3^6 InleUigfHce and MisceUa7ieoiis Articles. 



to say, by mixing hydrate of silica, dried to a certain degree, with 

 lamp-black, powdered sugar, and a sufficient quantity of oil to form 

 a uniform paste, wiiirh is to be calcined in a covered crucible. The 

 quantity of carbon contained in the different mixed substances ought 

 to be equivalent to at least half the weiglit of the silica employed. 



The carbonaceous residue of the calcination is introduced in small 

 fragments into a porcelain tube; to one end of which is adapted a 

 small retort containing bromine, and to the other a tube, which is 

 ))ut into a receiver surrounded with ice, and having at its tubulure a 

 long tube, terminated by a capillary opening. When the porcelain 

 tube is incandescent, the bromine is gradually volatilized by heat. 



The bromide of silicium is in a liquid form. When the operation 

 is over, it is to be re-distilled, as the chloride is, after it has been 

 agitated with mercury in the retort in which the operation is to be 

 performed, to separate the excess of bromine ; the temperature is 

 considerably raised, and a magma is formed, which appears to con- 

 tain scarcely any of the liquid, though a considerable quantity is ob- 

 tained by distillation. 



When the bromide of silicium is taken out of the receiver, it ex- 

 hales copious vapours, which are accompanied with a very marked 

 aethereal smell of bromide of carbon. 



Distilled bromide of silicium is colourless, forming by exposure to 

 the air dense vapours : when subjected to a freezing mixture it 

 solidifies at about 10° Fahr., being similar in this respect to bromine; 

 when shaken with a little water it decomposes that fluid readily, and 

 much heat is produced. It boils at about 300° Fahr. ; its density is 

 greater than that of sulphuric acid, for it falls readily through the 

 acid, in which it is slowly decomposed ; and after some days it is en- 

 tirely converted into silica and bromine ; the latter resulting from the 

 subsequent action of the sulphuric acid upon the hydrobromic acid. 



Potassium acts vividly upon bromide of silicium when slightly 

 heated ; detonation results, which frequently breaks the tube in 

 which it takes place, I took advantage of this opportunity to com- 

 pare some of the properties of bromide of silicium with those of the 

 chloride ; and I found, 



1st, That the boiling point of chloride of silicium, (which had not 

 previously been determined,) is 124° Fahr., whilst that of the bro- 

 mide is 302° ; 



2ndly, That chloride of silicium, which sinks in water, floats in 

 sulphuric acid, by which it is decomposed into silica and muriatic acid ; 

 while the bromide is heavier than sulphuric acid ; 



3rdly, That potassium undergoes no sensible change in boiling 

 chloride of silicium ; whereas a slight increase of temperature oc- 

 casions this metal to act violently on the bromide ; this appears to 

 depend upon the fusing of the potassium, before the ebullition of the 

 bromide ; and on the contrary, the chloride boils before the fusion, 

 and which indeed does not occur in the latter ; finally, if potassium, 

 which is beginning to fuse, be dropped into bromide of silicium, de- 

 tonation immediately occurs; 



4thly, That chloride of silicium may be cooled to zero without 



becoming 



