Galvanism. 



many facts which were well known, but the rea- 

 son of which was not before discovered. It had 

 been long observed, that porter and ma t liquors 

 have a different and a pleasanter taste when drunk 

 out of metal than out of glass or earthenware ; 

 and on the contrary that water out of a metallic 

 cup has a disagreeable and metallic taste ; these 

 effects are now known to be owing to a slight 

 galvanic shock, such as is experienced by placing 

 the tongue between two metals in contact. 



Mixtures of metals have been long known to 

 corrode each other, while pure metals have re- 

 mained unchanged ; thus the Etruscan inscrip- 

 tions engraven on pure lead are preserved to 

 this time, while medals of lead and tin of no great 

 antiquity are much defaced. The copper sheath- 

 ings of vessels when fixed on with iron nails be- 

 come very soon corroded ; and I believe it is now 

 customary to fix them to the bottoms with copper 

 nails. These effects are owing to the action of 

 the metals on each other, or rather on the mois- 

 ture which is interposed, which, being decom- 

 posed by the action of the metals, is separated 

 into its constituent parts (oxygen and hydrogen), 

 and one or both of the metals become oxidated, 

 rusted, or corroded. 



The conductors of electricity are also con- 

 ductors of galvanism : these are divided into two 

 classes; the .dry, such as metallic substances and 

 charcoal 5 and the wet, as water and certain other 

 fluids. 



G2 



