† potassan.
Chemistry. Obsolete.
1. In names of chemical compounds: = potash n. 3a.
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1801 J. Murray Elem. Chem. I. ii. ii. 218 In an impure state it forms the potashes of commerce; whence the name Potash, received into the new nomenclature, is derived. It would have been preferable, perhaps, to have given it the termination of Potassa, but the other is now established in chemical language.
1806 J. Murray Syst. Chem. II. iii. v. 76 Potassa, this alkali has long been known to chemists, and by various appellations; being in general obtained from the burning of vegetables.
1812 H. Davy Elements Chem. Philos. 324 The substance which has been called pure potash; but which ought to be called the hydrat of potassa.
1836–41 W. T. Brande Man. Chem. (ed. 5) 611 The Liquor Potassæ of the Pharmacopœia is directed to be prepared as follows:—‘Take of carbonate of potassa 15 ounces, lime 8 ounces, boiling distilled water a gallon [etc.].’
1872 M. D. Landon Saratoga in 1901 25 (table) Sulphate of Potassa.
1908 Jrnl. Therapeutics & Dietetics 2 134 Belladonna contains supermalate of atropa, pseudotoxin, malate of potassa, salts, wax, [etc.].
2.
a. Potassium oxide, K2O.
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1812 H. Davy Elements Chem. Philos. 324 This substance is pure potash or potassa, which was unknown in its uncombined state till I discovered potassium, but which has long been familiar to chemists combined with water in the substance which has been called pure potash; but which ought to be called the hydrat of potassa.
1813 H. Davy Elements Agric. Chem. ii. 46 Potassa, or the pure caustic vegetable alkali, consists of one proportion of potassium and one of oxygene.
1842 W. T. Brande Dict. Sci., Lit. & Art 966/1 Caustic potash, which is a compound of 48 potassa + 9 water.
b. Potassium hydroxide, KOH; caustic potash. More fully potassa fusa [ < potassa n. + classical Latin fūsa , feminine of fūsus , past participle of fundere to pour out, to melt (see found v.3)] .liquor potassae: see the first element.
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1824 Lancet 18 Jan. 85/2 The way it was used by baking the potassa fusa, and applying it to the fore part of the scrotum.
1832 W. F. Tolmie Jrnl. (1963) 61 Whately advocates the potassafusa [etc.].
1885 G. L. Goodale in A. Gray & G. L. Goodale Bot. Text-bk. (ed. 6) II. i. i. 36 Lignose: insoluble in water, alcohol, ether, and ammonia; soluble in solutions of potassa and soda.
1887 Chem. News 22 Apr. 188/2 The decomposition by potassa of the diacetones.
1895 New Sydenham Soc. Lexicon Potential cautery, nitrate of silver..or Potassa fusa, as distinct from the Actual cautery, or red-hot iron.
This entry has been updated (OED Third Edition, December 2006; most recently modified version published online December 2020).
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