How did Carl Wilhelm Scheele produce chlorine gas in his experiment?

In 1774, the Swedish chemist Carl Wilhelm Scheele produced chlorine gas by treating powdered black magnesia—a mineral known as pyrolusite or manganese dioxide—with hydrochloric acid.21

Upon reacting these substances, Scheele observed the development of a greenish-yellow gas. Operating under the prevailing phlogiston theory of the 18th century, he did not recognize the gas as a distinct chemical element. Instead, he identified it as "dephlogisticated muriatic acid," believing it to be a compound. It was not until 1810 that the English chemist Humphry Davy correctly identified the gas as an element and gave it the name chlorine, derived from the Greek word for its characteristic color.12