|
PRECIOUS STONES. 127
due prominence to, although Daubree in 1876 stated that highly heated water would, even in a few days transform
three times its weight of amorphous silicates into Quartz and
crystallised silicates. This in man's laboratory; in Nature's
laboratory, with great time and great stores of energy, how much
greater changes can conceivably be wrought! The formation of gneiss has
been assumed to be independent of the action of water; such is probably
not the case, water being on the contrary an essential factor.
Chemical Composition.
Diamond
consists of pure carbon, an element which also occurs in Nature in an
allotropic form, Graphite. As might be expected, the composition of
this remarkable mineral very long ago was the subject of speculation.
Boetius de Boot, in 1609, stated his supposition that it was a
combustible substance, and in 1673 Robert Boyle discovered that under
the influence of a high temperature it was "dissipated in acrid
vapours." About twenty years later two Academicians of Florence
experimented in the presence of the Duke of Tuscany and confirmed
Boyle's observation, and a hundred years after that again, Macquer and
Bergman continued the experiments with the same result. In 1772
Lavoisier showed that it was only when heated in contact with air or
oxygen that it so disappeared, and he further proved that the product
of its combustion caused a precipitate in lime water which effervesced
on treatment with an acid, as did also the product of the combustion of
carbon. Then, in 1797, Tennant showed that the amount of carbon dioxide
formed from a given weight of Diamond was the same as that
|
||
|
|
||