Boron trioxide B2O3 is the only known oxide of boron; and may be
prepared by heating amorphous boron in oxygen, or better, by strongly
igniting boric acid. After fusion the mass solidifies to a transparent
vitreous solid which dissolves readily in water to form boric acid
(q.v.); it is exceedingly hygroscopic and even on standing in moist
air becomes opaque through absorption of water and formation of boric
acid. Its specific gravity is 1.83 (J. Dumas). It is not volatile
below a white heat, and consequently, if heated with salts of more
volatile acids, it expels the acid forming oxide from such salts; for
example, if potassium sulphate be heated with boron trioxide, sulphur
trioxide is liberated and potassium borate formed. It also possesses
the power of combining with most metallic oxides at high
temperatures, forming borates, which in many cases show characteristic
colours. Many organic compounds of boron are known; thus, from the
action of the trichloride on ethyl alcohol or on methyl alcohol, ethyl
borate B(OC2H5)3 and methyl borate B(OCH3)3 are obtained. These are
colourless liquids boiling at 119 deg. C. and 72 deg. C. respectively,
and both are readily decomposed by water. By the action of zinc methyl
on ethyl borate, in the requisite proportions, boron trimethyl is
obtained, thus:--2B(OC2H5)2 + 6Zn(CH3)2 = 2B(CH3)3 +

/ CH3
+ 6Zn <
\ OC2H5

as a colourless spontaneously inflammable gas of unbearable smell.
Boron triethyl B(C2H5)3 is obtained in the same manner, by using zinc
ethyl. It is a colourless spontaneously inflammable liquid of boiling
point 95 deg. C. By the action of one molecule of ethyl borate on two
molecules of zinc ethyl, the compound B(C2H5)2.OC2H5 diethylboron
ethoxide is obtained as a colourless liquid boiling at 102 deg. C. By
the action of water it is converted into B(C2H5)2.OH, and this latter
compound on exposure to air takes up oxygen slowly, forming the
compound B.C2H5.OC2H5.OH, which, with water, gives B(C2H5).(OH)2. From
the condensation of two molecules of ethyl borate with one molecule of
zinc ethyl the compound B2.C2H5.(OC2H5)5 is obtained as a colourless
liquid of boiling point. 112 deg. C. Boron triethyl and boron
trimethyl both combine with ammonia.

The atomic weight of boron has been determined by estimating the water
content of pure borax (J. Berzelius), also by conversion of anhyd