Capital punishment in the United States
From 1924 to 1972, the United States executed about 600 people in gas chambers.  Most states used hydrogen cyanide gas.  However, by the mid-1970s and 1980s, many people had started to criticize the use of gas chambers.  Death from hydrogen cyanide poisoning can be long and painful, and in some executions, prisoners suffered long deaths.  After one of these executions, a federal court in California ruled that "execution by lethal gas under the California protocol is unconstitutionally cruel and unusual punishment."