54 
a small portion of copper is dissolved, and then precipitated 
on the zinc, producing so much local action that more of the 
zinc is wasted than is effectively consumed ; so that we can 
scarcely make any calculation of the comparative cost of 
such battery. It is, without doubt, the most expensive to 
maintain. And in the combination of copper and zinc, 
although the resistance is at first slight, the copper is soon 
covered with adherent bubbles of hydrogen gas, which 
materially increase the resistance, and, to a considerable 
extent, throw the copper surface out of action. 
When platinized silver is substituted for copper, which 
constitutes Mr. Smee's arrangement, the improvement is very 
great. There is then no difficulty in maintaining the amal- 
gamation in a good state, and avoiding local action for a 
considerable period ; and the peculiar action of the deposited 
platina prevents the great accumulation of hydrogen, which 
stops the action when a smooth metallic surface is used ; so 
that the average quantity of current may be estimated as 
about three times the amount given by simple copper and 
zinc, after the effect of first contact has subsided. And the 
intensity being taken, as represented, by 5.5, we will suppose 
that a certain number of plates are required for a given 
purpose ; for instance, to produce the electric light between 
the points. To do this with the platinized silver battery, 
100 pairs of plates would be required; and to produce a 
required light, the consumption of zinc in each cell is 
one grain per minute, or sixty grains per hour. Then 
60 X 100 = 6,000. Let us take the price of amalgamated 
zinc at 6d. per pound, which I consider about correct, if the 
mercury be partially recovered after the plates of zinc are 
used. 32.3 atoms of zinc take 8 atoms of oxygen (which, 
being derived from water, cost nothing,) and 40 atoms of 
sulphuric acid. As the sulphuric acid of commerce contains 
about one-fourth of its weight of water, and as the acid 
