406 



Wells's natural PHiLOSOPnY. 



In other and more efficient compound galvanic circuits, the exciting liquid 

 is placed in a series of separate cups, or glasses, arranged in a circle, or u- 

 parallel lines. Each cup contains one zinc and one copper plate, not immo 

 diately in connection with each other, but every zinc plate of one cup is coa 

 nected with the copper plate of the preceding, by a copper band, or wire. 

 This arrangement is represented in Fig. 337, the copper plate, and tlie direc- 

 tion of the positive current being indicated by the sign +, and the zinc pLita 

 and the direction of the negative current by the sign — . 



The simplest form of galvanic battery at present used i» 



attei-y. ^^^^ invented by Mr. Smee, and known aa Smee's battery 



(See Fig. 338.) It consists of a plate of silver coated with 



FlO. 338. 



FlQ. 339. 



platinum, suspended between two plates of zinc, z z, the sur- 

 faces of which last have been coated with mercury, or amal- 

 gamated, as it is called.* The three are attached to a wooden 

 bar, which serves to support the whole in a tumbler, G. par- 

 tially filled with a weak solution of sulphuric acid and water. 

 The wu-es, or poles for directing the current of electricity are 

 jonnected with the zmc and pliiinum plates by small screw- 

 jups, S and A. 



^ , Anot?.cr form of battery, called the sulphate 



wlphate of cop- of copper battery, from the fact that a solution 

 >er battery? ^j- guijijjate of copper (blue vitriol) is used a3 

 ..he exciting liquid, is represented by Fig. 339. It consists of two conceuirio 

 jylinders of copper tightly soldered to a copper bottom, 

 ind a zinc cylinder, Z, fitting in between them. The 

 'jnc cylinder, when let down into the solution, is pre- 

 /ented from touching the copper by means of tlu'oo 

 jieces of wood or ivory, shown in the figure. T>'ro 

 tcrew-cups for holding the connecting vrires are at- 

 ached, one to the outer copper cylinder, and the oiher 

 o the zinc. 



The principal imperfection of the gal- 

 vanic battery is the want of uniformity 

 in its action. In all the variois forma 

 the strength of the electric current ex- 

 cited continually diminishes from the moment the battery 

 a-'tion commences. In the sulphate of copper battery, especially, tne power 

 if reduced to almost notLirg in a comparatively brief space of time. This i» 

 '.- chiefly owing to the circumstance that the metallic plates soon become 

 ii^ated with the products of the chemical decomposition, the result af the 

 itiamical action, whereby the electricity is developed. 



This dilEculty is obviated, in a great degree, by the use of a diaphragm, ot 

 f orous pa-'tition, between the two metallic plates, which allows a free contact 



• It is found that by coating the zhic with mercury, the waste of the zinc is greatly 

 diminished. It is not well understood in what way the raercury contributes to this effect. 

 We have a parallel to it in the rubber of the electrical machine, which, when coated with 

 an amalgam of zinc and tin, acts with greater e£Sciency than under any other ciroum 

 •tauoea. 



i^at is the 

 jnncipiil im- 

 perfection of 

 :he galvanic 

 uattery ? 



