Action of Colloids on Radioactive Products in Solution. 619 



Almost at the same time, but by a different method, 

 Paneth * arrived independently at closely similar con- 

 clusions concerning the state of radioactive products in 

 solution. He found that it was possible to separate polonium 

 I'rom lead by means of a process of dialysis. In the process 

 the lead was shown to pass through parchment or animal 

 membrane, while the polonium remained. These results 

 were strikingly confirmed by the subsequent investigations 

 of Paneth t and HevesyJ. They, too, have observed a 

 change of direction in the migration of certain radioactive 

 products (ThB and Po), according as the solution was 

 acidulated or alkaline. They determined, moreover, the 

 coefficients of diffusion of these products, and found them 

 considerably smaller (especially in alkaline solutions) than 

 might have been anticipated from the valency of these 

 elements. Hence the order of magnitude of these colloidal 

 radioactive suspensions becomes approximately calculable, 

 and the writers quoted found that the suspensions consist of 

 no more than 8-3 or 2 atoms. According to this, solutions 

 of radioactive products form a transition between ordinary 

 colloidal and ionic solutions. 



If it is thus conceded that the centra of colloidal radio- 

 active suspensions consist of aggregations of atoms, we 

 can then easily explain an observation previously made 

 l>y the writer. In the above-mentioned paper it was shown 

 that by means of electrolysis of pure water saturated with 

 radium emanation together with its successive products, the 

 following deposits on the electrodes were obtained : — On 

 the anode, RaA and about one-third of the equivalent 

 quantity of RaC ; on the cathode, RaB and about one-third 

 of the equivalent quantity of RaC. In pure water RaA 

 is deposited only on the anode, i. e., it forms negative 

 hydrosols ; RaB appears only at the cathode, i. e., it forms 

 only positive hydrosols. The question arises, What does 

 the fact mean, that RaC is deposited in the same solution 

 equally well at the cathode as at the anode ? Must it be 

 supposed to form positive hydrosols or negative ones ? 



In order to elucidate this question, let us assume that 

 RaC in pure water gives rise to negative hydrosols, just 

 as RaA does. If the centre of the suspension of RaA 

 consists of an aggregation of several atoms, we easily see 

 that as soon as one of these is transformed into RaB, this 



* Paneth, Wien. Sitzber. cxxi. p. 2193, cxxii. p. 1079; Kolloid-Zeitschr. 

 xiii. p. 1. 



f Paneth, Kolloid-Zeitschr, xiii. p. 297. 

 \ Hevesy, Phi/s. Zeit. xiv. 1913, p. 1202. 



