) drilled through it lengthwise. If the
bottle is filled with water, and the stopper dropped in and tightened,
water will squirt out through the small hole in the stopper. On wiping
off stopper and bottle we have the bottle _exactly full_ of water. If
now the stopper is removed, the stone to be tested (which must of course
be smaller than the neck of the bottle) dropped in, and the stopper
replaced, exactly as much water will squirt out as is equal in volume to
the stone that was dropped in.

If we had weighed the full bottle with the stone _on the pan beside it_,
and then weighed the bottle with the stone _inside it_ we could now, by
subtracting the last weight from the first, find out how much the water,
that was displaced, weighed. This is precisely the thing to do. The
weight of the stone being known we now have merely to divide the weight
of the stone by the weight of the displaced water, and we have the
specific gravity number. Reference to a table of specific gravities of
precious stones will enable us to name our stone. Such a table follows
this lesson.

A SAMPLE CALCULATION. The actual performance of the operation, if one is
skilled in weighing, takes less time than it would to read this
description. At first one will be slow, and perhaps one should read and
re-read this lesson, making sure that all the ideas are clear before
trying to put them in practice.

A sample calculation may help make the matter clearer, so one is
appended:

Weight of bottle + stone (outside) = 53.51 carats
Weight of bottle + stone (inside) = 52.51 carats
------------
Weight of water displaced = 1.00 carat
------------
Weight of stone = 3.51 carats

Weight of stone 3.51
Specific gravity = --------------- = ---- = 3.51 Sp. g.
Weight of water 1.00

In this case the specific gravity being 3.51, the stone is probably
diamond (see table), but might be precious topaz, which has nearly the
same specific gravity.

It is assumed that the jeweler will weigh in carats, and that his
balance is sensitive to .01 carat. With such a balance, and a specific
gravity bottle (which any scientific supply house will furnish for less
than $1) results sufficiently accurate for the determination of
precious stones may be had if one is careful to exclude air bubbles from
the bottle, and to wipe th