led
him to a scale of hardness to he used in the application of emery in
polishing the surfaces of certain substances, —such as a slab of stone,
or a plate of" glass, or any other material upon which emery is
generally applied for polishing. Professor Smith's process consists in
the following method: he reduces the emery to a fine powder in a steel
mortar, similar to the one the diamond-grinders use ; the powder is
sifted very fine through a sieve. One gramme of this fine powder he
employs upon a glass plate of 0.10 inch diameter, and by means
of an agate pestle he rubs the powder circularly and rapidly, until the
powder meets with no resistance and makes no scratching noise ; the
quantity of glass-powder which is hereby taken up by the emery gives
the index, or the power, of the emery under trial. '
CHRYSOBERYL, CYMOPHANE.
The
name of this gem is derived from the Greek, and is expressive of its
color ; it is also called cymophane. It was formerly classed with the
beryl family, but was separated from that by Werner.
It
occurs, crystallized, in aprismatic forni, also in boulders and grains
; is transparent. to translucent, and possesses double refraction in a
high degree ; its lustre is between unctuous and vitreous ; exhibits
tricln-oism ; fracture conchoidal; its color asparagus and olive green,
with a tinge of brown, yellow, gray, or white. Some specimens display,
sometimes, a milky or bluish-white lustre. Chrysoberyl scratches topaz
and rock-crystal very distinctly, but is attacked by sapphire ; the
streak-powder is white, specific gravity, 3'68—3-,i5 ;
xv-s
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