In ordinary chemical changes it is the _molecules_ (groups of atoms) which are altered or rearranged; in radioactive change the atoms themselves suffer disintegration and rearrangements. The energy of radioactivity, then, is--according to the accepted view--intra-atomic--stored-up energy within the atom itself. It was calculated by Prof. Curie that the energy of one gram of radium would suffice to lift a weight of 500 tons to a height of one mile. If it were possible to obtain one cubic centimeter (a thimbleful) of the “emanation” from radium in the form of a gas, we should find that it possessed the power, altogether, of emitting more than seven million calories of heat! A thimbleful of this invisible gas would be more than sufficient to raise 15,000 pounds of water 1°. But in every mass of radium, small or large, not more than 13 trillionths of it is undergoing change per second. “The processes occurring in the radio-elements,” says Rutherford again, “are of a character quite distinct from any previously observed in chemistry. Although it has been shown that the radioactivity is due to the spontaneous and continuous production of new types of active matter, the laws which control this production are different from the laws of ordinary chemical reactions. It has not been found possible in any way to alter either the rate at which the matter is produced or its rate of change when produced. Temperature, which is such an important factor in altering the rate of chemical reactions, is, in these cases, entirely without influence. In addition, no ordinary chemical change is known which is accompanied by the expulsion of charged atoms with great velocity.... Besides their high atomic weights, [they] do not possess in common any special chemical characteristics which differentiate them from the other elements.” It was early observed by Curie and Laborde that the temperature of a radium salt is always a degree or two above that of the atmosphere, and they estimated that a gram of pure radium would emit about 100 gram-calories per hour. Giesel later showed that radium was always at a temperature 5° higher than the surrounding air, regardless of what the temperature of the air might be. This continues unchanged whether the temperature of the surroundings be 250° below zero Centigrade, or in the intense heat of an electric furnace.