a special sodium acetate solution 2 and heat the mixture to the boiling- 

 point. From a burette, run into the hot mixture, drop by drop, a standard solu- 

 tion of uranium acetate 3 until a precipitate ceases to form and a drop of the mix- 

 ture when removed by means of a glass rod and brought into contact with a 



1 Six and seven-tenths grams of benzidine (Merck reagent) are put in a i -liter flask, 29 

 c.c. of hydrochloric acid (sp. gr. i. 12) added and the solution diluted up to the mark. 



2 The sodium acetate solution is prepared by dissolving 100 grams of sodium acetate in 

 800 c.c. of distilled water, adding 100 c.c. of 30 per cent acetic acid to the solution, and 

 making the volume of the mixture up to i liter with water. 



3 Uranium Acetate Solution. Dissolve about 35.0 grams of uranium acetate in i liter 

 of water with the aid of heat and 3-4 c.c. of glacial acetic acid. Let stand a few days 

 and filter. Standardize against a phosphate solution containing 0.005 gram of P^Os per 

 cubic centimeter. For this purpose dissolve 14.721 grams of pure air-dry sodium am- 

 monium phosphate (NaNH 4 HPO 4 +4H 2 O) in water to make a liter. To, 20 c.c. of this 

 phosphate solution in a 200 c.c. beaker add 30 c.c. of water and 5 c.c. of sodium acetate 

 solution (see above) and titrate with the uranium solution to the correct end reaction as 

 indicated in the method above. If exactly 20 c.c. of uranium solution are required i c.c. 

 of the solution is equivalent to 0.005 gram PzO^. If stronger than this dilute accordingly 

 and check again by titration. 



