4 ESSAY I. 



At last the receiver, and soon after likewise the retort, were 

 become white in the inside. As soon as the vapours ceased 

 to rise with a gentle fire, the vessels were permitted to cool. 

 Their internal surface was found much corroded. The liquid 

 in the receiver was a mixture of water and of an acid which 

 the vitriolic acid had expelled from the fluor. The great 

 quantity of white matter, which had settled at the bottom 

 during the process, was separated from it by filtration. 



SECTION VII. 



The mass remaining in the retort was reduced to a fine 

 powder, and edulcorated with distilled water till no vestige 

 of acid appeared. This lixivium was filtered, and a little 

 evaporated by boiling. In a few days' time selenite was 

 deposited, with a little alum, weighing about 2 scruples. 

 The lixivium was then evaporated anew, and its superfluous 

 acid saturated with vegetable alkali; but no more crystals 

 were deposited. 



SECTION VIII. 



The lixivium, thus inspissated by evaporation, became 

 blue on the addition of phlogisticated alkali. In both 

 processes (Sees. v. vi.), I used the green fluor. In order 

 to know whether the solutions of every kind of fluor mineral 

 showed signs of iron, I made an experiment with the white 

 species, previously calcined with concentrated vitriolic acid 

 in a crucible ; but no Prussian blue was obtained by means 

 of the same phlogisticated alkali ; the green colour therefore 

 is owing to iron. 



