Arsenic Substance

Arsenic is a metallic chemical element in Group VA of the periodic table. Its symbol is As, its atomic number is 33, and its atomic weight is 74.9216. The Earth's crust contains only about 5.5 parts arsenic per million, but it occurs in many minerals.

Arsenic exist in three allotropic modifications, the yellow (alpha) and the black (betha) and metallic, or gray (gamma). Normally arsenic is found in its metallic form, which is the most stable and its normal pressure does not melt but sublimes at about 615^oC. It forms alloy with other metalls. The alpha and betha modifications have no metallic properties. Arsenic is fairly reactive. Above 400^oC it burns with a bluish flame, forming arsenic trioxide, As2O3. This compound is know as white arsenic and is used as a rat poison.

The toxic quality of arsenic has been known since ancient times. In the human body it accumulates in the nails and the hair, where it can be detected, even in the bodies of persons long dead, by the atomic absorption method. The acute symptoms are diarrhea and cramps. In cases of chronic poisoning, anemia and paralysis may appear. If there is prolonged contact with the skin, malignant skin tumors can develop. In medicine, 4-aminobenzene arsenic and 4-hydroxybenzene arsenic compounds are used to treat certain infections. The best known is Salvarsan, an antisyphilis drug. Commercially, arsenic is added to lead to harden it and is used in the production of herbicides and pesticides.

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