Decomposition of Water by the Galvanic Batterij. 89 



zinc plate is an inch broad and 4 inches long. The coil, when 

 made to follow the needle, drives it always before it, so that the 

 needle will never remain parallel to the coil. Hence, in Pouillet's 

 sine galvanometer, in which the centre of the needle is in the 

 centre of the coil, only feeble galvanic currents can be measured. 

 But by sliding the compass-box and needle to 2 or 3 feet from 

 the coil, a current of very great power may be measured. A 

 current which produces a deflection of 75° when the needle is in 

 the centre of the coil, will produce a deflection of only 3° when 

 the needle is at a distance of 3 feet from the coil and its centre 

 in the axis of the coil. Hence, by our galvanometer, in which, 

 and in which alone, the needle may be moved to a distance from 

 the mahogany circle or coil whilst its centre is in the axis of the 

 coil, currents of enormous power may be measured. With this 

 galvanometer I expect to determine, — first, the smallest number 

 of circles the currents of which will be fully effective, or at least 

 as efi'ective as any larger number of galvanic circles in decom- 

 posing water, and consequently the number which may be used 

 with the greatest advantage in decomposition ; secondly, whether 

 Mr. Faraday's law, viz. that the quantity of the mixed gases 

 produced by a voltaic current is proportional to the quantity of 

 electricity which passes, holds for currents of great power; 

 thirdly, the proportion which the surface of the decomposing 

 plates should bear to the acting surface of zinc in each circle ; 

 fourthly, whether a battery with a given charge will work longer 

 in producing the lime light by decomposing water than in pro- 

 ducing the coke light, and which of the two lights is the more 

 oeconomical. 



To determine the smallest number of cells of the cast-iron 

 battery which are as effective as any larger number in decom- 

 posing water, I measured the quantity of the mixed gases pro- 

 duced in two minutes by 3, 4, 5, 6 and 13 cells, and also the 

 deflection of the needle produced by the current from each bat- 

 tery when it passed through a solution of carbonate of soda in 

 which there was about an ounce and a half of soda to each quart 

 of water *. From the steadiness of the needle, it was evident that 

 the current from each battery was perfectly constant during the 

 two minutes it was allowe'd to act. The quantity of the gases 

 produced by 3 cells was less than three-fourths of the quantity 

 produced by 4, and less than half the quantity produced by 6. 

 Hence 3 cells arc not as efi'ective as 4, 5 or 6. The quantity 

 of the gases produced by 3 cells was sensibly less in proportion 

 to the sine of the angle of deviation shown by the sine galvano- 



* The quantities of the gases produced by 1 or 2 cells were so small, 

 compared with that which was produced by .3 or 4, that I did not mcasm-e 

 them. 



Phil. May. S. 4. Vol. 7. No. 43. Feb. 1854. H 



