and Properties of Sllicium. 259 



requires to be so much less elevated in order to determine the 

 action, as less carbonate of potash or of soda is taken. Thus, 

 for example, taking a portion of carbonate equal in bulk to 

 half the silicium, the inflammation takes place much below the 

 temperature of ignition. With greater quantities of the car- 

 bonate, the mass becomes distended by the production of the 

 carbonic oxide, takes fire, and burns with a blue flame. If a 

 still greater quantity of carbonate be employed, no signs of 

 combustion can be perceived ; the mass does not grow black, 

 and merely gives out carbonic oxide. 



From this mode of action of silicium with carbonate of 

 potash arises a very paradoxical pheenomenon. If some in- 

 combustible silicium is heated with saltpetre to a moderate 

 red, on a leaf of platinum or in a little crucible, no action will 

 be observed ; but if there is added a litde dry carbonate of 

 soda, so that it may touch the silicium, a detonation will take 

 place, at the expense of the carbonate, in the midst of the 

 saltpetre, and the mass will preserve for some time its black 

 colour. 



The cause from which the silicium burns at a low temperature 

 more easily with the carbonate than with saltpetre, is without 

 doubt owing to the affinity of the alkali for silica being neces- 

 sary to determine the combustion of the silicium, and not be- 

 ing able to manifest itself with the saltpetre except when the 

 temperature is sufficiently elevated for the decomposition of 

 the nitric acid. If the burnt mass continues black some time 

 longer, this arises from the new combination being compact, 

 and protecting the carbon until it enters into fusion. 



Silicium detonates with the hydrates of the fixed alka- 

 lies, producing a vivid incandescence at a temperature at 

 which they melt, but much below that of ignition. Hydro- 

 gen gas is given out, which is seen to burn when the bulk 

 of the mass is not too small. The same phaanomena are ob- 

 served with the hydrate of barytes. Incandescence also takes 

 place with the hydrate of lime ; but it is very feeble, and the 

 silicium is oxidated but imperfectly. With the acid fluate of 

 potash it detonates at the fusing temperature of the salt, that 

 is to say, much below a red heat: it is not affected by fused 

 borax. 



Silicium heated to a perfect red in the vapour of sulphur 

 inflames and burns, but with less intensity than in oxygen ; 

 and the combination even does not take place with the incom- 

 bustible silicium. The sulphuration is usually as incomplete 

 as the oxidation, and a scorified mass is obtained of a dark 

 gray colour. It sometimes happens, however, jiarticularly 

 when a vacuum is made in the vessels before volatilizing tlie 

 K k 2 sulphur, 



