548 Lord Kelvin [May 21, 



experiments by the presence of vapour of silica from the glass, sup- 

 plying the supposedly needful oxygen ! 



§ 37. The anti-Voltaists seem to have a super«3titious veneration 

 for oxygen. Oxygen is entitled to respect because it constitutes 

 60 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, plati- 

 num, 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 (SO4) 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 con- 

 dition without chemical difference, before Murray extended this funda- 

 mental discovery by finding the effect of burnishing. 



§ 38. Eeturning 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 I found that ice, or hot glass, pressed on 

 opposite sides by polished zinc and copper, produced 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. 



Experiments made by Maclean and Goto in the Physical Labo- 

 ratory of the University of Glasgow in 1890,* proved that polished 

 zinc and polished copper, with fumes passing up between them from 

 the flame of a spirit-lamp 30 centimetres below, gave, when metallic- 

 ally connected to the quadrants of an electrometer, deviations from 

 the metallic zero in the same direction, and of nearly the same amount, 

 as if cold water had been in place of the flame. This proved that 

 flame acted as an electrolytic conductor. They also found that hot air 

 from a large red-hot soldering bolt, put in the place of the spirit lamp, 

 had no such effect ; nor had breathing upon the plates, nor the vapour 



* Phil. Mag. Aug. 1890. 



