The selection of the proper lubricant in any particular case depends, of course, upon the class of machinery in which it is to be used. If on light-running and high-speed machinery, such as is used in the spinning, twisting, and other departments of textile mills, the light-bodied or more fluid oils give the best results. For slow-speed machinery, the heavier bodied oils are best. For use on slow-speed engines, where the oil is fed from cups, a heavy-bodied oil should be used. For highspeed work and engines where continuous oiling systems are used, a light-bodied oil is preferable. Cylinder oils have for their base what is known in the oil trade as cylinder stock, of which there are two classes - the light-colored or filtered stock, and the dark or steam-refined stock, the latter being almost universally used.

For steam turbine lubrication, a high-grade, pure mineral oil is best, as the oil is subjected to high pressure and constant churning, and consequently must be of good quality.

For gas cylinder lubrication, a pure mineral oil ranging in body from light to heavy is found most satisfactory. This type of oil burns freely without leaving a carbon ash.