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 referred to, indicate that radium B does not obtain a charge and so will remain in the gas. Dr. Bronson, working in the laboratory of the writer, has obtained evidence that a large amount of radium D remains in the gas even in a strong electric field. If the matter B exists to some extent in the gas, the difference between the theoretical curves for three successive changes would be explained; for, in transferring the emanation to another vessel, the matter B mixed with it would commence at once to change into C and give rise to a part of the radiation observed.

The equal division of the activity between the products A and C (see Fig. 90) supports the view that C is a product of A, for when radio-active equilibrium is reached, the number of particles of A changing per second is equal to the number of B or C changing per second. If each atom of A and C expels an α particle of the same mass and with the same average velocity, the activity due to the matter A should be equal to that due to the matter C; and this, as we have seen, is the case.

While it is a matter of great difficulty to give a definite experimental proof that radium A and B are consecutive products, I think there is little doubt of its correctness. Accurate determinations of the curves of rise and decay may throw further light on the complicated processes which undoubtedly occur between the breaking up of the atoms of the emanation and the appearance of the active deposit on the electrodes.

229. Relative activity supplied by the α-ray products of radium. There are four products in radium which give out α rays, viz. radium itself, the emanation, radium A and C. If these products are in radio-active equilibrium, the same number of particles of each product are transformed per second and, if each atom breaks up with the emission of one α particle, the number of α particles expelled per second should be the same for each product.

Since, however, the α particles from the different products are not projected with the same velocity, the activity, measured by the ionization current in the usual manner, will not be the same for all products. The activity, when measured by the saturation current between parallel plates at sufficient distance