What is "potassium arsenite"

Potassium arsenite (KAsO) is an inorganic compound that exists in two forms, potassium meta-arsenite (KAsO) and potassium ortho-arsenite (KAsO). It is composed of arsenite ions (AsO or AsO) with arsenic always existing in the +3 oxidation state, and potassium existing in the +1 oxidation state. Like many other arsenic containing compounds, potassium arsenite is highly toxic and carcinogenic to humans. Potassium arsenite forms the basis of Fowler’s solution, which was historically used as a medicinal tonic, but due to its toxic nature its use was discontinued. Potassium arsenite is still, however, used as a rodenticide.