IX. 0)1 the Sublimation of Silica, 



By J.IVfAcCuLLOCH, M.D. F.L.S, Chemist to the Ordnance, and Lecturer 

 on Chemistry at the Royal Military Academy at Woolwich. 

 V. Pr. Geo. Soc. 



S( 



^OME years ago, being In pursuit of another object, a mixture of 

 the oxides of tin and lead was exposed to the heat of an air furnace in 

 an English crucible, to the top of which was luted another of the 

 same sort. This apparatus was allowed to remain in the fire for 

 some hours. No account of the heat was taken, but I have on for- 

 mer occasions produced in the same furnace a heat sufficient to cou" 

 tract one of Mr. Wedgwood's original clay pieces to the 130th and 

 140th degree of his scale. On removing the crucibles, the insides 

 of both from the bottom of the lowermost to within a third part of 

 the top of the uppermost, were found covered with white brilliant 

 filamentous crystals crossing each other in all directions. I con- 

 cluded that they consisted of the oxide of tin, or perhaps that of 

 lead, and subjected them to the obvious experiments necessary for 

 ascertaining this circumstance. Failing to confirm this supposition, 

 I then conjectured that they might consist of silex. The quantity 

 I procured scarcely amounted to half a grain, and I therefore divided 

 it into two parts, that I might have the satisfaction of confirming or 

 refuting my own trials by comparison with those of some chemical 

 friend. Mr. Aikin was so good as to undertake the examination of 

 the reserved portion, and from his well known accuracy, the Society 



will naturally place confidence in our mutual results. On igniting 



2 M 2 



