The chief source of calcium carbide in this country is the electric furnace. Cheap electrical energy from hydro-electric developments, such as the Niagara plants, have done much to make the earth yield its elements. Aluminum is very prevalent in the soil of the earth's surface, because its oxide, alumina, is a chief constituent of ordinary clay. But the elements, aluminum and oxygen, cling tenaciously to each other and only the electric furnace with its excessively high temperatures has been able to separate them on a large commercial scale. Similarly, calcium is found in various compounds over the earth's surface. Limestone abounds widely, hence the oxide and carbonate of lime are wide-spread. But calcium clings tightly to the other elements of its compounds and it has taken the electric furnace to bring it to submission. The cheapness of calcium carbide is due to the development of cheap electric power. It is said that calcium carbide was discovered as a by-product of the electric furnace by accidentally throwing water upon the waste materials of a furnace process. The discovery of a commercial scale of manufacture of calcium carbide has been a boon to isolated lighting. Electric lighting has usurped its place on the automobile and is making inroads in country-home lighting. Doubtless, acetylene will continue to serve for many years, but its future does not appear as bright as it did many years ago. The Pintsch gas, used to some extent in railroad passenger-cars in this country, is an oil-gas produced by the destructive distillation of petroleum or other mineral oil in retorts heated externally. The product consists chiefly of methane and heavy hydrocarbons with a small amount of hydrogen. In the early days of railways, some trains were not run after dark and those which were operated were not always lighted. At first attempts were made at lighting railway cars with compressed coal-gas, but the disadvantage of this was the large tank required. Obviously, a gas of higher illuminating-value per volume was desired where limited storage space was available, and Pintsch turned his attention to oil-gas. Gas suffers in illuminating-value upon being compressed, but oil-gas suffers only about half the loss that coal-gas does. In about 1880 Pintsch developed a method of welding cylinders and buoys which satisfied lighthouse authorities and he was enabled to furnish these filled with compressed gas. Thus the buoy was its own gas-tank. He devised lanterns which would remain lighted regardless of wind and waves and thus gained a start with his compressed-gas systems. He compressed the gas to a pressure of about one hundred and fifty pounds per square inch and was obliged to devise a reducer which would deliver the gas to the burner at about one pound per square inch. This regulator served well throughout many years of exacting service. The system began to be adopted on ships and railroads in 1880 and for many years it has served well.