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36
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PRECIOUS STONES.
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(a) Method by Specific Gravity Bottle.
When
a solid is entirely immersed in water it is obvious that it displaces a
volume of water equal to its own volume. Thus if W = weight of the
substance in air and w = weight of the water displaced,
A
small flask of very thin glass, provided with an accurately-fitting
glass stopper (through which a small hole is drilled), is filled with
water; the stopper is then inserted so as to force a little water out
through the narrow aperture in the stopper ; the bottle is carefully
dried outside. The substance to be examined, preferably in small
fragments, is accurately weighed and the weight noted ; let the weight
be JV. Now weigh the bottle, full of water, and the substance together in the balance, and let the combined weight be x. Now
remove the stopper and carefully place the mineral in the bottle,
taking care that the fragments do not carry air-bubbles with them ;
replace the stopper and again dry and weigh the bottle; let this weight
be y. Now x — y is equal to the weight of the water displaced, or, in other words, to the weight of a volume of water equal to
the volume of the mineral. Hence
specific
gravity of the substance. In all accurate determinations a temperature
of 4° C. should be maintained to ensure the water remaining at the
maximum density.
(b) Method by Dense Solutions.
A small number of liquids may be obtained which have a density equal to or greater than most of the precious
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