Set/berPs Analysis of the Maclureite. 341 



strongly acid ; when treated with concentrated sulphuric 

 acid itetfervesced rapidly, disengaging a pungent gaz, giving 

 rise to dense white vapours in the surrounding atmosphere, 

 its solution in the acid was but partial ; this sublimate thus 

 presented properties analogous to the Fluate of silica. To 

 investigate this matter more satisfactorily, I made the fol- 

 lowing comparative experimeuts, viz. a portion of the pow- 

 dered mineral was heated in a glass retort with an excess 

 of sulphuric acid. A mixture of three parts ofFkiorspar 

 and one part of silica was then treated in the same manner, 

 the resuhs obtained were precisely similar, a white pun- 

 gent vapour was disengaged, which condensed, on coming in 

 contact with water, in the form of a white film, and the 

 neck of the retort was incrusted with a white sublimate, 

 which effervesced with sulphuric acid, yielding a gaz which 

 presented the properties of Fhio-silicic acid. These ex- 

 periments clearly demonstrated, that Fluoric acid was a 

 constituent of the mineral under examination, and I was 

 induced to repeat the experiments above stated according 

 to Professor Klaproth's method, but they were not attend- 

 ed with better success ; on examing the silica, obtained in 

 this manner, I observed that it possessed certain proper- 

 ties, which proved that it had retained Fluoric acid; when 

 thrown into water it decrepitated and rendered the liquor 

 acid ; with sulphuric acid it effervesced violently, yielding 

 Fluo-silicic acid : the silica, therefore, was intermixed 

 with Fluateof potash and silica, a compound described by 

 Gay Lussac* and Thenard. They state, that potash com- 

 bines with silica and Fluoric acid, forming a compound 

 which requires six or seven hundred times its weight of 

 water to dissolve it. I also ascertained, that the magne- 

 sia, although precipitated by an excess of caustic or carbo- 

 nated alcali, likewise retained a portion of the Fluoric acid ; 

 the cause of my not having obtained any Fluate of Lime 

 from the solutions above mentioned, was thus rendered 

 apparent. I thought to obviate this difficulty in employing 

 Soda instead of Potash, in this manner I succeeded in ob- 

 taining some Fluate of Lime, but I ascertained, that the 

 Silica and magnesia still retained a portion of the acid and 

 at length after various experiments, I resorted to thq 

 method employed, so successfully, by Professor Berzelius 



* Recherches Physico-Chimiques vol. ii. p. 19. 

 Vol. V. 44 



