274 MM. Wohler and Deville on Boron. 



mass with crystals of boron which are readily recognized. This 

 mass consists of aluminium containing crystallized boron. It is 

 treated with soda to dissolve aluminium, by hydrochloric acid to 

 free it from iron, and by nitric and hydrofluoric acid to dissolve 

 traces of silicon left by the soda in the boron. From adherent 

 alumina it can only be separated by mechanical means. 



Boron crystallizes in the dimetric system ; its fundamental 

 form is a rectangular prism with a square base; and M. Sella,_ 

 who has measured some crystals, considers it to be completely 

 isomorphous with tin. It appears to occur in three varieties of 

 form, all derivable from the above, according as the proportion 

 of the substances used in its preparation, the temperature em- 

 ployed, and the duration of the action are modified. These cir- 

 cumstances also alter very much the hardness of the boron, 

 although the least hard variety is harder than corundum, and 

 the hardest is almost as 'hard as diamond. Its colour varies 

 very much, from a deep, almost opake, garnet-red, to an almost 

 colourless honey-yellow; and analysis has shown that under 

 these various conditions its composition varies as its coloui*. 

 Boron possesses a lustre and refrangibility so great as to be 

 comparable to diamond alone in this respect. Its specific gra- 

 vity is 2*68, a little higher than that of silicon ; and it is remark- 

 able that whilst the density of silicon is equal to that of silicic 

 acid, that of boron is superior to that of boracic acid, and that 

 of carbon is much higher than that of liquid carbonic acid. 



The flame of the oxyhydrogen blowpipe does not sensibly fuse 

 crystallized boron. Oxygen acts upon it at the temperature at 

 which diamond burns, but a small layer of boracic acid hinders 

 further oxidation. Chlorine acts upon it with remarkable energy, 

 forming gaseous chloride of boron. All the acids, whether pure or 

 mixed, in the cold or when heated, are entirely without action 

 on boron ; and it is oxidized to boracic acid only by bisulphate 

 of potash at a red heat. Concentrated caustic soda does not act 

 upon it, but hydrate of soda and carbonate of soda dissolve it 

 slowly at a red heat. It is the most unattackable by chemical 

 agents of all elements. 



The circumstances of its formation exercise considerable influ- 

 ence on its composition, and it has never been obtained quite 

 pure. Carbon has been found to be contained in all the speci- 

 mens analysed, and aluminium in some of them. 



Its analysis was effected by exposing it to a high tempera- 

 ture in a current of chlorine ; gaseous chloride of boron is formed, 

 and a residue of carbon is left which is burnt off" in a current of 

 oxygen. It is probable that the carbon which is met with in 

 boron is in the state of diamond ; for the more its proportion in 

 the boron increased, the more did its transparency also increase. 



