Calcium
2 of the 7 encyclopedias on this shelf carry an entry for Calcium. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a dyad metallic element. Symbol, Ca; at. wt., 40; sp. gr., 1.57; obtained by Davy by decomposing the chloride by electricity; also by heating the iodide with sodium in a closed vessel. Calcium is a yellowish white, ductile, malleable metal, which oxidizes in damp air; it decomposes water, and dissolves easily in dilute acids. Heated in the air, it melts at red heat, and burns with a bright orange-red light. Calcium occurs in nature chiefly as a carbonate, silicate, and sulphate. Calcium oxide, CaO, called also lime, is obtained by heating the carbonate of calcium to red- 19-Vol. II-Cyc It is a white, earthy, infusible ness. powder, phosphorescent at high temperatures; it is strongly alkaline, and readily absorbs carbonic anhydride. It unites vigorously with water, throwing out great heat, and forms a hydrate, CaOH₂O, which is slightly soluble in cold water; it is used in medicine as lime-water. Impure lime mixed with sand forms mortar. Calcium sulphate, CaSO4, found as hydride of gypsum, CaSO42H₂O, and selenite and alabaster. The water is given off by heating it, and a white powder is left, which dissolves in 500 parts of cold water. Mixed with water, it sets in a hard substance; it is used under the name of plaster of Paris for making casts of medals and statues, etc. Calcium carbonate, CaCO3, forms the chief constituent of limestone, marble, chalk, etc. It occurs crystallized as calcspar and aragonite. Calcium carbonate is insoluble in water, but is dissolved by water containing carbonic acid gas; it is deposited from this solution by boiling, hence boiler deposits. Calcium phosphates occur in the bones of animals and are native in Apatite. Calcium chloride, CaCl₂, is obtained by dissolving the carbonate in hydrochloric acid. It crystallizes in white prismatic crystals; it is very deliquescent. Fused calcium chloride is used to dry gases, etc. It absorbs ammonia gas. Calcium fluoride, CaFl2, occurs as fluor spar. Calcium sulphides and phosphides have been obtained. Salts of calcium are not precipitated by H2S, either in an acid or alkaline solution. Alkaline carbonates and ammonia carbonate give a white precipitate insoluble in excess; oxalate of ammonia gives a white precipitate from a neutral solution; the precipitate is not soluble in acetic acid. A solution of sulphate of calcium gives no precipitate. The chloride gives an orange-red flame with alcohol. The spectrum of calcium gives several characteristic lines, especially an orange-red and a green line. Chloride of lime, or bleaching powder, is a mixture of calcium chloride and calcium hypochlorite.
Aiton's Encyclopedia (1910)
kal'si-um, an important chemical element. It ranks fifth among the elements in point of abundance, making up about four per cent of the earth's crust. It forms an important part of lime, limestone, marble, plaster of Paris, chalk, shell, pearl, bone, egg shells, coral, and glass. It is present in all hard water. It was obtained free from other elements in 1808 by Sir Humphry Davy. In a pure condition it is a silver-white metal with a brilliant luster. Ordinarily, however, It is harder than lead and somewhat softer than gold. Calcium is a caustic. It unites chemically with nearly all of the elements, possibly all except argon. Calcium burns in oxygen with a brilliant white flame known as a limelight, Drummond's light, etc. The world requires about 100 tons of pure calcium yearly. See Lime ; Limestone