UNDULATOKY KOHCBS. El, l-:r T Kt> M KT A LLURGT. [LAWB OF DKI-OM 



UetaU. The second elect ? 'itimi to be ob>. 



Is, that in every CMO of deposition t licit! is an olei 

 difference between the dimolving a 

 and tti.it tlie f< miicr U always electro-positive, the ! 

 i-gative, rvl.itivcly to each other; tin 

 solving metal, consequently, h.ia the itronMt laatrioJ 

 attraction for the electro-negative or acid elements of 

 tin- h.pi:d, :iinl the receiving metal has the strongest 

 :i.al attraction for the electro-positive or metallic 



ice 



il'ith Oiw Mit.il and One Liquid. Iron placed in 

 & solution <>f sulphate of copper, being electro-po- 

 to tin' copper of the Rait, has a stronger electric :r 



for the acid or electro-negative elements than the 



per, !iinl ooniliines with them, netting the copper 



free ; but in a solution of sulphate of zinc, iron being 



:ro-negative to the zinc of the salt, has a weaker 



attraction for the aciil than the zinc, aad therefore does 



ubine with or set the zinc free. 



2nd. Ttco Metals and One Liquid. If we immerse a 

 piece of iron and a piece of copper in a solution of sul- 

 phate of copper, and connect them by wires with a 

 galvanometer (Fig. 78),* the copper will receive a de- 

 Fig. 78 



posit, and the needle N of the instrument will be 

 strongly deflected in such a direction as to indicate 

 that the iron is positive, and the copper negative ; but 

 if a piece of iron and a piece of zinc are immersed in a 

 solution of sulphate of zinc, and connected with the 

 instrument, no deposit will take place upon either 

 metal, and scarcely any deflection of the needles will 

 be produced. 



ord. Wifh One Metal and Two Liquids. If one piece of 

 copper be immersed in dilute sulphuric acid, and another 

 in a ncMitral solution of sulphate of copper, the two 

 liquids being s. by a porous partition, and the 



pi<vi"< of copper connected by wires with the galvanome- 

 ition will take place upon the piece of copper 

 in tlio metallic solution, and the instrument will in- 

 a, by the direction of the deflection of its needles, 

 that the dissolving piece of metal is positive, and the 

 receiving piece negative ; but if we substitute two pieces 

 of plat ina, for the pieces of copper, no deposition of 

 i rcely any difference of electric 

 ,: ion between the two pieces of metal will be indi- 

 cated by the galvanometer. 



4th. 'With Two Metal* and Two Lvpi'uh. If a piece 

 of x.inc Ixi immersed in dilute sulphuric acid, and a piece 

 ;'|"T in a solution of sulphate of copper, the two 

 liquids being separated by a porous partition, and the 

 metals connected with the galvanometer, deposition will 

 take place freely upon the nipper, and t lie needles of the 

 instrument will be powerfully deflected, indicating, by 

 the amount and dn 'heir movement, the zinc 



to be strongly posithe and the cupper negative; but if a 

 piece of platina be substituted for the zinc, there will lie- 

 no .^position, and scarcely an\ detleetion of the needle. 



6th. With a Separate Depositing Liquid. If w. im- 

 merse two pieces of silver in a solution of the donlile 

 cyanide of silver and pota- TH. and connect them with 

 any source of depositing power, interposing a gah 

 meter in the circuit, deposition of silver will occur, and 

 the needles will be strongly deflected in such a direction 



Boo ante, f. 1'Ji. 



as to indicate the dissolving piece of M posi- 



and the receiving piece negative; but if we sub- 

 stitute two pieces of iron for the pieces of silver, 

 will bo scarcely any deposition of silver, anil veiy little 

 deflection of the net-die, the n ing feebly 



negative. From these and i. r similar cases, 



we conelude, that in every ease where deposition occurs, 

 the diRsolving metal is electro-positive, and the reeeiving 

 .1 electro-negative, and that the former has the 

 n for the negative elements of 



the liquid, and the latter for the basic <>r metallic ele- 

 ment. In all electric phenomena, positive substai 

 repel positive and ; and negative sub- 



atancos repel negative and attract positive t 



36. Alternation and Circulation of AY '.firs 

 necessary. The third electric condition is, that in every 

 case of de]>sitiou, the positive and negative surfaces, or 

 metals, alternate with each other in the circuit, and 

 electric forces circulate through the circuit. For in- 

 stance 



1st. With One Metal and One Liquid. When a piece 

 of iron is immersed in a solution of sulphate of copper, 

 innumerable minute electric currents are generated upon 

 the surface of the metal, and circulate to a very minute 

 depth within the opposed surface of the liquid ; while 

 the positive electricity, passing out of innumeralile points 

 of the iron into the solution, causes it to dissolve pass 

 through the solution, re-enter the iron at inniimeralilo 

 other points, and deposit the copper ; but when a piece 

 of gold is immersed in this solution, there are no cur- 

 rents of electricity generated, and the gold is neither 

 dissolved nor does it receive a deposit. 



2nd. With Two Metals and One Liquul When a 

 piece of zinc and a piece of silver are immersed in 

 mutual contact in a solution of nitrate of silver, the 

 zinc dissolves and the silver receives a deposit, and an 

 electric current is developed which circulates through 

 the metals and liquids, and may be rendered further 

 evident by connecting the metals with a galvanometer 

 (Fig. 78) : the zinc is positive, and the silver negative. 



3rd. With One Metal and Two Liquids. When two 

 pieces of copper are immersed, one in dilute sulphuric 

 acid, and the other in a solution of sulphate of copper, the 

 two liquids being separated by a porous diaphragm, and 

 the pieces of copper connected with a galvanometer, an 

 electric current circulates, the piece of copper in the 

 is positive and dissolves, and the piece in the metallic 

 solution is negative and receives a deposit. 



4th. With Two Metals and Two Liquids. When a 

 of zinc is immersed in dilute sulphuric acid, and a 

 of silver in a solution of double cyanide of silver 

 and potassium, and the two are connected with a galvano- 

 meter, the two liquids being separated by a porous parti- 

 tion, electricity circulates, the zinc is positive and dis- 

 solves, and the silver is negative and receives a deposit. 



5th. With a Separate Depositing Liquid. When two 

 pieces of antimony, immersed in the ordinary cliloride of 

 antimony, are connected with any source of electricity, 

 one piece becomes positive and dissolves, and the other 

 ;ve and receives a deposit, and an electric current 

 circulates, as may easily be proved by the galvanometer, 

 in the foregoing manner. 



Citli. With <i No-/.* of Depositing Liquid*. If a series 

 of depositing vessels (Figs. 73 and 75), containing solu- 

 tions of sulphate of copper, and pieces of copper, 

 nneeted by their extreme pieces with a sheet of 

 /.iiK', and a sheet of copper bo immersed in a solution of 

 sulphate of copper, every alternate piece of metal in the 

 series will be electro-positive and dissolve, and every 

 other alternate piece electro -negative and receive a 

 it, and a current of electricity will circulate through 

 the whole series. 



37. Electrical Conducting Circuit necessary. In every 

 case where deposition is proceeding, the whole of the 



it must be capable of conducting voltaic electricity ; 

 and this is one important condition of the result ; for if, 

 in any such case, wo interpose nn imperfect electric con- 

 ductor in the circuit such as a long iron wire, or a short 



t Sftantf,f. 178. 



