ARÆOMETER

ARÆOMETER, an instrument to measure the density or gravity of fluids.

The areometer, or waterpoise, is usually made of glass; consisting of a round hollow ball, which terminates in a long slender neck hermetically sealed at top: there being first as much running mercury put into it as will serve to balance or keep it swimming in an erect position.

The stem is divided into degrees (as represented Plate XXXVI. fig. 23.); and by the depth of its descent into any liquor, the lightness of that liquor is concluded: for that fluid in which it sinks least must be heaviest; and that in which it sinks lowest lightest.

Mr. Homberg has invented an areometer, described in Phil. Transact. No. 262. thus: A is a glass bottle or matras, with so slender a neck that a drop of water takes up in it above five or six lines, or half of an inch. Near that neck is a small capillary tube D, about six inches long, and parallel to the neck.— To fill the vessel, the liquor is poured in at the mouth B (which is widened to receive a funnel), till it run out at D, that is, till it rise in the neck to the mark C, by which means you have always the same bulk or quantity of liquor; and consequently, by means of the balance, can easily tell, when different liquors fill it, which weighs most, or is most intensely heavy.

Some regard, however, is to be had in these trials to the season of the year, and degree of heat and cold in the weather; because some liquors rarefy with heat and condense with cold more than others, and accordingly take up more or less room.

By means of this instrument, the ingenious author has made a table to show the different weights of the same bulk of the most considerable chemical liquors both in summer and winter as follows:

Weighed in summer. In winter.

The instrument itself weighed, when empty, one drachm twenty-eight grains. See HYDROMETER.