Fig. 64.
CHAPTER V.
SPECIFIC GRAVITY.
It is recorded of the great Dr. Wollaston, that when Sir Humphry Davy placed in his hand, what was then considered to be the scientific wonder of the day—viz., a small bit of the metal potassium, he exclaimed at once, "How heavy it is," and was greatly surprised, when Sir Humphry threw the metal on water, to see it not only take fire, but actually float upon the surface; here, then, was a philosopher possessing the deepest learning, unable, by the sense of touch and by ordinary handling, to state correctly whether the new substance (and that a metal), was heavy or light; hence it is apparent that the property of specific gravity is one of importance, and being derived from the Latin, means species, a particular sort or kind; and gravis, heavy or weight—i.e., the particular weight of every substance compared with a fixed standard of water.
Fig. 65.
a. A large cylindrical vessel containing water, in which the egg sinks till it reaches the bottom of the glass. b. A similar glass vessel containing half brine and half water, in which the egg floats in the centre—viz., just at the point where the brine and water touch.