The only mystery we observe in these experiments is the liberation of the hy drogen, in a situation where no oxygen is manifested, either in the form of gas, or in any other state. Nor does the new doctrine, lathly advanced by Mn-Davy, throw much light on this subject. The zinc, in this experiment, is said to be po sitively electrified, and the copper or sil ver to be negative. That the zinc, on that account, attracta the oxygen of the water, and the silver the hydrogen. That the constituent parts of water are by the same law made to appear in situations where the decomposition did not take place, is very evident ; hence it would appear that the hydrogen is carried by some means from the zinc to the silver ; or that the oxygen passes from the silver to the zinc; or, according to Mr. Davy's hypothesis, the decomposition ofthe water takes place between the metals, the oxygen passing inevitably to the zinc, and the hydrogen in a similar way to the silver. To the latter there are several objections, which will appear from the following experi ments.
Let a tube of three feet in length be filled with dilute muriatic acid, and cork ed at both ends, having a wire of zinc inserted in one end, and one of silver or platina in the other. The zinc will im mediately begin to give out hydrogen, but no effect will be observed at the sil ver wire. Let a communication be esta blished between the wires on the outside of the tube. The silver does not imme diately give out bubbles, as was the case in the experiments of Dr. Wollaston, nor does that effect take place till a few se conds after the contact of the metals. Can we for a moment suppose that the slight negative and positive electricity produced by the contact of two small wires, which would not affect the most delicate electrometer, can have the pow er, the one of attracting oxygen, and the other hydrogen, at the distance of eigh teen inches, reckoning from the middle of the tube ? Ifthe same tube be bent in the middle to an acute angle, like the letter V, ac cording to Mr. Davy's hypothesis, the appearance of the hydrogen at the silver wire ought to take place as soon after the contact, as with the straight tube ; but what is very singular, it will not take place at all. This experiment would seem to prove, that one of the constitu ents of the water is carried through the whole length of the tube ; and that by some law which differs from those of elec tricity, since the angle of the tube appear ed to interrupt its passage. The interrup tion is still greater, even with a shorter tube, when the tube is bent in different places, forming a sort of zig-zag.
The idea that hydrogen is carried from the zinc to the copper-wire, is strongly favoured by another experiment. Take the glass tube A B, fig. 2, filled with di lute muriatic acid, having a cork at B, through which the wires, z and c are passed, z being a wire of zinc, and c a wire of platina, silver, or copper. So long as the wires remain unconnected at z, the platina-wire appears unchanged ; but as soon as the contact is formed, bubbles of hydrogen are first seen at d; they then very slowly begin to appear in the lower parts of the wire ; but what is singular, the moment they begin to appear atf, they are also seen at a, and some seconds are elapsed before any bubbles are seen at g. If the hydrogen in the last experi
ment were attracted by the negative state of the platina-wire, since the metal is the best conductor, it would seem, that the point s would be the last part to have parted with its electricity; and, of course, the bubbles of hydrogen ought to have appeared the last at that point, whicn is contrary to fact. It therefore appears more likely that the hydrogen has been held in combination by the elec tricity, the latter of which is taken by the nearest metallic conducter in the circuit, leaving the hydrogen in its gaseous form: the law, however, by which it moves along the liquid, does not appear to agree with any known properties of electricity, since the hydrogen is some seconds in reaching the point ,g.
It will appear from the above experi ments, that the galvanic phenomena are essentially promoted, by having two me tallic surfaces so situated that one shall be oxydated, and that the other shall be situated as near it as possible, for the purpose of receiving its electricity. We have shewn, that the current is not only interrupted by distance,"but that it is essential the passage should be a direct line.
In Dr. Wollaston's experiments, when the wires were placed in a metallic solu tion, such as that of copper and silver, and the contact formed between the zinc and silver wires, no hydrogen was evolv ed by the latter, the contrary of which was the case with the dilute acid ; but the metal in solution became reduced upon the silver.
There does not appear any thing mys tefious in the reduction of the metal, since the hydrogen does not appear, be ing employed in the cleoxydation of the metal. A further proof that this is the case is, that no other metals can be re duced in this way but such as do not de compose water. This singular process enables us to account for several facts which have hitherto appeared anomalous. If a glass plate be smeared over with a solution of nitrate of silver, and a com mon pin be laid in the middle of the plate, beautiful ramifications of metallic silver will soon appear, as if vegetating from the pin. If the process be examined by a magnifying glass, the ramifications of silver may be fairly seen to grow from their ends. Though the more oxydable metal, the pin, may, in the first instance, have reduced a portion of silver, it does not account for the vegetative appear.. ance which is afterwards observed. The pin cannot reduce the silver at so great a distance from itself, which is sometimes more than an inch. In order to prove, that the agency of the oxydable metal was not essential to the reduction of the metal, the writer of this article covered one half of the plate with liquid nitrate • , of silver, and the other half with dilute muriatic acid, suffering the liquids to touch each other ; a wire of zinc was laid in the dilute acid, and one of pla tina in the nitrate of silver. As soon as the opposite ends of the wires were brought in contact, beautiful ramifica tions of silver soon began to appear from the platina wire, but no gas was ob served.