Jeremiah 2:22

“For though thou wash thee with nitre, etc.] The word rtn, “nitre”, is only used in this place and in (<202520>Proverbs 25:20) and it is hard to say what it is. Kimchi and Ben Melech observe, that some say it is what is called “alum”; and others that it is a dust with which they wash the head, and cleanse everything; and so Jarchi says it is a kind of earth used in cleaning garments; and “nitre” is mentioned by the Misnic doctorsf42 among those things which are used for the washing of garments, and taking spots out of them; though about what it is they are not agreed; and it seems the nitre of the ancients is unknown to usf43; and saltpetre is put in the room of it; and some render the word…”

“nitre--not what is now so called, namely, saltpeter; but the natron of Egypt, a mineral alkali, an incrustation at the bottom of the lakes, after the summer heat has evaporated the water: used for washing (compare Job 9:30; Pro 25:20). soap--potash, the carbonate of which is obtained impure from burning different plants, especially the kali of Egypt and Arabia. Mixed with oil it was used for washing. marked--deeply ingrained, indelibly marked; the Hebrew, catham, being equivalent to cathab. Others translate, "is treasured up," from the Arabic. MAURER from a Syriac root, "is polluted."”

“Nitre - Or, natron, a mineral alkali, found in the Nile valley, where it effloresces upon the rocks and surfaces of the dykes, and in old time was carefully collected, and used to make lye for washing (see Proverbs 25:20). Sope - A vegetable alkali, now called “potash,” because obtained from the ashes of plants. Its combination with oils, etc., to form soap was not known to the Hebrews until long after Jeremiah’s time, but they used the lye, formed by passing water through the ashes. Thus then, though Israel use both mineral and vegetable alkalies, the most powerful detergents known, yet will she be unable to wash away the stains of her apostasy. Thine iniquity is marked - i. e., as a stain.…”

“Nitre - Though interpreters do greatly vary in describing what is particularly meant here by Nitre and Soap, and would be superfluous to mention here; yet all agree, they are some materials that artists make use of for cleansing away spots from the skin. The blot of this people is by no art to be taken out; nor expiated by sacrifices; it is beyond the power of all natural and artificial ways of cleansing. Marked - Thy filthiness is so foul that it leaves a brand behind which cannot be hid or washed out, but will abide, Jer 17:1. Jeremiah 2:23”

“2:22 The metaphor changes from a planted vine to a dirty cloth that soap or lye cannot wash clean. However hard the Israelites scrubbed, their guilt was still apparent (cp. Isa 1:18).”

“For though: Job 9:30, Job 9:31 yet thine iniquity: Jer 16:17, Jer 17:1; Deu 32:34; Job 14:17; Psa 90:8, Psa 130:3; Hos 13:12; Amo 8:7 Jeremiah 2:23”