The principal use of petroleum is for the manufacture of refined products, of which the number and uses are legion. The lightest gravity, etherial products are employed as anaesthetics in surgery. The gasolines are the universal fuels of internal-combustion engines, and the naphthas are widely used as solvents and for blending with raw casinghead gasoline in the manufacture of commercial gasoline. The kerosene group includes a variety of products utilized primarily as illuminants, but in annually increasing quantities as fuel in farm tractors. The lubricating oils and the greases derived from petroleum are indispensable to the operation of all types of machinery. The waxes derived from petroleum of paraffin base are utilized in many forms as preservatives and as sources of illumination, and in the last three years have become indispensable constituents of surgical dressings in the treatment of burns. Petroleum coke, because of its purity, is in demand for use in certain metallurgical processes and for the manufacture of battery carbons and arc-light pencils. Fuel oils obtained as by-products of petroleum refining satisfy the fuel needs of many industrial plants, railroads and ocean steamers. Road oils, as the name implies, are employed for minimizing dust on streets and highways; and artificial asphalt, a product of certain types of petroleum, has in many localities superseded the use of other forms of asphalt for paving purposes. =Substitutes.=--For petroleum as a fuel under boilers in the generation of steam there are numerous substitutes, including wood, charcoal, coal, peat, natural gas, artificial gas, and electricity; as a fuel in internal-combustion engines some demonstrated substitutes are natural gas, artificial gas, benzol, and alcohol, and in the Diesel type of engine certain vegetable and fish oils can be utilized. For illuminating purposes, animal fats, oils distilled from coal, natural gas, artificial gas, acetylene gas and electricity may be substituted for kerosene. For certain types of lubrication carefully refined vegetable and mineral oils are acceptable, but for lubricating high-speed bearings and for all lubrication in the presence of high temperature and of steam no satisfactory substitutes for mineral lubricants derived from petroleum are known. Substitutes for petroleum asphalt are available in the form of native asphalts, bituminous rocks, and coal-tar residues. For petrolatum, animal fats and vegetable oils can be substituted, and for paraffin wax, ozokerite might be made to satisfy such essential requirements as could not be met by refrigeration or by vegetable and animal oils. CHANGES IN PRACTICE