108 Electrical Conduction in Gases and Luminosity. [Mar. 13, 



once presents itself not merely as a possibility, but practically as a 

 necessity. There is every reason to suppose that hydrogen peroxide 

 is a necessary product of oxidation by -ordinary oxygen whatever the 

 substance oxidised ; but the conditions under which it is produced are 

 usually such as to engender its own immediate decomposition — so that 

 it either escapes observation or is met with only in minute quantity. 

 The oxidation of zinc may be taken as an example. The oxidation 

 necessarily takes place in a circuit comprising (a) the impure metal — 

 which because it is impure furnishes both negative and positive elec- 

 trode— (b) conducting (impure or dirty) water and (r) oxygen, of which 

 the last acts as depolariser. The water is electrolysed, its oxygen 

 going to the metal ; at the same time, the hydrogen from the water 

 becomes associated with the depolarising oxygen molecule, forming 

 hydrogen peroxide, PLOo : the products, in fact, are zinc oxide and 

 hydrogen peroxide in equivalent quantities, not merely zinc oxide as is 

 taught by the text-books. 



It does not seem to me that Sir Win. Crookes has disproved the 

 possibility that the effects may be due to hydrogen peroxide by his 

 experiment in which one limb of a U-tube passed through the cork in 

 a bottle containing a solution of the peroxide, the open end of the 

 other limb being put close to a sensitive film, the result being that no 

 photographic effect was observed in 72 hours, although a strong effect 

 was produced when the film was kept over the mouth of the bottle 

 during only 24 hours. The peroxide molecules would undoubtedly 

 tend towards the walls of the tube, especially at the bend ; but colli- 

 sion therewith would probably have fatal effects, as the alkaline surface 

 of the glass would promote their destruction. 



The argument may be applied to recent researches on the so-called 

 ionisation of air and other gases. If this term implied the recognition 

 of nothing more than the power of conducting, little difficulty would 

 arise. Faraday, with characteristic and truly scientific caution, used 

 the word ions simply " to express those bodies which can pass to the 

 electrodes." Unfortunately, of late years the signification of the 

 word has been entirely altered : ionisation now connotes a schism — a 

 process of molecular suicide ; and the ions are looked upon as discrete 

 particles enjoying separate existence, as the electrically charged, 

 wandering elements of molecular disruption. Before we assume that 

 such ions are present in air under ordinary conditions, and that they 

 alone can condition conductivit}^, it behoves us to examine carefully 

 into the nature of the evidence which is relied on in proof of their 

 presence. It appears to me that much of the work done in this field 

 is open to criticism. Thus, in Mr. C. T. R. Wilson's experiments,* 

 even the minute amount of chemical change occurring at the surface 

 of the sulphur bead attaching the gold leaf of the electroscope to its 

 * ' Rot. Sec. Proc.,' 1901, vo 1 . 68, p. 151 ; vol. GO, 277. 



