Free Ions in Aqueous Sokitions of Electrolytes. 239 



^o direct experimental proof Avas attempted until Ostwald 

 and j^ernst,^ in 1889, performed the following experiment. 

 It will be given substantially in their own language. 



A glass tube about 30 or 40*^"^ in length, provided with a 

 stopcock, was drawn out to a fine capillar j at one end. The 

 tube was then partly filled with mercury and hung upright, 

 with the capillary in a solution of dilute sulphuric acid. By 

 suction at the upper end the mercury was drawn up and the 

 sulphuric acid after it. When at a convenient height, about 

 the middle of the capillary, the stopcock was closed and the 

 liquid thus held in place. A platinum wire fused into the 

 tube connected with the mercury. 



A large glass flask was now filled with dilute sulphuric acid 

 and insulated by placing it on a disk of hard rubber. The 

 outer surface of the fiask was coated with tinfoil and its neck 

 varnished with shellac. The contents of the flask were con- 

 nected with the sulphuric acid into which the capillary tube 

 dipped, by means of a wet string. The positive pole of a 

 small electric machine was brought in contact with the tin- 

 foil, and the mercury of the capillary electrometer connected 

 with the earth. 



As soon as the electric machine was set in motion the mer- 

 cury of the electrometer rushed up and at the same time bub- 

 bles of gas separated, which broke the thread of mercury in a 

 number of places. 



This is the explanation given. — By charging the outer cov- 

 ering of the flask with positive electricity, the negative elec- 

 tricity on the inner side would be attracted and held, while 

 the positive would be repelled. The latter would go by the 

 wet string to the capillary electrometer and then by the plati- 

 num wire to the earth. There is no closed current ; the entire 

 movement of electricity is produced by induction. This proves, 

 they say, that free ions were present and that they moved. 



They performed several other experiments, but all are on the 

 same principle, and the same conclusions are drawn. 



There seems to be good reason for the belief that the con- 

 clusion arrived at does not necessarily follow, but that we need 

 further proof. 



The potential of an electric machine is very high and the 

 flask they used in connection with the capillary electrometer 

 is really a condenser. As no substance insulates absolutely 

 there must be in such an arrangement some current, and in 

 such a restricted path there is a possibility of a considerable 

 difference of potential. They do not say that the potential 

 difference, between the two ends of the capillary electrometer, 

 was measured. If this exceeded about 1"22 volts there was 

 electrolysis and consequently a formation of gas bubbles. 



*Zeitschr. Phys. Chem., iii, 271, 1889. 



