450 



EXCRETION 



After standing some time the reaction is usually alkaline, owing to fer- 

 mentation processes. The reaction may vary also according to the food, 

 vegetable foods tending to produce alkaline urine, while with animal foods 

 the reaction is acid. 



6. The Total Quantity of Solids. Determine the solids of urine 

 by evaporating 25 cc. of a mixed sample of urine to dryness in a weighed 

 platinum or porcelain dish over a water bath. The residue should be dried 

 to constant weight in a drying oven at 105 C. 



A useful rule for approximately estimating the total solids in any given 

 specimen of healthy urine is to multiply the last two figures representing the 

 specific gravity by 2 . 33. Thus, in urine of specific gravity 1025, 2.33X25 = 

 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 cc. of albumin-free urine 



and heat to precipitate earthy phosphates, filter. To a 

 sample of the filtrate 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 

 Volhard'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 chem- 

 ical 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 pre- 

 cipitated, 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 sul- 



FIG. 308. The 

 Urinometer. 



