Colloids on Radioactive Products in Solution. 



629 



when it is desired to concentrate radioactive products not 

 only in the case o£ radium but equally well in the case of 

 actinium, mesotborium, and uranium. The results o£ these 

 researches, showing that in these cases too we have to deal 

 with colloidal radioactive hydrosols, will be published else- 

 where together with results obtained by the cataphoresis of 

 the products. We may in the meantime point out, however, 

 that the use of the methods described is subject to such 

 restrictions as will allow of the colloidal state of the products 

 being maintained. 



6. Capillary Analysis of Radioactive Products. 



Investigating, as aforesaid, the dependence of the activity 

 of a filter on the quantity of added colloid, I found that the 

 filter manifested considerable activity, even when no foreign 

 colloids were added. When water saturated with emanation 

 together with its successive products was passed through a 

 filter, a good part of the products (though not all) remained 

 on it. I endeavoured to eliminate all possible impurities in 

 the filter-paper, and for this reason I employed, after many 

 trials, filters No. 590 (Schleicher & Schull) having very little 

 (0*03 mg.) ash remainder, previously extracted in hydro- 

 chloric and hydrofluoric acid. A filter so prepared showed 

 again very strong actiA-ity. 



One instance may be given here. 16 cm. 3 of water 

 saturated with emanation were passed through the filter. 

 After careful washing of the filter and desiccation by means 

 of aBunsen burner, it was introduced at once into the testing 

 vessel, where its activity was measured. The results are 

 shown below : — 



Table I. 



Time 

 in minutes. 



Activity. 



2 



254 



6 



278 



10 



318 



15 



355 



28 



387 



40 



323 



103 



174 



