352 Prof. J. J. Thomson on the 



close to this, but in the gas there is a coating of the opposite 

 kind of electricity. The quantity of positive electricity on 

 one coating is equal to the quantity of negative electricity on 

 the other. With an electro-negative gas like oxygen, the 

 negative layer of this double coating of electricity is in the 

 oxygen when the drop is formed of distilled water, or of a 

 solution of readily oxidizable substances, such as pyrogallic 

 acid, or phenol, or of dilute solutions of eosine and fluorescene. 

 If the oxygen is replaced by the electro-positive gas hydrogen, 

 then the positive layer of the coating is in the hydrogen, not 

 only for the drops mentioned above but also for all the drops 

 I have tried, with the exception of mercury. This sub- 

 stance I have always found to be positively electrified 

 whether it fell through air or hydrogen. I hope, however, 

 to test this point further by trying still purer hydrogen. 

 When the drops are solutions of strongly oxidizing sub- 

 stances, such as chromium trioxide, hydrogen peroxide, 

 potassium permanganate, or weak solutions of certain dyes, 

 such as rosaniline or methyl violet, the positive coating seems 

 always to be in the gas, whether this be oxygen or hydrogen; 

 the electrical effect is, however, greater in the latter case 

 than in the former. With chlorine, however, the negative 

 coating seems always to be in the gas. These results, together 

 with the fact that when water falls through its own vapour, 

 or when chlorine water falls through chlorine, no electrical 

 effect is produced, seem clearly to indicate that the electrifi- 

 cation owes its origin to chemical processes. In fact the 

 phenomena point to the conclusion that over the surface of 

 the drop a substance is formed which is in a state intermediate 

 between that of complete chemical combination and complete 

 separation between the gas and the liquid forming the drop : 

 a state in which the constituents have electrical charges of 

 the same sign as in actual chemical compounds, but in which 

 the connexion between the constituents is so loose that they 

 can easily be shaken apart. We must regard this state rather 

 as an attempt or tendency towards chemical combination than 

 the formation of a definite stable chemical compound, for we 

 could not suppose that such a compound would be split up 

 when the drop struck against a wet plate. 



The greatest electrical effect will occur when there is a 

 tendency towards chemical combination, though not of suffi- 

 cient intensity to result, in the time taken by the drop to fall 

 from the funnel to the plate, in the formation of a definite 

 chemical compound. The influence of this tendency in in- 

 creasing the electrical effect is shown by the experiments on 

 weak solutions of the three isomeric substances, resorcin, 



