30 APATITE. 



dissolved in dilute nitric acid,* and the chlorine pre- 

 cipitated by nitrate of silver. 



In order to detect the small quantity of fluorine 

 which is contained in some specimens of apatite, the 

 finely powdered mineral is mixed, in a platinum cru- 

 cible, with concentrated sulphuric acid, and the crucible 

 covered with a glass plate coated with a thin film of 

 wax, through which some characters have been written 

 with a needle; the crucible is then heated with a flame 

 so small as not to melt the wax. If fluorine be pre- 

 sent, the characters are found etched upon the glass 

 after the removal of the wax. The quantity of the 

 fluorine is inferred from the loss of weight in the whole 

 analysis. 



The phosphoric acid and lime may be determined 

 by the methods described in the analysis of bone-ash. 

 The following process may also be employed. 



The mineral is dissolved in nitric acid, in a dish, and 

 so much pure mercury added that, after saturating the 

 acid, a portion still remains undissolved. The mixture 

 is then evaporated to perfect dryness on the water-bath. 

 Should it still emit an odor of nitric acid, this acid 

 must be completely expelled by adding more water, 

 and again evaporating to dryness. The mass is treated 

 with water, filtered through the smallest possible filter, 

 and the residue, which contains all the phosphoric 

 acid, well washed. 



The solution contains, besides the excess of the mer- 

 cury-salt, the whole of the lime. The suboxide of 

 mercury is precipitated by hydrochloric acid. Any 

 protoxide of mercury which may have been formed, is 

 precipitated from the filtrate by ammonia. If the mine- 

 ral contain iron, or other bases precipitable by ammo- 



* Many compact apatites, when treated with nitric acid leave 

 a small quantity of crystalline powder, which is cryptolite (phos- 

 phate of protoxide of cerium). 



