METALS FIT FOR BATTERIES. 29 



According to this arrangement, each metal is positive with respect 

 to all that stand before it, and the electrical conditions of any pair 

 become the more contrasted the further apart they stand in the scale. 

 Thus, a battery composed of zinc and platinum is much more power- 

 ful than one composed of zinc and copper ; and again, copper and 

 iron make a very weak battery. 



A battery may also be formed by having one metal and two kinds 

 of solutions, separated by a porous diaphragm. For example, we 

 may have strong nitric acid in one division, and dilute sulphuric 

 or muriatic acid in the other ; and by putting into each a piece of 

 clean iron, a powerful current is obtained. These, and several other 

 arrangements of solutions and metals, are expensive, and troublesome 

 to keep in order, and are therefore never used for practical purposes 

 in the art of electro-metallurgy. 



Properties of Metals fit for Batteries. In looking to the above 



table, it may be asked, " Since lead stands next to copper, and is so 

 much cheaper, why should it not be used instead ?" The reason is, 

 that there are other properties which a metal, especially that used as 

 the negative element, ought to possess to fit it for use in a voltaic 

 arrangement ; such as the power of freely conducting an electric 

 current, of keeping a bright surface, and not becoming oxidized ; 

 none of which properties belong to lead. Could that metal be kept 

 from oxidizing, a very powerful current of electricity might be ob- 

 tained by using it with zinc ; but its surface soon gets coated with 

 an oxide possessing none of the properties of the metal, and hence 

 the arrangement becomes zinc and oxide of lead, which produces 

 but a weak current of electricity. These remarks refer to any metal 

 that is subject to oxidization an incident which is often a source of 

 annoyance to the electrotypist when using copper plates. 



Lead slightly amalgamated, and used as the negative metal with 

 zinc, produces a very constant current for a time. 



Lead is also a very bad conductor of the electric current, which 

 renders it unsuitable for an element in the battery, the negative 

 metal being considered as only acting the part of a conductor : this 

 property materially affects the available power of an arrangement. 



The following table shews the relative Conducting power of the 

 respective metals : 



Silver . . . 120 



Copper . . .120 



Gold ... 80 



Zinc ... 40 



Platinum . . 24 



Iron ... 24 



Tin . . . 20 



Lead 12 



