Chlorine oxygen

Scheele isolated the gas chlorine, which was colorless and greenish-yellow in color, named from the Greek word for 'green'. However, Scheele thought it was a combination of some substance with oxygen and did not recognize it as an element, which prevented him from obtaining the credit for its discovery until about thirty years later.
 Carl Wilhelm Scheele Sweden 1774 Chlorine oxygen

Scheele isolated the gas chlorine, which was colorless and greenish-yellow in color, named from the Greek word for 'green'. However, Scheele thought it was a combination of some substance with oxygen and did not recognize it as an element, which prevented him from obtaining the credit for its discovery until about thirty years later.