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.