ELECTROLYTIC DISSOCIATION. 3«7 



heated by an air-bath, so that the piece of sal-ammoniac was volatilized. 

 After this a current of hydrogen was led through both glass tubes D 

 and E. Now ammonia diffuses more rapidly than hydrochloric acid; 

 if, therefore, the vapor of sal-ammoniac is partially decomposed into 

 ammonia and hydrochloric acid, we should expect that above the as- 

 bestos diaphragm there would be an excess of hydrochloric acid and 

 beneath it an excess of ammonia. This v. Pebal showed to be the case. 

 The hydrogen-current from D showed an acid reaction on a piece of 

 litmus-paper in A, and that from E showed an alkaline reaction on a 

 similar piece of litmus-paper placed in B. It was objected that the 

 decomposition might possibly be caused by the asbestos of the dia- 

 phragm, or by the hydrogen. V. Than, therefore, made a diaphragm 

 of sal-ammoniac, and substituted nitrogen for hydrogen, but the effect 

 was the same. 



These experiments were performed in the years 1862 and 1864. 

 They were based on the doctrine of dissociation, which was at that 

 time (1857) worked out by Ste. Claire-Deville, and developed by his 

 pupils. From the most ancient times use was made of the fact that 

 limestone at high temperatures gives off carbonic acid, and that quick- 

 lime remains. This and similar processes were studied by Ste. Claire- 

 Deville. He found that the same law is valid for the pressure of 

 carbonic acid over limestone and for the pressure of water vapor over 

 liquid water at different temperatures. On these fundamental re- 

 searches the theory of dissociation was based, a theory which has sub- 

 sequently played an ever-increasing role in chemistry, and whereby a 

 broad bridge was laid between physical and chemical doctrines. 



At almost exactly the same time we find in the writings of Clausius 

 on the conductivity of salt solutions the first traces of an idea that 

 salts or other electrolytes may be partially dissociated in aqueous solu- 

 tions. Buff had found that even the most minute electric force is suffi- 

 cient to drive a current through a solution of a salt. Now after the 

 scheme of Grotthuss, at that time generally accepted, the passage of 

 the electric current through a solution is brought about in such manner 

 that the conducting molecules, e. g., of potassium chloride (KC1), are 

 divided into their ions, which combine again with one another in the 

 following manner: At first, as the current is closed, the electrode A 

 becomes positive and the electrode B negative. All the conducting 

 molecules KC1 arrange themselves so that they turn their positive ions 

 (K) to the negative electrode B, and their negative ions (CI) to the 

 positive electrode A. After this, one chlorine ion is given up at A 

 and one potassium ion at B, and the other ions recombine, so that the 

 E of the first molecule takes the CI of the second molecule, and so on 

 (Fig. 2). Then the molecules turn round under the influence of the 

 electric force, so that we get the scheme 3 and a new decomposition 



