Pumice-Stone. Is a kind of spongy fibrous stone, very porous and friable, found in the ashes of most volcanoes. Dr. Woodward considers pumice as only a sort of slag or cinder; and affirms it is only found either where forges of metal have anciently been, or near some volcano or burning mountain. Other authors will have it to arise from the bottom of the tea, whence they suppose it to be detached by subterranean fires ; and hence account both for its lightness and porosity, and its saline taste, alleging that several parts of the Archipelago are frequently found covered with it all at once, alter a few inward shakes and hearings of the bottom of the sea. It consists of 77 parts silex, 17 alumina, and the remainder of a 100 in iron, manganese, and alkali. Pumice makes a very considerable article in commerce, and is much used in the arts and manufactories, to glaze pottery, and to dish and smooth several works. The mar-lers and parchment-makers use the largest and lightest - the curriers, the heaviest and flattest - pewterers, the smallest.