Polytechnic Association. 

 Table of Equivalents. 



965 



Electro-motive Force. 



58. We are now possessed of the elements for determining the 

 electro-motive force of a battery. 



Refering to the formula before given (44) for determining the inte- 

 rior resistance of a battery, and to the application of Ohms' law, to be 

 found in all modern books on electricity, we see that 



rs = e, 

 i. e., the whole resistance in ohms, multiplied by the strength in 

 vebers, gives the electro-motive force in volts. 



59. Such are the laws of electrolysis, as discovered and laid down 

 by Faraday, who announced that " The elytrolytic action of a cur- 

 rent is the same in all its parts / that the same electric current decom- 

 poses chemically equivalent quanities of all the bodies which are tra- 

 versed ;" from which it follows that " The weights of elements sep- 

 arated in these electrolytes are to each other as their chemical equiva- 

 lents ;" and that " The quantity of a body decomposed in a given 

 time, is proportional in the intensity of the current. 



On this is founded the use of Faraday's voltameter, in which the 

 intensity of a current is ascertained from the quantity of water which 

 is decomposed in a given time. (Ganot's Physics, p. 653.) It would 

 seem, then, reasoning a priori, that a constant multiplier obtained for 

 a true tangent galvanometer, should give correct and reliable results in 

 all cases of electrolysis ; that any one enaged in electroplating of any 

 kind, having one of these galvanometers in the circuit, might readily 

 know how many grains of the metal is being deposited per second, 

 by multiplying the tangent of the angle of deflection by the constant, 

 and the product by the proper number in the right-hand or fifth col- 

 umn of the foregoing table of equivalents (57). And so it would be 

 if we were always dealing with elements that were perfectly pure, 

 and with their salts that were perfectly neutral ; but such perfection 

 and purity we do not find in ordinary practice. Results, therefore, 



