Of the various methods employed for determining the density of liquids, none appear to be so well adapted for ordinary service as the hydrometer (aerometer). While this class of instruments does not yield results quite as accurate as could be had with a specific gravity bottle, yet for all practical purposes the hydrometer proves the most advantageous, being easily understood and consuming but little time in its application.

The particular kind of hydrometer chiefly made use of is not one denoting the specific gravity, but one representing a scale, which, while not claiming to be as scientific as some others, is, as experience proves, for various reasons the best adapted to meet the requirements.