194 



FNDULATORY FORCES. ELECTRICITY. 



[CHEMICAL tmcrm. 



i.i M. 



A and B repreaenl the two tube* In- 

 tended to rcceire the gase* ; C and 

 Z the wires coming from thetopper 

 or ptauna, and cine end* of the 

 battery, and tipped with platina ; 

 I>, a corer in which the tubes rent ; 

 40 bindtng-ecrewft, through 

 which the battery win* an p<L 



to which we (hall refer, BO secondary or disturbing oanse 

 will interfere with the effect* resulting from the action of 

 electru it v mi the chemical com pound* we shall examine. 

 If the wire* proceeding from a battery furnished with 

 platina pole*, are dipped into a mint ion of sulphuric acid 

 in water, the platina surface alone being exposed, abun- 

 dance of gas will be giren off from each plate. If these 

 gases are collected separately, it will be found, that one 

 is pure oxygen, and the other hydrogen gaa ; and these 

 are given off from the platina terminals in the proportions 

 required in their reunion to form water. A convenient 

 airaii^'-iiiciit fr collecting the gases separately is repro- 

 vn tod in the following figure. By such an instrument, 



the two gases, which when 

 combined produce water, 

 may be collected apart 

 from each other, and their 

 characters may be readily 

 examined. The left-hand 

 tube, iu Fig. 54, is supposed 

 to be receiving oxygen gas ; 

 aud that on the right hand 

 is being tilled with hy- 

 drogen, the other consti- 

 tuent of pure water. By 

 bulk, one of oxygen to two 

 of hydrogen is given off; 

 but, by weight, one pound 

 of hydrogen to eight 

 pounds of oxygen are re- 

 quired to produce nine 

 JH minis of water. 



If the gas (oxygen) re- 

 ceived in the left-hand tube 

 be tested, it will be seen 

 that the combugtiou of a 

 taper or match is rapidly 

 increased by it. On the contrary, the gas (hydrogen) 

 received in the right-hand tube, will not support com- 

 bustion ; and, indeed, it will at once catch fire if a light 

 be presented to it. 



It U f<mnd. that these gases, evolved during the de- 

 composition of water by electricity, always present 

 themselves in the same part of the instrument. For 

 instance, hydrogen is invariably found at that terminal 

 or pole (as it is frequently called) which ends the wire 

 proceeding from the zinc end of the battery ; whilst 

 oxygen is always noticed as proceeding from that 

 terminal, or pole, which is connected with the platina, 

 or copper plate of the battery. It hence follows, that 

 that pole which proceeds from, or ends the positive 

 plate of a battery, is negative to that which terminates 

 or proceeds from the negative plate of the battery itself. 

 The wire or plate connected with the negative plate of a 

 battery, is positive in any solution undergoing decom- 

 position. We may simply state, that the poles or 

 terminals of a battery, when immersed in any solution 

 undergoing decomposition, have opposite electrical states 

 to the plate of the battery from which they proceed ; and 

 this results from the laws of induction, already explained 

 in a previous page.* 



These poles, or terminals, have had other names 

 applied to them. Dr. Faraday has suggested the term 

 les," from the Greek "odos, lj a way ; and the 

 negative pole, or that terminating the wire from the zinc 

 end of the battery, has been called the "zincode," or 

 " cathode ;" while that proceeding from, and ending the 

 wire of the copper or platina plate of a battery, ha* been 

 termed the "platinode," or "anode." These terms 

 include the idea of the "passage" of a "current" from 

 the copper pole to that of the zinc a question on which 

 we have already made some remarks in our earlier pages, f 

 The changes which occur, both electrically and che- 

 mically, may be represented as in the following diagram : 



No. 1 OH OH OH 



No. 2 



HO 



UO 



In No. 1, we observe the constitution of pure water 



Sac MM, P- 17, f rf . Bee (/, p. 169. 



represented as a combination of oxygen (o) with hy- 

 drogen (n) ; but when the poles of a voltaic battery are 

 placed in the I inn id, then the oxygen of one atom is set 

 free, and its hydrogen combines with the oxygen of that 

 next to it ; and so on, until hydrogen is given off from 

 the last atom in the series. The two gases obtained 

 from water may be collected together by a very simple 

 piece of apparatus. Into a glass tube or a gas chimney, 

 fit two corks, so that when finally fixed they shall 1. 

 water-tight On each side of the inside of the glass put 

 a small piece of platina foil facing each other, and ex- 

 tending half an inch outside of the glass. These pieces will 

 serve the double purpose of conductors both inside and 

 outside. Now press one of the corks into the glass, and so 

 keep the foil in its place. The small pieces of platina on 

 the outside may be bent outwards, and are intended to 

 receive the conducting wires of the battery. This will 

 complete the bottom part of the arrangement. Into the 

 top of the glass fit the other cork, in which has been fixed 

 a bent pewter or glass tube, and through which the gas 

 produced will afterwards be carried away. The glass 

 should previously be half filled with some acid water, 

 and may then be cemented, by means of some sealing-wax, 

 to a piece of wood, which will serve as a stand. Fig. 55 

 represents the arrangement we have described. 



On bringing the wires into contact with D D, the water 



A A, two pieces of platina foil, part of each extending outside the Clara ; 

 It. the bottom cork, to keep A A in their place ; C, a cork holding a 

 tube through which the gasei are to pass : D D, the two outride pieces 

 of platina foil, on which the wires of the battery are to be placed, and 

 by which the electricity enters and leares the water. 



inside the glass will be decomposed ; and if the bent tube 

 bo dipped beneath the water in a pneumatic trough, the 

 two gases may be collected in any vessel, after the usual 

 manner. When the tube is filled with gas, apply a light, 

 and an explosion will at once take place, and water will 

 be formed. 



The philosophical instrument-makers sell an arrange- 

 ment of a similar, but more complete kind : the student, 

 however, who has to consult economy, will find that 

 which wo have described to answer every purpose. 

 Some patents have been taken out, the object of which 

 has been to apply the mixed gases thus obtained to 

 illuminating purposes. The mixed gases may be pro- 

 duced at the rate of 200 cubic inches per minute, by 

 means of a Grove's battery of five cells, each platina ex- 

 posing one hundred square inches of active surface ; and 

 if the gases so afforded are passed through a Hemming 

 safety-jet, and their flame be thrown on a cylinder of 

 lime, the ordinary lime or Drummond light will be 

 produced. We have frequently tried an arrangement of 

 this kind ; but much prefer the ordinary mode of pro- 

 ducing oxygen and hydrogen, and burning them from. 

 gasometers or gas-bags. Independent of any other con- 

 sideration, the expense of the voltaic battery is a serious 

 item, in a commercial point of view, in this application. 



If two pieces of platina, attached to each end of tho 

 battery, be immersed in a solution of any neutral salt, 

 chemical decomposition at once ensues, and the acid 

 and the base are readily separated from each other. An 

 ordinary tumbler, or any other glass vessel, may be em- 

 ployed. It should be divided by means of a stout 

 card, as shown in Fig. 56 ; in which tho two platina 

 plates, and tho wires proceeding from the battery, are 

 also represented. 



Experiment 40. A solution of common salt in water, 



