The London, Edinburgh and Dublin philosophical magazine and journal of science . nium oxide kept undisturbed on ametal plate, which repeated work has shown to be a perfectlyconstant source of radiation. The remainder of the nitratewas used for other experiments. The following table gives an example of one of a numerousseries of observations made with different preparations atdifferent times. The maximum value obtained by thehydroxide and the original value of the ThX are taken as 100:— Time in davs. Activity of Hvdroxide. Activity of TkX. 0 44 100 1 37 117 2 48 100 3 54 88 4 62 72 5 6S 6 71 53
The London, Edinburgh and Dublin philosophical magazine and journal of science . nium oxide kept undisturbed on ametal plate, which repeated work has shown to be a perfectlyconstant source of radiation. The remainder of the nitratewas used for other experiments. The following table gives an example of one of a numerousseries of observations made with different preparations atdifferent times. The maximum value obtained by thehydroxide and the original value of the ThX are taken as 100:— Time in davs. Activity of Hvdroxide. Activity of TkX. 0 44 100 1 37 117 2 48 100 3 54 88 4 62 72 5 6S 6 71 53 8 78 9 . 29-5 10 83 25-2 13 ... 15-2 15 ... 11-1 17 96-5 21 99 28 100 Fig. 2 shows the curves obtained by plotting the radio-activities as ordinates. and the time in days as II. illustrate- the rate of recovery of the activity ofthorium, curve I. the rate of decav of activity of ThX. It 2 C 2 * 380 Prof. E. Rutherford and Mr. F. Soddy on will be seen that neither of the curves is regular for the firsttwo days. The activity of the hydroxide at first actually. diminished and was at the same value after two days as whenfirst prepared. The activity of the ThX, on the other hand,at first increases and does not begin to fall below the originalvalue till after the lapse of two days (compare section IX.).These results cannot be ascribed to errors of measurement,for they have been regularly observed whenever similarpreparations have been tested. The activity of the residueobtained from thorium oxide by the second method of wash-ing decayed very similarly to that of ThX, as shown by theabove curve. If for present purposes the initial periods of the curve aredisregarded and the later portions only considered, it will beseen at once that the time taken for the hydroxide to recoverone half of its lost activity is about equal to the time takenby the ThX to lose half its activity, viz., in each case about4 days, and speaking generally the percentage proportion ofthe lost ac
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