630 Prof. T. Godlewski on the Action of 



It will be observed that the activity collected on toe filter 

 indicates the presence o£ RaB and RaC, and the corre- 

 sponding curve o£ activity is identical with that shown by 

 the cathode after electrolysis of pure water containing 

 emanation. Hence it is natural to conclude that the deposits 

 on the filter are positive hydrosols. 



The well-known researches of Schonbein and Goppels- 

 roder on the so-called capillary analysis were extended to 

 the case of colloids by Fichter * and Sahlboomf . The writers 

 showed that various colloids do not ascend to equal heights 

 in sheets of filter-paper : the negative colloids rise with the 

 water, whereas the positive are precipitated in the immersed 

 part of the sheet of paper ; in a similar manner positive col- 

 loids are precipitated when filtered. Fichter and Sahlboom 

 attribute the phenomena they observed to a negative elec- 

 trization of the fibres of the paper taking place as the 

 water passes through ; this produces a neutralization and a 

 consequent precipitation of the positive colloids. 



The precipitation on the filter of the radioactive products 

 which form positive hydrosols shows that in this case we 

 have to do with the same phenomenon as that observed by 

 Fichter and Sahlboom in the case of ordinary colloids. This 

 inference was confirmed by further investigations. A small 

 quantity of aluminium sulphate in solution was added to 

 water containing emanation ; the activity of the filter 

 through which this water was passed is found to be greater 

 than in the case when pure water with emanation was filtered ; 

 the curve of activity shows that in this case all the products 

 (RaA, RaB, and RaC) remain on the filter. Now we know 

 that under the influence of aluminium ions the negative 

 hydrosols become inversely charged, and when electrolysis is 

 going on are deposited at the cathode. 



In like manner we may obtain a greater quantity of RaO 

 and RaA on a filter by adding hydrochloric acid to the 

 solution : this also produces a change of sign of negative 

 hydrosols J. The activities of filters through which acidu- 

 lated solutions of emanation were passed changed in the 

 same way as did the activities of the cathodes, when the 

 solutions were electrolysed. In presence of acid in greater 

 concentration RaB no longer appears at the filter, only RaA 

 and RaC. In the case of a very strong concentration of the 

 acid used (1 normal solution or more) the filter proved to be 



* Fichter, Zeit. f. Kolloide, viii. p. 1 ; Verh. d. Naturfor. Ges. Basel, 

 xxi. p. 1. 

 t Sahlboom, Kolloidchemische Beihefte, ii. p. 79. 

 X Godlewski, loc. cit. 



