764 URINE. 



smallest amount of soluble uranium salt. The solutions necessary for 

 the titration are: 1. A solution of a uranium salt of which each cubic 

 centimeter corresponds to 0.005 gram P2Os and which contains 20.3 

 grams of uranium oxide per liter. 20 cc. of this solution corresponds 

 to 0.100 gram P 2 O5. 2. A solution of sodium acetate. 3. A freshly 

 prepared solution of potassium ferrocyanide. 



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 titrat- 

 ing withasolution of sodium phosphate of known strength (10.085 grams crystallized 

 salt in 1 liter, which corresponds to 0.010 gram P 2 05 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 cor- 

 responds 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 deter- 

 minations gives the quantity of phosphoric acid combined with the 

 alkalies. The results obtained are not quite accurate, as a partial trans- 

 formation 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 



