He thought they were "compounded" of a certain earth, or calx, and phlogiston.
I should have sent you my Defence of Phlogiston, but that I presume you have seen it.
It was phlogiston and that only which occasioned the electric current.
Coal, for example, was thought to be very rich in phlogiston.
"Phlogiston" and "vortices" had their day and are forgotten.