LEAKS.--Leaks in tanks can be repaired temporarily, with tire cement, and patches, but as gasoline affects the rubber it should be properly soldered up at the first opportunity. Water in gasoline is the most serious trouble. All fuel of this kind should be strained through chamois leather. This will effectually prevent water from getting in. LUBRICANTS.--A necessary element in gasoline engines, is a lubricant. This is as essential as the fuel itself. The object is to remove friction between the moving parts. Cylinders of engines are heated to high temperatures, and this makes wear between the parts not lubricated a most serious one. While ordinary gasoline would be a good lubricant for some uses, it would be of no avail in the cylinders of an explosion engine, for two reasons: First, it has but little viscosity,--that is, it has no body which holds together so as to produce a film on the surface of the contacting metals. VISCOSITY.--The film produced by gasoline, for instance, is very thin, but that of castor oil is very thick. The latter, therefore, has greater viscosity. Then again, gasoline, is readily affected by temperature. If it ignites readily, and thus loses its character as a lubricant, it can be of no service. It is necessary, therefore, that the lubricant should not be affected or changed in its character at a low heat. CARBONIZATION.--Some oils when subjected to heat, or when exposed to air, will become sticky or gummy. This is one of the most serious things possible in a gas engine cylinder, because a deposit is formed which causes carbonization through the continued application of heat, resulting in the scratching of the cylinder by breaking the packing rings. ACID IN LUBRICANTS.--In the early production of lubricants, acid was one of the elements in oils not carefully guarded against; and even now, with all the skill of the manufacturer, a small percentage will be found in most products. The presence of this produces corrosion, or pitting of the working parts. This, and the presence of foreign matter, will condemn any oil for cylinder purposes. COMPOSITION OF LUBRICANTS.--Lubricants are composed of either animal, vegetable, or mineral matter, and they may be liquids or solids, or a combination of both. Of the latter, graphite is the best and most widely known. It is one form of carbon, and is used in a finely-divided state, either dry, or mixed with a good lubricating oil. Soapstone is also frequently employed and generally with a liquid lubricant. GREASE.--Grease, usually of animal origin, used in connection with graphite, makes by far the best lubricant for bearings, and for similar purposes, as it can be readily retained in the bearings.