Iridium
3 of the 7 encyclopedias on this shelf carry an entry for Iridium. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
i-rid i-um, a metallic element much like platinum. It was identified in 1802. With the exception of osmium, also a newly discovered metal, it is the heaviest substance known. It is very difficult to melt, requiring a temperature of at least 3600 Deg. F. It is insoluble in acid and does not rust. It is used frequently for the tips of gold and stylographic pens. Also in the construction of electric instruments, as the resistance coil. Small quantities are obtained in California, Borneo, Brazil, and in the Ural Mountains . It forms three oxids. The solutions made from the salts of the metal take on various tints; hence the name, from Iris, the rainbow.
Collier's New Encyclopedia (1921)
a tetrad metallic element of the platinum group; symbol Ir.; at. wt. 193.1; discovered by Tennant in 1804, in the black powder which remains when crude platinum is dissolved in nitro-hydrochloric acid. This powder is an alloy of iridium and osmium, called iridosmine or osmiridium. Iridium is a white, brittle, very hard metal, fusible with great difficulty, in the blow flame of the oxy-hydrogen blowpipe. It is insoluble in all acids, but when reduced by hydrogen at a red heat it oxidizes slowly and dissolves in nitro-hydrochloric acid.
The Encyclopedia of Founding (1892)
A white brittle metal, which may be fused by means of a powerful oxyhydrogen blast-furnace. In its isolated form it is unacted upon by any acid or by aqua regia, but as an alloy it is dissolved in the latter fluid. Its specific gravity is 21.15. An alloy of iridium and osmium is very hard, and is used for pointing gold pens. See METALS.