and Properties of Silickiin. 255 



Hca, and left a deep brown matter, insoluble in acids, and 

 which did not burn on exposure to the action of fire. Was 

 this the radical of the fluoric acid, or that of silica, or a com- 

 bination of both ? 



To procure this substance in greater quantity I proceeded 

 in the following manner : I introduced into a glass retort of 

 the capacity of about ten cubic inches a small vessel of porce- 

 lain on which, was a piece of potassium of the size of a large 

 nut. After having rapitlly exhausted the retort I let in some 

 silicated fluoric gas, from a reservoir over mercury, and I ap- 

 plied the heat of a spirit-lamp. The potassium at first became 

 white, but afterwards it became browner and browner, and at 

 last as black as a coal: it was not long in becoming inflamed,and 

 it burnt with a large flame of a deep-red colour, not however 

 intensely; whilst the mercury rose rapidly in the reservoir, on 

 account of the absorption of the silicated fluoric gas. As soon 

 as the combustion ended, a vacuum M'as made in the apparatus, 

 in order to prevent the formation of the fluate of silica and 

 potash, and it was then left to cool. The product was a hard, 

 porous, agglutinated,, and deep-brown mass, which did not 

 change in the air, but which, like manganese, emitted the smell 

 of hydrogen when it was pressed between the fingers or when 

 breathed upon. In the retort, aiound the porcelain vessel, a 

 light powder of a yellow-brown was remarked, which was 

 preserved. The burnt mass when thrown into water imme- 

 diately produced a copious evolution of hydrogen gas. The 

 water dissolved much fluate of potash, and the brown mass 

 was precipitated in the form of a chestnut-brown powder, slowly 

 evolving gas. The alkaline solution was decanted and re- 

 placed by pure water. The evolution of gas visibly dimi- 

 nished ; and the water having again been renewed after some 

 time, it entirely ceased; so that the brown powder did not de- 

 compose the water, even at the temperature of ebullition. The 

 solution obtained by boiling it being very acid, it was boiled 

 with fresh portions of water, until no signs of acidity were 

 manifested, and the solution afterwards passed through the fil- 

 tre. The water was saturated with fluate of silica and potash, 

 and the brown powder was washed as long as the water left 

 the slightest residuum by evaporation. 'I'he powder, being 

 dried, was of a chestiuit-brown,and evidently contained hetero- 

 geneous parts of a brighter colour. The brown matter which 

 was deposited on the glass during the combustion of the jio- 

 tassium was nnich more homogeneous. Water did not dis- 

 engage hydrogen by its action, but (juickly became acid. This 

 powder was wasiied with the same care as the ])receding. 

 Now, for the purpose oidelcnnining the change undergone 



