CHAP, in.] ELECTRICITY AND MAGNETISM. 177 



213. The following equation embodies the rule for 

 finding the weight of any given ion disengaged from an 

 electrolytic solution during a known time by a current 

 whose strength is known. Let C be the strength of the 

 current (in webers per second), / the time (in seconds), 

 z the electro-chemical equivalent, and w the weight (in 

 grammes) of the element liberated ; then 



or, in words, the weight (in grammes) of an element 

 deposited by electrolysis is found by ^multiplying its 

 electro-chemical equivalent by the strength of the current 

 (in webers per second), and by the time (in seconds) 

 during which the current continues to flow. 



EXAMPLE. A current from five Daniell's cells was passed 

 through two electrolytic cells, one containing a solution 

 of silver, the other acidulated water, for ten minutes. 

 A tangent galvanometer in the circuit showed the 

 strength of the current to be *5 webers per second. 

 The weight of silver deposited will be -ooii34Ox -5 

 x 10 x 60= '3402 gramme. The weight of hydrogen 

 evolved in the second cell will be "0000105 x *5 x 10 

 x 60 = '003 1 5 gramme. 



214. Voltameters. The second of the above laws, 

 that the amount of an ion liberated in a given time is 

 proportional to the strength of the current, is sometimes 

 known as Faradafs Law, from its discoverer. Faraday 

 pointed out that it affords a chemical means of measur- 

 ing the strength of currents. He gave the name of 

 voltameter to an electrolytic cell arranged for the 

 purpose of measuring the strength of the current by 

 the amount of chemical action it effects. 



215. Water -Voltameter. The apparatus shown 

 in Fig. 92 might be appropriately termed a Water- 

 Voltameter, provided the tubes to collect the gases 

 be graduated, so as to measure the quantities evolved. 



N 



