256 M. Berzelius on the Preparation 



by the brown matter during combustion, it was first perfectly 

 dried and heated to a dull red in a current of hydrogen gas, 

 and, after being weighed, exposed in a proper apparatus to 

 a current of oxygen gas. As soon as the air of the vessel 

 seemed to be displaced by oxygen gas, the brown matter was 

 heated with a spirit-lamp: it immediately took fire, and burnt 

 vividly for some time, having a pale blue flame on its surface. 

 The remaining oxygen being passed into barytlc water, ren- 

 dei'ed it very turbid, and gave a precipitate which entirely dis- 

 solved with effervescence in muiuatic acid, and which, conse- 

 quently, was carbonate of barytes. The burnt mass was greatly 

 diminished in bulk, but was of much the same colour as before. 

 Its weight was augmented scarcely half a hundredth part. 

 There was not perceived either in the glass balloon where the 

 combustion took place, or in the glass conducting tube, the 

 least indication of the presence of fluoric acid ; and this showed 

 plainly that this acid was not produced by the combustion of 

 the brown matter; and that the presence of it in the experi- 

 ments of MM. Gay-Lussac and Thenard, as also in the first 

 which I made, arose from the circumstance that the bi'own 

 matter contained fluate of silica and potash, which was de- 

 composed by the heat of the combustion, and gave out silicated 

 fluoric acid. This result likewise deprives us of the hope of 

 learning by these means the composition of fluoric acid ; but 

 it is not less interesting, since it seems to show that the pul- 

 verulent brown matter is really silicium. Its combustion in 

 oxygen, with the production of carbonic acid, without much 

 increase of weight, was now not so difiicult to understand, 

 since it is a property of the oxides which contain three atoms 

 of oxygen, that their quadri-carburet burns without increase 

 of weight. But whence comes this carbon? how is it com- 

 bined with the silicium ? I thought at first that it might be 

 attributed to the presence of the oil of naphtha in which the 

 potassium was preserved, and I repeated the experiment with 

 potassium which had not been in this oil. The result was the 

 same. I then began to think that this metal might contain 

 carbon ; for it had been prepared after the advantageous pro- 

 cess lately given by Brunner, which consists in distilling at a 

 high temperature a mixture of carbonate of potash and of 

 carbon in a vessel of forged iron. The potassium, distilled in 

 a glass vessel, accordingly left a coally residuum, which, by 

 treatment with water, yielded some potash and much carbon. 

 In repeating the experiment of the combustion of potassium 

 in silicated fluoric gas [employing the metal thus purified], 

 the powder was not so brown, and when burnt in oxygen ac- 

 quired an increase of 40 percent without producing carbonic 



acid. 



