28 



GALVANISM. 



unable to obtain the same effects from 

 the calorimeter, which amply fulfils the 

 conditions of quantity and continuity. 

 The electricity which it furnishes, how- 

 ever abundant in quantity, does not 

 possess sufficient intensity to overcome 

 the obstacle presented by the smallest 

 thickness of water, or other liquid of 

 low conducting power ; and is, for the 

 same reason, incapable of penetrating 

 through the skin, or traversing through 

 any other part of an animal body. 

 Hence we can obtain from it neither 

 chemical nor physiological effects. The 

 electricity furnished by the electric 

 column of De Luc, again, though of 

 sufficient intensity to produce the shock 

 and other effects of a sudden influx, is 

 too deficient in quantity to produce 

 chemical action ; and the same general 

 observations apply to the electricity of 

 the torpedo. 



(95.) Every circumstance that faci- 

 litates the passage of the electric current 

 in all parts of the circuit, will tend to 

 increase the quantity that circulates. 

 The degree of conducting power pos- 

 sessed by the fluid parts of the circle, 

 will, therefore, have an important in- 

 fluence on the power of the apparatus. 

 Hence the addition of various saline 

 bodies to the fluid is found to increase 

 the efficacy of the voltaic battery, pro- 

 bably, in part at least, by increasing the 

 conducting power of the fluid ; but as 

 such substances generally also promote 

 chemical action, it is always in some 

 degree doubtful what part of the effect 

 is to be ascribed to the one or the 

 other of these causes. 



(96.) As the fluid element of the 

 circle is the part having the smallest 

 conducting power, the electric current 

 will be retarded by having to pass 

 through any considerable extent of fluid. 

 "With a view to augment the activity of 

 the battery, it is an object to bring the 

 two metallic surfaces of Z and C very 

 near each other, so that the distance the 

 electricity has to pass from the one to 

 the other, through the fluid, shall be as 

 small as possible ; and for the same rea- 

 son the surface of C, which collects the 

 electricity from the fluid, should be suf- 

 ficiently extensive to effect this purpose 

 completely. We hence perceive the reason 

 of the advantage derived from employ- 

 ing in the common trough battery, ac- 

 cording to the suggestion of Dr. Wol- 

 laston, a double plate of copper to each 

 plate of zinc, so that each surface of the 

 latter metal acted upon by the fluid, 



may have a surface of copper opposite 

 to it, ( 18.); and also of enveloping 

 each coil of zinc plate, in the calori- 

 motor, by a coil of sheet copper, (8.) 

 Mr. Marianini has extended this prin- 

 ciple still further, and has found that 

 the maximum of effect takes place when 

 the surface of the copper is no less 

 than eight times greater than that of the 

 zinc. 



(97.) There is yet another cause of 

 impediment to the motion of the electric 

 current of a singular kind, and which 

 produces very considerable effect. It 

 appears from the experiments of Mr. 

 Augustus De la Rive, that voltaic elec- 

 tricity, in passing out of one conducting 

 body into another of a different kind, 

 always sustains some loss of its intensity.* 

 The amount of this loss varies much in 

 different cases, according to the nature 

 of the two conductors ; and it is differ- 

 ent with different degrees of intensity. 

 In the case of the passage of the elec- 

 tricity from a fluid to a metal, or vice 

 versa, it is very great, and it is sensible 

 even when it has to pass from one li- 

 quid to another, or along a mixed con- 

 ductor composed of two different kinds 

 of solids. The impediment arising from 

 the mere change, of conductor is quite 

 independent of the peculiar conducting 

 powers of the one or the other of the 

 substances through which the electri- 

 city passes. Mr. De la Rive found, for 

 example, that a much greater obstacle 

 existed to the transmission of the elec- ' 

 tricity between sulphuric acid, especially 

 when concentrated, and platina, than be- 

 tween nitric acid and the same metal ; 

 and accordingly, on sending the electric 

 current from a voltaic battery through a 

 number of portions of sulphuric acid, 

 contained in separate glasses, and con- 

 nected by arcs of platina wire, it proved 

 to be a much worse conductor than when 

 nitric acid was employed in a similar 

 arrangement. But the conducting powers 

 of each system of compound conductors 

 were immediately rendered equal by 

 dipping the ends of the platina wires in 

 nitric acid, before immersing them in 

 the sulphuric acid.t 



(98.) In general the more readily a 

 metal is acted upon by liquid conductors, 

 the less is the diminution of intensity 

 which is sustained by the passage of 

 electric currents through them. Mr. 

 De la Rive states it to be a general 



* Annales de Chimie et de fhytique, xxx*ii. 267. 

 f Ibid. p. 2/3.; 



