Metals of the Platinum Group
Platinum exhibited a moderate amount of sensitiveness. Spongy platinum also showed the same action. The absorption of hydrogen made the action slightly better, but the improvement was not very marked.
Palladium.—This made a more sensitive coherer than platinum. The adjustment is, however, more troublesome.
Osmium.—The specimen was in the form of powder. It required a higher E. M. F. to bring it to a sensitive condition. The sensitiveness was moderate.
Rhodium was found to be more sensitive than osmium.
Copper, Gold and Silver
Copper required a much smaller E. M. F. The sensitiveness was only moderate.
Gold was more difficult to adjust, but the action was a little stronger.
Silver.—The receiver was extremely unstable. It exhibited sometimes a diminution and at other times an increase of resistance.
It will be seen from the above that all metals exhibit contact-sensitiveness to electric radiation, the general tendency being towards a diminution of resistance.
The most interesting and typically exceptional case, however, is the receiver made with potassium, which not only exhibits an increase of resistance by the action of radiation, but also a remarkable power of self-recovery. In the instances of increase of resistance exhibited by other metals, an increase of pressure or E. M. F. generally brought the coherer to the normal condition, which showed a diminution of contact resistance by the action of electric waves. With potassium
