Electrodes in the Galvanic Arc of Light. 11 



which had evidently, therefore, come later, doubtless thrown 

 back again from the copper electrode, as the iron electrode itself 

 was certainly not heated to fusion. It is thus seen that an elec- 

 trode, under the circumstances present in these experiments, 

 may take up again already-disintegrated metal and subject it to 

 a fresh disintegration. Consequently the numerical results of 

 all such experiments are completely illusory. 



More success could perhaps be expected from an arrangement 

 in which chemical alterations of the disintegrated metal are 

 taken advantage of to avoid repeated disintegrations ; and this 

 comes nearer to Grove's experiment. If in experiments in air 

 the powdered metal were completely oxidized and thus pre- 

 sented no mechanically conducting connexion with the rest of 

 the electrode, this purpose would perhaps have been attained. 

 But determinations according to this method have not only the 

 difficulty experienced by Grove, namely that oxidation readily 

 takes place also on the mass of the electrode, but also one of an 

 exactly opposite nature ; and even this makes them as ill adapted 

 as the previous determinations to answer the question proposed. 

 That is to say, in general the whole of the disintegrated sub- 

 stance of an oxidable electrode is not actually oxidated in air, 

 but the oxidation extends more towards the circumference of the 

 arc of light, while pure metal readily passes in its interior. 



On this I have made various experiments, and will only cite 

 one case, which speaks distinctly. I placed two electrodes of 

 nickel opposite each other in air, and caused the arc to pass 

 over, during which 60 cub. centims. of hydrogen w r ere developed 

 in the voltameter. Both electrodes obtained an oxidized layer, 

 which with a little care could be very well separated clean from 

 the metal. After this the positive electrode gave a loss of weight 

 of 4 milligr., and the negative one of 13 milligr. But the posi- 

 tive electrode showed in front a projecting piece of pure metal 

 parted off from the rest of the electrode by a fine fissure. I 

 sprung it off at the fissure, and found that it had been seated on 

 a fully oxidated base. This piece had therefore first arrived 

 thither during the experiment, and, indeed (since neither elec- 

 trode had once become red-hot), from the opposite electrode. It 

 was, however, oxidated only on the outermost surface ; through- 

 out its interior was pure metal : it amounted to 6 milligr. 



It is thus just as little possible to measure in this way. Also 

 an artificial blast of air or oxygen into the arc would hardly give 

 serviceable experiments. 



It may therefore certainly be maintained generally that no 

 experiments can answer our question in w T hich both electrodes 

 take part in the disintegration. We must accordingly endeavour 

 to take away the cooperation of one of the electrodes. For this 



