284 Mr. Lane on the magnetic Attraction , &c. 
mable substances mixed with them do not render them mag- 
netic, until they are by heat chemically combined with the 
oxides, and that when the combustible substance is again 
separated by heat, the oxides return to their unmagnetic state. 
That magnetic oxides cannot be distinguished from calcined 
oxides by their colour. I entertain a hope, however, that this 
subject may be found worthy of the accurate investigation of 
some other member of this learned Society. 
