lis M, Berzelius on SiUcium. [Aug. 



Article VIL 



On Fluoric Acid, and its most reynarkable Combinations, 

 By Jac. Berzelius. 



(Cotttiuuedfrom vol. ix. p. 131.) 



Decomposition of Silicated Fluoric Acid by Potassium, 

 The description of the experiments raade by the French 

 chemists leads unavoidably to the conclusion, that they had 

 succeeded in decomposing fluoric acid ; and when I undertook, 

 therefore, to repeat them, my sole object was to acquire more 

 accurate information regarding the composition of the reduced 

 products. In my first trials I obtained the same results which 

 they had already described, with this single exception, that the 

 product of the decomposition did not become white by ignition 

 in oxygen gas, but retained its original brown colour almost 

 unaltered. Expecting that this calcined mass would contain 

 silicated fluate of potash, I poured over it concentrated sulphuric 

 acid ; but no trace of fluoric acid was disengaged, nor was the 

 slightest alteration produced upon it by evaporating the mixture 

 to dryness. All other acids, with the exception of the fluoric, 

 proved equally inactive. This acid extracted a quantity of 

 silica, and left behind a darker brown-coloured matter, which 

 was insoluble in acids, and incombustible when ignited. Was 

 this the radical of the fluoric acid or of the silica, or a combina- 

 tion of both? 



To obtain a larger supply of this substance, I ignited some 

 potassium in a suitable apparatus in contact with an atmosphere 

 of silicated fluoric acid gas. The metal gradually darkened in 

 colour, until it finally became as black as coal ; soon after, it 

 took fire, and burned with a large dark red coloured flame; 

 which, however, was by no means intense, and the gas was at 

 the same time rapidly absorbed. The product of the combus- 

 tion was a hard, porous, dark brown-coloured mass, unaltered by 

 exposure to the air, but imparting, when touched or breathed 

 upon, that peculiar odour of hydrogen gas, which is observed 

 when we handle metallic manganese. On being thrown into 

 water, it occasioned a copious disengagement of hydrogen gas, 

 and much fluate of potash passed into solution. By degrees, 

 the evolution of gas became less and less considerable, and the 

 mass disintegrated to a powder. When the action in the cold 

 appeared to have ceased, the alkaline solution was replaced by 

 fresh water, and the mixture was heated to ebullition. No 

 additional disengagement of hydrogen was produced by this 

 treatment, but the liquid now became strongly acid, and proved 

 to be a saturated solution of silicated fluate of potash. The 



