Brigg’s breathing valves, used in mine rescue equipment. From The Department of Scientific and Industrial Research, Advisory Council, Second Report of the Mine Rescue Apparatus Committee, Published by His Majesty’s Stationary Office, 1920, page 48.
Brigg’s breathing valves, used in mine rescue equipment. From The Department of Scientific and Industrial Research, Advisory Council, Second Report of the Mine Rescue Apparatus Committee, Published by His Majesty’s Stationary Office, 1920, page 48.