And even if the supply of petroleum were far less limited than the experts estimate it to be, even if there were enough of it to last for many decades to come, the fact that it is practically the one lubricant of the industrial world makes it a social crime to burn it as a substitute for coal. Without it, every railroad wheel would run hot and stop; the great turbines in our ships and modern power plants move on bearings that are smothered in petroleum oil. And for petroleum as a lubricant there is no commercially available substitute. Closely associated with petroleum and originally derived from it, is natural gas. There is no way of telling how great the supply of this has been in the past, how much there is in reserve, or what the present outflow is, because the waste of natural gas has been and is notorious. We do know, however, that the per capita consumption in 1915, according to the U. S. Geological Survey, was approximately four times the consumption of artificial gas, and seven times that of the by-product coke-oven gas, and that its average price to the consumer was sixteen cents a thousand cubic feet as against ninety-one cents for artificial gas and ten cents for coke-oven gas. About one-third of the natural gas is used for domestic purposes, about two-thirds is used for manufacture. It is conservatively estimated that 100,000,000 gallons of gasoline can be recovered from it annually and it is the primary source of the lamp black from which all the printers' ink in present use is made. The supply of natural gas in reserve is not calculable, but since most of the wells show a diminished flow, it is believed to be on the way to exhaustion. Although the supplies of oil and gas have supplemented coal for half a century and protected the coal industry from the same sort of economic pressure which has forced reorganization upon most other enterprises, the time is at hand when they can no longer do so.