Plat·i·num n.  Chem. A metallic element of atomic number 78, one of the noble metals, classed with silver and gold as a precious metal, occurring native or alloyed with other metals and also as the platinum arsenide (sperrylite). It is a heavy tin-white metal which is ductile and malleable, but very infusible (melting point 1772° C), and characterized by its resistance to strong chemical reagents. It is used for crucibles in laboratory operations, as a catalyst, in jewelry, for stills for sulphuric acid, rarely for coin, and in the form of foil and wire for many purposes. Specific gravity 21.5. Atomic weight 195.1.  Symbol Pt.  Formerly called platina.
 Platinum black Chem., a soft, dull black powder, consisting of finely divided metallic platinum obtained by reduction and precipitation from its solutions. It absorbs oxygen to a high degree, and is employed as an oxidizer.
 Platinum lamp Elec., a kind of incandescent lamp of which the luminous medium is platinum. See under Incandescent.
 Platinum metals Chem., the group of metallic elements which in their chemical and physical properties resemble platinum. These consist of the light platinum group, viz., rhodium, ruthenium, and palladium, whose specific gravities are about 12; and the heavy platinum group, viz., osmium, iridium, and platinum, whose specific gravities are over 21.
 Platinum sponge Chem., metallic platinum in a gray, porous, spongy form, obtained by reducing the double chloride of platinum and ammonium. It absorbs oxygen, hydrogen, and certain other gases, to a high degree, and is employed as an agent in oxidizing.

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 Sponge n.  [Formerly written also spunge.]
 1. Zool. Any one of numerous species of Spongiae, or Porifera. See Illust. and Note under Spongiae.
 2. The elastic fibrous skeleton of many species of horny Spongiae (Keratosa), used for many purposes, especially the varieties of the genus Spongia.  The most valuable sponges are found in the Mediterranean and the Red Sea, and on the coasts of Florida and the West Indies.
 3. Fig.: One who lives upon others; a pertinacious and indolent dependent; a parasite; a sponger.
 4. Any spongelike substance. Specifically: (a) Dough before it is kneaded and formed into loaves, and after it is converted into a light, spongy mass by the agency of the yeast or leaven. (b) Iron from the puddling furnace, in a pasty condition. (c) Iron ore, in masses, reduced but not melted or worked.
 5. Gun. A mop for cleaning the bore of a cannon after a discharge. It consists of a cylinder of wood, covered with sheepskin with the wool on, or cloth with a heavy looped nap, and having a handle, or staff.
 6. Far. The extremity, or point, of a horseshoe, answering to the heel.
 Bath sponge, any one of several varieties of coarse commercial sponges, especially Spongia equina.
 Cup sponge, a toilet sponge growing in a cup-shaped form.
 Glass sponge. See Glass-sponge, in the Vocabulary.
 Glove sponge, a variety of commercial sponge (Spongia officinalis, variety tubulifera), having very fine fibers, native of Florida, and the West Indies.
 Grass sponge, any one of several varieties of coarse commercial sponges having the surface irregularly tufted, as Spongia graminea, and Spongia equina, variety cerebriformis, of Florida and the West Indies.
 Horse sponge, a coarse commercial sponge, especially Spongia equina.
 Platinum sponge. Chem. See under Platinum.
 Pyrotechnical sponge, a substance made of mushrooms or fungi, which are boiled in water, dried, and beaten, then put in a strong lye prepared with saltpeter, and again dried in an oven. This makes the black match, or tinder, brought from Germany.
 Sheep's-wool sponge, a fine and durable commercial sponge (Spongia equina, variety gossypina) found in Florida and the West Indies. The surface is covered with larger and smaller tufts, having the oscula between them.
 Sponge cake, a kind of sweet cake which is light and spongy.
 Sponge lead, or Spongy lead Chem., metallic lead brought to a spongy form by reduction of lead salts, or by compressing finely divided lead; -- used in secondary batteries and otherwise.
 Sponge tree Bot., a tropical leguminous tree (Acacia Farnesiana), with deliciously fragrant flowers, which are used in perfumery.
 Toilet sponge, a very fine and superior variety of Mediterranean sponge (Spongia officinalis, variety Mediterranea); -- called also Turkish sponge.
 To set a sponge Cookery, to leaven a small mass of flour, to be used in leavening a larger quantity.
 To throw up the sponge, to give up a contest; to acknowledge defeat; -- from a custom of the prize ring, the person employed to sponge a pugilist between rounds throwing his sponge in the air in token of defeat; -- now, throw in the towel is more common, and has the same origin and meaning. [Cant or Slang] “He was too brave a man to throw up the sponge to fate.” --Lowell.
 Vegetable sponge. Bot. See Loof.
 Velvet sponge, a fine, soft commercial sponge (Spongia equina, variety meandriniformis) found in Florida and the West Indies.
 Vitreous sponge. See Glass-sponge.
 Yellow sponge, a common and valuable commercial sponge (Spongia agaricina, variety corlosia) found in Florida and the West Indies.