aker of water, just as much water will be displaced as though the
vessel were full, and it will be displaced _upward_ as before, for lack
of any other place to go. Consequently its weight will tend to buoy up
or float the stone by trying to get back under it, and the stone when in
water will weigh less than when in air. Anyone who has ever pulled up a
small anchor when out fishing from a boat will recognize at once that
this is the case, and that as the anchor emerges from the water it seems
to suddenly grow heavier. Not only does the stone weigh less when in the
water, but it weighs exactly as much less as the weight of the water
that was displaced by the stone (which has a volume equal to the volume
of the stone). If we weigh a stone first in the air, as usual, and then
in water (where it weighs less), and then subtract the weight in water
from the weight in air we will have the _loss of weight in water_, and
this equals the _weight of an equal volume of water_, which is precisely
what we got by our bottle method.

We now need only divide the weight in air by the loss of weight in
water, and we shall have the specific gravity of the stone.

[Illustration: FIG. 6.]

To actually weigh the stone in water we must use a fine wire to support
the stone. We must first find how much this wire itself weighs (when
attached by a small loop to the hook that supports the balance pan and
trailing partly in the water, as will be the case when weighing the
stone in water). This weight of the wire must of course be deducted to
get the true weight of the stone in water. The beaker of water is best
supported by a small table that stands over the balance pan. One can
easily be made out of the pieces of a cigar box. (See Fig. 6.)

The wire that is to support the stone should have a spiral at the bottom
in which to lay the gem, and this should be so placed that the latter
will be completely submerged at all times, but not touching bottom or
sides of the beaker.

Example of data, and calculation, when getting specific gravity by the
method of weighing in water:

Weight of stone = 4.02 carats
-----------
Weight of stone (plus wire) in water = 3.32 carats
Weight of wire = .30 carat
-----------
True weight of stone in water = 3.02 carats
-----------
Loss of weigh