the residuum of petroleum distillation, and vary so greatly in their properties that many of them are not applicable to delicate mechanism; but as the lighter varieties seem to fulfill all the necessary conditions, the writer will here consider their source and method of treatment.

12. Petroleums are obtained from many different localities, being fluid, bituminous oils, all having the same general characteristics and origin. They are all hydrocarbons, and contain little or no oxygen. As their origin is thoroughly discussed in many works on that subject, and as there is such a diversity of opinion regarding it, the reader is referred to such works.[3]

13. Paraffine, both liquid and solid, is obtained by the distillation of crude petroleum by means of superheated steam. When the heavier hydrocarbons begin to come over the receiver is changed and the butyraceous distillate is filtered through a long column of well dried animal charcoal. The first portion of the percolate is colorless or nearly so.

The distillate is made water white by some refiners by an acid treatment, followed by a water-and-alkali washing. On exposing this mass to a low temperature it becomes thick, somewhat like "cosmoline" but white. (59.) It is then shoveled into cotton bags of very strong material and subjected to powerful pressure by means of a hydraulic press. This operation divides the paraffine into two parts: the solid paraffine wax from which candles, etc., are made remaining in the bags, while that which is expressed is paraffine oil. If the operation is carefully performed the oil will be free from crystaline paraffine at a very low temperature.

Fig. 5.—Extracting Oil from the Head of a Porpoise.

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.)

Fig. 6.—Rendering Room in D. C. Stull's Factory.

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.

18. Gravitation. That attraction which is exerted on all matter, at all distances, is called gravitation. Gravitation is universal, that is, every molecule of matter attracts every other molecule of matter in the universe. The whole force with which two bodies attract one another is the sum of the attraction of their molecules, and depends upon the number of molecules the two bodies collectively contain, and the mass of each molecule. Hence, all bodies attract, and are attracted by, all other bodies.

In a ball suspended from the ceiling by a thread an attraction exists between the ball and the ceiling, but on account of a greater attraction existing between the ball and the earth, if we cut the thread the ball will move toward the earth, or in the direction of the greater attraction.

19. The Effect of Distance. Gravitation varies inversely with the distance by which two bodies are separated.

As the sun is many times greater than the earth, the attraction between the ball (18) and the sun would cause the ball to leave the earth and move toward the sun were it not for the fact that the ball is so much nearer to the earth than to the sun.

20. Cohesion. The attraction which holds the molecules of the same substance together so as to form larger bodies is called