ive
results. These experienced chemists kept an emerald at the temperature
of melted copper for an hour, and found that, although the stone had
become opaque, the color was not affected. They therefore considered
the oxide of chromium to be the coloring agent, without, however,
denying the presence of organic matter. The amount of the oxide of
chromium found by many chemists varies from one to two per cent.,
while Lewy and others found it in a quantity so small as to be
inappreciable, and too minute to be weighed.

Before the ordinary blowpipe the emerald passes rapidly into a whitish
vesicular glass, and with borax it forms a fine green glass, while its
sub-species, the beryl, changes into a colorless bead: with salt of
phosphorus it slowly dissolves, leaving a silicious skeleton.[A]

M. Lewy visited the mines at Muzo in Granada, and from the results
of his analyses, together with the fact of finding emeralds in
conjunction with the presence of fossil shells in the limestone in
which they occur, he arrived at the conclusion that they have been
formed in the wet way--deposited from a chemical solution. He also
found that when extracted they are so soft and fragile that the
largest and finest fragments can be reduced to powder by merely
rubbing them between the fingers, and the crystals often crack and
fall to pieces after being removed from the mine, apparently from loss
of water. Consequently, when the emeralds are first extracted they are
laid aside carefully for a few days until the water is evaporated.

This statement relative to the softness of the gem and its subsequent
hardening has been met with a shout of derision from some of the
gem-seekers--none louder than that of Barbot, the retired jeweler.
Barbot seems to forget that the rock of which his own house in Paris
is constructed undergoes the same change after being removed from
the deep quarries in the catacombs under the city. This phenomenon is
observed with many rocks. Flints acquire additional toughness by the
evaporation of water contained in them. The steatite of St. Anthony's
Falls grows harder on exposure, and other minerals when quarried from
considerable depths become firmer on exposure to the action of the
air. Observations of this kind led Kuhlman to investigate the cause,
and he believes that the hardening of rocks is not owing solely to
the evaporation of quarry-water, but that it depends upon the
tendency which all earthy matters possess to u