220 § 113. FERTILIZERS. 



nation. In the urine of ruminants, pliosphoric acid u 

 found in hardly determinable quantity, while in that of 

 swine and often of calves, it is present in larger quantit}-, 

 and should be estimated. 



(/. Chlorine and urea. — These are determined with the 

 aid of the standard solution of mercuric nitrate. The 

 urine must first be freed from phosphoric and hippuric 

 acids. 



Acidify 200 c.c. with nitric acid, boil the mixture to ex- 

 pel the carbonic acid, neutralize the nitric acid with 

 freshly ignited magnesia, and cool the liquid to the tem- 

 perature of the room, by immersing the flask in cold wa- 

 ter ; transfer the liquid to a graduated cylinder, rinse the 

 flask into the cylinder and bring the volume of its con- 

 tents to 220 c.c; add 30 c.c. of an aqueous solution of fer- 

 ric nitrate of such a degree of concentration that, with 

 this quantity of the solution added, the salt will be shghtly 

 in excess ; the excess may be recognized by a weak reac- 

 tion of the solution on a slip of filter paper soaked in a 

 dilute solution of potassic ferrocyanidc ; too large an ex- 

 cess of the ferric salt will be indicated by a re-solution of 

 the precipitate that was formed at first, on its addition ; 

 filter the liquid immediately through a large, dry, ribbed 

 filter, and to 150 c.c. of the filtrate add 50 c.c. of a solu- 

 tion of baryta mixed with a little calcined magnesia, filter 

 again, and for each determination of sodic chloride and 

 urea take 15 c.c. of this filtrate, corresponding to 9 c.c. of 

 urine. 



1. Chlorine (common salt). — Acidify exactly 15 c.c. of 

 the liquid with a drop of nitric acid, and allow the stand- 

 ard solution of mercuric nitrate to flow in from the burette, 

 with constant stirring until a permanent turbidity ap- 

 pears. A mere opalescent appearance of the liquid, which 

 may be presented even in the beginning, is easily distin- 

 guished from the cloudy turbidity which is the real indica- 

 tion of saturation. 



