Pumice-stone
A spongy lava of a very porous nature, and so light that it will float on water. It is found in volcanic districts, being composed chiefly of silica and alumina, with some potash and soda. See POLISHING SUBSTANCES. Pure Iron is of very rare occurrence, and can be obtained only by purely chemical methods in the laboratory. See NATIVE IRON. Putty is whiting and linseed-oil kneaded into a thick paste. See WHITING.