[Illustration: _Fig. 6.--Rendering Room in D. C. Stull's Factory._]
[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.
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._