PHOSPHATE DETERMINATION. 725 



The uranium solution is prepared from uranium nitrate or acetate. Dissolve 

 about 35 grams uranium acetate in water, add some acetic acid to facilitate solu- 

 tion, and dilute to 1 liter. The strength of this solution is determined by titrating 

 with a solution of sodium phosphate of known strength (10.085 grams crystallized 

 salt in 1 liter, which corresponds to 0.100 gram P 2 O 5 in 50 cc). Proceed in the 

 same way as in the titration of the urine (see below), and correct the solution by 

 diluting with water, and titrate again until 20 cc. of the uranium solution corre- 

 sponds exactly to 50 cc. of the above phosphate solution. 



The sodium-acetate solution should contain 10 grams sodium acetate and 

 10 grams cone, acetic acid in 100 cc. For each titration 5 cc. of this solution 

 is used with 50 cc. of the urine. 



In performing the titration, mix 50 cc. of filtered urine in a beaker 

 with 5 cc. of the sodium acetate, cover the beaker with a watch-glass, 

 and warm over the water-bath. Then allow the uranium solution to 

 flow in from a burette, and when the precipitate does not seem to increase, 

 place a drop of the mixture on a porcelain plate with a drop of the potas- 

 sium-ferrocyanide solution. If the amount of uranium solution added 

 has not been sufficient, the color will remain pale yellow and more uranium 

 solution must be added; but as soon as the slightest excess of uranium 

 solution has been used the color becomes a faint reddish brown. When 

 this point has been obtained, warm the solution again and add another 

 drop. If the color remains of the same intensity, the titration is ended; 

 but if 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 cc. of the urine. The calculation is so simple that 

 it is unnecessary to give an example. 



In the above manner one determines the total quantity of phosphoric 

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

 with alkaline earths and with alkalies, we first determine the total phos- 

 phoric acid in a portion of the urine and then remove the earthy phos- 

 phates in another portion by ammonia. The precipitate is collected on 

 a filter, washed, transferred into a beaker with water, treated with acetic 

 acid, and dissolved by warming. This solution is now diluted to 50 

 cc. with water, and 5 cc. sodium-acetate solution added, then titrated 

 with uranium solution. The difference between the two determinations 

 gives the quantity of phosphoric acid combined with the alkalies. The 

 results obtained are not quite accurate, as a partial transformation of 

 the monophosphates of the alkaline earths and also calcium diphosphate 

 into triphosphates of the alkaline earths and ammonium phosphate takes 

 place on precipitating with ammonia, and the method gives too high 

 results for the phosphoric acid combined with alkalies and remaining 

 in solution. 



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

 small extent from the sulphates of the food. A disproportionately 

 greater part is formed by the burning within the body of the proteins 

 which contain sulphur, and it is chiefly this formation of sulphuric acid 

 from the proteins which gives rise to the previously mentioned excess 

 of acids over the bases in the urine. The quantity of sulphuric acid 

 eliminated by the urine amounts to about 2.5 grams H2SO4 per day. 



