GALVANISM. 



given to the effects of these combina- 

 tions of a single metal with two fluids, 

 by a disposition of the plates similar to 

 the trough of Cruickshanks, with par- 

 titions alternately of metal and of horn 

 or glass; and with the cells filled al- 

 ternately with the different solutions, 

 according to the kind of combination 

 employed ; these fluids being connected 

 in pairs with each other, by slips of 

 moistened cloth, carried over the non- 

 conducting plates. 



(85.) Efficient galvanic circles may 

 also be formed with a single metal and 

 with the same fluid solvent, (an acid, 

 for example,) provided the action of 

 the latter is different on the two sides 

 of the metal, by being of different de- 

 grees of strength. Thus, if one of the 

 branches of a tube, bent in the form of 

 a V, contain concentrated sulphuric 

 acid, while the same acid in a diluted 

 state occupies the other branch, in which 

 case the two fluids will, on account 

 of the difference in their specific gra- 

 vities, remain without mixing with each 

 other; and two portions of the same 

 metal, zinc for instance, be then im- 

 mersed in these fluids, and made to 

 communicate with each other, galvanic 

 electricity will be evolved, and deter- 

 mined from the metal to the diluted 

 acid, in consequence of the action of 

 this portion of acid upon the zinc being 

 greater than that of the concentrated 

 acid. But with those metals, which are 

 more acted upon by the latter than by 

 the former, the influence of the concen- 

 trated acid will preponderate, and the 

 current will be determined in an op- 

 posite direction. In like manner it has 

 been observed, that two solutions of 

 common salt, the one concentrated, the 

 other diluted, form a galvanic circle 

 with copper; that metal being more 

 acted upon by the latter than by the 

 former, became negative to the one 

 and positive to the other.*" 



(86.) The application of these princi- 

 ples will explain a variety of apparently 

 anomalous facts, which are continually 

 presenting themselves in the course of 

 experimental researches. Sir H. Davy 

 observed, for instance, that when two 

 pieces of the same polished copper were 

 introduced at the same moment into the 

 same solution of hydro-sulphuret of pot- 

 ash, there was, as might be expected, no 

 action ; but if they were introduced in 

 succession, there was a distinct, and 



* Becquerd, Annalcs de Chimie et de Physique, 

 xxxv. 120. 



often, if the interval of time was consi- 

 derable, a violent electrical effect; the 

 piece of metal first plunged in being ne- 

 gative with relation to the other. This 

 is owing to the rapid formation at the 

 surface of contact of sulphuret of cop- 

 per, which, by its presence, prevents, or 

 at least diminishes, the further action of 

 the fluid ; the clean surface of the plate 

 last introduced is therefore attacked 

 comparatively with greater force, and 

 determines a galvanic effect.* Many 

 singular and apparently capricious 

 changes of electric states occur in these 

 and other experiments of the same kind, 

 whenever new substances are produced 

 by the chemical action, which at first 

 adhere to the metal, but are liable to 

 be detached in smaller or larger por- 

 tions, and thus occasion sudden altera- 

 tions in the conditions of the galvanic 

 elements. 



(87.) Having thus seen how, under 

 certain circumstances, it is possible to 

 form various galvanic combinations 

 with a single metal and a single fluid, it 

 remains for us to notice the attempts 

 that have been made to produce the 

 same effect without the aid of any me- 

 tallic substance, or even of charcoal. 

 Lagrave announced that by placing upon 

 each other alternate layers of muscle 

 and of brain, from a human body, with 

 pieces of moistened cloth or leather in- 

 terposed, he formed a pile which pro- 

 duced galvanic effects/!- Dr. Baconio, 

 of Milan, composed a galvanic pile en- 

 tirely of vegetable substances : namely, 

 discs of red beet-root, two inches in 

 diameter ; and discs of walnut-tree, of 

 the same size, divested of their resin by 

 digestion in a solution of cream of tar- 

 tar in vinegar. With a pile so con- 

 structed, and with a leaf of scurvy- 

 grass as a conductor, he is said to have 

 excited galvanic convulsions in a frog.$ 

 Aldini also succeeded in producing the 

 same effect without the intervention of 

 any metallic substance ; sometimes by 

 bringing into contact the nerve of one 

 animal with the muscle of another, and 

 at other times by employing the nerves 

 and muscles of the same animal. In 

 some of his experiments the most pow- 

 erful contractions were excited, .by 

 bringing the parts of a warm-blooded 

 animal into contact with those of a cold- 

 blooded animal. On introducing, for 



* Philosophical Transactions for 1826, p. 393. 

 t Journal de Physique, Ivi. 235 ; and Nicholson's 

 Journal, v. 62. 

 $ NicJwlsvu's /0Kr/a/,.xviii. 159. 



