400 



EXCRETION 



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 c.c. 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, 

 2.33 X 25 = 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 remembered 

 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 chlo- 

 ride 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 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. Reprecipitate 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 chlorine 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 hydro- 

 chloric 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 



FIG. 308. The 

 Urinometer. 



