The Melting Ray was the signature weapon of The Candle, a 1960s supervillain. The Candle possessed a personal variation, which could be fired as a sidearm weapon to melt people or small objects. He also devised several larger versions to melt larger targets. Most such weapons had an "Off" switch (enabling 1960s Middleman Guy Goddard to save the day by turning them off); near the end of his supervillain career, the Candle grew tired of being defeated in this manner and built a melting ray on Snake Island without an "Off" switch.
After abandoning supervillainy, the Candle hid his melting ray, but left instructions to his neighbor on how to find it after his death, hoping it could be donated to science and used for good. Instead, the boy went on a crime spree before being caught by the Middleman and Guy Goddard. The sidearm melting ray was presumably locked up in Middleman HQ, while the Snake Island melting ray was destroyed by Guy Goddard.