METHOD OF HALLE EXPERIMENT STATION 95 



filled with absolute alcohol to the mark, closed with a stopper, 

 and, with frequent shaking, allowed to stand for two hours ; it is 

 thereupon filtered as quickly as possible; 50 cubic centimeters of 

 the filtrate, corresponding to one gram of the substance, is used 

 for the estimation. This is evaporated on a sand-bath to a sirupy 

 consistence, diluted with water and treated as in the case of the 

 soluble phosphates above mentioned. In all cases, as described 

 above, after the solutions are obtained they are treated with the 

 ammonium citrate solution and the phosphoric acid estimated as 

 in the method for soluble acid. 



(6) Solutions Employed. 



(a) The citrate solution is made as follows : Fifteen hundred 

 grams of citric acid are dissolved in water, treated with five 

 liters of 24 per cent, ammonia, and made up to 15 liters. 



(b) The magnesia mixture is made as follows: Five hundred 

 grams of magnesium chlorid, 1050 grams of ammonium chlorid, 

 three and five-tenths liters of 24 per cent, ammonia, and six and 

 five-tenths liters of distilled water are used. 



In the case of the superphosphates 50 cubic centimeters of 

 the citrate solution are employed and with the basic slags 100 

 cubic centimeters; and in both cases 25 cubic centimeters of the 

 magnesia mixture. 



(7) Details of the Manipulation. On the addition of the citrate 

 solution there should be no permanent troubling of the liquid, but 

 any precipitate at first formed should entirely disappear after the 

 addition of the whole quantity of the reagent. In order to facili- 

 tate this, after the addition of the citrate solution the flasks should 

 be gently shaken so as to distribute the solution throughout 

 the mass. Solutions from bone-black superphosphates show 

 scmetimes, after the addition of the citrate solution, a more or 

 less strong opalescence, but this opalescence does not influence 

 the results. Should it happen that with superphosphates which 

 are made from raw material containing large excesses of iron or 

 clay 50 cubic centimeters of the citrate solution are not suffi- 

 cient to prevent the other bases from being precipitated, an addi- 

 tional quantity up to 25 cubic centimeters may be added. 

 The addition of the magnesia mixture must follow as quickly as 



