1825 J M, Eerzelius on Siliciuhf^ 117 



powder was now repeatedly boiled in water until it was rendered 

 completely free from all soluble matter : it was then collected 

 upon a filter and dried. 



To determine the alteration which this substance would 

 undergo by combustion, I ignited it in a current of oxygen gas. 

 It instantly took fire, and burned with some intensity, a pale 

 blue-coloured flame being at the same time visible over its sur- 

 face. The gaseous product of the combustion produced an 

 abundant precipitate in barytes water, and this precipitate proved 

 on examination to be pure carbonate of barytes, unmixed with 

 silicated fluate. The calcined mass had diminished greatly in 

 volume, but retained its original colour almost unaltered, and the 

 increase of weight which it had sustained scarcely amounted to 

 a half per cent, No corrosion by fluoric acid, and no deposition 

 of silica, could be observed in any part of the apparatus ; conse- 

 quently fluoric acid did not form one of the products of the com- 

 bustion. I was therefore disappointed in my expectation of 

 ascertaining by this means the composition of fluoric acid ; yet 

 the result was not the less interesting, for it appeared to me that 

 I had succeeded in isolating the radical of silica, and that the 

 brown pulverulent body was in reality silicium. That it should 

 undergo combustion in oxygen gas and give off carbon without 

 becoming heavier, was easily intelligible ; because the same cir- 

 cumstance is observable when we calcine the quadricarburets of 

 most of the metals whose oxides contain three atoms of oxygen. 

 The presence of so much carbon appeared at first to be some- 

 what unaccountable : I speedily ascertained, however, that iJ, 

 had previously existed in a state of chemical combination with 

 the potassium. This potassium had been prepared by Brunner'a 

 process, in which a mixture of carbonate of potash and charcoal 

 IS strongly ignited in a retort of malleable iron : and by redistil- 

 ling it in a glass vessel, I found that it left behind a carbonace- 

 ous matter which took fire when exposed to the air^ and which 

 in water caused the disengagement of hydrogen gas ; whilst, at 

 the same time, potash was formed, and a large quantity of car- 

 bon deposited. On repeating the experiment v/ith potassium 

 purified in this manner by distillation, the powder which I 

 obtained was not so dark brown-coloured, and when burned in 

 oxygen gas it increased in weight 40 per cent, without giving oft' 

 any carbonic acid. Its colour, however, was scarcely altered by 

 the combustion. This circumstance may be explained by sup- 

 posing, either that silicium possesses a lower degree of oxidation 

 which is produced by calcination, or that (as happens with boron) 

 the portion oxidized at the commencement of the process pre- 

 vents the perfect oxidation of the remainder. The residue of 

 the combustion was treated with fluoric acid. The silica was 

 by this means separated, escaping in the state of silicated fluoric 

 acid gas, and the colour of the undissolved powder became 



