ON ELECTROLYSIS. 347 



green. We may explain this hy assuming that at the lower temperature a highly 

 hydrated salt is contained in the solution, and that this is changed intoa lower hydrate 

 as the temperature rises. In what follows we communicate the results obtained 

 from a single solution only. This solution contained 15 parts CuCU + SHjO in 

 100 parts water. The conductivity of the solution at 5° is taken as unity. The 

 conductivity of a 15 per cent, solution of sodium chloride was examined at the 

 same titue. In the appended table the column headed T contains the temperatures, 

 L the conductivities, D the increase in conductivity for a rise of 10°. 



The solution of sodium chloride shows, in agreement with results obtained by 

 other investigators, a conductivity which increases with temperature more rapidly 

 as the temperature rises ; it agrees therefore in its behaviour with the majority of 

 salts. For copper chloride, however, the rate of increase is nearly constant up to 

 about 60°, and beyond this point rapidly diminishes. Solutions of other degrees 

 of concentration than the above behave in a similar way ; and this is true whether 

 free hydrochloric acid be added to the solution or not. 



The fact here ascertained, that the conductivity of salts varies with their degree 

 of hydration, shows that it is absolutely necessary not merely to determine the 

 constants under discussion for small temperature intervals and very dilute solutions, 

 but also to vary the conditions of experiment in every way possible, since only then, 

 and not always even then, can we determine whether such hydration has gone on 

 or not. 



_ The behaviour of copper chloride may be paralleled pretty closely by that of 

 acid potassium sulphate, studied by Kohlrausch and Bouty. 



I shall publish later the results obtained with other solutions of copper chloride, 

 with those of cobalt chloride and other salts. 



The experiments have been carried out with the assistance of J. Seyiferth. 



Oil some Points in Electrolysis and Blectro-convedion. 

 By Professor G. Wiedemann. 



I must congratulate the British Association on the reports of the Committee on 

 Electrolysis, and specially that Professor Oliver Lodge has directed the course of 

 its procedure, for it could not have been entrusted to abler hands. 



Some time ago I read a very interesting report which Professor Armstrong 

 communicated at the last meeting of the British Association, and the hypotheses 

 he has advanced on the subject of electrolysis. There is a great deal that is 

 hypothetical in these things. Allow me, therefore, to give expression to some 

 aphoristical suggestions about some points more accessible to observation which I 

 think ought first to be discussed. 



I. The first question is, What is an electrolyte ? What compounds are elec- 

 trolytes ? What are the ions of the electrolytes ? Now, one generally says that 

 electrolytes are salts, that they are binary compounds. But what i's a binary 

 compound ? It is a compound decomposed by a current into two different com- 

 pounds or elements ; and when you say that electrolytes are salts you may as well 

 say salts are electrolytes. Therefore it is vei-y difficult to give a definition, and, 

 even if we assume the general though not clearly defined idea of salts, we get into 

 great difficulties. For instance. Professor Hittorf has said that electrolytes are 

 compoimds which by double affinity may exchange their elements with those of 

 another recognised electrolyte. But that is not generally true. First, we have 

 certain bodies which seem not to be decomposed by the current, though they 

 exchange their elements with those of other compoimds whicli are electrolytes. 

 Take, for instance, anhydrous hydrochloric acid. It does not conduct. Neverthe- 

 less, as Dr. Gore has shown, if you put it upon carbonate of lime the carbonic 

 acid is chased away and chloride of calcium is formed. And, to give another 

 example, the chloride of propyle is a non-conductor ; nevertheless, when you treat 

 it with bromide or iodide of silver the chloride gets changed into bromide or 

 iodide. 



With just reason you may object that this is no proof, for perhaps the chloride 



