Lubricants

Lubricants, unguents interposed between surfaces in machinery which work on one another, with the object of lessening the Friction (q.v.), and thereby diminishing the wear and tear, and lessening the waste power taken up in overcoming friction. Various unguents are in use: animal fats and oils, such as tallow, sperm-oil, lard, &c.; vegetable oils, as, for example, olive-oil and rape-oil; and many mineral oils. The particular unguent best suited for any purpose is a matter of considerable importance. Where the pressure between the two surfaces is great it is necessary to use oils with body or thickness, since the lighter oils are readily squeezed out from position. Sperm-oil, for instance, is a very good lubricant, but not so satisfactory for heavy loads and high temperatures. Many oils again, especially vegetable oils, deteriorate much faster in use than others by evaporation of their volatile constituents.