H& vt 





Figure lo. — Pepys' plunge battery as con- 

 structed for the Royal Institution. From 

 H. M. Noad, Student's Textbook of Electricity, 

 London, 1867, p. 168. 



Figure 1 1 . — One of the 200 plunge batteries in 

 the "Great Battery" of the Royal Institution. 

 From Philosophical Transactions oj the Royal 

 Society oj London, 1810, vol. 100, pi. Q, fig. 6. 



Robert Hare '^ tried to attack the problem on a 

 more general basis. He made what he called a 

 "calorimotor" by connecting all the copper plates 

 together and all the zinc plates together, so that 

 "instead of multiplying the pairs of galvanic plates 

 [he increased the effect] by enlarging one pair" (fig. 

 14). He further increased the area of the electrodes 

 that would fit in a given volume by rolling them up 

 in a close spiral. His "galvanic deflagrator" ^^ sim- 

 plified battery construction in the same manner as 

 had Oersted's copper trough battery. Instead of a 

 cell for each pair of elements, only one trough was 

 used. Michael Faraday, Peter Barlow, and Joseph 

 Henry all used batteries based on the construction of 

 Hare's calorimotor for their experiments. 



Due to the nullifying chemical reactions of polar- 

 ization and local action, both the trough battery 

 and the plunge battery had extremely limited lives. 

 Local action results from the use of impure metals, 

 where the impurity forms a voltaic pair with the mate- 

 rial of the electrode and prevents the affected portion 

 of the electrode from contributing to the electrical 



output of the cell. Since over half the energy, and in 

 some cases as much as three-quarters of the energy, of 

 the zinc electrode could be wasted in local action, 

 the impure zinc that was available commercially at 

 the time led to considerable inefficiency. 



Auguste de la Rive found that electrodes made 

 from distilled zinc would eliminate local action, but 

 the method was too expensive for ordinary pur- 

 poses. However, the application of mercury to the 

 zinc electrode permitted the zinc to interact with the 

 electrolyte and at the same time prevented the im- 



1' Robert Hare, "A New Theory of Galvanism, Supported 

 by Some Experiments and Observations Made by Means of 

 the Calorimotor, a New Galvanic Instrument," American 

 Journal oj Science, 1819, voL 1, pp. 413-423. 



2" Robert Hare, "A Memoir on Some New Modifications of 

 Galvanic Apparatus, with Observations in Support of His New 

 Theory of Galvanism," American Journal oj Science, 1821, vol. 3, 

 pp. 105-117. "Correspondence between Robert Hare . . . 

 and the Editor, on the Subject of Dr. Hare's Calorimotor and 

 Deflagrator, and the Phenomena Produced by Them," American 

 Journal oj Science, 1822, vol. 5, pp. 94-112. 



240 



BULLETIN 228 : CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



