XVII.] THE INORGANIC CONSTITUENTS OF (TRINE. 113 



are soluble in water, and not precipitated by alkalies, and never 

 occur as urinary deposits. The quantity is 2 to 4 grams (30 to 

 60 grs.). They are chiefly derived from the food, and perhaps 

 a small amount from the oxidation of the phosphorus of nerve- 

 tissues. 



(a.) To fresh, clear-filtered urine add ammonia, caustic soda, or 

 potash, and heat gently until the phosphates begin to separate ; let 

 it stand for some time = a white precipitate of the earthy phosphates. 

 Allow it to stand, and estimate approximately the proportion of the 

 deposit. [If a high-coloured urine be used, the phosphates may go 

 down coloured.] 



(A.) To urine add about half its volume of nitric acid, and then 

 add solution of ammonium molybdate and boil = a canary-yellow 

 crystalline precipitate of ammonium phospho-molybdate. N.B. 

 The molybdate is apt to decompose on keeping. 



(<'.} To urine add half its volume of ammonia, and allow it to 

 stand = a white precipitate of earthy phosphates. Filter and test 

 the filtrate as in 7 (ft.). 



(d.) It gives the reaction for phosphates. This method separates 

 the alkaline from the earthy phosphates. 



(<".) To urine add half its volume of baryta mixture [Lesson 

 XIX. 12 (<-.)! = a copious white precipitate. Filter and test the 

 filtrate as in 7 (c.). It gives no reaction for phosphoric acid, 

 showing that all the phosphates are precipitated. 



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

 = a white precipitate of earthy phosphates and oxalate of lime. 

 Filter, and to the filtrate add a solution of magnesic sulphate = a 

 precipitate of the alkaline phosphates as triple phosphate. If the 

 filtrate be tested for phosphoric acid by 7 (e.), no precipitate will 

 be obtained. 



((/.) Instead of 7 (/.), use magnesia mixture, composed of 

 magnesic sulphate and ammonium chloride, each i part, distilled 

 water 8 parts, and liquor ammonise i part. It gives the same 

 result as in 7 (/.). 



(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^U 2 3 )NII 4 P0 4 . 

 This reaction forms the basis of the process for the volumetric 

 estimation of the phosphoric acid. 



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. 



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

 ferrocyanide = a brown colour. 



H 



