Nitre

(Prov. 25:20; R.V. marg., "soda"), properly "natron," a substance so called because, rising from the bottom of the Lake Natron in Egypt, it becomes dry and hard in the sun, and is the soda which effervesces when vinegar is poured on it. It is a carbonate of soda, not saltpetre, which the word generally denotes (Jer. 2:22; R.V. "lye").

נתר, Prov. xxv, 20; Jer. ii, 22. This is not the same that we call nitre, or saltpetre, but a native salt of a different kind, distinguished among naturalists by the name of natrum. The natrum of the ancients was an earthy alkaline salt. It was found in abundance separated from the water of the lake Natron in Egypt. It rises from the bottom of the lake to the top of the water, and is there condensed by the heat of the sun into the hard and dry form in which it is sold. This salt thus scummed off is the same in all respects with the Smyrna soap earth. Pliny, Matthiolus, and Agricola, have described it to us: Hippocrates, Galen, Dioscorides, and others, mention its uses. It is also found in great plenty in Sindy, a province in the inner part of Asia, and in many other parts of the east; and might be had in any quantities. The learned Michaëlis plainly demonstrates, from the nature of the thing and the context, that this fossil and natural alkali must be that which the Hebrews called _nether_. Solomon must mean the same when he compares the effect which unseasonable mirth has upon a man in affliction to the action of vinegar upon nitre, Prov. xxv, 20; for vinegar has no effect upon what we call nitre, but upon the alkali in question has a great effect, making it rise up in bubbles with much effervescence. It is of a soapy nature, and was used to take spots from clothes, and even from the face. Jeremiah alludes to this use of it, ii, 22.