arsenic

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A highly poisonous metallic element having three allotropic forms, yellow, black, and gray, of which the brittle, crystalline gray is the most common. Arsenic and its compounds are used in insecticides, weed killers, solid-state doping agents, and various alloys. Atomic number 33; atomic weight 74.922; valence 3, 5. Gray arsenic melts at 817°C (at 28 atm pressure), sublimes at 613°C, and has a specific gravity of 5.73. See Table at element.
2. n. Arsenic trioxide.
3. adj. Of or containing arsenic, especially with valence 5.

Century Dictionary and Cyclopedia

1. n. A yellow mineral, called specifically yellow arsenic; the trisulphid of the element to which it has given its name; orpiment.
2. n. Chemical symbol, As; atomic weight, 75. A chemical element having a grayish-white color, a metallic luster, and a specific gravity of 5.727. Under ordinary pressure it does not melt, but at 356° F. it passes from the solid state into vapor of a lemon-yellow color. It tarnishes rapidly in moist air at ordinary temperature, and heated in air is oxidized to arsenic trioxid, As₂O₃. Arsenic occurs in nature uncombined, but much more commonly in combination. The chief ores are the two sulphids, realgar (As₂S₂) and orpiment (As₂S₃), arsenical pyrites or mispickel (FeSAs), and arsenides of iron, nickel, and cobalt. Most of the arsenic of commerce is prepared in Bohemia and Saxony or in England. Arsenic itself is little used in the arts. Its salts, however, have great commercial importance. With oxygen arsenic forms two compounds, the more important of which is arsenic trioxid (As₂O₃), a violent poison, the ratsbane, white arsenic, or simple arsenic of the shops. It is prepared by a process of sublimation from arsenical ores, and is sold as a white crystalline powder or in glassy translucent masses, which are odorless, nearly tasteless, and slightly soluble in water. The most reliable antidote is freshly prepared hydrated sesquioxid of iron, which should be given in considerable quantity after the stomach has been freed from the poison as completely as possible by an emetic given with bland liquids, such as milk, flour and water, or white of egg and water, which serve to envelop the poison and effect its complete ejection from the stomach. In the absence of hydrated sesquioxid of iron, large quantities of a paste made of chalk or magnesia and castor-oil may be used. Arsenic trioxid is used in medicine, especially in the treatment of certain nervous and skin diseases, and in the arts as the basis for preparing arsenical salts and certain pigments, and largely in the manufacture of glass. Arsenic has two oxygen acids, whose salts are the arseniates and arsenites. Free arsenious acid is not known. Arsenic acid occurs in commerce as a thick acid liquid, and is largely used in the manufacture of aniline red, and sodium arseniate is much used in calico-printing. Arsenic disulphid (As₂S₂) occurs native as realgar (see realgar), and is made artificially under the name of ruby sulphur. Both the native and the artiflicially prepared sulphids are used as pigments, as is also arsenic trisulphid (As₂S₃), or orpiment, also called king's yellow.
3. n. The popular name of arsenic trioxid (As₂O₃), the preparation of arsenic usually retailed in trade. See above.
4. Containing arsenic; specifically, containing arsenic in smaller proportion than arsenious compounds. See arsenious.

Wiktionary

1. n. A nonmetallic chemical element (symbol As) with an atomic number of 33.
2. n. Arsenic trioxide.
3. adj. Of, or containing arsenic with a valence of 5.

GNU Webster's 1913

1. n. (Chem.) One of the elements, a solid substance resembling a metal in its physical properties, but in its chemical relations ranking with the nonmetals. It is of a steel-gray color and brilliant luster, though usually dull from tarnish. It is very brittle, and sublimes at 356° Fahrenheit. It is sometimes found native, but usually combined with silver, cobalt, nickel, iron, antimony, or sulphur. Orpiment and realgar are two of its sulphur compounds, the first of which is the true arsenicum of the ancients. The element and its compounds are active poisons. Specific gravity from 5.7 to 5.9. Atomic weight 75. Symbol As.
2. n. (Com.) Arsenious oxide or arsenious anhydride; -- called also arsenious acid, white arsenic, and ratsbane.
3. adj. (Chem.) Pertaining to, or derived from, arsenic; -- said of those compounds of arsenic in which this element has its highest equivalence.

WordNet 3.0

1. n. a white powdered poisonous trioxide of arsenic; used in manufacturing glass and as a pesticide (rat poison) and weed killer
2. n. a very poisonous metallic element that has three allotropic forms; arsenic and arsenic compounds are used as herbicides and insecticides and various alloys; found in arsenopyrite and orpiment and realgar