~14. Neutral Oils~[4] "are refined paraffine oils varying in specific gravity from 0.8641 to 0.8333. For the purpose for which these oils are employed it is especially necessary that they be thoroughly deodorized. They are largely used for the purpose of mixing with animal and vegetable oils. It is said that a mixture of 95 per cent of a good neutral oil of the right gravity, and 5 per cent of sperm oil, has been sold for pure sperm. Ordinary inspection as to the odor and general appearance would fail to detect the adulteration. Having been subjected to the usual process for the extraction of crystaline paraffine, they will stand a very low cold test, and having been passed through bone black cylinders, they are free from odor and have but little color. They are usually exposed for a few days in open shallow tanks for the purpose of removing the flurescence of petroleum oils. Unmixed with heavier oils they are too light in body (especially the lighter varieties) to be employed as spindle or machinery oils, but when mixed with such oils in the proper proportions they form admirable lubricating compounds for general lubricating purposes when very high speed is not required." (70-71.) [Illustration: _Fig. 6.--Rendering Room in D. C. Stull's Factory._] FOOTNOTES: [1] Brannt. Animal and Vegetable Fats and Oils. [2] Brannt. Animal and Vegetable Fats and Oils. [3] Crew; Practical Treatise on Petroleum. Lesquereaux; Transactions American Philosophical Society. Winchell; Sketches of Creation. Henry; Early and Later History of Petroleum. [4] Crew. Practical Treatise on Petroleum. CHAPTER II. ELEMENTARY PHYSICS RELATING TO FRICTION AND LUBRICATION. ~15.~ Most of those who may read this work, are no doubt familiar with the laws of elementary physics; but as _all_ may not be, for a better understanding of that which follows, it may be well to treat briefly of some of the physical laws bearing on the subject. ~16. The Molecule.~[5] _Every visible body of matter is composed of exceedingly small particles called molecules._ This is the basis of the theory of the constitution of matter which physicists have usually adopted. It is estimated that if we should attempt to count the number of molecules in a pin's head, counting at the rate of 10,000,000 per second, we should require 250,000 years. ~17. Porosity.~ The term _pore_ in physics is restricted to the invisible space that separates molecules. All matter is porous; thus dense gold will absorb (24) liquid mercury, much as chalk will water; but the cavities to be seen in a sponge are not pores.