MODIFICATION OF WYATT 265 



Five grams of the finely ground phosphate are fused in a 

 platinum dish with 15 grams of the mixed carbonates of sodium 

 and potassium and two grams of very fine sand. After fusing 

 very thoroughly with a strong heat for a quarter of an hour, the 

 dish is removed from the fire and cooled. Its contents, dis- 

 solved in hot water, are then put into a half-liter flask, and a 

 considerable excess of ammonium carbonate is added to the 

 liquid. All the soluble silica falls out of solution, and the flask, 

 after cooling, is made up to the mark with distilled water, well 

 shaken, and then set aside for 24 hours to settle. At the end 

 of this time 200 cubic centimeters are carefully decanted through 

 a filter; the filter is well washed, and the filtrate, after being 

 nearly neutralized with hydrochloric acid, is treated with an 

 excess of calcium chlorid solution. 



The precipitate, consisting of phosphate, fluorid, and some 

 calcium carbonate, is allowed to settle, and is then carefully 

 washed with boiling water, first by decantation several times, 

 and finally on the filter. After being properly dried in the gas- 

 oven, calcined, and cooled, the residue is treated with acetic 

 acid, placed upon the water-bath, and evaporated to complete 

 ilryness. 



The calcium acetate is now well washed out by several treat- 

 ments with boiling water, and the residue is brought upon a 

 filter, dried, calcined, and weighed. The weight represents the 

 calcium phosphate and fluorid contained in two grams of the 

 original sample; and if the calcium phosphate in the residue 

 "be determined according to the usual methods, the difference will 

 be calcium fluorid and may be thus estimated. 



For this purpose the mixed phosphate and fluorid is placed in 

 a platinum dish and the fluorin expelled by treatment with sul- 

 furic acid. The residue is taken up with alcohol, 100 cubic cen- 

 timeters, the undissolved portion washed with an additional 100 

 cubic centimeters of alcohol, and the phosphoric acid determined 

 in the alcoholic solution by precipitation as ammonio-magnesium 

 phosphate. 



Example. Assuming the calcined residue of calcium phos- 

 phate and fluorid in two grams of the original sample to have 



