Acetylene
2 of the 6 encyclopedias on this shelf carry an entry for Acetylene. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a colorless gas having a faint ethereal odor. It is formed in small quantities by direct union of carbon and hydrogen in the electric arc. When calcium carbide is dropped into water, violent effervescence occurs, the carbide is disintegrated, slaked lime is formed, and acetylene passes off as a gas. The gas burns in air with a strongly illuminating, somewhat smoky flame, but gives a white light in a special form of burner in which a flat stream of the gas is burned in a rich supply of air. When used as an illuminant, it is developed in a suitable generator as it is needed. It is commonly used for lighting railway cars, offices, and shops. As prepared from commercial calcium carbide, acetylene is more or less impure, and the disagreeable odor and alleged poisonous properties are attributable to the impurities. The gas is subject to violent explosion when mixed, even in small proportion, with air and ignited, or when subjected to sudden pressure. It may, however, be safely handled at ordinary pressures, but when contained in cylinders at more than two atmospheres pressure it is readily exploded by any shock. To produce the calcium carbide required in the commercial manufacture of acetylene, a mixture of pulverized limestone and coke is fused in the intense heat of an electric furnace. The carbide is a hard, grayish, slag-like mass, in which form it is placed on the market. There are extensive calcium carbide factories at Niagara Falls, the electricity required by the furnaces being generated by the water power. JULIUS HORTVET.
Collier's New Encyclopedia (1921)
a hydrocarbon having the formula C2H2, also called ethine. The carbon atoms are united to each other by three bonds. It is produced by passing an electric current between carbon poles in an atmosphere of hydrogen, and also by the incomplete combustion of hydrocarbons. It is a colorless gas, specific gravity, 0.92, has a peculiar odor, and burns with a bright flame; it forms a red precipitate with ammoniacal cuprous chloride, which, by the action of nascent hydrogen, is converted into ethylene, C2H4.
What Has Changed in the Last Century
Aiton's contributors in 1910 described acetylene chiefly as an illuminant, "commonly used for lighting railway cars, offices, and shops," generated from calcium carbide on the spot as needed. That market was gone within a generation, killed by electric lighting; carbide lamps survived only for miners' helmets and cavers, and even there battery lamps have replaced them. The explosion hazard both accounts stress "when contained in cylinders at more than two atmospheres" was solved by dissolving the gas in acetone held in a porous filler, which is why acetylene can now be shipped in ordinary bottles and burned with oxygen in welding and cutting torches, still its most familiar use. As a chemical raw material it dominated plastics and solvent manufacture into the mid-20th century before cheap ethylene from petroleum displaced it, though carbide-based acetylene chemistry remains large in China.
Written for this edition, 2026.