and Chemical Theories of' Galvanism:. 153 



theory is founded on false principles, T shall now very shortly 

 examine the truth of the most generally received chemical 

 theory of galvanism. 



3. Dr Wollaston assumes that positive electricity is set at 

 liberty by the combination of oxygen with one of the metals. 

 This principle is frequently true, but in many cases it is 

 totally false. This will be rendered obvious by the following 

 experiments : — 



Exp. III. — Immerse two equal discs of zinc, connected by 

 wires with the galvanometer, into the chambers of the rectan- 

 gular box formerly used, and fill both compartments with 

 water ; no action will of course take place. Pour a little sul- 

 phuric, nitric, or muriatic acids into one of the chambers, a 

 considerable galvanic effect will be produced, and the needle 

 will turn in the same direction as it does when copper is sub- 

 stituted for the plate of zinc immersed in the chamber contain- 

 ing the water alone. This agrees with the chemical theory. 

 Again, instead of the above acids use nitrous acid, and the 

 needle will turn round in the opposite direction. The same 

 thing holds when discs of copper or iron are employed. This 

 is completely at variance with the chemical theory, since that 

 plate is negative, or corresponds with copper in the standard 

 battery, on which the greatest chemical action of the fluid 

 .takes place. The following experiment is also hostile to the 

 generally received theory. 



Exp. IV. — Having taken two pieces of block tin, I cut the 

 surface of one of them into ridges by means of a three-corner- 

 ed file, so that the surface was doubled. With these two pieces 

 I formed a binary combination, and immersed them in diluted 

 nitro-muriatic acid ; a very considerable electro-magnetic ef- 

 fect was produced, and the needle turned round in the same 

 direction as it does when a plate of zinc is substituted for the 

 plane disc in the standard battery. It is obvious that there 

 must be a greater chemical action between the acid and the 

 furrowed plate than the other, and yet the furrowed plate cor- 

 responds with copper in the standard battery, on which the 

 least chemical action takes place. The results obtained in the 

 following experiment were also unexpected : — 



Exp. V. — Take equal pieces of soft zinc, copper, iron, or 



