112 Mr. Joule on the Intermittent Character of the Voltaic 



of inactivity and so to produce the electrolysis of water by the 

 following means : — 



1st. By putting the negative electrode in contact, for a 

 moment, with the positive electrode of iron. The instant they 

 are separated again a lively disengagement of hydrogen from 

 the negative electrode takes place, which, however, soon begins 

 to diminish, and ceases entirely at the end of some seconds. 



2nd. By opening the circuit of the pile for some instants. 

 When it is closed again a lively disengagement of gas takes 

 place upon the negative electrode, which is soon succeeded by 

 the state of inactivity. 



3rd. By putting the immersed portion of the positive elec- 

 trode of iron in contact with an oxidable metal, as, for example, 

 zinc, tin, copper, or even silver. But in this case the disen- 

 gagement of hydrogen from the negative electrode does not 

 last longer than some seconds. 



4th. By establishing a communication between the two 

 mercury cups for a few moments, by means of a copper wire 

 three inches long and half a line thick. Then, the moment 

 the wire is removed again, a lively disengagement of hydrogen 

 takes place on the negative electrode, which does not however 

 last longer than a few seconds. 



5th. By briskly agitating that portion of the positive iron 

 electrode which is immersed in the liquid, but without break- 

 ing the circuit. 



Passing a variety of other interesting observations in Schcen- 

 bein's memoir, we come to that part of it which is most inti- 

 mately connected with our subject. At p. 278 of the Archives 

 he states, that when a communication is established between 

 the mercury cups by means of a wire of a certain length, there 

 succeed each other, at certain intervals, a lively disengage- 

 ment of gas on the negative electrode, and a time of cessation 

 of the electrolysis in the cell of decomposition. He observes 

 also, that after some time the alternations cease, and the posi- 

 tive iron electrode takes a permanent inactivity. 



My own experiments on the intermittent states of a positive 

 electrode of iron differ from the prior experiments of the phy- 

 sicist of Bale with regard to the intensity of the pile employed. 

 His was a powerful single pair (Grove's?), mine was a series 

 of from two to five cells of Daniell. Hence, when the passive 

 state was assumed by the iron in Schcenbein's experiments, 

 the current was entirely cut off, because the battery used by 

 him had not sufficient intensity to produce the electrolysis of 

 water, except where the oxygen liberated could enter into 

 combination with the positive metal. But in consequence of 

 the intensity of the battery employed in my own experiments, 



