Boron (sym. B, eq. 11) is a non-metallic element present in boracic acid and Borax (q.v.). It was discovered in 1808 by Gay-Lussac and Thenard in France, and Davy in England. In some respects boron resembles carbon, existing like it in the so-called amorphous, graphitoid, and diamond forms. In the amorphous or pure state, prepared by heating boric anhydride with sodium, it is an olive-green powder, very slightly soluble in water, and unaltered by exposure to moist air. When heated in air, it takes fire, uniting with oxygen to form boric anhydride, (see BORACIC ACID). The graphitoid and diamond boron are not pure forms of the element, but contain a definite proportion of Aluminium (q.v.). The diamond boron is obtained by heating the amorphous form to a high temperature, along with aluminium, when boron is left as minute crystals interspersed through the earth alumina. These crystals possess great interest from their similarity in properties to pure crystallised carbon, or the diamond. They are remarkably transparent, are tinged yellow or red (though the colours may be accidental), and rival the ordinary diamond in their lustre and refractive power. Boron diamonds not only scratch glass, but also the corundum and the sapphire; they are, however, somewhat softer than real diamonds.
Resembling as in some degree they do the carbon diamond, it was at first hoped that as the method of manufacture became perfected, they would be obtained sufficiently large to become a serious rival to the natural carbon diamond; but as yet they have only been obtained in very small crystals, and their advent in the diamond-market is therefore problematical. They are very indestructible, even withstanding a temperature sufficient to burn the ordinary diamond.
Boron forms but one oxide, Boracic or Boric Anhydride, (see BORACIC ACID), while it unites with chlorine and bromine directly to form a chloride, , and bromide, .