Tlie Phosphates of America. 149' 



Fluorine (Fl). 



This element may first of all be tested for, qualitatively, in order 

 to save much unnecessary trouble. 



Two or three grammes are placed in a platinum dish with about 

 2 c.c. of concentrated sulphuric acid. The dish is covered with a 

 watch-glass thinly coated with wax, through which the operator 

 may trace some mark with a fine needle-point Heat is then 

 gently applied, and, at the end of, say, ten minutes the watch- 

 glass is removed, and the wax upon it is washed off. The etching 

 of the characters traced on the glass proves the presence of fluor- 

 ine, and the analysis may be proceeded with as follows : 



Five grammes of the finely-ground phosphate are fused in a 

 platinum dish, with 15 grammes of the mixed carbonates of sodium 

 and potassium, and 2 grammes 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, cooled down, and its contents dissolved in 

 hot water and treated with ammonium carbonate in excess, in order 

 to remove the last trace of soluble silica. The liquid is now 

 filtered and washed with great care ; the filtrate is nearly neutral- 

 ized with hydrochloric acid and then treated with an excess of 

 calcium chloride solution (CaCl 2 ). 



The precipitate, consisting of phosphate, fluoride and some 

 carbonate of lime, is washed several times by decantation with 

 boiling water, collected on an ashless filter, dried and calcined. 

 After being allowed to cool, the residue ig freated with acetic acid 

 and evaporated to dryness on the water-bath in order to trans- 

 form the carbonate of lime into acetate of lime. The acetate 

 is next well washed out with boiling water several times, and 

 the final residue is brought on^an ashless filter, dried, calcined 

 and weighed. This time, the weight represents only the phosphate 

 and fluoride of lime contained in the five grammes of the original 

 sample. 



After taking due note of this weight, the residue is returned to 

 the platinum dish, 5 c.c. of concentrated sulphuric acid are added 

 to it, heat is applied, and the fluorine is all driven off. When 

 no more fumes are evolved, the source of heat is removed, the resi- 

 due in the dish is treated with 100 c.c. alcohol, filtered and washed 

 with alcohol up to 200 c.c. 



The alcoholic filtrate contains the phosphoric acid, and this is 

 precipitated as ammonio-magnesium phosphate. The precipitate 





