50 Self-sustaining Voltaic Battery. 
in one place than in another, might evolve the hydrogen; but 
fortunately having a most perfect polish, it binds the hydrogen 
oit, This action of the polished metal we will consider 
presently. 
But as the consumption of the zinc goes on, the impurities ac- 
cumulate on the surface, and project so far that the mercury can- 
(a depth of ;';th of an inch) will leave the impurities projecting 
so far that the quantity of mercury which can adhere to the zine 
when in a vertical position, cannot prevent violent chemical ac- 
tion in the minute galvanic circles. But the zinc known in com- 
merce as the “ Musselman’s”’ is so easily protected that I find the 
corrosion may go to the depth of one-fourth of an inch, and th 
mercury still be efficient when flooded over the surface. Here, 
then, is the answer to the question as to how far the zinc plate 
may be protected or efficiently amalgamated by standing it in a 
flood of mercury. If the plate is not to be dissolved to a very 
great depth, the good commercial zinc will be sufficiently pro- 
tected ; but for a longer time the zine should be redistilled, and 
fora very long time nothing but chemically pure eae should » 
employed. Practically I find that the “ Musselman 
From what has been said concerning the action of the i impuri- 
ties of the zinc, it will be perceived that if any carbonaceous 
matter falls on the battery, it may attach itself to the zinc, and 
thus rapidly destroy the voltaic conditions by consuming the ma- 
terials; since the evolution of hydrogen would continue while 
there remained zinc to be oxydized, acid to dissolve the oxyd, 
and water to dissolve the salt. This shows the necessity of a 
box to prevent currents of air from sweeping over the battery; 
for even the dust which subsides from the atmosphere, may set 
up the destructive action. 
From the same kind of reasoning, it is obvious that the pres- 
ence of the least particle of any salt reducible by zinc or by hy- 
drogen should be avoided; and such a salt coming in contact 
with the zinc, wonld instantly forma conducting plate. If we 
would avoid every risk of this destructive action, the fixtures of 
the battery must not be made of a metal which can form a solu- 
ble salt with sulphuric acid. 
1all have occasion to refer again to the employment of the 
oxydable metals for the battery fixtures ; here I will merely state 
that I = found by experience that even silver is unsuital 
for when I employed a silver bar and silver pendants to hold the 
conducting plate, sulphate of silver was formed. 
