HYDROMETER

n. Hid-ro2m'e2t-u6r. Lat., hydro met rum (from ii , water, and utrpov, a measure). Fr., areometre. Ger., H. An instrument for measuring the density, etc., of fluids. liaumfi's h. A gla tube with a bulb blown in its end and loaded with mercury so as to float upright in a liquid. For determining the densities of liquids lighter than water the stem of the h. is so graduated that 10 mark the level to which it sinks in distilled water, and the level to which it sinks in a solution of 10 parts of salt in 90 of water; the graduation being" continued upon the same scale up to the top of the instrument. For liquids heavier than water, the h. is so made that the point marked is at the top of the stem and indicates the level to which it sinks in distilled water; the lower part of the stem is then so graduated that 15 represents the level to which it sinks in a mixture of 15 parts of salt and 85 of water. [B.] Cartier's h. See Cartier's ALCOHOLOMETER. Fahrenheit's h. A gla tube loaded with mercury like Baume's h., and having a standard mark on the stem and a scale-pan on the top. The n. is floated in the liquid to be examined, the specific gravity of which can then be deduced from the weight of the load that has to be placed in the scale-pan in order to sink the stem to the mark. [BJ H. of constant volume. Ger., Gewichtsaraometer. A h. in which, like Nicholson's h. and Fahrenheit's h., the stem is always immersed to the same extent, while the load which the h. carries varies in each case and by the amount of its variation indicates the specific gravity. [B.] H. of constant weight. Ger., Scalen-Ardometer. A h., such as Baume's, in which the load remains constant and the amount to which the stem is immersed varies, the amount of the variation indicating the specific gravity sought. H. of variable volume. See H. of constant weight. H. of variable weight. See H. of constant volume. Nicholson's h. A hollow metal cylinder loaded with lead so as to float upright in water, and having a standard mark on its stem and a scale-pan at the top of the stem, and also one at the bottom of the cylinder. The body whose specific gravity is to be determined is placed first in the upper and then in the lower (or submerged) pan, and the weight of the additional load that has to be placed in the upper in each case in order to sink the h. to the level of the standard mark is ascertained. From a comparison of these weights and of the weight required to sink the h. to the same level when no substance is added, the specific gravity can be determined. [B.] [s. 387]