Contact Electricity of Metals. 113 



if it had been performed in some locality of the universe a 

 thousand kilometres away from any place where there is 

 oxygen ? The insulators may be supposed to be made of 

 rock-salt or solid paraffin, so that there may be no oxygen in 

 any part of the apparatus. This I say because I understand 

 that some anti-Voltaists have explained Bottomley's experi- 

 ments by the presence of vapour of silica from the glass, 

 supplying the supposedly needful oxygen ! 



§ 37. The anti-Voltaists seem to have a superstitious venera- 

 tion for oxygen. Oxygen is entitled to respect because it 

 constitutes 50 per cent, of all the chemical elements in the 

 earth's crust ; but this gives it no title for credit as coefficient 

 with zinc and copper in the dry Volta experiment, when there 

 is none of it there. Oxygen has more affinity for zinc than 

 for copper ; so has chlorine and so has iodine. It is partially 

 true that different metals — gold, silver, platinum, copper, 

 iron, nickel, bismuth, antimony, tin, lead, zinc, aluminium, 

 sodium — are for dry Volta contact-electricity in the order of 

 their affinities for oxygen ; but it is probably quite as nearly 

 true that they are in the order of their affinities for sulphur, 

 or for oxy-sulphion (S0 4 ) or for phosphorus or for chlorine 

 or for bromine. It may or may not be true that metals can 

 be unambiguously arranged in order of their affinities for 

 any of these named substances ; it is certainly true that they 

 cannot be definitely and surely arranged in respect to their 

 dry Volta contact-electricity . Murray's burnishing, performed 

 on a metal which has been treated with Pellat's washing with 

 alcohol and subsequent scratching and polishing with emery, 

 alters the Volta quality of its surface far more than enough 

 to change it from below to above several metals polished only 

 by emery ; and, in fact, Pellat had discovered large differences 

 due to molecular condition without chemical difference, before 

 Murray extended this fundamental discovery by finding the 

 effect of burnishing. 



§ 38. Returning to Professor Lodge's supposed oxygen 

 bath (§ 35) ; if it exists between the zinc and copper plates, 

 it diminishes or annuls or reverses the phenomenon, to explain 

 which he invokes its presence (see § 5 above) . 



§ 39. Many years ago 1 found that ice, or hot glass, 

 pressed on opposite sides by polished zinc and copper, pro- 

 duced deviations from the metallic zero of the quadrants of 

 an electrometer metallically connected with them in the same 

 direction as if there had been water in place of the ice or hot 

 glass. From this I inferred that ice and hot glass, both of 

 which had been previously known to have notable electric 

 conductivity, acted as electrolytic conductors. 



Phil. Mag. S. 5. Vol. 46. No. 278. July 1898. I 



