62% Prof. T. Godlewski on the Action of 



Various colloids, in different, accurately known quantities, 

 were added to water which was saturated with radium 

 emanation and its successive products. The solution was 

 then electrolysed between platinum electrodes, a P.D. of 

 220 volts being employed. The experimental arrangements 

 used in this part of the work were the same as those 

 described in my previous paper*. The a activity of the 

 electrodes was determined after the electrolysis by means 

 of a quadrant electrometer ; the measurements were sub- 

 sequently repeated, in order to identify the deposited 

 products. The activity is expressed below in arbitrary 

 units, which, however, are invariably the same throughout 

 this paper. The water used in these experiments was 

 obtained by distillation from ordinary distilled water, a 

 quartz condenser being employed. 



3. The Influence of Negative Colloids on Radium Products 

 in solution. 



Experiments with arsenious sulphide. — Colloidal arsenious 

 sulphide was obtained in the usual way, i, e., by passing 

 a stream of gaseous hydrogen sulphide through a dilute 

 solution of arsenious acid. After driving off the remainder 

 of hydrogen sulphide and filtering, a solution was obtained 

 which in flasks of Jena glass could be preserved for weeks. 

 The solution was suitably diluted, and 1 cm. 3 of variable 

 concentration (7) was added to 16 cm. 3 of water saturated 

 with radium emanation. The results of measurements of 

 the activity of both electrodes and its variation in time are 

 plotted in fig. 1. The continuous curve on the figure refers 

 to the cathode, the dotted one to the anode. 



It will be noticed that the influence of arsenious sulphide 

 on the result of electrolysis is very marked ; the direction of 

 the variation is that which was to be expected on account of 

 the sign of the colloid. 



When this negative hydrosol is added, the amount of 

 products deposited at the cathode decreases at first. The 

 decrease of the maximum ordinates of the continuous curves 

 points to a diminution of the amount of RaB with increasing 

 concentration of arsenious sulphide ; the diminution of the 

 initial ordinates indicates a decrease of the quantity of RaC 

 deposited at the cathode. The continuous curves on fig. 1 

 show that when arsenious sulphide is used in feeble concentra- 

 tion, the quantity of RaO deposited at the cathode decreases, 



but the relative amount of -^ ~ at first must increase. This 



KaC 



* Godlewski, loc. cit. 



