Arsenic
. Arsenic, symbol As, extremely poisonous semimetallic element. The atomic number of arsenic is 33. Arsenic is in group 15 (or Va) of the periodic table . Chemically, arsenic is intermediate between metals and nonmetals. Its properties lie, in general, in the middle of the series formed by the family of the elements nitrogen , phosphorus , arsenic, antimony , and bismuth. Arsenic ranks about 52nd in natural abundance among the elements in crustal rocks. When arsenic is heated, it sublimes, passing directly from solid to gaseous form at 613° C (1135° F). A common form of arsenic is gray, metallic in appearance, and has a specific gravity of 5.7. A yellow, nonmetallic form also exists and has a specific gravity of 2.0. The atomic weight of arsenic is 74.9216. Arsenic is used in large quantities in the manufacture of glass to eliminate a green color caused by impurities of iron compounds. A typical charge in a glass furnace contains 0.5 percent of arsenic trioxide. Arsenic is sometimes a