74 CHEMICAL PHYSICS. 



that each magnetic molecule is traversed by a closed electric circuit, which 

 currents become parallel upon magnetization of ordinary iron. According to 

 this theory, magnetism is a manifestation of electrical energy. 



The shape given to magnets is usually that of a bar or of a horse- 

 shoe. A bar of soft iron laid over the poles of a horseshoe magnet 

 is called an armature; it serves to retain the full power of the 

 magnet. 



When fine iron filings are sprinkled on a piece of glass or card- 

 board which has been placed over a magnet, the filings arrange 

 themselves in lines radiating from either pole, forming graceful 

 curves from pole to pole. These lines, called lines of magnetic force, 

 represent the resultant of the combined action of the two poles, the 

 space surrounding a magnet as far as its influence extends being 

 termed its magnetic field. A magnetic needle placed anywhere in 

 this field follows the lines of magnetic force, always assuming a 

 position tangent to the magnetic curve. 



The explanation given for the fact that the magnetic needle points 

 north and south is that the earth itself is an immense magnet, pos- 

 sessing two magnetic poles which are close to the geographical poles. 



Electricity generated by chemical action. On placing a strip 

 of ordinary zinc in diluted sulphuric acid, bubbles of hydrogen gas 

 are evolved on its surface and the zinc gradually dissolves ; a piece 

 of platinum placed in the acid is not affected at all. If, however, 

 strips of zinc and platinum are placed in a vessel containing diluted 

 acid, on connecting the plates above the liquid by a conductor, 

 for instance by a piece of copper wire, characteristic changes take 

 place. First, the evolution of gas stops on the zinc, while bubbles 

 of hydrogen escape from the surface of the platinum. Next, on 

 placing the connecting wire near a magnetic needle, this is turned 

 from its course i. e., deflected. And again, on cutting the wire and 

 placing the tongue between the two ends, a metallic taste and a 

 tingling sensation are perceived. All these phenomena cease as soon 

 as the connection between the plates is broken, and reappear when 

 connection is again established. 



Undoubtedly something takes place in the wire while the plates 

 are in the diluted acid. Further investigation shows that during 

 the action of the acid on the metals electricity is generated, which 

 travels through the wire, imparting to it characteristic properties. 



Galvanic or voltaic cells. In place of zinc, platinum, and sul- 



