480 Mr. W. Coldridge on the Electrical and 



expressly state, that also in this case double layers are formed 

 on the drops, whose negative electricity comes from the elec- 

 trolyte. The supply of this electricity depends therefore on 

 the conductivity of the electrolyte. The process can, however, 

 no longer be a lasting one, because the secondary electrode is 

 immediately polarized. Mr. Brown can easily convince him- 

 self (if he has not already noticed it), that the current pro- 

 duced under such circumstances is much weaker than the one 

 earlier mentioned, and that it becomes continually weaker 

 owing to the polarization, while the other current can be kept 

 for days at its original strength. 



Finalty, it follows from the theory of v. Helmholtz, that a 

 diminishing current of opposite direction must be obtained if 

 the secondary electrode is connected, not with the dropping 

 mercury, but with that collecting on the bottom of the vessel. 

 This current can also easily be observed. According to Mr. 

 Brown's ideas, if I have correctly understood them, in this 

 case no current whatever could be produced. 



Briider Strasse, Leipzic. 



LV. On the Electrical and Chemical Properties of Stannic 

 Chloride ; together icith the Bearing of the Residts therein 

 obtained on the Prolans of Electrolytic Conduction and Che- 

 mical Action. — Part I. Experimental Observations. Part II. 

 Theoretical Considerations. By Ward Coldridge, B.A., 

 Scholar of Emmanuel College, Cambridge. 



[Concluded from p. 394.] 

 Part II. — Theoretical Considerations. 



THE first problem that presses forward for consideration is 

 that involved in the nonconductivity of stannic chloride. 

 It is a truism to write that its insulating-power is a function 

 of its constitution ; but it has hitherto been difficult, from the 

 lack of experimental observations, to advance beyond that 

 truism. The fact is that a column of stannic chloride, some 

 three to four centimetres in length with a cross section of one 

 to two square centimetres, has a resistance the lower limit of 

 which is certainly not less than 1600 megohms. This pheno- 

 menon is not an isolated one. Other pure liquids — water, 

 hydrochloric acid, hydrofluoric acid — are also nonconductors, 

 but liquid hydrocyanic acid is said to be an electrolyte ; and 

 the fused salts, of which the silver halogen compounds may be 

 taken as typical, easily electrolyse. Wherein, then, do these 

 liquids which are nonelectrolytes differ from those which are 

 electrolytes ? In order to progress towards a solution of this 



