Some time in the late 1940s, the eastern states converted from coal gas to natural gas. I was about 10 at the time and I remember that someone from the gas company came around to every house and adjusted the gas stoves because natural gas had something like twice the hear content of coal gas. (Coal gas also was half CO and therefore highly toxic.) What I cannot recall and would like to know is how the transition was carried out. I mean they could not adjust the entire city of Philadephia in one day; there were doubtless people who just happened to be out of town, people who refused to open their doors, etc. etc. It must have been a massive operation, but I have never seen anything about it.