568 PHYSIOLOGICAL CHEMISTRY 



(e) Neutral Sulphur. Neutral sulphur is most readily determined by dif- 

 ference. Subtract from the total sulphur as determined by one of the methods 

 given above the amount of total sulphates. 



Interpretation. The neutral sulphur of the urine is made up of 

 cystine and related bodies, thiocyanate, oxyproteic acids, etc. It 

 makes up ordinarily from 5-25 per cent of the total sulphur of the urine, 

 or on the average 0.2 to 0.4 gram per day calculated as SOs. The 

 absolute amount is fairly constant for a given individual through wide 

 variations of protein intake, indicating that its origin is mainly en- 

 dogenous, that is, that it arises principally from the decomposition of 

 tissue protein. On this account the percentage of the total sulphur 

 excretion existing in the neutral form may rise to 25 per cent on a very 

 low protein diet and decrease to 5 per cent on a high protein diet, the 

 absolute amount remaining nearly constant. In fasting percentages 

 as high as 70 have been noted. In many disorders as tuberculosis, 

 cancer, cystinuria, etc., the amount may be relatively and in some 

 cases absolutely increased but no fixed relations have been determined 

 for the various conditions. 



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 1 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 



(Jour. Biol. Chem., 46, 285, 1921) has suggested a method which is applicable 

 to small volumes of urine. 



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 P2O per 

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

 monium phosphate (NaNH 4 HPO4+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 PjO B . If stronger than this dilute accordingly 

 and check again by titration. 



