Electrodes in the Galvanic Arc of Light. 13 



denly moving the silver knob away from the plate, it does not 

 make its appearance; there metallic silver alone is to be seen. 

 Precisely the same powder is seated, at the commencement of an 

 experiment, on the knob itself; but it vanishes there, and does 

 not appear again, as soon as the knob approaches a red heat, by 

 which it is reduced to the metallic condition. It is not an im- 

 probable conjecture that this oxidation of the silver is to be 

 ascribed to the presence of ozone in the voltaic arc produced in 

 air ; and therein might be seen a further argument for the 

 opinion entertained probably by the majority of physicists— 

 that in the voltaic arc the movement of the electricity is not 

 brought about exclusively by the transport of the substance of 

 the electrodes, but that a partial leap of the intervening layers 

 of gas takes place, analogous to the induction-spark f. 



Now the quantity of the silver that goes over in this way (that 

 is, the disintegrated powder) can be settled by simply weighing- 

 it, since no permanent oxidation of the knob itself takes place. I 

 obtained thus, with two silver knobs of from 5 to 6 grammes 

 weight, the following results in the order given : — 





Silver Knob I. 





The knob was 



Hydrogen developed in the 

 voltameter, in 



Loss of silver, 

 in milligr. 



Ratio of the 

 weight of the 



silver lost to 

 the hydrogen 









cub. centims. 



milligr. 





developed. 



-f electrode 



22 



1 97 



6-2 



3-15 



+ 



32-5 



291 



16 



5-50 



+ 



24-6 



2-20 



14 



6-36 



+ 



85-6 



7-67 



51-4 



6-70 



j» 



76-4 



6-84 



9 



1-32 



+ 



85 



7-60 



34 



4-47* 



+ 



29-8 



2-67 



16 



6 



>» 



28-8 



2-58 



12 



4-65* 



» 



98 



8-78 



38-5 



4-39 





Silver Knob ] 



I. 





+ 



29 



260 



6 



231 



»> 



535 



4-79 



7 



1-47 



+ 



168-8 



1512 



113 



7-47 



+ 



29-4 



2-63 



16 



609 



+ 



767 



6-87 



51 



743 



j> 



70-7 



633 



26 



4 09 



+ • „ 



168-2 



1507 



130-5 



8-66 



+ 



44-8 



401 



21 



5-24* 



t Compare also Grove's account (Phil. Mag. S. 4. vol. iv. p. 498) of 

 similar phenomena of oxidation of silver in the induction-spark. 



