PREPARATION OF REAGENTS 57 



ly neutral ; reduce the specific gravity to nearly i .09 and 

 proceed as follows : Prepare a solution of fused calcium 

 chlorid 200 grams to the liter, and add four volumes of 

 strong alcohol. Make the mixture exactly neutral, using a 

 small amount of freshly prepared corallin solution as a prelimi- 

 nary indicator, withdrawing a portion, diluting with an equal 

 volume of water, and testing with cochineal solution. Fifty cubic 

 centimeters of this solution will precipitate the citric acid from 

 10 cubic centimeters of the citrate solution. To 10 cubic centi- 

 meters of the nearly neutral citrate solution add 50 cubic centi- 

 meters of the alcoholic calcium chlorid solution, stir well, filter 

 at once through a folded filter, dilute with an equal volume of 

 water and test the reaction with neutral solution of cochineal. If 

 acid or alkaline, add ammonia or citric acid, as the case may be, to 

 the citrate solution, mix, and test again as before. Repeat this pro- 

 cess until a neutral reaction of the citrate solution is obtained. 

 The specific gravity must be 1.09 at 20. 



The reagents employed in the separation of the phosphoric 

 acid are prepared according to the following formulas: 



Molybdate Solution. Dissolve 100 grams of molybdic acid in 

 144 cubic centimeters of ammonia, specific gravity 0.90, and 271 

 cubic centimeters of water ; pour the solution thus obtained, slow- 

 ly and with constant stirring, into 489 cubic centimeters of nitric 

 acid, specific gravity 1.42, and 1148 cubic centimeters of water. 

 Keep the mixture in a warm place for several days, or until a 

 portion heated to 40 deposits no yellow precipitate of ammo- 

 nium phosphomolybdate. Decant the solution from any sedi- 

 ment and preserve it in glass-stoppered vessels. 



Ammonium Nitrate Solution. Dissolve 200 grams of com- 

 mercial ammonium nitrate in water and dilute with water to two 

 liters. 



Magnesia Mixture. Dissolve 22 grams of recently ignited 

 calcined magnesia in dilute hydrochloric acid, avoiding an ex- 

 cess of the latter. Add a little calcined magnesia in excess, and 

 boil a few minutes to precipitate iron, alumina, and phosphoric 

 acid ; filter ; add 280 grams of ammonium chlorid, 700 cubic centi- 

 meters of ammonia of specific gravity 0.96, and water enough to 



