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may be gently boiled and again cooled before determining the weight.
(3) Heavy Liquids and Westphal's Balance
This
method is particularly useful when the mineral is not obtainable in
sufficient quantity. A number of heavy liquids, organic as well as
inorganic, are used which could be diluted to give a solution of any
given specific gravity. The gem whose specific gravity is to be
determined is immersed in the liquid and it is noticed whether it sinks
or floats. The liquid has to be diluted or concentrated until the stone
neither sinks nor floats. The specific gravity of the liquid could be
easily determined by the Westphal's balance. The value obtained for the
liquid is obviously the' specific gravity of the stone. It could be
used for stones whose specific gravity does not exceed the specific
gravity of the liquid used.
Westphal's Balance
It
has a graduated beam and from one end of it a weighed sinker is
suspended in the liquid contained in a cylinder. When the sinker is
properly immersed in water, the beam is horizontal as indicated by the
pointer on the left hand side. When the liquids are substituted in the
cylinder—-weights or riders are adjusted on the beam until the sinker
neither rises nor sinks. The specific gravity of the liquids can be
directly read from the positions of the riders on the beam.
The
Westphal's balance could also be used to determine the specific gravity
of solids, insoluble in water. The sinker is removed and the pans are
attached to the screwed end of the beam. The cylinder is filled with
water at 15°C. so that the lower pan is completely covered during the
whole of the time it is swinging. The adjustable weight is now turned
until the beam is again in equilibrium.
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