Figure i6. — Laboratory battery of Daniell cells. From A. Niaudet, Electric 

 Batteries, New York, 1880, p. 86. 



ably and the potential was only 1.1 volts, this voltage 

 was so reliable and unchanging that it was used as a 

 standard up through the 1870's. A simpler version 

 of the Daniell cell, the "gravity" cell, was worked out 

 in the 1850's by Cromwell F. Varley in England and 

 by Heinrich Meidinger^' in Germany. Meidinger's 

 three forms of the Daniell cell are shown in figure 18. 

 In these later cells the different densities of the two 

 fluids prevented them from mixing. A. Callaud ^^ 

 reduced the cell to its simplest form (fig. 19), and a 

 version of this, called the "crowfoot" cell, was occa- 

 sionally seen until quite recently. The gravity cell 

 was used in the early days of telegraphy and railroad 

 signaling where there were closed circuits with a con- 

 stant but light drain on the cell. 

 William Grove '' devised another variation of a 



29 French Patent 38820, November 22, 1858; Heinrich 

 Meidinger, "Uber eine vollig konstante galvanische Batterie," 

 Annalen der Physik und Chemie (title varies, hereinafter referred 

 tD as Annalen der Physik), 1859, vol. 108, pp. 602-610. 



30 French Patent 36643, May 19, 1858. 



3' W. R. Grove, "On a Nevi Voltaic Combination," Philo- 

 sophical Magazine, 1838, vol. 13, pp. 430-431; "On a Small 

 Voltaic Battery of Great Energy; Some Observations on Voltaic 

 Combinations and Forms of Arrangement; and on the Inactivity 

 of a Copper Positive Electrode in Nitro-Sulfuric Acid," ibid., 

 1839, vol. 15, pp. 287-293. 



cell of two solutions separated by a porous diaphragm 

 (figs. 20, 21). He used zinc in dilute sulfuric acid 

 and platinum in strong nitric acid. The 1.9-volt 

 output of the Grove cell was almost double the out- 

 put of the Daniell cell, and its low internal resistance 

 enabled it to give currents as high as 10 amperes. 

 However, the Grove cell was expensive to make, and 

 it gave off highly corrosive fumes. It occurred to a 

 number of researchers ^^ to replace the platinum 

 electrode by a cheaper material, but credit for this 

 innovation is usually given to the German chemist 

 Robert Bunsen ^^ who modified the Grove cell by 

 replacing the platinum electrode with a charcoal 

 rod and by replacing the nitric acid with fuming 

 nitric acid (fig. 22). The Bunsen cell's voltage was 

 slightly less than that of the Grove cell, but its current 

 was doubled, and it was much cheaper to make. 



32 For example, J. T. Cooper, "On the Employment of 

 Carbon in Voltaic Combinations," Philosophical Magazine, 1840, 

 vol. 16, pp 35-37; and Silliman, op. cit. (footnote 9). 



33 Robert Bunsen, "Ueber die Anwendung der Kohle zur 

 Volta'schen Batterie," Annalen der Physik, 1841, vol. 54, pp. 

 417-420; "Ueber Bereitung einer das Platin in der Grove'schen 

 Kette ersetzenden Kohle," Annalen der Physik, 1842, vol. 55, 

 pp. 265-276. 



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