Hastings' Dictionary of the Bible (1898)
SOAP. Jer 2:22; Mal 3:2. Several kinds of shrubby alkaline plants, one of which is figured, grow very abundantly in the vicinity of the Dead Salsola Kali. and Mediterranean Seas. The Arabs dry and burn these, and obtain a large proportion of potash from their ashes. With this, from oil and other fatty substances, a soft soap has been made by the Jews from very early times. They used it not only for washing their persons and their clothes, but in
smelting metals as a flux, or substance which cleansed them and made them flow more readily. In Isa 1:25 the reading should be, instead of "purely," "as with alkali." Making hard soap from olive oil is the only important manufacturing business of modern Jerusalem. There is considerable exportation from Palestine of the alkali mentioned above. See Nitre