382 PHYSIOLOGICAL CHEMISTRY. 



the color varies, add more uranium solution, drop by drop, until a 

 permanent coloration is obtained after warming, and now repeat 

 the test with another 50 c. c. of the urine. The calculation is so 

 simple that it is unnecessary to give an example. 



In the above manner we determine the total quantity of phos- 

 phoric acid in the urine. If we wish to know the phosphoric acid 

 combined with alkaline earths or with alkalies, we first determine 

 the total phosphoric acid in a portion of the urine and then remove 

 the earthy phosphates in another portion by ammonia. The precip- 

 itate is collected on a filter, washed, transferred in a beaker with 

 water, treated with acetic acid, and dissolved by warming. This 

 solution is now diluted to 50 c. c. with water, and 5 c. c. sodium- 

 acetate solution added, and titrated with uranium solution. The 

 difference between the two determinations gives the quantity of 

 phosphoric acid combined with the alkalies. 



Sulphates. The sulphuric acid of the urine originates only to a 

 very small extent from the. sulphates of the food. A dispropor- 

 tionally greater part is formed by the burning of the proteids con- 

 taining sulphur within the body, and it is chiefly this formation of 

 sulphuric acid from the proteids which gives rise to the previously- 

 mentioned excess of acids over the bases in the urine. The quan- 

 tity of sulphuric acid eliminated by the urine amounts to about 2.5 

 grms. H 2 S0 4 per twenty-four hours. As the sulphuric acid chiefly 

 originates from the proteids, it follows that the elimination of 

 sulphuric acid and the elimination of nitrogen are nearly parallel, 

 and the relationship N : H 2 S0 4 is about 5 : 1. Sulphuric acid 

 occurs in the urine partly preformed (sulphate-sulphuric acid) and 

 partly as ethereal sulphuric acid. 



The quantity of total sulphuric acid is determined in the fol- 

 lowing way, but at the same time the precautions described in 

 other works must be observed: 100 c. c. of filtered urine are 

 treated with 5 c. c. concentrated hydrochloric acid and boiled for 

 fifteen minutes. While boiling precipitate with 2 c. c. of a satu- 

 rated BaCl 2 solution and warm for a little while until the barium 

 sulphate has completely settled. The precipitate must then be 

 washed with water or with alcohol and ether (to remove resinous 

 substances) and then treated according to the usual method. 



The separate determination of the sulphate-sulphuric acid and 

 the ethereal sulphuric acid may be done, according to BAUMASTN'S 

 method, by first precipitating the sulphate-sulphuric acid from the 

 urine acidified with acetic acid, by BaCl a , and then decomposing 

 the ethereal sulphuric acid by boiling after the addition of hydro- 



