Jamieson, Fausset and Brown on Jeremiah 2:22

22. 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; Pr 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."