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 witli 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 coming here conspicuously into play. Thus ill a variety 
