SOLID ELEMENTS OF THE VOLTAIC CIRCLE. 217 



circle is an obstacle to induction, and reacts on the whole 

 series, reducing the chemical action and evolution of hydrogen 

 in each of the active cells by at least one third. In that retard- 

 ing cell itself, the amount of decomposition, is necessarily the 

 same as in the other cells. Mr. Daniell found the chemical 

 action reduced to one tenth, in a series of eight active and 

 two such retarding cells; and entirely stopped by three re- 

 tarding to seven active cells. 



OF THE SOLID ELEMENTS OF THE VOLTAIC CIRCLE. 



The elements of a voltaic circle are obviously of two diffe- 

 rent kinds, the metals or solid portions, through the substance 

 of which chemical induction is propagated without decom- 

 position, and the liquids in the cells, which yield to the 

 induction and suffer decomposition. In reference to the first, it 

 is to be observed that, as only iron and one or two other 

 metals of the same natural family are susceptible of magnetic 

 polarity, so the susceptibility of chemical polarity which appears 

 in the voltaic battery is not possessed by solids in general, 

 but is confined to the class of bodies to which zinc belongs, 

 the metals, all of which possess it, with the addition of carbon 

 in the form of charcoal, and the sulphuret of silver when 

 heated. The non-metallic elements with their compounds, 

 and the oxides, sulphurets and other compounds of the metals, 

 some of which exhibit the metallic lustre, are all destitute of 

 this power, and cannot, therefore, be used as solid elements 

 of the circle. A body available for this purpose is termed a 

 conductor on the electrical hypothesis, a name which may be 

 retained as it is not at variance with the function assigned to 

 the metals in the circle viewed as a chemico-polar arrangement. 

 Two different metals are combined in a circle, one of which 

 is acted on by the liquid, and, therefore, called the active or 

 the positive metal, while the other is not acted upon, and is, 

 therefore, called the inactive or the negative metal ; and it has 

 already been stated that the more easily acted on by the liquid 

 or the more highly positive the one metal, and the less easily 

 acted upon, or more negative the other metal, the more proper 

 and efficacious is the combination. In the following table 

 several of the metals are arranged in the order in which they 

 appear positive or negative to each other, when acted on by 



