504 REPORTS ON THE STATE OF SCIENCE. 



substances which are supposed to give off electrons when heated are 

 all substances that are more or less easily dissociated and the experi- 

 ments made with such substances have not been carried out with the 

 scrupulous care to remove ' impurities ' which the observations made 

 by Brereton Baker and Dewar have shown to be necessary. There is 

 nothing at present to prove that ' electrons ' are given off otherwise 

 than in cases in which an ordinary discharge will pass. Moreover, the 

 argument on which the determination of the size of negative electrons 

 is based is in no sense one which serves to place their existence beyond 

 question. It is now admitted by prominent physicists that molecules 

 can carry charges — those of helium, for example — so that it is not even 

 necessary to assume the existence of dissociated charged ions as carriers 

 of electricity. The admission is of some importance, as, in the early 

 days of the discussion on electrolysis, the contention that molecules 

 and aggregates of molecules might act as carriers was scorned. Com- 

 pare ' The Conditions Determinative of Chemical Change and of Elec- 

 trical Conduction in Gases and on the Phenomenon of Luminosity. ' x 

 H. E. A.] 



Professor Bone, writing in reply, hoped that this discussion would 

 lead to a more active co-operation between physicists and chemists in the 

 further investigation and interpretation of gaseous combustion. If it 

 be admitted (1) that the forces holding the atoms of a molecule together 

 are electrical in character, and (2) that the unit of electricity is corpus- 

 cular and capable of independent movement outside the boundary of 

 the chemical molecule, it seems probable that such corpuscular electric 

 units (' electrons ') play some part in gaseous combustion. The utility 

 of the ' electron ' theory to chemists, however, will largely depend upon 

 its ability to interpret some of the more obscure factors in combustion 

 dealt with in the report. 



With regard to the subject of ' surface combustion,' recent experi- 

 ments carried out by Mr. H. Hartley and himself (the details of which 

 would be published shortly) had proved that certain ordinarily non- 

 oxidisable metals (silver, gold, &c.) become negatively charged when 

 heated at 200° to 400° in either hydrogen or carbon monoxide, and 

 positively charged on being similarly heated in oxygen. These surfaces 

 also become negatively charged during the catalytic combustion either 

 of hydrogen or of carbon monoxide, although there is so far no evidence 

 that the main body of the gas outside of the catalysing surface becomes 

 ' ionised ' to any appreciable extent. 



If the + or - charging of the surface really implies the escape 

 therefrom of — or + ' electrons ' respectively with velocities insuffi- 

 cient either to ionise the gas outside, or even to allow of their travelling 

 far from the surface (so that they would be likely to remain within 

 range of the attraction of the layer of opposite sign on the surface), it 

 seems at least conceivable that such slowly moving electrons may attach 

 themselves to, or condense around them, the molecules of combustible 

 gas or of oxygen, which, thus charged, would be attracted to the 

 surface. Some such view, if admissible from the standpoint of the 



1 Roy. Soc. Proc., 1902, 72 , 99. 



