GALVANISM. 



13 



order to exhibit these effects, the me- 

 tallic leaves .should be suspended to a 

 bent wire proceeding from one extre- 

 mity of the battery, and then a broad 

 metal plate connected with the opposite 

 extremity should be gradually brought 

 near to them till contact is produced. 

 The brilliancy of the effect is heightened 

 by covering the plate with gilt foil. 

 Gold leaf, thus treated, burns with a 

 vivid white light tinged with blue, and 

 produces a dark purple or brown oxide. 

 Silver leaf gives out a brillant emerald 

 green light, and leaves an oxide of a 

 dark grey colour. Copper produces a 

 bluish white light, accompanied with 

 red sparks ; its oxide is dark brown. Tin 

 exhibits nearly the same phenomena, 

 excepting that its oxide is of a lighter 

 hue. Lead burns with a beautiful pur- 

 ple light ; and zinc with a vivid white 

 lighCinclining to blue, and fringed with 

 red. For the distinct appearance of 

 these colours, it is necessary that the 

 contacts should be made with a metal, 

 and not with charcoal ; for the intense 

 white light emitted by the latter, would 

 overpower the peculiar colours arising 

 from the combustion of the metal.* 



(35.) A beautiful effect, noticed by 

 Van Marum, is produced by connecting 

 a slender iron wire with one of the poles 

 of a powerful voltaic battery, and bring- 

 ing its end in contact with the surface 

 of some mercury connected with the 

 other pole. Vivid combustion takes 

 place both in the mercury and in the 

 wire ; giving rise to an abundant emis- 

 sion of sparks, and appearing like a star 

 or sun dispersing thousands of rays on 

 every side. TmV splendid spectacle may 

 be prolonged at pleasure, by taking care 

 to continue the depression of the iron 

 wire, in proportion as the metallic par- 

 ticles are dispersed by the combustion. 



(36.) Inflammable bodies, such as 

 oils, alcohol, ether, and naphtha, are 

 easily inflamed by means of galvanism, 

 when charcoal points in the circuit of 

 the battery are brought near each other 

 on the surface of these fluids ; and gun- 

 powder may readily be made to explode 

 under the same circumstances. 



(37.) The difference in the operation 

 of voltaic and ordinary electricity is 

 very manifest in their mechanical effects. 

 The forcible separation of the particles 

 of bodies, and destruction of their cohe- 

 sion, characterize more especially the 

 electrical explosion, in which the fluid 



* Singer's Elements of Electricity, p. 408. 



appears to force for itself a passage 

 through every obstacle ; while the heat 

 which occasionally manifests itself dur- 

 ing this sudden effect, seems as if it were 

 merely the effect of the compression and 

 collision of the particles which are thus 

 forcibly impelled. But the elevation of 

 temperature which accompanies the 

 passage of voltaic electricity, on the 

 contrary, appears to be its immediate 

 and direct effect; for the mechanical 

 texture of the substance which conveys 

 the electricity remains unaltered. If 

 electricity in its common form possess 

 any power of igniting bodies, its opera- 

 tion is too transient and momentary to 

 produce any extensive effect ; and its 

 tendency is rather to separate and dis- 

 perse the body into minute fragments, 

 than to unite the particles into globules 

 by fusion. We have seen that charcoal 

 is very readily ignited by galvanism, but 

 it will sustain a strong discharge from 

 an electric battery without any percepti- 

 ble rise in its temperature; nor is it 

 possible to ignite it by this means. 

 Whether reduced to fine powder, or cut 

 into thin plates, or made to taper to a 

 point, it resists all attempts to raise it to 

 a red heat, or even to impart to it any 

 sensible warmth, though subjected to 

 the action of the most powerful battery 

 that has yet been tried. Even when an 

 apparently continuous stream of electri- 

 city, obtained from a large electrical 

 machine, was made to pass through 

 pointed wires coated with spermaceti, no 

 part of the spermaceti was melted. 



4. Electro-Magnetic Effects of Gal- 

 vanism. 



(38.) We must rank among the more 

 remarkable of the physical effects pro- 

 duced by the transit of voltaic electricity 

 through conducting bodies, the induc- 

 tion ot magnetism in iron, and the influ- 

 ence exerted on bodies which possess 

 magnetic properties. But as the study 

 of the connections which subsist between 

 these phenomena implies a previous 

 knowledge of magnetism, and consti- 

 tutes, indeed, a distinct branch of 

 science, it will be proper to reserve their 

 consideration for a future treatise. It 

 may be as well, however, to remark 

 in this place, that the discovery of the 

 electro-magnetic effects of galvanism 

 have furnished us with the most delicate 

 tests for detecting very minute portions 

 of voltaic electricity, so that many of the 

 results of simple galvanic arrangements, 



