Sodium
3 of the 6 encyclopedias on this shelf carry an entry for Sodium. All 3 are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a widely distributed and well known chemical element. In combination with chlorine it forms common salt. In plant life sodium seems to bear somewhat the same relation to plants on the seashore that potassium does to inland plants, but common salt is not a requisite of plant growth. The stalks and leaves of saline plants store up salt, but their seeds contain little of it. In its pure form sodium resembles potassium in weight and appearance. When laid on water, it acts like it, only not so energetically. Several compounds of sodium are important. Sodium chloride, or salt, has been mentioned. Sodium nitrate is the saltpeter of Chile from which common saltpeter is made. Sodium sulphate, or Glauber's salt, is the medicinal principle of Carlsbad and other mineral waters. Sodium carbonate or soda is essential to the manufacture of glass and of soap. It was obtained formerly from the ashes of sea plants, but processes have been devised for getting a commercial supply from salt. Soda is used in the manufacture of baking powder , in sodawater, and as a medicine. Sodium borate is common borax. Alkali water is impregnated commonly with sodium. See Potassium ; Salt ; Borax ; Baking Powder
The Encyclopedia of Founding (1892)
This is a very widely diffused and abundant element. As chloride, it occurs in rock-salt, sea-water, salt-springs, and many mineral waters; and as silicate, in many minerals. Metallic sodium was first discovered by Sir Humphry Davy. It is prepared in the same manner as potassium, requires the same measures for its preservation, and exhibits properties similar to those of that metal. See POTASSIUM; SALT; SODA; FLUID ALLOY.
Collier's New Encyclopedia (1921)
the alkaline metal of which soda is the oxide. It was discovered in 1807 by Sir Humphry Davy. It occurs in large quantities in nature, chiefly in combination with chlorine, as sea salt.
What Has Changed in the Last Century
The chemistry in these entries still holds: sodium is element 11, isolated by Humphry Davy in 1807, and it still reaches us mostly as chloride in rock salt and sea water. What has moved is industry and medicine. Aiton's 1910 note that Chile saltpetre is the source of nitrate was overtaken within a decade by the Haber-Bosch synthesis of ammonia, which made synthetic nitrogen compounds cheap and gutted the Chilean trade; and the metal itself has been made since 1924 by the Downs electrolytic cell, fed with molten salt, on a scale Davy's laboratory method could not approach. Sodium found wholly new twentieth-century jobs, as the yellow glow of street lamps, as the liquid coolant in fast reactors, and lately in sodium-ion batteries, while the dietary sodium in that same common salt became one of the most-studied factors in high blood pressure.
Written for this edition, 2026.