1825.] M. BerzeUiis on Silicium. 129 



from the crucible. On the contrary, when the boroflaate of 

 potash has been sufficiently dried, the sound at the instant of 

 the reduction is scarcely audible, and for every atom of potas- 

 sium expended we obtain the corresponding quantity of boron. 

 The only inconvenience attending this operation is the tedious 

 edulcoration which is requisite m order to remove the unde- 

 composed borofluate of potash: perhaps this disadvantage 

 might be obviated by employing sodium and the borofluate of 

 soda. The boron must be washed with a solution of sal- 

 ammoniac, and finally with alcohol ; because when pure water 

 is employed for this purpose, a considerable portion passes in a 

 dissolved state through the filter. 



Suiphiiret of Boron, — Boron is capable of forming a sul- 

 phuret, but, contrary to what has been hitherto supposed, no 

 combination takes place between the two substances except m 

 a temperature greatly exceeding the boiling point of sulphur. 

 It takes fire and burns, when strongly ignited in the vapour of 

 sulphur. The sulphuret is a white opaque mass. When put 

 into water, it is rapidly converted into sulphuretted hydrogen 

 gas and boracic acid; the liquid at the same time becomes 

 more or less milky, in consequence of the precipitation of 

 sulphur. I am disposed to think, from the observations which 

 I have made, that boron is capable of combining in several 

 distinct proportions with sulphur. 



Chloride of Boron. — Sir H. Davy ascertained that boron 

 even without the application of heat takes fire spontaneously in 

 chlorine gas and undergoes brilliant combustion ; but he did 

 not examine the product of the combination. J have con- 

 firmed Davy's statement; if, however, the boron be very pure, 

 and if it has been previously ignited moderately in vacuo, no 

 combination takes place until heat is applied. The product of 

 the combustion is a new gas, which, in contact with atmospheric 

 air, smokes as strongly as fluoboric acid gas. It must be col- 

 lected over mercury, which absorbs the excess of chlorine. 

 This gas is colourless, and, in consequence of the formation of 

 muriatic acid at the expense of the atmospheric humidity, it 

 has a strong suffocating odour. It is rapidly, but not instan- 

 taneously, absorbed by water, and when the proportion of the 

 water is small, a quantity of boracic acid is deposited upon its 

 surface. Alcohol also dissolves it, and acquires the same odour 

 of ether, as when it has absorbed muriatic acid gas. 



Chloride of boron, when Uiixed with ammoniacal gas, Con- 

 denses and forms a salt, which may be sublimed unaltered, but 

 which is less volatile than sal-ammoniac. If the salt be 

 moistened previously to sublimation, there remains behind a 

 quantity of boracic acid. One volume of the gas condenses 

 14- volume of ammoniacal gas. Chloride of boron is com- 

 posed of . - 



New Series, vol. x. k 



