Science Museum inventory number 1876-590.
The pyrophone sings when flames of burning gas heat up the air inside its pipes.
This pyrophone was made by Frédérik Kastner in 1869 and has pipes made of glass. There are several gas nozzles inside each glass pipe. These are close together but they separate when you active the pipe by pressing a note on the keyboard. As the nozzles separate, hot air moves swiftly through the pipe, causing the pipe to sing. Longer pipes sing (i.e. resonate) at lower pitches.
A large pyrophone.
(from MichelMoglia, YouTube)