DERIVATION OF GALVANIC FORCE, 73 



its quantity is very considerable, and constitutes, indeed, the 

 entire dynamic energy we have at our disposal in the galvanic 

 battery. 



(77.) When the zinc and platinum plates of the battery 

 communicate freely with each other, the combination-heat of the 

 attacked zinc is manifested solely by a rise of temperature in the 

 contents of the cell, precisely as in. the case we have just consi- 

 dered of the simple solution of granulated zinc in hydrochloric 

 acid. But the battery is a machine for enabling us to apply and 

 transform this combination-heat of the zinc in a variety of ways. 

 For instance, if I complete the communication between the zinc 

 and platinum plates by means of a platinum wire, you observe 

 that the small coil of wire assumes an intense state of ignition. 

 Now, the heat of this platinum wire is nothing more than a por- 

 tion of the translated heat of the zinc burning in the cell ; which, 

 instead of being manifested at the point of action in the cell, is 

 manifested at a distance in the wire ; much as a portion of the 

 furnace heat absorbed in the evaporation of water may be mani- 

 fested at a distance by the friction of a drill. The heat exhibited 

 by the platinum wire does not originate in the wire, but in the cell, 

 and so much of the heat of the burning zinc as appears in the 

 wire is lost to the cell. Just as the contracting muscle strikes 

 its blow at a distance of many yards by means of the conducting 

 javelin, so does the burning zinc strike its blow at the spot whereto 

 it is conducted by the copper strands. 



(78.) In electro-motive machines, the heat of the burning 

 zinc is employed in doing mechanical work, just as the heat of 

 burning coal is employed, though with far greater economy, in a 

 steam-engine. But in the decomposition of water taking place 

 upon the table, the heat of the burning zinc is employed in the 

 chemical work of pulling oxygen and hydrogen apart from one 

 another. Of the heat producible by the combustion of a given 

 weight of zinc, the proportion manifested externally in the 

 ignition of platinum wire, or employed externally in the separa- 

 tion of oxygen and hydrogen, is supplemental to the quantity 

 absorbed in heating the cell ; so that in the electrolysis of water, 



