Pie-zom′e-ter.
An instrument invented by Oersted for measuring the compressibility of liquids. It consists of an elongated bulb a having a graduated stem of small bore. The instrument is filled with any liquid up to a certain mark on the stem, and a globule of mercury is placed above the liquid. It is then placed in a cylindrical vessel b filled with water, to which pressure is applied by means of a screw piston. The number of graduations through which the globule of mercury is thus caused to descend indicates the apparent diminution in bulk of the liquid; that is, the excess of its contraction over that of the bulb which contains it. This depends on the quality of the glass of which the bulb is composed; its amount is ascertained and the proper correction is applied by deducting the increase in volume due to the difference of the two expansions, from the indication of the mercurial index; this gives the absolute con traction of the liquid.Piezometer. |