Potassium arsenate is a chemical compound of potassium and arsenic. It is derived from arsenic acid. Arsenic is a chemical element that has the symbol As and atomic number 33. It is a poisonous metalloid that has many allotropic forms: yellow (molecular non-metallic) and several black and grey forms (metalloids) are a few that are seen. Three metalloidal forms of arsenic with different crystal structures are found free in nature (the minerals arsenopyrite and the much rarer arsenolamprite and pararsenolamprite), but it is more commonly found as a compound with other elements. Potassium arsenate is used in the textile, tanning and paper industries, and as an insecticide, especially for fly paper. In medicine arsenic was the preferred treatment for syphilis for many years. It was also thought to treat malaria, leukemia, and chorea. One type of arsenic preparation that became a popular type of patent medicine of the late 1800’s on into the early 1900s’ was Fowler’s solution, which was sold as a treatment for syphilis as well as a general tonic. Fowler’s solution was not a brand of patent medicine but rather a formula containing 1% potassium arsenate, proposed by Thomas Fowler in 1786. Potassium arsenate is toxic and carcinogenic to humans.