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LECTURE VIII.

In my third lecture of the present course, I havebrought forward those experiments of Creve andFabroni, in • which the decomposition of water andother chemical phenomena were displayed ; and as weare now about to enter the interesting field of electro-chemistry somewhat extensively, for the purposeof exhibiting to you the treasures which it contains,and examining them minutely, it will be necessarythat your attention be again directed to those beautifulexperiments, in which the first germs of this divisionof our subject were developed ; a division of Gal-vanism, which, in its present state of cultivation,assumes such an immense degree of importance inexperimental philosophy, as justly to entitle it to thedignity of a distinct branch of science.

In the experiments of Creve and Fabroni, themetals that were employed had contact with eachother below the surface of the water; but it is nowwell known that it is a matter of no consequencewhether the metals, constituting a Galvanic pair,touch each other below, or above, the surface of thewater; the result, as far as its character is concerned,will be precisely the same in both cases. If, forexample, we take a slip of zinc, made perfectlybright, and also a slip of copper, and bend the latterin such a manner that it shall hang freely on theupper end of the former, without touching any otherpart of it; and place this Galvanic pair in a glassvessel, containing pure water, in themanner represented by fig. 50, the elec-tro-chemical action will immediatelycommence, and in a short time a streakof black oxide will appear on the zincsurface, directly opposite to the vicinaledge of the copper, as far as both areimmersed below the surface of the water,showing that the metallic contact on theoutside of the water is as efficient, for

Fig. 50.