This section is from the book "A Practical Treatise On Friction, Lubrication, Fats And Oils", by Emil F. Dieterichs. Also available from Amazon: A practical treatise on friction, lubrication, fats and oils.
Solid lubricants consist principally of filtered stock or vaseline, and they are fed to the bearings through cups especially devised for that purpose, and furnished with screw pressure, or provided with copper rods, which latter, touching the shaft, cause feeding of the vaseline or other greases by communicating the frictional heat to them, whereby they are liquified, and caused to flow onto the shaft and into the bearing.
Greases for lubricating consist principally of tallow or lard, of either or both, together with palm oil, rapeseed oil, degras, rosin oil and petroleum oils brought to a proper consistency by semi-saponification with weak lye, limewater, or lime-soap, or lime-paste.
Fatty matter of all kinds and quality, residuum and tar from refineries, in short all that can be worked into this kind of lubricant, and can be given a greasy appearance and consistency, is worked into what is known and sold in the market under the name of "Lubricating Grease" Cup Grease, Axle Grease, etc.
The character of the machinery for which this kind of lubricant is used is of the coarser, heavier kind ; hence less attention is generally given to ascertain the indirect advantage that would result from the use of grease of best quality, cost being generally the only point considered.
Here also, as with the lubricating oils, it is the fatty acid alone which is the lubricating, that is, the heat-absorbing and eradiating principle, held to the moving surfaces by medium of the stearin, palmitin, rosin or, paraffin, the latter being ultimately left as concentrated and charred gummy deposits.
With grease lubricants the wear and abrasion of the metal is always greater than with oil lubrication, as the consistency of the grease requires greater accumulation of frictional heat to melt and convert it into a liquid state before it is enabled to reach the place where it is expected to do its work.
Carefully conducted experiments have demonstrated the fact that it takes some twenty-five per cent less power to move machinery lubricated with oil than when lubricated with grease, and at a some thirty to thirty-five per cent lower temperature.
The additions of lime, graphite (plumbago), lead, asbestos fibre, mica, sulphur, soapstone (talc) and all other inert matter, to grease, used on machinery moving under great pressure and heat, act only as a medium, filling the interstices in the metal, and serve only as a sort of cushion for the real lubricant, the fatty matter contained in the grease. These inert substances cannot vaporize with the frictional heat and must, therefore, remain as gummy accumulations and metallic abrasions on the bearings.