110 Mr. Joule on the Intermittent Character of the Voltaic 



specimens of iron and steel I could not succeed at all, whilst 

 with a piece of rectangular iron wire a quarter of an inch broad 

 and one-eighth of an inch thick, I was able to obtain intermit- 

 tent effects when using a battery consisting of two, three, four 

 and even five cells of Daniell. In this case the negative elec- 

 trode was a plate of platinized silver, the solution consisted of 

 six parts of water to one of strong oil of vitriol, and a dia- 

 phragm was employed in order to prevent the hydrogen rising 

 from the negative electrode from troubling the liquid in con- 

 tact with the positive iron. The results of the experiments 

 are given in the Table below, the second and third columns 

 of which give the deflections of the needle during the passive 

 and the active states of the iron, whilst the fourth contains the 

 difference between the currents observed in the two states. 



In each of the four instances given in the table, the differ- 

 ent states succeeded each other at intervals of about half a 

 minute; and it was uniformly observed that the active state 

 was assumed with greater suddenness than the passive. It 

 will be seen also on inspecting the table, that, as might have 

 bsen anticipated from theory, the difference between the cur- 

 rents flowing in the different states is nearly a constant quan- 

 tity. ' 



On repeating my old experiments with a positive electrode 

 of amalgamated zinc, I find that whenever a battery of six or 

 ten large cells is connected with a plate of amalgamated zinc 

 immersed as a positive electrode in a dilute solution of sul- 

 phuric acid, the curious phaenomenon already adverted to 

 occurs. It commences at the bottom and edges of the amal- 

 gamated zinc, and generally goes on extending until the whole 

 surface is under its influence : the amalgamated zinc loses its 

 brightness in consequence of a white shade overspreading its 

 surface and giving it the appearance of frosted silver; this is 

 hardly formed before it suddenly disappears, and then a new 

 shade overspreads the surface only to vanish again as suddenly 

 as the one which preceded it. These alternations generally 

 succeed each other very rapidly, but I have sometimes seen 

 them occur at intervals of five seconds or more, and then I 



