EXAMINATION OF NORMAL AND ABNORMAL URINE. 383 



over sulphuric acid), until it is found that no more loss in weight 

 ensues on continued exposure of the dish in the drying appa- 

 ratus. By now reweighing the dish, plus contents, and deduct- 

 ing from the weight that of the empty dish, the weight of total 

 solids is found. 



Determination of inorganic constituents. The platinum dish 

 containing the known quantity of total solids is exposed to the 

 action of a non-luminous flame, and the heat continued until all 

 organic matter has been destroyed and expelled. By reweigh- 

 ing now, and deducting the weight of the platinum dish, plus 

 ash from the weight of the dish, plus total solids, the quantity 

 of total organic matter is determined; and by deducting weight 

 of dish from weight of dish plus ash, the total quantity of inor- 

 ganic matter is found. 



The analysis of this ash is effected by the methods given in 

 connection with the consideration of the various acid and basic 

 constituents themselves. Chlorine is determined by precipitating 

 the solution of the ash in nitric acid with silver nitrate, sulphuric 

 acid by barium chloride, phosphoric acid by ammonium molyb- 

 date, calcium by ammonium oxalate, potassium by platinic chlo- 

 ride, iron by potassium ferrocyanide, etc. 



For the determination of many of the inorganic constituents, 

 it is not necessary to destroy the organic matter as described 

 above, but this determination can be effected directly. Thus, 

 chlorine may be precipitated directly from urine (slightly acidu- 

 lated with nitric acid) by silver nitrate; the precipitated silver 

 chloride is collected upon a small filter, well washed, dried, and 

 weighed in a porcelain crucible, after the filter (to which par- 

 ticles of silver chloride adhere) has been burned separately and 

 its ash added to the contents of the crucible, which is moderately 

 heated before weighing. 



The so-called earthy phosphates (phosphates of calcium and 

 magnesium) may be approximately determined by adding a few 

 drops of an alkaline hydrate to about 50 c.c. of urine, heating 

 to the boiling-point, collecting on a filter, washing, igniting, 

 and weighing in a platinum crucible. 



The methods for estimating urea and uric acid have been de- 

 scribed in the preceding chapter. 



