264 



DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



platina, produce no discharge of the electricity, nor cause any diminution of the 

 power of the trough. This is a necessary consequence of the resistance to the passage 

 of the current which I have shown occurs at the place of decomposition (1007. 1011.); 

 for that resistance is fully able to stop the current, and therefore act as insulation to 

 the electricity of the contiguous plates, inasmuch as the current which tends to pass 

 between them never has a higher intensity than that due to the action of a single pair. 



1 122. If the metal surrounding the zinc be copper (1045.), and if the acid be nitro- 

 sulphuric acid (1020.), then a slight discharge between the two contiguous coppers 

 does take place, provided there be no other channel open by which the forces may 

 circulate ; but when such a channel is permitted, the return discharge of which I 

 speak is exceedingly diminished, in accordance with the principles laid down in the 

 eighth series of these Researches. 



1123. Guided by these principles I was led to the construction of a voltaic trough, 

 in which the coppers, passing round both surfaces of the zincS;, as in Wollaston's 

 construction, should not be separated from each other except by an intervening thick- 

 ness of paper, or in some other way, so as to prevent metallic contact, and should thus 

 constitute an instrument compact, powerful, economical, and easy of use. On ex- 

 amining, however, what had been done before, I found that the new trough was in 

 all essential respects the same as that invented and described by Dr. Hare, Professor 

 in the University of Pennsylvania, to whom I have great pleasure in referring it. 



1124. Dr. Hare has fully described his trough*. In it the contiguous copper 

 plates are separated by thin veneers of wood, and the acid is poured on to, or off, 

 the plates by a quarter revolution of an axis, to which both the trough containing 

 the plates, and another trough to collect and hold the liquid, are fixed. This arrange- 

 ment I have found the most convenient of any, and have therefore adopted it. My 

 zinc plates were cut from rolled metal, and when soldered to the copper plates had 

 the form delineated, fig. 1 . These were then bent over a gauge into the form fig. 2, 

 and when packed in the wooden box constructed to receive them, were arranged as 

 in fig. S-f-, little plugs of cork being used to keep the zinc plates from touching the 



Fig. 2. Fig. 3. 



/i 



copper plates, and a single or double thickness of cartridge paper being interposed 



* Philosophical Magazine, 1824, vol. Ixiii. p. 241 ; or Silliman's Journal, vol. vii. See also a previous 

 paper by Dr. Hare, Annals of Philosophy, 1821, vol. i. p. 329, in which he speaks of the non-necessity of in- 

 sulation between the coppers. 



t The papers between the coppers are, for the sake of distinctness, omitted in the figure. 



