One product has been observed in uranium, four in thorium, four in actinium and seven in radium. It is not improbable that a closer examination of the radio-elements may reveal still further changes. If any very rapid transformations exist, they would be very difficult to detect. The change of thorium X into the emanation, for example, would probably not have been discovered if the product of the change had not been gaseous in character. The electrolysis of solutions is, in many cases, a very powerful method of separating active products from one another, and its possibilities have not yet been exhausted.