KEVISIONS OF THE THEORY OF ELECTROLYSIS. 149 



tell against Volta's contact theoi\y of the electromotive force of a 

 voltaic cell. Yolta himself asserted that the chemical actions going 

 on in a voltaic cell have practically no essential significance. 



In this same celebrated year of 1800 Cruikshank decomposed lead 

 acetate between silver wires. A minute or two after connection was 

 made he observed lustrous metallic lead crystals on the negative 

 electrode, while gas was released at the positive. Cruikshank called 

 attention to the fact that only liquids containing oxygen conduct 

 electricity, and he appears to have concluded that electricity seizes 

 on the oxygen and transports it invisibl}^ to the positive pole. Not 

 so far removed from this conception is the present view that the 

 oxygen conveys an electric charge rather than that the charge con- 

 veys the ox3'gen. 



The separate appearance of the two products of decomposition at 

 the electrodes was the most noteworthy, and at the same time the most 

 inexplicable fact of electrolysis to all the chemists and physicists of 

 the day. An unknown correspondent in Nicholson's Journal ex- 

 pressed himself as follows : 



I should like to inquire how it can happen in any system that the two com- 

 ponents of water can be caused to appear at such a distance from each other. 

 Does the hydrogen from the dissociated particles of water at the zinc side of 

 the pile fly from it at the instant when the oxygen is liberated there? If that 

 is so, why does not one see the gas bubbles on the way? Or does the oxygen 

 migrate from the silver side to the zinc side? Or are there two streams at 

 once? 



It should be remembered that Volta attached an extra zinc plate to 

 the silver at the positive end and an extra silver plate to the zinc at 

 the negative end, both in the case of his dry pile and crown of cups 

 or voltaic batter3^ Hence, in the early literature the zinc side means 

 the positive and the silver the negative. 



Sir Humphry Davy was early in the field of electric research, and at 

 once distanced all his English confreres by the number and importance 

 of his detail discoveries. In particular at the outset he obtained oxygen 

 and hydrogen in dilferent tubes separated in the circuit by the inter- 

 position of his own person as a conductor, and he proved conclusively 

 that the two gases are evolved in the same relative proportion in 

 which they exist as elements in water. But Sir Humphry Da\'y 

 added little to the theory of electric action in electrolysis. Near the 

 close of one of his papers published in December, 1800, he remarks : 



On these facts I shall not presume to. speculate * * *. Many obser- 

 vations must be collected, probably, before we shall be able to ascertain whether 

 water is decomposed in galvanic processes. Supposing its decomposition, we 

 must assume that at least one of its elements is capable of rapidly passing in 

 an invisible form through metallic substances, or through water and many 

 connected oi'gauic bodies, and such an assumption is incommensurable with 

 all known facts. But a short period has elapsed since philosophers beheld 



