with the Brush Discharge. 49 



produced by the formation of ozone, which then decomposes 

 the iodide, it would correspond to the formation of 

 0'000112 gramme of ozone. 



Condensing the electricity produces very little effect. For 

 with the jars on, similar results have been obtained to those 

 without the jars. Thus with points 4 centims. away and a 

 potential-difference of about 40,000 volts, 0*001778 gramme 

 of iodine was produced at the negative brush, and 0*000190 

 gramme at the positive in one hour. 



A diminution of potential-difference reduces the amount of 

 chemical action ; but the substance of which the point is 

 composed is immaterial. Thus, with 25,000 volts difference, 

 0*000698 gramme of iodine was set free by the negative in 

 half an hour, as against 0*000762 gramme with 40,000 in the 

 same time. 



The distance of the point from the surface of the liquid 

 makes an important difference. It has already been stated 

 that all the experiments were made when the points were 

 farther away than that at which a spark could pass. The best 

 effects are caused when the points are just farther away than 

 this. Thus when the points were 12 centims. away 0*000021 

 gramme was liberated by the negative, as against 0*000063 

 gramme when 8 centims. away, and 0*000508 gramme when 

 4 centims. away. 



Similar experiments to the above made with the brushes 

 obtained with the coil have given different results. In this 

 case it was found that invariably the brush from the positive 

 terminal liberates the greater amount of iodine. The difference 

 between the amounts produced by the positive and negative 

 brushes is not, however, so great as that by the machine. In 

 this case also we find differences between individual experi- 

 ments, but as before always an excess by the same pole. 

 The average of many experiments gave from three to five 

 times as much iodine set free under the positive brush to 

 that set free under the negative. These numerical results 

 apply to the coil whose dimensions are given above. 



It was found that with the machine and coil as described, 

 a much greater quantity of decomposition was caused by 

 brushes from the machine than from the coil. This corre- 

 sponds to the amount of visible brush produced. 



Actum on other Substances. 



The power of the brushes to produce other chemical 

 actions has been partially investigated. So far no reducing 

 actions have been observed, but oxidizing ones are always 

 present. In these cases with the machine brushes more action 



Phil. Mag. S. 5. Vol. 47. No. 284. Jan. 1899. E 



