250 AGRICULTURAL ANALYSIS 



to the liquor one gram of phosphate of soda containing about 20 

 per cent, of phosphoric acid. It is necessary to call attention to 

 the fact that the liquor is to contain enough of phosphoric acid 

 to completely saturate the lime and that the acid be in excess at 

 least one decigram. It will be necessary, therefore, to increase 

 a little the quantity indicated if the phosphate is very rich in car- 

 bonate. For certain chalky phosphates, it will be necessary to use 

 as much as two grams of the phosphate of soda. 



The soda liquor thus prepared is poured in a fine stream into 

 the solution of the phosphate prepared a? above, and its constant- 

 ly stirred with a metal spatula. After the addition of the soda, the 

 mixture is heated to about 100 for half an hour, but it is pref- 

 erable to prolong the heating for an hour, stirring from time to 

 time. After cooling, the mixture is placed in a flask marked at 

 250 cubic centimeters, and the volume completed with water to 

 the mark. 



To be able to take account of the volume of the precipitate, a 

 half cubic centimeter of water, in addition, is added. The mix- 

 ture is strongly shaken several times and left for half an hour 

 in ordec to permit the complete diffusion of the liquid through- 

 out the precipitate. The contents of the flask are next poured 

 upon a dry filter and 200 cubic centimeters of the filtrate cor- 

 responding to one gram of the original phosphate, in case two 

 grams have been used, employed for the estimation of the alum- 

 ina. 



It has been proved that by this treatment all the bases, except 

 alumina, which can be present, have been retained as phosphates, 

 while the phosphate of alumina has remained completely soluble. 



The 200 cubic centimeters of the filtrate, obtained as above, are 

 placed in an erlenmeyer and hydrochloric acid added until the 

 precipitate at first formed is just dissolved. There are then added 

 25 cubic centimeters of a solution of ammonium chlorid contain- 

 ing 125 grams per liter. Ammonia is then added until there is 

 formed a precipitate which persists. The mixture is next heated 

 to near ebullition and with great care a solution of dilute ammonia 

 is added. The heated mixture should not give off more than a 

 feeble odor of ammonia, and it is highly important that the ammo- 



