624 Prof. T. Godlewski on the Action of 



fact seems to confirm our hypothesis concerning the appearing 

 of RaC at the cathode. If it is true indeed that RaC only 

 travels to the cathode if carried along by the RaB atoms 

 which remain in the positive colloidal agglomerate, this 

 aggregate must have a smaller positive charge than one con- 

 sisting solely of RaB atoms. The compound hydrosols 

 (containing RaB and RaO) will thus be more easily pre- 

 cipitated, and precipitation will occur at a lower concentration 

 of arsenious sulphide. At the cathode, therefore, with the 

 concentration, e. g. 7 = 0*01 mg., we get almost pure RaB. 



It is only with concentrations ten times stronger, or more, 

 that the characteristic change of sign and the traction of 

 RaB towards the anode occurs. The almost horizontal trend 

 of the dotted curve (fig. 1), corresponding to times from 

 15 to 35 min., proves unmistakably the appearance of RaB 

 at the anode. For this, as well as for all higher concentra- 

 tions, we observe that all the products (RaA, RaB, RaC) are 

 deposited at the anode. In accordance with what the theory 

 of colloids demands, the products are adsorbed by the colloid 

 of opposite sign, which is present in great excess. 



From an inspection of the figure, we conclude that at con- 

 centrations at which RaB appears at the anode the activity 

 of the cathode is exceedingly feeble, and falls in presence of 

 greater concentrations of arsenious sulphide to below 1 per 

 cent. 



Experiments with colloidal platinum. — Colloidal platinum 

 was prepared by Bredig's well-known method, i. e., by 

 pulverization of platinum in an electric arc. The chief 

 solution contained 7*6 mg. platinum in 100 cm. 3 . Certain 

 quantities of that solution were added to 16 cm. 3 of water 

 saturated with radium emanation ; the resulting solution 

 was electrolysed during 90 sec, under the same conditions 

 as heretofore. The results of these experiments are shown 

 in fig. 2. 



From the curves we see that the influence of platinum is 

 the same as that of arsenious sulphide. Small quantities 

 produce a decrease of activity of the cathode, and (as before) 

 the quantity of RaC deposited at the cathode is the first to 

 decrease. It is thus seen that the positive sols, containing 

 RaC along with RaB, are precipitated first as if they had a 

 lower charge. 



In the presence of still greater concentrations RaB also 

 disappears from the cathode ; at a yet higher concentration, 

 when the activity of the anode is exceedingly feeble, RaB 

 appears at the anode. The positive hydrosols become now nega- 

 tively charged, all the products being deposited at the anode. 



