ANALYSIS OF SUPERPHOSPHATE 131 



material are weighed out, transferred to a small mortar 

 and rubbed up with a little water (about 30 c.c). The 

 clear liquid is filtered off and the residue twice subjected 

 to the same operation, and finally boiled with a small 

 quantity of water, the whole being then transferred to 

 the filter, where the insoluble matter is washed until 

 the washings are free from acid. Filtrate and washings 

 are then made up to 250 c.c. 



Fifty c.c. of the solution are pipetted into a beaker, 

 mixed with 10 c.c. of concentrated nitric acid and 

 then with 60 c.c. of ammonium molybdate solution. 

 The mixture is allowed to stand in a warm place 

 overnight, and the yellow precipitate of ammonium 

 phospho-molybdate then filtered off and washed with 

 I per cent, nitric acid solution. The precipitate is 

 dissolved off the filter with strong ammonia, the 

 solution nearly neutralised with hydrochloric acid and 

 mixed with 25 c.c. of magnesia mixture.^ The liquid is 

 allowed to stand for twelve hours at the ordinary 

 temperature. If all the phosphoric acid has been 

 precipitated (determined by testing the supernatant 

 liquid with ammonium molybdate) the magnesium 

 ammonium phosphate is filtered off, washed with 

 ammonia water (i part of -SSo ammonia to 3 parts 

 of water), dried, and then ignited together with the 

 filter paper. The ignition should be carried out first 

 over the Bunsen flame, and then for five or ten minutes 

 over the blowpipe. The residue is Mg2P207 ; i part 

 of this equals 0-6379 part of P2O5, or 1-3907 parts 

 Ca^CPO,),. 



^ Magnesia Mixture is prepared as follows : — 80 grams of 

 crystallised MgS04 and 160 grams of ammonium chloride are 

 dissolved in about 600 c.c. of water and then mixed with 120 c.c. 

 of strong ammonia solution (o-88o). The liquid is diluted to i litre, 

 allowed to stand for some time, and then decanted into a clean 

 bottle. 



