Natron, the nitre of the ancients, is one of the fixed alkalies. It is found in great abundance in many parts of Asia, where the natives sweep it up from the surface of the ground, and call it "soup-earth." The earliest account we have of it is in the Scriptures, where we find that the salt called nitre in those times would ferment with vinegar, and that it possessed a detergiving quality, in consequence of which it was used in baths and in washing. Solomon compares the singing of songs with a heavy heart, to the contrariety of vinegar and nitre; and Jeremiah says, that even if the sinner should wash himself with nitre, his sin would not be cleansed off. These are properties which perfectly agree with this salt, but not at all with our saltpetre, which is the nitre of the moderns.