Professor Rutherford says that "each of the alpha ray products present in one gram of radium product (_sic_) expels 6.2 x 10^{10} alpha particles per second." He also remarks on "the experimental difficulty of accurately determining the number of alpha particles expelled from radium per second."-- ED.] [Footnote 42: See Rutherford, op.cit.p.

150 .-- ED.] If radium transforms itself in such a way that its activity does not persist throughout the ages, it loses little by little the provision of energy it had in the beginning, and its properties furnish no valid argument to oppose to the principle of the conservation of energy.

To put everything right, we have only to recognise that radium possessed in the potential state at its formation a finite quantity of energy which is consumed little by little.

In the same manner, a chemical system composed, for instance, of zinc and sulphuric acid, also contains in the potential state energy which, if we retard the reaction by any suitable arrangement--such as by amalgamating the zinc and by constituting with its elements a battery which we cause to act on a resistance--may be made to exhaust itself as slowly as one may desire.
There can, therefore, be nothing in any way surprising in the fact that a combination which, like the atomic combination of radium, is not stable--since it disaggregates itself,--is capable of spontaneously liberating energy, but what may be a little astonishing, at first sight, is the considerable amount of this energy.
M.Curie has calculated directly, by the aid of the calorimeter, the quantity of energy liberated, measuring it entirely in the form of heat.

The disengagement of heat accounted for in a grain of radium is uniform, and amounts to 100 calories per hour.