Alkali. In Hebrew the word for alkali is neʹther, a carbonate of soda, also called natron. It is termed “mineral alkali,” to distinguish it from “vegetable alkali.” Natron was a native grade of the chemical, commercial grades of which are known as soda ash and sal soda. Its effervescence when mixed with a weak acid is alluded to at Proverbs 25:20. Though in some translations it is called “niter,” it should not be confused with modern niter (nitre), also called saltpeter, which may be either potassium or sodium nitrate.

By itself or as a soap builder this alkali is a very effective cleaner. This fact adds force to Jehovah’s words as to the depth of Israel’s sinfulness: “Though you should do the washing with alkali and take to yourself large quantities of lye, your error would certainly be a stain before me.”​—Jer 2:22.

Lye. The Hebrew word bo·rithʹ, translated “lye” (in some translations, “soap”), refers to a vegetable alkali as distinguished from neʹther, the so-called mineral alkali. The distinction was not one of chemical composition but, rather, was based on the difference in the source of supply. At Jeremiah 2:22 both words occur in the same verse. Chemically the lye of Bible times was sodium carbonate or potassium carbonate, depending on whether the vegetation from which the ashes were obtained was grown near the sea on saline soil or grown inland. The chemicals in the ashes were separated by leaching or filtering with water. This lye is different from the modern-day chemical termed “lye,” the very caustic potassium hydroxide.