What did William Crookes discover?

In 1861, William Crookes discovered thallium while attempting to extract selenium from the remains of sulfuric acid production. Thallium is derived from the Greek word "thallos," which describes the bright green color of the element.

As a result of this discovery, thallium became a beneficial treatment for venereal diseases, such as syphilis and gonorrhea, and was used as a treatment for tuberculosis and an agent to remove excess hair, reports Medscape. The importance of Crookes' discovery of thallium is reflected today by its use in optical equipment, artist's paints, electronic components and as a contrasting agent for cardiac and tumor visualization.