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.-arsenious oxide or arsenious anhydride; -- called also arsenious acid, white arsenic, and ratsbane.-pertaining to, or derived from, arsenic; -- said of those compounds of arsenic in which this element has its highest equivalence; as, arsenic acid.