Iodine
2 of the 6 encyclopedias on this shelf carry an entry for Iodine. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
i o-din, a chemical element akin to chlorine and bromine. It was obtained originally, 1811, from the ashes of a seaweed called kelp, but is now produced more cheaply from an earth abounding in the mountains of northern Chile. A ton of ashes of kelp yields about eight pounds of iodine. The name is Greek signifying "like a violet." The solid is a soft, grayish substance, but its vapor is of a beautiful deep blue. Starch is used to detect the presence of iodine, and iodine is used in many experiments and botanical examinations to detect the presence of starch. A pinch of starch dropped into a glass of water containing a millionth part of iodine turns blue at once. Tincture of iodine--iodine dissolved in alcohol--is a valuable medicine. It is an irritating poison if taken in too large a quantity. Iodine kills the microbes of certain diseases. It is peculiarly valuable as an ointment for rheumatism. It is also used in photography in the preparation of sensitive plates, and in the preparation of coal tar colors. Iodine is a nonconductor of electricity.
Collier's New Encyclopedia (1921)
in chemistry, a haloid monatomic element; symbol I; at. w. 127. Obtained from the ash of sea-weeds called kelp. In pharmacy, iodine is used externally in chronic skin diseases and over enlarged and indurated parts and diseased joints to alter action or cause absorption, or to kill parasites. It may be applied in the form of a liniment, a solution, a or an ointment. The vapor tincture iodi (vapor of iodine) may be used as an inhalation in some forms of chronic bronchitis and phthisis. A solution of iodine is useful for rendering very transparent objects more distinct.
What Has Changed in the Last Century
Both accounts treat iodine chiefly as an external antiseptic and reagent — Collier's in 1921 recommends it for "diseased joints" and as an inhaled vapour for bronchitis and phthisis — and neither mentions the body's own need for it. That link was being established just as these entries went to press: Edward Kendall isolated thyroxine from thyroid tissue in 1914, and in 1924 Michigan began adding iodine to table salt to prevent goitre, a practice now standard in much of the world and credited with preventing widespread deficiency-related brain damage in children. Radioactive iodine-131, unknown in 1921, became a routine tool for imaging and treating thyroid disease from the 1940s. Aiton's 1910 note that Chilean deposits had displaced kelp still holds — Chile's Atacama caliche remains the world's main source — but tincture of iodine has largely given way to milder povidone-iodine preparations.
Written for this edition, 2026.