Arsenic is made from arsenopyrite by heating it. This makes arsenic trioxide which sublimes (along with sulfur dioxide), while the iron oxide stays behind. The arsenic trioxide is condensed, while the sulfur dioxide does not condense. The arsenic trioxide can be reduced with carbon. Another way is to heat the arsenopyrite without air. Then gray arsenic is made. Realgar can be heated to make arsenic trioxide as well.