is mentioned twice in the Old Testament, first in Proverbs, xxv, 20,
“As vinegar upon nitre, so is he that singeth songs to a heavy heart.”
In the Revised Version soda is given instead of nitre in the margin.
The other reference is in Jeremiah, ii, 22, “Though thou wash thee
with nitre, and take thee much sope.” In this passage the Revised
Version changes nitre to lye. The Hebrew word is Nether, the natrum
of the East, an impure carbonate of sodium which was condensed from
certain salt lakes, or obtained from marine plants. Vinegar would cause
effervescence with this substance, but not with nitrate of potash. The
soap in the same passage in Jeremiah, in Hebrew Borith, was either the
soap wort or a salt obtained from the ashes of herbs by lixiviation.