A
set of standard specific gravity liquids with fixed intervals could be
kept ready by diluting any one of the first five liquids. It could be
used without the Westphal's balance by matching liquids with a series
of stones of known specific gravity. This permits a quicker mode of
determining the specific gravity. Methylene iodide has a density of
3-3. It is a clear pale-yellow liquid. Stones with higher specific
gravity than 3-3 will sink and those with less than 3-3 will float. It
is miscible with benzene in all proportions, arid so a series of
liquids from 0-88 to 3-33 could be prepared. But there may be variation
in the values due to the presence of impurities, cavities or flaws in
the stones and also due to variation in composition (chemical). With
the larger stones Jolly's balance could be used. (See Table on pp.
166-167 for a List of Gem minerals with specific gravity, etc.)
(4) Jolly's Spring Balance
This
enables a most rapid determination of specific gravity of a gem, but
the method is not quite so accurate as described in (1) and (3), but
results obtained are usually good enough for determination of gems and
could be used with advantage with larger stones.
It consists of a spiral spring suspended vertically from a horizontal rod at 0 and hangs against a graduated mirror.
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