From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter from a lubricant manufacturer defining the difference between grease and oil.
| Identifier | ExFiles\Box 27\1\ Scan212 | |
| Date | 25th May 1929 | |
| RESEARCH DEPARTMENT. Telephone: 5202 CENTRAL (4 LINES) X3806 C. C. Wakefield & Co. Limited. MANUFACTURERS of HIGH CLASS LUBRICANTS. GOVERNING DIRECTOR, SIR CHARLES WAKEFIELD, BART. MANAGING DIRECTOR, W. R.{Sir Henry Royce} GRAHAM. DIRECTOR & SECRETARY, J.{Mr Johnson W.M.} BROWNE. EAE/CJR. LABORATORY: Wakefield House, 30&32, Cheapside, London E.C.2. 25th May, 1929. Messrs. Rolls-Royce Ltd., D E R B Y . Dear Sirs, For the attention of Mr. Gaye. In reply to your letter of the 15th instant, it is not easy to make a sharp distinction between a grease and an oil. Generally speaking, however, greases are referred to as emulsions of a soap and oil. In the trade this is called a soap grease, and is usually of a white, yellow or brown colour, depending upon the state of purity or composition. On the other hand, there are the mineral greases which are pure hydrocarbon materials allied to the more viscous mineral oils. It is very common to find that the soap greases have a much higher melting point than the mineral greases. Of course, there is no difficulty in distinguishing a soap grease and an oil because it definitely contains soap, but a mineral grease may not be so easily defined because any mineral oil will assume the appearance of mineral grease provided the temperature is lowered sufficiently. Unfortunately the physicist's definition can hardly be applied. He says that if a body is continuously deformed by a very small sharing stress it is a liquid, whereas if the deformation stops increasing after a time, the substance is a solid. In the sphere of lubrication we regard a grease as a solid and an oil as a liquid. Yours faithfully, C. C. WAKEFIELD & Co., LIMITED. E.{Mr Elliott - Chief Engineer} A.{Mr Adams} Evans CHIEF CHEMIST | ||