 In the classic experiment of Lavoisier, mercury-2 oxide is heated, producing mercury, metal, and oxygen gas. In the test tube we have a sample of red mercury-2 oxide. We will heat the sample and it will decompose to give mercury-metal, which will condense at the top of the test tube, and oxygen gas, which we will collect by the displacement of water. The mercury-metal we can see as a metallic gray ring in the test tube. We can demonstrate that the gas collected is oxygen by testing the gas with a glowing splint. As the glowing splint is brought into the test tube, the combustion accelerates in the oxygen and the splint reignites.