The specific gravity of solids



In ordinary language the terms density and specific gravity (s. g.) are used to represent the relative weights of equal bulks or volumes of different substances. In order to compare these conveniently, pure water at 60 is taken as the standard. A cubic foot of water weighs 100 oz., hence to determine the weight of a given bulk of any body the specific gravity of which is known, multiply the cubic content in feet by 1000, and this by the s. g., and the product will be the weight in ounces avoirdupois. Thus, the s. g. of cast-iron is 7.207, that is, it is 7.207 times heavier than an equal bulk of water. A cylinder of cast-iron 1 foot in diameter and 10 feet high, would contain 10 cubic feet, 10 X 1000 X 7.207 = 72.070 oz. = 4500 lbs.

1. By the Pitcher.--Fill a pitcher, or similar vessel, brim full; put in the body; it will displace its own bulk of water; catch this water as it overflows and weigh it. Divide the weight of the body by that of the water displaced, the quotient will be its specific gravity. A very neat instrument for performing this process accurately has been contrived by Messrs. Eckfeldt and Dubois, of the United States Mint.

2. By the Hydrostatic Balance.--Weigh the body, fasten it, preferably by a horse-hair, immerse it in water, and note the loss of weight. The weight in air divided by the loss of weight in water = the s. g.

3. When the Body is Lighter than Water.--Attach to it some heavy body of known weight in air and water. Weigh the two together, first in air and then in water, note the loss. The loss of weight of the heavy body in water being known the difference between these losses divided into the weight of the light body in air, will give the specific gravity. Thus, a bit of wood weighed in air 200 grains, attached to a piece of copper the two weighed in air 2247 grains, and in water 1620 grains suffering a loss of 627 grains, the copper alone loses in water 230 grains, 627 - 230 = 397, the loss of the wood; 200/397 = 0.504, s. g. of the wood.





Return to The Household Cyclopedia of General Information