GALVANISM. 



355 



common electrical experiments !>e performed by 

 means of galvanism, but it has been shown by doctor 

 Wollaston, that the chemical effects of the galvanic 

 battery may be produced by electricity. The condi- 

 tions required for producing the electrical effects of 

 the voltaic battery are different. Electrical attrac- 

 tions and repulsions take place in the highest degree, 

 when a great number of small plates are employed, 

 and the cells filled with water. For acting on the 

 electrometer, therefore, a battery of numerous small 

 plates is peculiarly suited, and common river water 

 is the best material for its excitation. For producing 

 sparks, or giving shocks, a numerous series of plates, 

 about four inches square, and excited with dilute 

 acid, is required. For burniHg metallic leaves, fusing 

 wire, and igniting charcoal, a small number of large 

 plates answer better than a great number of small 

 ones ; a strong acid solution should also be em- 

 ployed. 



3. Chemical Effects of Galvanism. The most simple 

 chemical effect of the galvanic battery is the ignition 

 and fusion of metals, which has already been alluded 

 to above. The facility of being ignited, in the dif- 

 ferent metals, appears to be inversely proportional to 

 their power of conducting heat. Hence platina, 

 which has the lowest conducting power, is most 

 easily ignited ; and silver, which conducts heat with 

 greater facility than any other metal, is ignited with 

 more difficulty than any of the rest. The combus- 

 tions produced by galvanic arrangements have also 

 been spoken of above. The plates for this purpose 

 should not be less than four inches square, and an 

 aggregate of not less than 150 pairs of plates em- 

 ployed. The metals are burnt, or rather deflagrated, 

 in the form of very thin leaves. Gold emits a very 

 vivid white light, inclining a little to blue ; the flame 

 of silver is a vivid green, somewhat like that of 

 emerald, and zinc a bluish white flame, fringed with 

 red. The most striking effect of the voltaic battery, 

 however, is the intense light, which is produced by 

 placing two pieces of charcoal, cut into the shape of 

 pointed pencils, at the two ends of the wires of an 

 interrupted circuit. When the battery is a very 

 powerful one, and the charcoal points are brought 

 within the thirtieth or fortieth of an inch of each 

 other, a bright spark is produced. By withdrawing 

 the points from each other, a constant discharge 

 takes place through the heated air, in a space of 

 from one to four or more inches, according to the 

 energy of the apparatus, producing a most brilliant 

 arch of light, of considerable breadth, and in the form 

 of a double cone. Platina, introduced into this arch, 

 melts as wax does in the flame of a candle. This 

 light equals the brilliancy of the sun, and cannot be 

 borne by eyes of common strength, unless protected 

 by glasses. That it does not arise from combustion, 

 is proved by the fact, that very little of the charcoal 

 is wasted by its continuance for some time. In the 

 use of the deflagrator, it was observed by professor 

 Silliman, that, during the discharge, the charcoal 

 point of the positive pole shot out into a little stalac- 

 tical knob, in the direction of the opposite point ; 

 while, in the charcoal of the negative pole, on the 

 contrary, a crater-shaped cavity was formed at the 

 same time, appearing as if matter was actually trans- 

 ferred from the negative to the positive side. The 

 subsequent examination of the matter thus appar- 

 ently transferred, as it had all the marks of having 

 been fused, induced the belief that the charcoal 

 passed, in the state of vapour, through the ignited 

 arch of flame, and concreted again on arriving at the 

 positive pole. 



The most important chemical effect of galvanism, 

 is that of producing decomposition. The substance 

 first decomposed by it was water. When two gold 



or platina wires are connected with the opposite poles 

 of a battery, and their free extremities are plunged 

 into the same cup of water, but without touching 

 each other, hydrogen gas is disengaged at the nega- 

 tive wire, and oxygen at the positive side. By col- 

 lecting the gases in separate tubes as they are formed, 

 they are found to be quite pure, and in the exact 

 proportion of two measures of hydrogen to one of 

 oxygen. If wires of a more oxidable metal are em- 

 ployed, the hydrogen gas will appear as usual, but 

 the oxygen, instead of escaping, combines with the 

 metal, converting it into an oxide. Numerous other 

 compounds, such as acids and salts, are found to be 

 decomposable in the same manner, one of these 

 elements appearing at one side of the battery, and 

 the other at the opposite extremity. 



A remarkable law in the circumstances attending 

 the decomposition is also observed. Tims, in decom- 

 posing water or any other compound, the same con- 

 stituent principle is always disengaged at the same 

 side of the battery ; so that the principles which 

 collect around each pole have a certain analogy ; in- 

 flammable bodies, alkalies, and earths go to the 

 negative side, while oxygen and acids go more to the 

 positive side. It is also found, that not only are the 

 elements of a compound fluid separated by galvanic 

 energy to the opposite wires in distant parts of the 

 containing vessel, without the movement of these 

 elements being perceptible, but that the elements may 

 even be evolved in separate portions of the fluid 

 placed in distinct vessels, and connected only by some 

 slight link, as a few fibres of moist cotton or amian- 

 thus. Thus two glasses may be filled with pure 

 water, and connected with moistened thread; the 

 positive wire immersed in the water in one vessel, 

 and the negative in that of the other ; and imme- 

 diately oxygen gas will be disengaged at the extre- 

 mity of the former, and hydrogen gas at the extremity 

 of the latter. Now, in this instance, it is obvious a 

 difficulty immediately presents itself in attempting to 

 account for the separate evolution of the elements. 

 If they were both produced in one vessel, it might 

 be conceived that they arose from the decomposition 

 of one portion of water, and had been attracted to 

 the opposite poles. But how can this happen in 

 separate vessels. What becomes of the hydrogen in 

 the vessel where the positive wire is placed, and why 

 does oxygen not appear in the other vessel, in which 

 the negative wire is immersed ? The only explana- 

 tion that can be given, is to suppose that one or both 

 of these ingredients must have passed from one vessel 

 to the other, along the connecting fibres of thread, 

 although we are unable to perceive such a transmis- 

 sion. 



Numerous other facts of a similar nature are also 

 now known, particularly with respect to the decom- 

 position of saline solutions. Thus, let two cups of 

 agate or gold (as glass is liable to be acted upon) be 

 connected by a few fibres of amianthus moistened by 

 water, and a solution of sulphate of soda or of potash, 

 nitrate of potash, nitrate of silver, or any other com- 

 pound salt, be placed in each of the cups. Now, if 

 we introduce into one the positive wire, and into the 

 other the negative wire, of a galvanic battery in 

 action, in a short time the principles of the salt will be 

 separated, and all the acid will be collected in the 

 vessel with which the positive pole communicates, 

 and all the base in the other ; each being conveyed 

 by the medium of the moistened amianthus, and, as 

 it would appear, in opposite currents, passing one 

 another in so narrow a space, without combining or 

 otherwise interfering with each other's movements. 

 Again, if the saline solution be placed in one of the 

 cups, and distilled water in the other, and the positive 

 wire inserted in the latter, the acid will leave both 

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