Fig. 5.
A, Flask-like Bottle; B, Indicates Ground Glass Stopper;
C, Shows Hole Drilled through Stopper.
The Specific Gravity Bottle. A small flask-like bottle (see [Fig. 5]) is obtained. This has a tightly fitting ground glass stopper (B). The stopper has a small hole (C) 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 |
| Specific gravity = | Weight of stone | = | 3.51 | = 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.