ELECTRICITY. 89 



and precipitated upon the interior of the vessel in, chemically 

 speaking, an unaltered state. Thus, to take a very striking 

 example, if the voltaic discharge be taken between zinc ter- 

 minals in an exhausted receiver, a fine black powder of zinc 

 is deposited on the sides of the receiver ; this can be collect- 

 ed, and takes fire readily in the air by being touched with a 

 match, or ignited wire, instantly burning into white oxide of 

 zinc. To an ordinary observer, the zinc would appear to be 

 burned twice first in the receiver, where the phenomenon 

 presents all the appearance of combustion, and secondly in 

 the real combustion in air. With iron the experiment is 

 equally instructive. Iron is volatilised by the voltaic arc in 

 nitrogen or in an exhausted receiver ; and when a scarcely 

 perceptible film has lined the receiver, this is washed with an 

 acid, which then gives, with ferrocyanide of potassium, the prus- 

 sian-blue precipitate. In this case we readily distil iron, a 

 metal by ordinary means ftisible only at a very high tempera- 

 ture. 



Another strong evidence that the voltaic discharge con- 

 sists of the material itself of which the terminals are compos- 

 ed, is the peculiar rotation which is observed in the light 

 when iron is employed, the magnetic character of this metal 

 causing its molecules to rotate by the influence of the voltaic 

 current. 



If we increase the number of reduplications in a voltaic 

 series, we increase the length of the arc, and also increase its 

 intensity or power of overcoming resistance. With a battery 

 consisting of a limited number, say 100 reduplications, the 

 discharge will not pass from one terminal to the other with- 

 out first bringing them into contact, but if we increase the 

 number of cells to 400 or 500, the discharge will pass from 

 one terminal to the other before they are brought into contact. 

 The difference between what is called Franklinic electricity, or 

 that produced by an ordinary electrical machine, and voltaic elec- 

 tricity, or that produced by the ordinary voltaic battery, is that 



