Question

phosphine is used in holmes signal why

Answer 1

Phosphine gets ignited spontaneously as it comes in contact with air and also ignites acetylene. Thus a bright red flame is produced which is accompanied by huge smoke due to the burning of phosphine. This serves as a signal to the approaching ships.

Answer 2

phosphine act as a signal for other ships/ aeroplane that they need some sort of help. container containing calcium carbide and calcium phosphide are pierced and serve as a signal. is is also used in smoke screen