Forms of Carbon In 1772 Lavoisier and other chemists bought a diamond and placed it in a closed glass jar. They used a remarkable giant magnifying glass to focus the sun’ s rays on the diamond. The diamond burned and disappeared. Lavoisier noted the overall weight of the jar was unchanged, even though all of the diamond had disappeared. This observation would later be part of the evidence convincing him that his law of mass conservation was correct. Whether diamond or charcoal were burned by the giant lens, the same gas was produced – we now call it carbon dioxide. Lavoisier realized that diamond and charcoal are different forms of the same element. He gave this element the name carbon.
Oxygen and Combustion In 1772 people did not understand the process of burning. We now know that combustion happens when substances react with oxygen at high temperatures. In 1772, however, when Lavoisier began working in this field, oxygen’ s discovery by Joseph Priestley still lay two years in the future. In 1772 Lavoisier discovered that when phosphorus or sulfur are burned in air the products are acidic. The products also weigh more than the original phosphorus or sulfur, suggesting the elements combine with something in the air to produce acids. But what? In 1779 Lavoisier coined the name oxygen for the element released by mercury oxide. He found oxygen made up 20 percent of air and was vital for combustion and respiration. He also concluded that when phosphorus or sulfur are burned in air, the products are formed by the reaction of these elements with oxygen.