No. v.] APPENDIX. 167 



The form wHoh is most suitable for the battery appears to me a 

 matter of fancy rather than of importance — one circumstance alone being 

 requisite ; that is, if we are desirous of obtaining the greatest power with 

 the utmost economy of silver, it is requisite that every portion of silver 

 should be opposed to a piece of zinc, but the size of the latter, within 

 moderate limits, is but of little consequence.* Thus, if we use the many- 

 celled porcelain trough, it is better to sun-ound the silver by zinc in the 

 same way as the copper surrounds the zinc in the old WooUaston battery. 

 If the circulai- form be adopted, a piece of zinc should be placed in the 

 interior as weU as the exterior of the cylinder, as by that means both sur- 

 faces of the silver are brought into action; if the Oruikshanks be adopted, 

 one surface is necessarily lost, but in this case plated copper answers 

 sufSciently well, as the edges are sunk into the cement which, if exposed as 

 in the other forms, are apt to have a portion of the copper dissolved, which 

 is again deposited on the silver, and is liable to become oxidized and be 

 detrimental to the power of the battery. The closer the zinc can con- 

 veniently be brought to the other metal, the more favourable will it be. 



Whichsoever form is adopted, the power will depend on the series and 

 size of the plates. For decomposition of water and most other purposes, 

 it IS better to have twelve pairs of plates and then to increase their size. 

 The battery having twelve 5 -inch plates, which was exhibited to the Com- 

 mittee of the Society of Arts, gave off fifteen cubic inches of mixed gas in 

 the first minute, and showed great calorific power by immediately burning 

 stout steel music wire. 



The duration of the action of the battery will depend, Kke a fire, upon 

 the quantity of fuel supplied to it in the first instance, for, as there is no 

 local action, it follows that the solution of the zinc will be exactly propor- 

 tionate to the power produced ; and for this reason, when the battery is 

 required to continue in operation for a long period, as in the method 

 which I detailed elsewhere for the production of electrotypes, a larger 

 receptacle for acid should be employed, or a contrivance can easily be 

 adopted to cari-y off gradually, by means of syphon tubes, the saturated 

 solution of sulphate of zinc, whilst at the same time dilute acid is supplied 

 from another tube. 



A galvanic battery thus constructed owes its increase of power to the 

 mechanical evolution of the gas ; and as the experiments of Faraday have 

 shown that the source of power in any voltaic pile is chemical action, I 

 have ventured to call my form of apparatus the " Ohemico-Mechanical 

 Battery." 



To those versed in electrical science it may be needless to mention 

 that, this form of battery simply increasing the quantity of electricity, it 

 is most important that large communications and large wires should be 

 used in its construction, or else the whole of the additional power might 

 be lost.t 



The advantages of the Ohemico-Mechanical Battery are, the cheap- 



* It is of great disadvantage to employ the zinc too small, as a simple rod to 

 a large cylinder of silver. A certain quantity of zinc seems absolutely necessary 

 to elicit the full power of this arrangement. 



t This I have actually known to be the case ; the power of the battery being 

 almost destroyed by the use of small wires and small connexions. 



