ELECTROLYSIS 187 



that of their conductivities in equivalent solutions. This circum- 

 stance led me to suppose that chemically active molecules are 

 identical with electrically active ones, and therefore the con- 

 ductivity of an acid was regarded as a measure of its strength. 

 In consequence it was argued that the velocity of a reaction, 

 which may be brought about by different acids, is proportional 

 to the conductivity of the acid used. . . . Generally speaking, 

 there seems to be a certain parallelism between electrical con- 

 ductivity and chemical reactivity. Gore found that pure 

 anhydrous hydrochloric acid does not (appreciably) attack 

 oxides and carbonates ; also it is practically a non-conductor of 

 electricity. Similarly, one can understand why concentrated 

 sulphuric acid may be transported in iron vessels, whereas 

 diluted sulphuric acid attacks them very rapidly." 



He then goes on to show that electrolytes differ from non- 

 electrolytes in giving, when in solution, greater osmotic pressures, 

 and greater effect on the freezing, boiling-points, and vapour 

 pressures. This has already been sufficiently explained in the 

 preceding chapter on " Solutions." 



An idea of great importance was introduced into chemistry 

 by the late Professor Alexander Williamson about 1850, in the 

 endeavour to explain the remarkable process by which alcohol 

 and sulphuric acid react to form ether. He says, 1 " We are 

 forced to admit that in an aggregate of molecules of any com- 

 pound there is an exchange constantly going on between the 

 elements which are contained in it. For instance, a drop of 

 hydrochloric acid being supposed to be made up of a great 

 number of molecules of the composition C1H, the proposition at 

 which we have just arrived would lead us to believe that each 

 atom of hydrogen does not remain quietly in juxtaposition with 

 the atom of chlorine with which it first united, but on the 

 contrary is constantly changing places with other atoms of 

 hydrogen, or what is the same thing, changing chlorine. Of 

 course this change is not directly sensible to us, because one 

 atom of hydrochloric acid is like another ; but suppose we mix 

 with the hydrochloric acid some sulphate of copper (of which the 

 component atoms are undergoing a similar change of place), the 

 basylous elements, hydrogen and copper, do not limit their 

 change of place to the circle of the atoms with which they were 

 at first combined, the hydrogen does not merely move from 



1 Quarterly J. Chem. Soc., vol. 4, p. 111. 



