In the 1920s, the first gas chamber was built in Nevada, and it was a real gas (get it?). The idea was to use hydrogen cyanide to, you know, take care of business. But, things didn't quite go as planned - the first execution took 10 whole minutes to complete, and the prisoner was still alive after the first round of gas.
So, what did they do? They improved the design, of course! They added more gas, better ventilation, and even a viewing window so people could watch (because, why not?). But, despite the upgrades, the gas chamber remained a pretty messy way to go.
