178 Dr. 0. Hahn on Radioactinium. 



as previously employed. The experimental values are shown 

 by crosses on Curve I. ; the agreement between the theory and 

 experiment is clearly seen. The initial activity, experi- 

 mentally found, is 2*4 per cent. ; after about 4 days the 

 experimental values lie closely on the curve for about one 

 month. After that time, the experimental values lie some- 

 what above the theoretical curve. 



We previously pointed out that the value of k is uncertain 

 between limits, and varies for different experiments. Taking 

 this factor into consideration, there is an excellent agreement 

 between theory and experiment. For comparison, a curve is 

 drawn in fig. 3 (Curve II.), which represents the rise-curve 

 for actinium, if the latter produced actinium X directly, as was 

 generally believed before the separation of radioactinium. 

 The difference between the two curves is striking. While in 

 Curve II. the activity has reached half of its final value after 

 10*2 days, the experimental Curve I. shows that more than 

 30 days are required for the activity of actinium to reach half 

 of its maximum value. 



We therefore see conclusively that the rise-curve for 

 actinium is not complementary to the decay-curve of 

 actinium X, but behaves just as it should do theoretically under 

 the assumption that radioactinium is a product between 

 actinium and actinium X. 



III. Other Properties of Radioactinium. 



It is not possible to make any definite statement in regard 

 to the chemical properties of radioactinium. The various 

 methods employed for its separation are very similar in 

 nature, and cannot be considered to be definite chemical 

 reactions in the ordinary sense. 



It is well known that barium sulphate possesses the property 

 of dragging down many radioactive products from a solution, 

 and the methods used for the separation of radioactinium 

 appear to depend on a similar principle. A satisfactory 

 explanation of these facts has not so far been given. It 

 must not be forgotten that, with the exception of such slowly- 

 changing substances as radiolead, polonium, and radiothorium, 

 most of the products of the various radioelements exist in 

 almost infinitesimal proportion mixed with the parent matter. 



Methods of separation, similar in principle to those employed 

 in the case of radioactinium, ought never betaken as a means 

 of description of these products, and any system of classifi- 

 cation based on such facts is liable to be very erroneous *. 



* A discussion of these points for the case of actinium has been given 

 too by Godlewski, Jahrb. d. Had. u. Elektr. vol. ii. 1906. 



