Black Flux is prepared by heating in a covered crucible ordinary or crude cream of tartar, the bitartrate of potash, , when the tartaric acid, , is decomposed, and charred, forming carbonic acid, , which remains in combination with the potash as carbonate of potash, , accompanied by much free carbon. This very intimate mixture of carbonate of potash and carbon, otherwise called black flux, is a fine black powder of great service in the fluxing of metallic ores, as of Lead (q.v.), and the separa- tion of the metal therefrom. In the preparation of black flux it is usual to add to the cream of tartar half its weight of nitre, while white flux is produced when twice its weight of nitre is used. The black flux is likewise employed as the raw material from which, on the application of heat in iron vessels, the metal potassium can be obtained.
Black Flux
Chambers's Encyclopaedia, Volume 2: Beaugency to Cataract, p. 200
Source scan(s): p. 0211