Taking into account all these factors, it is estimated that the entire supply now known to exist would be exhausted before the middle of the present century. It appears more probable, however, that increasing prices long before that time will help to conserve the supply; and that petroleum will be produced for a long time to come, though not in sufficient quantities for industrial and general use. The principal uses of petroleum are for burning as crude oil in furnaces and under boilers, particularly in locomotives. The refined products have various uses. Probably the most important is the lubricating oil. This is necessary in the development of all kinds of power. At least one-half pint of lubricating oil is used for every ton of coal consumed for power. All engines, all street and steam railways, steamships, sewing-machines, clocks, watches, and automobiles, in fact all operating machinery requires its use; so that a large amount of oil must always be conserved for lubricating purposes. Coal oil, or kerosene, may be regarded as absolutely necessary for the lighting of houses or other establishments not connected with gas or electric supply. Gasolene is sometimes used for lighting, though such use is not common. It is largely used for cooking, and still more largely used in the various types of gasolene engines. Naphtha is used for power, especially for motor-boats, and for cleaning, in which it is very valuable by reason of its power to dissolve dirt. Paraffin is used in polishing, in laundry work, for waxing floors, and as a covering to exclude air in preserving articles. Waste has been markedly absent in the petroleum industry. It is necessary that oil drilling outfits shall contain steel storage tanks for holding the oil when it is reached. Usually the supply is large enough, but sometimes, as in the case of the big well at Beaumont, Texas, the oil gushes forth in such volume that the drillers are not prepared to take care of the overflow, and much is wasted before the well can be capped. In general there is no waste in storage in this country. In European countries where there is oil, the loss through lack of tanks and by using wooden tanks which leak, is very great. Another form of waste which is common in foreign countries, but which has been avoided in the United States, is evaporation of gasolene and similar light products when the petroleum is exposed to the air in open tanks. This is the most valuable part of petroleum, and if it be exposed to the sun a single day it loses greatly in value.