EFFECTS OF THE GALVANIC CURRENT. 669 



allowed to touch the tongue separately, is perfectly 

 tasteless, but as soon as the circuit is closed by the 

 tongue itself, the nerves of taste are thrown into a 

 state of activity, and the sensation of a pungent taste 

 is felt. The sensation is, however, somewhat different 

 at the two terminals; at the negative terminal the 

 taste is acid, while at the positive terminal the taste 

 somewhat resembles that of caustic soda. 



For this experiment the current of the small battery, fig. 336, is 

 sufficient, or, still better, two Bunsen's or Grove's elements may be 

 employed. 



When a galvanic current passes through a metallic 

 wire the wire becomes heated, but the heating effects 

 of the galvanic current are more easily observed than 

 those produced by the discharge of an electric battery, 

 because the latter is instantaneous, whereas the current 

 goes on for some time. 



With powerful batteries, all metals may not only be 



heated so as to become incandescent, but even the least 



fusible of them may be melted and volatilised. The 



current of two Grove or Bunsen elements of moderate 



size is sufficient to render a copper wire, a few decimetres 



long arid O mm> 5 thick, sensibly hot. If a small strip of 



tinfoil, 3 cm long and 2 mm wide, be placed upon a wooden 



support, and first one terminal be pressed upon one 



end of the strip and then the other upon the opposite 



end, the strip becomes so hot that some part or other 



fuses; if the experiment be made in the dark, it 



will be seen that the fused portion as a rule becomes 



incandescent before it melts. An iron wire of 10 cm 



length and O mm *2 thickness is made red hot by the 



