422 A MANUAL OF PHYSIOLOGY 



Suppose x cc. of the sulphocyanide solution are required, then 

 the chlorine in 10 cc. of urine evidently corresponds to (15-^, 

 o'oi gramme Nad. 



4. Phosphates. (i) Qualitative Tests. (a) Render the urine alka- 

 line with ammonia. A precipitate of earthy phosphates (calcium 

 and magnesium phosphates) falls down. Filter. To the filtrate add 

 magnesia mixture (a mixture of sulphate or chloride of magnesium, 

 ammonium chloride and ammonia) ; a precipitate shows the presence 

 of alkaline phosphates (sodium, potassium, or ammonium phos- 

 phates). The precipitate is ammonio-magnesic or triple phosphate. 

 (b) Add to urine half its volume of nitric acid and a little molybdate 

 of ammonium, and heat. A yellow precipitate of ammonium phospho- 

 molybdate shows that phosphates are present. This test is given 

 both by alkaline and earthy phosphates. 



(2) Quantitative Estimation. The quantitative estimation of phos- 

 phoric acid in urine is best done volumetrically, by titration with a 

 standard solution of uranium nitrate, using ferrocyanide of potassium 

 as the indicator. Uranium nitrate gives with phosphates, in a solu- 

 tion containing free acetic acid, a precipitate with a constant pro- 

 portion of phosphoric acid. As soon as there is more uranium in 

 the solution than is required to combine with all the phosphoric acid, 

 a brown colour is given with potassium ferrocyanide, due to the 

 formation of uranium ferrocyanide. In carrying out the method, 

 5 c.c. of a mixture of acetic acid and sodium acetate (there are 

 10 grammes of sodium acetate and 10 grammes of glacial acetic acid 

 in 100 c.c. of the mixture) are added to 50 c.c. of urine, which is 

 then heated in a beaker on the water-bath to about 80 C. The 

 standard uranium solution (which contains 35*5 grammes of uranium 

 nitrate in the litre, and i c.c. of which corresponds to 0*005 gramme 

 P 2 O 5 ) is now run in from a burette, until a drop of the urine gives, 

 with a drop of potassium ferrocyanide solution, on a porcelain slab, 

 a brown colour. Uranium acetate may be used instead of uranium 

 nitrate, but the latter keeps best. 



5. Sulphates (i) Qualitative Test. Add to urine a drop of 

 hydrochloric acid and then a few drops of barium chloride. A 

 white precipitate comes down, showing that inorganic sulphates 

 are present. The hydrochloric acid prevents precipitation of the 

 phosphates. 



(2) Quantitative Estimation of the Sulphuric Acid united with 

 Inorganic Bases. Acidulate 100 c.c. of albumin-free urine with acetic 

 acid, add excess of barium chloride, and heat on the water-bath till 

 the precipitate has settled ; filter through an ash-free filter, wash the 

 precipitate with water, with dilute hydrochloric acid, then again with 

 water. Dry, incinerate in a platinum or porcelain dish, and weigh. 

 From the weight of barium sulphate the inorganic sulphuric acid is 

 easily calculated (SO 4 in i gramme of barium sulphate = 0-4 1187 

 gramme). 



(3) Quantitative Estimation of the Sulphuric Acid united with 

 Aromatic Bodies (aromatic or organic sulphuric acid). Add to the 

 filtrate and the washings from (2) a little hydrochloric acid, and heat 



