Second, by weighing the stone in air and then in distilled water or alcohol, and thus learning the weight of an equal bulk of water.
Third, by measuring or weighing the water which the stone displaces when immersed in a small vessel of known capacity.
Fourth, by means of the Nicholson hydrometer, a simple instrument consisting of a hollow glass cylinder, two dishes, and a glass vessel.
As the jewelers’ balances are well adapted for the ordinary work of taking specific gravity, or can be easily adapted for such work, the second method will usually be the more practical to follow.
The author has had very satisfactory service from a $30 balance, and any well adjusted balance will give fair results.
The following accessories are necessary to take the specific gravity of a stone:
Distilled water about 60° Fahr.
A very fine thread of platinum wire with which to suspend the stone ([fig. 4]).
A glass-beaker for the water ([fig. 3, C]).
A bench to hold the beaker over the pan ([fig. 2]).