LUBRICANTS (from Lat. lubrica•c, to make smooth, from labricus. slippery). Substances ap plied to the friction surfaces of machinery to reduce the resistance of friction to motion. Lubrication is the process of applying lubri cants. Lubricants may he either solid or liquid. The requisities of a good lubricant are: I I) `liody• enough to prevent the surfaces to which it is applied in contact with each other; (2) freedom from corrosive acid. either of min eral or organic acid origin; (3) as great fluidity as possible consistent with hody': (4) a mini mum coefficient of friction; (5) high 'flash' and burning points; and (0) freedom from all ma terials liable to produce oxidization or 'gum ming.' Engineers have suitaide tests for de termining all of these properties of lubricants. Prof. R. 11. Thurston states the be,t In iricants for different purposes to be: For low tempera tun's, such as roek-drills driven by compressed air, light mineral lubricating oils; tor very great pressures, with slow speed, graphite, soapstone, and other solid lubricants; for heavy pressures, with slow speed, solid lubricants and lard, tal low, and other greases; for heavy pressure-, and high speed, sperm oil, castor oil, and heavy min eral oils; for light pressures and high speed, sperm. refined petrolenni, olive, rape, and cotton seed oils; for ordinary maehinery, lanl oil, tal low oil, heavy mineral oils, and the heavier vegetable oils; for steam cylinders. heavy min
eral oils, lard, and tallow: for watt le, and other delicate mechanism, clarified spert t. •at-foot, porpoise oil, olive oil, and light mineral lubri cating oils; for mixture with mineral oils. sperm is best. lard oil is much used, olive oil and cot tonseed oil are good. The preceding list give, a reasonably eomprehensive ri•stun6 of the ordinary special lubricating compositb ns sold under various trade na Ines are combinations of these and they may be either soli I or fluid. Lubrication may be performed by manual application of the lubricant, or mechanical de vices may he used for this purpose. These me chanical devices are called and they are made in a of forms and often are rather elahorate in character. In all cases they consist essentially of a reservoir for the lubri cant from which one or a number of pipes lead to suitable discharge points at the different bear or rather friction surfaces. Consult: Kent, Mechanical Engineers' l'ock(t Book ( New York. 1900); Thurston, Treatise on Friction and Lost ll ork ire Machinerit and Mill Work (New York, 18941. See OILS.