THE INORGANIC CONSTITUENTS OF THE URINE. 219 



Of other inorganic constituents, every urine also contains iron 

 (partly in organic combination), silicates, fluorides, hydrogen per- 

 oxide, and nitrates, all of which, however, are present only in 

 traces. The nitrates are probably introduced with vegetable food, 

 and disappear from the urine during starvation. During ammo- 

 niacal fermentation they are reduced to nitrites, and later disappear. 



The quantitative variations of the inorganic constituents of human 

 urine are shown in the following table : 



Chlorides (calculated as HC1) 6.2-9.4 grammes. 



Phosphates (calculated as P 2 O 5 ) 2.5-3.0 " 



Sulphates (calculated as II 2 SO 4 ) 2.0-2.5 " 



Sodium (calculated as Na. 2 O) 4.0-6.0 " 



Potassium (calculated as K 2 O) . 2.0-3.0 " 



Ammonium (calculated as NH 3 ) 0.7 gramme. 



Magnesium (calculated as MgO) 0.5-0.6 " 



Calcium (calculated as CaO) 0.2-0.4 " 



Quantitative Estimation of the Mineral Ash. 



Ten c.c. of urine are placed in a weighed crucible and evaporated 

 at a temperature of about 100 C. The crucible is then covered 

 with its lid and carefully heated over a small flame until the organic 

 matter has been carbonized and fumes are no longer evolved. On 

 cooling, the residue is extracted with boiling water. The washings 

 are passed through a small filter, the weight of the ash of which is 

 known, and the filter, together with the carbonaceous residue, is 

 incinerated until a white ash is obtained. This process may be 

 aided, if necessary, by moistening the material with a little alcohol 

 or water. The washings are then placed in the crucible and evapo- 

 rated at 100 C. The residue is finally dried in a hot-air bath, 

 heated until the bottom of the crucible just turns red, and is then 

 allowed to cool over sulphuric acid and weighed. The weight of the 

 mineral ash of the 10 c.c. of urine is then ascertained by deducting 

 that of the crucible and the ash of the filter. 



Quantitative Estimation of the Chlorides. 



The chlorides of the urine are most conveniently estimated accord- 

 ing to the method of Salkowski-Volhard. To this end, 10 c.c. of 

 urine are diluted with 50 c.c. of distilled water, and treated with 4 

 c.c. of concentrated nitric acid and 15 c.c. of a standard solution of 

 silver nitrate. The mixture is further diluted to 100 c.c., thor- 

 oughly agitated, and passed through a dry filter. In a carefully 

 measured portion of the filtrate the excess of silver is then titrated 

 with a solution of potassium sulphocyanide of such strength that 25 

 c.c. correspond to 10 c.c. of the silver solution. A few drops of a 

 saturated solution of ammonio-ferric alum serve as indicator. The 

 amount of silver solution used in the precipitation of the chlorides 

 in the 10 c.c. of urine is then calculated. The number of cubic 

 centimeters which was necessary for this purpose, multiplied by 



