122 M. Berzelius on the Decomposition of Silica. [Aug. 



binra, tungsten, molybdena, chromium, selenium, antimony, and 

 arsenic ; with the hyposulphurous and sulphurous acids, and 

 probably with the phosphorous and hypophosphorous ; but I 

 have not yet examined the latter. 



Fluoric acid is one of the most convenient reagents for the 

 analysis of inorganic substances, since it dissolves every thing 

 that is not attacked by the other acids. It has enabled me to 

 determine more accurately the weights of the atoms of many of 

 those substances about which I was still in doubt. To extract 

 alkali from minerals, it is sufficient to treat them with fluoric 

 acid, or a mixture of fluate of lime and sulphuric acid. In 

 attempting to reduce fluoric acid by potassium, I have succeeded 

 in reducing silica, zirconia, and the other earths, but I have only 

 been able to insulate silicium and zirconium. The rest decom- 

 pose water with great energy. Pure silicium is incombustible, 

 even in oxygen gas. It is not attacked by water, nitric acid, nor 

 aqua regia, nor by caustic potash ; but fluoric acid has a slight 

 solvent action on it, particularly with the addition of nitric acid. 

 It does not decompose saltpetre, unless in a very intense fire, 

 but it detonates with carbonate of potash at an incipient red 

 heat: carbonic oxide gas is disengaged, and charcoal set free. 

 When silicium is heated with nitre, if a morsel of dry carbonate 

 of soda be plunged into the mixture, detonation immediately 

 ensues. By passing the vapour of sulphur over silicium heated 

 to redness, the metal suddenly becomes incandescent. If the 

 combination be complete, which seldom happens, the compound 

 appears as a white earthy mass ; it decomposes water with 

 extreme rapidity, the water dissolves the silica and sulphuret- 

 ted hydrogen gas is evolved. In this way we may obtain so 

 concentrated a solution of silica in water that it thickens and 

 coagulates during evaporation, and lets fall portions of that 

 earth in the form of a gummy transparent mass. Siliciuret of 

 potassium, heated with sulphur, burns vividly, and leaves, when 

 dissolved, pure silicium. In chlorine, silicium takes fire at a 

 red heat, and there is formed a colourless, or slightly yellow 

 liquid, with an odour similar to that of cyanogen, extremely 

 volatile, and which sets with water and deposits gelatinous 

 silica. I have not yet examined how silicium conducts electri. 

 city and heat, nor its specific gravity, &.c. Nothing is easier 

 than to procure this substance ; the following is the method I 

 have adopted : — The double fluate of silica and potash, or soda, 

 heated nearly to redness to drive oft' the hygrometric water, is 

 put into a glass tube, closed at one end. Bits of potassium are 

 added and mixed with the powder by fusing the metal and 

 gently rapping the tube. It is then heated by the spirit-lamp, 

 and before it is red-hot a feeble detonation ensues and the 

 silicium is reduced. The mass is suffered to cool, and then 

 treated with water as long as it dissolves any thing. Hydrogen 



