"This gas comes out of volcanoes as well as sulfur dioxide, and... is called . ...It has a phenomenally unpleasant smell of rotten eggs. Apart from that, it's unbelievably poisonous. ...[I]t undergoes an extraordinarily interesting reaction with sulfur dioxide. ...The lower jar is going yellow ...[W]e have made sulfur. ...also ...water. ...Two gases have reacted together to make a solid and a liquid. Secondly, two compounds of sulfur have made the element sulfur... Furthermore... it's... a redox reaction in which sulfur is reduced in one... and oxidized in the other. ...[M]any geologists believe that these two gases come out of volcanoes together and... make huge deposits of sulfur... found at the mouths of volcanoes."