Barium
2 of the 6 encyclopedias on this shelf carry an entry for Barium. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a metallic element closely related to calcium, and hence to lime. The name was proposed by Davy. It is Greek, meaning heavy. It is doubtful whether barium has ever been seen in a pure state. It is variously described as silver-white, golden-yellow, and bronze. It is known to be ductile and malleable. Its specific gravity is about four, that is, it is about four times as heavy as water. A hydrate or combination of barium and water is manufactured at Niagara Falls. It is used in clearing sugar. Barium hydrate unites with lime readily. It is used to soften water, and thus prevent the formation of lime incrustations on the inside of boilers. Barium is used in sizing paper and to adulterate the white lead used for painting. The spectroscope test for barium is a number of green lines. Barium salts are poisonous. See Chemistry
Collier's New Encyclopedia (1921)
a dyad netallic element; symbol Ba; atomic weight, 137. Barium is prepared by the decomposition of barium chloride, BaCl2, by the electric current, or by the vapor of potassium. It is a white, malleable metal, which melts at red heat, decomposes water, and oxidizes in the air. Bariu occurs in nature as barium carbonite and sulphate. Its salts are prepared by dissolving the carbonate in acids, or by roasting the native sulphate of barium with one-third its weight of coal, which converts it into barium sulphide, BaS; this is decomposed by hydrochloric or nitric acid, according as a chloride or nitrate of barium is required. All soluble salts of barium are very poisonous; the best antidotes are alkaline sulphates. The salts of barium are employed as re-agents in the laboratory, and in the manufacture of fireworks, to produce a green light.
What Has Changed in the Last Century
Aiton's 1910 entry said "it is doubtful whether barium has ever been seen in a pure state"; the silvery metal is now made routinely by reducing barium oxide with aluminium, and its properties are settled — element 56, density 3.51 (not the "about four" Aiton gave), melting near 727°C. The old uses have largely gone: barium compounds are no longer added to white lead paint, and by far the biggest modern use is barite (barium sulphate) as a weighting agent in oil-well drilling mud. Two applications neither account could foresee are the barium meal, swallowed to make the gut visible on X-ray films, and barium titanate, the ceramic in billions of electronic capacitors. Barium also sits in the 1987 high-temperature superconductor YBa2Cu3O7, which conducts without resistance above the boiling point of liquid nitrogen. Collier's warning that all soluble barium salts are very poisonous, with alkaline sulphates as antidote, still holds.
Written for this edition, 2026.