and the atmosphere of the chamber then replaced with either purified nitrogen, carbon dioxide, oxygen, an oxygen-carbon dioxide mixture, or unpurified nitrogen from which the oxygen had not been wholly removed. Before passing through the chamber the purified nitrogen was washed in dilute sulphuric acid, to remove traces of ammonia, alkaline pyrogallol, to remove traces of oxygen, and distilled water. On escaping from the chamber this nitrogen was passed through distilled water and alkaline pyrogallol. The other gases were passed through distilled water before and after passing through the chamber. The gases used were from commercially prepared cylinders. Rubber leads were used to connect the apparatus.