These were used in the early 1950 to make scuba regulators with instructions on how to in July 1953 Popular Science magazine. They claimed in Popular Science, July 1953, "Did you know you can stay under water almost an hour" Build your own. Take two surplus CO2 Bottles and $40.00 is all it will cost. INTERESTING! Mine was serviced in 1988 and is ready to get converted. Stay tuned.