602 FRAGMENTS OF SCIENCE. 



of zinc burned in water falls short of that produced in pure 

 oxygen, the reason being that to obtain its oxygen from 

 the water the zinc must first dislodge the hydrogen. It 

 is in the performance of this molecular work that the 

 missing heat is absorbed. Mix the liberated hydrogen 

 with oxygen and cause them to recombine; the heat 

 developed is mathematically equal to the missing heat. 

 Thus in pulling the oxygen and hydrogen asunder an 

 amount of heat is consumed which is accurately restored 

 by their reunion. 



This leads up to a few remarks upon the voltaic 

 battery. It is not my design to dwell upon the technical 

 features of this wonderful instrument, but simply, by 

 means of it, to show what varying shapes a given amount 

 of energy can assume while maintaining unvarying quanti- 

 tative stability. When that form of power which we call 

 an electric current passes through Grove's battery, zinc is 

 consumed in acidulated water; and in the battery we are 

 able so to arrange matters that when no current passes no 

 zinc shall be consumed. Now the current, whatever it 

 may be, possesses the power of generating heat outside the 

 battery. We can fuse with it iridium, the most refractory 

 of metals, or we can produce with it the dazzling electric 

 light, and that at any terrestrial distance from the battery 

 itself. 



We will now, however, content ourselves with causing 

 the current to raise a given length of platinum wire, first 

 to a blood-heat, then to redness, and finally to a white 

 heat. The heat under these circumstances generated in 

 the battery by the combustion of a fixed quantity of zinc 

 is no longer constant, but it varies inversely as the heat 

 generated outside. If the outside heat be nil, the inside 

 heat is a maximum; if the external wire be raised to a 

 blood-heat, the internal heat falls slightly short of the 

 maximum. If the wire be rendered red-hot, the quantity 

 of missing heat within the battery is greater, and if the 

 external wire be rendered white-hot, the defect is greater 

 still. Add together the internal and external heat pro- 

 duced by the combustion of a given weight of zinc, and 

 you have an absolutely constant total. The heat generated 

 without is so much lost within, the heat generated within 

 is so much lost without, the polar changes already adverted 

 to Corning here conspicuously into play. Thus in a variety 



