VOLTAIC BATTERIES.] 



UNDULATORY FORCES. ELECTRICITY. 



187 



There are several circumstances into which we shall 

 here inquire, which modify, increase, or diminish the 

 power of voltaic batteries. They may be shortly summed 

 up as follows : 



1. The extent and rapidity of chemical action. 



2 The size of the plates. 



3. The conducting power of the liquid used as an 

 excitant; and of the wire, <fcc., joining the plates, 

 external to the cell. 



We have already mentioned, that there have been 

 those who have strongly advocated the idea, that the 

 production of electricity by the voltaic battery, is due 

 to the contact of dissimilar metals. The causes of the 

 modification of the power of the voltaic battery, which 

 we have given above, recognise no such an opinion. 

 Indeed, it is not necessary that we should bring into 

 contact the two metals at all ; for in all chemical de- 

 compositions affected by voltaic electricity, the metals 

 are never connected by a wire as shown in Fig. 37 ;* 

 but merely by the liquid which is the subject of the 

 electric action. 



1. That the power of a cell depends on the rapidity of 

 the chemical action which proceeds on one of the metals, 

 is made evident by the following experiment : 



Experiment 33. Connect a piece of zinc and copper 

 plate, each four inches square, by means of a very tine 

 piece of steel wire. This is best done by soldering a 

 thick copper wire to each plate, round which the steel 

 wire is to be twisted, so as to leave about half an inch of 

 the fine wire between them. Dip the plates into common 

 water, and no effect will be perceived on the fine wire. 

 Now replace the water by strong sulphuric acid, diluted 

 wit I, six times its bulk of water, and introduce the plate 

 it. The steel wire between the two copper wires 

 will be instantly melted. 



2. The size of the plates has the effect of increasing 

 the power of a cell, in respect to the quantity of 

 electricity wnich is set free. Thus, in the last experi- 

 ment, a very thin wire was recommended, because the 

 plates were small. If, however, large plates be employed, 

 tlii-ii just in proportion to the extent of the surface of 

 the plates, so will greater thicknesses of wire of the same 

 kind be melted. It is hence usual to adjust the size of 

 all voltaic batteries to the work which they are expected 

 to perform. This will be particularly noticed when we 

 have to refer to the chemical decomposition, cfce. , carried 

 on during the electrotype process. 



3. The conducting power of the liquid in each cell, 

 and that of the wire, <tc. , external to it, are matters of 

 the highest importance. Liquid*, in an electrical point 

 of view, are, generally speaking, bad conductors ; but, in 

 a voltaic battery, this fact is modified by means of 

 mixing acids, (fee. , with the water used as an excitant. 

 Pure water has so little chemical action on zinc, and is 

 so bad a conductor, as to afford only the most feeble 

 evidences of disturbing electricity ; whereas, if a little 

 acid be added thereto, the result is, that rapid chemical 

 action may bo speedily induced. The conducting power 

 of a liquid is inversely as its length ; hence it is essential 

 that the two plates of a cell should be placed as near as 

 possible to each other without touching. As an illustra- 

 tion of this, we may state, that twelve sets of copper and 

 zinc plates, each at a distance of an inch from each 

 other, do not afford a tenth part so much effect as when 

 they are so arranged as to be in as close proximity as 

 possible without touching. The addition of sulphuric, 

 nitric, and hydrochloric acids, of salts, <kc., to the water 

 of a cell, increases its conducting power almost in pro- 

 portion to the extent of their presence; hence strong 

 solution* of the above are always employed when 

 brilliant effects are desired from voltaic batteries. The 

 wires forming the terminals of a battery or single cell, 

 always, like the liquid in the cell, afford a resistance to 

 the passage of electricity ; and this depends on their 

 thickness and length. Different metals vary in their 

 conducting power gold, silver, and copper standing the 

 highest, and lead, tin, zinc, etc., lowest in the scale. 

 For all practical purposes, copper wire is employed as a 



Sec anfr. p. 186. 



conductor in all voltaic batteries ; and we suggest the 

 use of flat ribbons of the metal in place of wire, as 

 being more convenient where long conductors have to be 

 arranged. 



A voltaic battery consists simply of a number of single 

 cells joined together. The zinc of one cell is attached, 

 by means of a wire, to the copper of the next ; and so on, 

 throughout the series. By this arrangement, one zinc 

 and one copper, at the extreme ends of the battery, will 

 be unconnected; and it is to these that the terminal 

 wires, by means of which the experiments are carried 

 on, are attached. 



The intensity, or power of a battery to overcome 

 resistance offered by bad conductors, such as air and 

 water, depends on the number of cells employed. 



The quantity, or power to overcome the resistance of 

 good conductors, such as metallic wires, in melting them, 

 depends on the size of the plates. On the regulation of 

 these two particulars in the construction of voltaic 

 arrangements, their efficiency for all purposes is governed. 

 It may be well that we should here give some general 

 directions as to the management of voltaic batteries 

 generally, before proceeding to describe the various 

 kinds which have been invented. And first, the 

 zinc should always be amalgamated. This prevents 

 the acid acting on the metal, except when the battery 

 is in action ; and it is easily performed. The zinc 

 plate should be dipped into some strong sulphuric 

 acid and water, until abundance of gas arises from its 

 surface. It may then be laid on a plate, and mercury is 

 to be rubbed over it until the whole presents a highly 

 polished appearance on both sides. If the metal bo now 

 dipped again into the acid water, no gas will arise from 

 its surface, because the mercury has covered over a vast 

 number of impurities, consisting of iron, <tc., which 

 are in the zinc, and which formed little batteries on its 

 surface. This process has been of the utmost importance 

 in the application of voltaic batteries ; and diminishes to 

 a great extent their working cost, by economising the 

 zinc. 



Every junction of metals, wires, binding-screws, <fec., 

 should be kept quite bright ; and, wherever possible, 

 soldering should be employed, as complete contact of all 

 connecting arrangements is very essential. We have 

 seen batteries in a dirty condition wliich would scarcely 

 melt an inch of wire ; and yet, with the same charge, they 

 would melt five or six feet, after all the connections were 

 carefully cleaned. For this purpose common sand-paper 

 should be used, or sand may be rubbed on to the inutiils, 

 by means of a damp cloth, until they are quite polished. 

 In winter-time the action of a battery will quite cease, 

 if the weather be very cold. Of course, the only remedy 

 is, to carry on the experiments in a warm room, or to 

 heat the solutions before charging the battery. 



In using those batteries having porous cells and two 

 liquids (Daniell's and Grove's), great care should be 

 taken not to allow the two liquids to mix, as this would 

 ruin the zinc : and the porous cells, when done with, 

 should be completely emptied, and left to soak in water, 

 so as to remove aU salts, which would crystallise and 

 break them to pieces. 



It will occasionally happen, in large batteries, that the 

 middle cells will get very hot, and the liquid will 

 evaporate from them. This of course must be watched, 

 and, if necessary, they must be refilled. The student 

 should bear in mind, that the power of the battery is 

 regulated by the action of the feeblest cell of the whole 

 series. It is therefore essential that each should have 

 the same charge, equal-sized plates, and that the con- 

 nection sh->uld be perfect throughout. Alter using wires 

 for voltaic experiments, they sometimes become com- 

 pletely rotten, and break with the least touch. This is 

 remedied by heating them red-hot, which at once softens 

 them. 



DIFFERENT FORMS OF VOLTAIC BATTERIES 



HAVING explained the construction and principles of an 

 elementary battery, we now proceed to notice the various 



