Page 36 - statbility for masters and mates

24 Ship Stability for Masters and Mates
The variable immersion hydrometer
The variable immersion hydrometer is an instrument, based on the Law of Archimedes, which is used to determine the density of liquids. The type of hydrometer used to ®nd the density of the water in which a ship ¯oats is usually made of a non-corrosive material and consists of a weighted bulb with a narrow rectangular stem which carries a scale for measuring densities between 1000 and 1025 kilograms per cubic metre, i.e. 1.000 and 1.025 t/ m3.
The position of the marks on the stem are found as follows. First let the hydrometer, shown in Figure 4.4, ¯oat upright in fresh water at the mark X. Take the hydrometer out of the water and weigh it. Let the mass be Mx kilograms. Now replace the hydrometer in fresh water and add lead shot in the bulb until it ¯oats with the mark Y, at the upper end of the stem, in the
Fig. 4.4