During a science lesson on changes, Ms. Sloan's students made mixtures of sulfur (the yellow substance) and iron filings (the black substance. Ms. Sloan challenged her students to separate the two substances and one group easily completed the task by using a magnet to lift the iron filings from the mixture. Next, Ms. Sloan poured the same mixture into a test tube and heated it in the Bunsen burner flame. What was the result of heating the mixture?