"250 Sir J. J. Thomson : Further 



i. <?., that the total charge on each atom forming a part of a 

 gaseous molecule is zero, but that in each atom the positive 

 and negative charges are so arranged that the force between 

 adjacent atoms is attractive. I have not yet, however, tried 

 -any compound which is a strong electrolyte, it is possible that 

 the atoms in such a compound might be charged. 



There is, I think, other evidence besides that derived from 

 positive rays in favour of the view that the atoms as a rule 

 are not charged. For example, dissociation of gases at quite 

 low temperatures (say 70° C), such as takes place with nickel 

 carbonyl, is not accompanied by any abnormal conductivity. 

 And although, as I showed many years ago (Phil. Mag. [5] 

 xxix. pp. 358-441), there is considerable conductivity at high 

 temperatures in gases which dissociate at these temperatures, 

 yet this conductivity seems to depend greatly on the contact of 

 these gases with the hot metal of the electrodes between which 

 the current is measured ; suggesting that the charging up of 

 the atoms in this case may be due to the electricity which we 

 know to be emitted by hot metals. Quite recently Schmidt 

 (Ann. d. Pliys. xxxv. p. 401) has observed considerable 

 conductivity at temperatures less than 200° C. in a vessel 

 containing the vapour of cadmium iodide, obtained by heating 

 the salt in the vessel in which the conductivity is observed. 

 The cadmium iodide is dissociated, but we do not know 

 whether the conductivity is due to cadmium iodide which has 

 existed as vapour and then been dissociated, or whether it is due 

 to systems which were dissociated when driven off from the 

 salt by the heating. In the second case other considerations 

 would come in, which can be illustrated by considering the 

 case of electrolytes in solution, when the dissociation of the 

 salt seems to be accompanied by the charging up of the atoms. 

 If the atoms get charged in the electrolyte, it may be asked, 

 why should they not get charged in the case of gases ? The 

 conditions are very dissimilar. We may regard the two 

 atoms in the molecule as analogous to the two plates of a 

 condenser, and the acquisition of a charge by the atoms as 

 analogous to the charging up of the condenser. Now the 

 work required to give a fixed charge to a condenser is 

 inversely proportion al to the capacity of the condenser, so 

 that the smaller the capacity the greater is the amount of 

 energy required to charge it. We should, however, expect 

 that the capacity of a molecule when in the gaseous state 

 would be much less than when it was in solution in a liquid 

 of large specific inductive capacity ; the specific inductive 

 capacity would of itself increase the capacity, and in addition 

 there would be the opportunity of the atoms in the molecule 



