On August 1, 1774, he conducted his most famous experiment. Using a 12-inch-wide glass “burning lens,” he focused sunlight on a lump of reddish mercuric oxide. This was placed in an inverted glass container, which then was placed in a pool of mercury.
The gas emitted, he found, was “five or six times as good as common air.” In tests after that one, it caused a flame to burn intensely and kept a mouse alive for about four times as long as a similar quantity of air . We know now that that is because the oxygen was purer in that sample than normal atmospheric air, which contains more carbon dioxide, nitrogen, and other gases.
Statue in Chamberlain Square, Birmingham by Francis John Williamson.
Priestley’s discoveries are very important. They paved the way for other experiments to be done by scientists with more technology to better understand gases. A couple universities were also named in honor of Priestley’s experiments. Many have been able to learn from his life. Some would also say that it is quite amiable of him to stand so firmly for his religious beliefs, along with his scientific ones. A mob burned down his house because he refused to give up his stand on the revolutions and religion. Regardless of if you agree with him or not, the man wasn’t your typical scientist. He was very smart, and proved this in his experiments. He deserves to be remembered and revered in the science world, and is to this day.