and its Successive Products. 37 



had been used by Kutherford and Soddy for the separation 

 o£ ThX from thorium. 



The experiments were made with the emanating substance 

 of Giesel, which, according to numerous -investigations*, has 

 been found to contain the same radioactive constituent as the 

 actinium of Debierne. The saturation current due to the 

 a-ray activity of the products under investigation was 

 measured with a quadrant electrometer of sensibility 120 

 divisions per volt ; the needle was kept at the standard 

 potential of 300 volts. The /3 activity was measured by 

 means of a sensitive electroscope. Four different sets of 

 experiments were made which gave very concordant results. 



In each case 0*15 gr. of the emanating substance, of activity 

 about 300 times that of uranium, was dissolved in 250 cm. of 

 hydrochloric acid (about 8 per cent, concentration). The 

 solution was evaporated on the water-bath to about 100 c.cm. 

 When ammonia was added to the solution, a reddish-brown 

 substance (probably hydroxide) was precipitated. The pre- 

 cipitate, collected on a filter-paper, was dried as quickly as 

 possible, and then its activity was measured. The filtrate 

 was then evaporated to dryness, and when ammonium salts 

 were driven off by ignition a small amount of a brown-black 

 residuum was left behind on the dish. On raising this to a 

 red heat, the colour of the residue changed from black to 

 white. This residue was intensely active compared with 

 the weight. Immediately after the dish was cold the activity 

 of the residue was measured and was found to decrease slowly 

 with the time according to an exponential law. In the same 

 period the actinium, which by precipitation had been rendered 

 almost inactive, recovered its activity, the recovery curve 

 being complementary to the curve of decay. 



From analogy to ThX, which it so closely resembles in radio- 

 active properties, the active substance separated from actinium 

 will be termed Actinium X (AcX). 



The results of one of the series of experiments are given in 

 Table I. and graphically represented in fig. 1. In Table I. 

 the first column gives the days measured from the time of 

 separation ; the second column gives the activity. The 

 activity of AcX is expressed as a percentage of the initial 

 activity, the maximum activity soon after separation being- 

 taken = 100. But for actinium (deprived of AcX) the final 

 value is taken = 100. 



In fig. 1, curve A represents the activity of AcX as a 

 function of the time, the activity of AcX being expressed in 

 the same units as in Table I. In the recovery curve B the differ- 

 ence between the maximum and the first value is taken = 100. 

 * See f. i. Kutherford, Bakerian Lecture, loc. cit. p. 188. 



