[D0106AAM], Letter from Thomas Alva Edison to C A Gardner, September 4th, 1901
https://edisondigital.rutgers.edu/document/D0106AAM
Transcription
Why don't you keep on experimenting yourself, perhaps if you incorporate oxide of lead with it, then when we set on fire the Sulphur will combine with the lead after reduction + the oxygen will also combine with the Sulphur to form SO2 +the stuff will not flame any more than wood Edison