Jamieson, Fausset & Brown

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."