GRAPHITE.--On the other hand, graphite, if introduced in a cylinder with a good liquid lubricant, will, in time, fill up the pores of the metal, and thus produce a good surface, and it also protects the cylinders from carbonizing, and prevents the pistons from “Freezing” as it is called when it is caused to stick together by the heat. THE TEST OF CYLINDER LUBRICANTS.--For cylinders the lubricant should have a flash point of at least 375, and a fire test of 430 degrees, Fahrenheit. _Flashpoint_ has reference to the temperature at which it will give off inflammable vapor. _Fire test_ has reference to the temperature at which the oil will actually ignite and burn. Any oil, in burning, will deposit more or less carbon, because being a fuel, it must have carbon. As mineral oils will stand higher temperatures before igniting, than animal or vegetable oils they are best suited for cylinders. LUBRICATING SYSTEMS.--Various systems are employed in automobiles. The _splash_ system has the advantage of simplicity since the cylinders, as well as the bearings, are provided with a modicum of oil at every revolution of the crank, the latter, or the connecting rods, being adapted to strike the pool of oil in the bottom of the chamber. The cylinder walls do not get the greatest benefit from this method of distributing the lubricant, as the splash is at the point when the piston reaches the lowest turn, so the lubrication on the cylinder is effectual only so far as the piston is able to draw it up or entrain it in its upward movement. PRESSURE METHOD.--Supplementing the splash, and frequently used as the sole mean is the plan adopted by many, and known as the pressure system, which not only lubricates the bearings and cylinders, but also the other mechanism in the car, is the use of pressure, which may be exerted by gravity, or by the use of hand pumps. Some employ the exhaust of the engine to draw up the oil. This requires ducts leading to all the parts which are adapted to take a liquid lubricant. THE PRECISION SYSTEM.--The most positive method is that which has a pump connected with the engine, which forces the oil to all the bearings at each turn of the engine, and for that reason is called the _precision_ system. It has the advantage that every bearing must get a certain portion of the lubricant, and as arrangement is made to catch and return the unused oil, it is also economical in use, although more expensive to apply. [Illustration: Fig. 106. Lubricating System.] COMBINED FORCE FEED AND SPLASH SYSTEM.--In Fig. 106 is illustrated one of the latest improved systems, in which there is utilized an internal force feed and a constant level splash system. In this equipment a reservoir under the crank case contains the supply of oil.