Cadmium
3 of the 6 encyclopedias on this shelf carry an entry for Cadmium. All 3 are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a diatomic metallic element, discovered in 1818; symbol, Cd; at. wt., 112; sp. gr., 8.6; melting point, 320°, boils at 778°. It is a white. ductile, malleable metal; scarcely tarnishes in the air; burns when heated in the air, forming a brown oxide, CdO. It dissolves readily in nitric acid, and decomposes water at red heat. Cadmium is found in some zinc ores; when these are distilled it rises in vapor before the zinc does so. It also occurs in the form of sulphide in greenockite. Cadmium is easily separated from zinc by passing HS. into their solution in HCl; the cadmium is precipitated as yellow sulphide, CdS. Cadmium can be separated from copper in analysis by dissolving their sulphides in nitric acid and adding ammonia in excess, filtering off oxides of other metals; then potassium cyanide is added till the precipitate first formed redissolves, then H₂S gas is passed through the liquid, from which it throws down the cadmium as sulphide.
Aiton's Encyclopedia (1910)
a metallic element. It has somewhat the appearance of tin. It crackles when bent. Its chemical properties resemble those of zinc. In combination with sulphur it occurs in most zinc ores. This combination is known as greenockite, and when prepared artificially is of great use to painters who call it cadmium yellow. This sulphide of cadmium gives paint a bright yellow color of great durability. Cadmium may be obtained usually by roasting zinc-blende, as cadmium is more volatile than zinc. Our commercial supply is obtained chiefly from Belgium and Silesia. An iodide of cadmium is used in photography.
The Encyclopedia of Founding (1892)
A somewhat rare metal found associated with zinc in nature, and is similar to that metal in its chemical relations. When exposed to the air it tarnishes. Cadmium is a lustrous bluish-white metal; melts and volatilizes at a temperature below redness, and if heated in the air it takes fire and burns to a brown oxide. See ZINC.
What Has Changed in the Last Century
The chemistry in these entries still holds — cadmium melts near 321°C, boils around 767°C, and is still won as a by-product of zinc smelting — but not one of the three accounts mentions that the metal is poisonous. That silence ended after mass cadmium poisoning from mine runoff in Japan's Jinzu river basin, recognised as itai-itai disease in the 1950s and 60s; cadmium and its compounds are now classed as human carcinogens and the metal is banned from most electrical goods in Europe under the RoHS rules that took effect in 2006. Aiton's praise in 1910 for cadmium yellow "of great durability" reads differently now: the pigment survives in artists' oils but has been squeezed out of consumer paints and plastics. Aiton's Belgium and Silesia have also been displaced — China, South Korea and Japan now dominate refined output — while the twentieth century found the metal two large new jobs, nickel–cadmium batteries and cadmium-telluride thin-film solar panels.
Written for this edition, 2026.