Pumice Stone

(püm'is.) [From L. pu mes.] (Min.) A porous volcanic product, composed chiefly Fig. 546. PULPIT, (14th century.) of silica and alumina, with traces of potash, soda, and oxide of iron. It floats in water, is hardly acted on by the acids, and may probably be looked on as stony froth. It is found in almost all volcanic countries; and is known to be produced especially by Mts. Etna,Vesuvius, andHecla, during the eruptions of which it is thrown up in great D B M J a A Fig. 547.- SUCTION-AND FORCING-PUMP. abundance. It is used for polishing ivory, wood, mar ble, metals, gla , ., as also skins and parchment. [s. 741]