86 CHEMICAL PHYSIOLOGY. 



(/.) To urine add excess of ammonium chloride, and 

 ammonia = a white precipitate of earthy phosphates and 

 oxalate of lime. Filter, and to the nitrate add a solution of 

 magnesic sulphate = a precipitate of the alkaline phosphates 

 as triple phosphate. If the filtrate be tested for phosphoric- 

 acid by 6 (c.) no precipitate will be found. 



(g.) Instead of 6 (/) use magnesia mixture, composed of 

 magnesic sulphate and ammonium chloride, each 1 part, 

 distilled water 8 parts, and liquor ammonise 1 part. It gives 

 the same result as in 6 (f.) 



(h.) To urine add a few drops of acetic acid, and then 

 uranium acetate or nitrate - bright yellow or lemon- 

 coloured precipitate of uranium and ammonium double 

 phosphate. 2(Ur 2 O 3 )NH 4 PO 4 . 



This reaction forms the basis of the process for the volumetric 

 estimation of the phosphoric acid. 



7. The other fact connected with the volumetric estimation of 

 phosphoric acid is, that when a uranic salt is added to a solution 

 of potassium ferrocyanide, a reddish-brown colour is obtained. 



(a.) To a very dilute solution of uranium acetate add 

 potassium ferrocyanide = a brown colour. 



8. In some pathological urines the phosphates are deposited on 

 boiling. 



(a.) Boil such a urine = a precipitate. It may be phos- 

 phates or albumin. An albuminous precipitate falls before 

 the boiling point is reached, and phosphates when the fluid 

 is boiled. Add a drop or two of nitric or acetic acid. If 

 it is phosphates, the precipitate is dissolved; if albumin, it is 

 unchanged. 



9. Microscopic Examination. As the alkaline phosphates are 

 all freely soluble in water, they do not occur as a urinary deposit. 

 The earthy phosphates, however, may be deposited. 



(a.) Examine a preparation or a deposit of calcic phos- 

 phate, which may exist either in the amorphous form, 



