The new chemistry / by Josiah P. Cooke, Jr.

  • Josiah P. Cooke
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: The new chemistry / by Josiah P. Cooke, Jr. Source: Wellcome Collection.

    74/376 page 68
    one can be most readily reduced to either of the other two. In order to make clear these last relations, I must ask you to distinguish between two terms which are constantly confounded in the ordinary use of language, namely, density and specific gravity. The density of a substance is the amount of matter in a unit-volume of the substance. In the English sys- tem it is the weight in grains of a cubic inch, and in the French system the weight in grammes of a cubic centi- metre. Thus the density of wrought-iron is 1,966 grains English, or 7.788 grammes French. So also the density of water at 4° centigrade (the point of maxi- mum density) is 252.5 grains, or 1 gramme. The specific gravity of a substance is the ratio be- tween the weight of the substance and that of an equal volume of some other substance taken as a standard. For liquids and solids, water is always the standard selected, and the specific gravity, therefore, expresses how many times heavier the substance is than water. It can evidently be found by dividing the density of the substance by the density of water, because, as we have just seen, these densities are the weights of equal volumes. Hence the specific gravity of iron equals— 1966 grains 7.788 grammes w neo tr ^— 01 —; ' — 7.788 252.5 grams i gramme Of course, the specific gravity of a substance will be expressed by the same number in all systems; and, fur- ther, in the French system, as the example just cited shows, this number expresses the density as well as the specific gravity. Density, however, is a weight, while specific gravity is a ratio, and the two sets of numbers are identical in the French system only because in that system the cubic centimetre of water has been selected as the imit of weight.
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