PHOSPHATES 



427 



58.25 grains of solids are contained in 1,000 grains of the urine. Or the 

 total solids are 5.825 per cent. In using this method it must be remem- 

 bered that the limits of error are much wider in diseased than in healthy 

 urine. 



The solids of urine consist of inorganic salts of sodium, potassium, and 

 calcium, and of a long list of organic compounds, chiefly nitrogenous. 



7. Chlorides. Large quantities of sodium chloride are always present 

 in the normal urine. Add ammonia to 25 or 50 c.c. of albumin-free urine 

 and heat to precipitate earthy phosphates, filter. To a 



sample of the nitrate add an excess of strong nitric acid 

 and a few drops of i per cent, silver nitrate. A white 

 flocculent precipitate of silver chloride comes down. This 

 precipitate is soluble in an excess of ammonia. Repre- 

 cipitate by adding nitric acid again. The test may be 

 made without removing the phosphates, though in this 

 case, upon adding ammonia, the disappearance of the 

 silver precipitate is complicated by the appearance of 

 insoluble phosphates. 



The chlorides may be estimated quantitatively by 

 Yolhard's method, or some one of its modifications, which 

 depends upon the determination of the amount of chloride 

 precipitated by the silver. The student is referred to 

 chemical text-books for this and other quantitative 

 methods. 



8. Sulphates. Sulphates exist in the urine both in 

 inorganic and organic compounds, chiefly the former. 

 Add a few drops of hydrochloric acid to a sample of 



urine in a test-tube, then a solution of barium chloride, the insoluble barium 

 sulphate settles out. If the test is made on the normal urine without the 

 addition of the acid, the inorganic sulphate will be precipitated, while the 

 ethereal or compound sulphate will remain in solution and can be filtered 

 off. This filtrate, when boiled with strong hydrochloric acid to 10 per cent, 

 over a water bath for a short time, will have the sulphates split off from the 

 organic radicle and may be precipitated by the addition of barium chloride 

 in hot solution. 



9. Phosphates. The phosphates of urine consist of the earthy and 

 alkaline salts, the latter predominating. Take a 50 c.c. sample of urine, 

 add strong ammonia, and heat. The phosphates of calcium and magnesium 

 separate out, as they are insoluble in alkaline solution. Filter. 



To the filtrate add a solution of magnesium sulphate. This precipitates 

 the sodium and potassium phosphates as a triple phosphate of magnesium 

 which is insoluble. Test for phosphates in general are: 



Add nitric acid to a sample of urine, warm gently, then add a few drops 



FIG. 308. The 

 Urinometer. 



