METHOD OF LASNE IOI 



(2) Magnesia mixture. Dissolve 400 grams of crystallized 

 magnesium chlorid, 800 grams of ammonium chlorid, and 1600 

 cubic centimeters of ammonia of 0.96 specific gravity in water, 

 and dilute to five liters. 



The quantity used for the analysis is five grams where the fer- 

 tilizer contains less than six per cent, of phosphoric acid (mixed 

 fertilizers) ; two grams where it contains more than six and less 

 than 15 per cent, (common superphosphates) ; and one gram 

 where it contains more than 15 per cent, (double superphos- 

 phates). Place the weighed substance in a mortar and cover 

 with loo cubic centimeters of citrate solution. Gently rub up, 

 wash into a half liter flask, and heat on a water bath for an hour 

 to a temperature between 35 and 38. Allow to cool, fill up to 

 500 cubic centimeters, and filter through a dry double filter. If 

 the liquid is not clear at the first titration, pour through the filter 

 again, repeating this till clearness is attained. To 100 cubic centi- 

 meters of the filtrate add 75 cubic centimeters of magnesia mix- 

 ture, allowing the latter to flow into the former very slowly, and 

 constantly stirring during the influx. Allow to stand 15 hours, 

 filter, wash with ammonia of 0.96 specific gravity, dry, ignite, and 

 weigh. 



The per cent, of phosphoric acid, except where otherwise indi- 

 cated, is always to be given as per cent, of phosphorus pentoxid 



(P 2 5 ). 



94. Method of Lasne. Lasne recalls some previous observations 

 which are confirmed by later ones, as follows : 71 



(1) The precipitation of ammonio-magnesium phosphate takes 

 place without loss when conducted in the presence of citrate of 

 ammonia, and with a sufficient excess of magnesia. 



(2) Lime, oxid of iron, alumina and manganese are carried 

 down by the precipitate. 



(3) The presence of silica and of fluo-silicates causes an excess 

 of weight in the precipitate over the probable amount due to phos- 

 phorus. 



(4) Without the addition of an excess of magnesia the precipi- 



71 Bulletin de la Societ chimique de Paris, 1897, [3], 17:823 and 

 following. 



