GALVANISM. 409 



tiow may vol- '^'^^- When the wire from one end of a vol- 

 interr^uptedand ^^^^ battery is conuected with the wire from 

 renewed? ^^q opposite end, voltaic action instantly com- 



mences ; and it as instantaneously ceases when the con- 

 nection is interrupted. The rapidity with which the elec- 

 tric circuit may be completed and broken has no ascertained 

 limit ; nor does it appear to be controlled by resistance 

 caused by traversing miles of wire. 



779. The most ordinary effects produced by 

 most ordinary thc dcvelopcd clectricitY of a larsre g:alvanic 



effect* of gal- 1 ^ , , ■/ „ r 1 1 -1 



vanic electric!- battcry, are the production of sparks and bril- 

 liant flashes of light, the heating and fusing 

 of metals, the ignition of gunpowder and other inflam- 

 mable substances, and the decomposition of water, saline 

 compounds, and metallic oxyds. 

 _ Heat is evolved whenever a galvanic cur- 



Whendoesfral- . ^ -i ^ 



vanic eiectrici- rcut passcs ovcr a conductmfi^ body, the amount 



tyevolTeheat? ., a j ? ^ 



of which will depend on the quantity and in- 

 tensity of the electricity transmitted, and upon the re- 

 sistance which the body offers to the passage of the cur- 

 rent. 



The metals differ greatly in their conducting power. Thus, if vre link 

 together pieces of copper, iron, silver, and platinum wire, and pass a galvanic 

 current along them, they will be found to be unequally heated, the platinum 

 being the most, and the copper the least. 



The easiest method of showing by experiment the heating 

 liwUn™^^ect» power of the galvanic current is to connnect the poles of a 

 of galvanic battery by means of a fine platinum wire. If the wire is very 

 Ulu^stratedf * long it may become hot; shorten it to a certain extent, and 

 it will become red-hot ; shorten it still more, and it will bo- 

 come white-hot, and finally melt. If such a wire is carried through a sma'.l 

 quantity of salt water on a watch-glass, the liquid will boil ; if through alco- 

 hol, ether, or phosphorus, they will bo inflamed ; if through gunpowder, it wiU 

 be exploded. 



This power has been applied to tho purpose of firing blasts. 

 What practical *^ „ , " . , . , , ^ , 



application hag or mmcs of gunpowder, an operation which may bo effected 



^eii made of ^j^j^ equal facility under water. The process is as follows: — 

 The wires from a sufficiently powerful battery are connected 

 by a piece of fine platinum wire, which is placed in a mass of gunpowder con- 

 tained in a cavity of a rock, or inclosed in a vessel beneath tho surface of 

 water. The wire may bo of any length, but tho moment conr^ectioq ia made 



18 



