THE ELECTRIC CURRENT. 21 



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copper cylinder of which the inside diameter is 12 centimeters. 

 1 5 centimeters of length of anode and cathode are submerged in 

 the electrolyte, and a current of 25 amperes is passed through 

 the cell, (a) Find the current density at the cathode, and (&) 

 find the current density at the anode. Ans. (a) 0.044 ampere 

 per square centimeter; (b} 0.177 ampere per square centimeter. 

 2. An electric current is sent through an ammeter and through 

 a silver coulombmeter. The current gives a steady reading of 

 i. 068 amperes on the ammeter, and the amount of silver depos- 

 ited in i hour and 20 minutes is found by weighing to be 5.635 

 grams. Find the error of the ammeter reading. Ans. 0.018 

 ampere too high. 



Note. The silver coulombmeter is usually arranged as shown in Fig. n. The 

 silver nitrate solution is contained in a clean platinum bowl which serves as the cathode 

 on the interior of which the silver is 

 deposited, and the anode consists of a 

 plate of pure silver surrounded by a 

 covering of filter paper to prevent de- 

 tached particles from falling to the 

 bottom of the platinum bowl. 



3. Calculate the electro- 



chemical equivalents of the theet of metal 



following : (a) Cuprous cop- 

 per ; (&) cupric copper ; (c) zinc ; (</) hydrogen ; (i) aluminum ; 

 and (/) ferric iron. The valencies of the respective metals may 

 be inferred from the following formulae of their chlorides : (a) 

 CuCl; ()CuCl 2 ; )ZnCl 2 ; (rf)HCl; (e) A1C1 3 ; (/) Fed, 

 Ans. (a) 0.0006587 gram per ampere per second; (b) 0.0003293 

 gram per ampere per second ; (c) 0.000339 g r am per ampere per 

 second; (</) 0.00001046 gram per ampere per second; (n 

 0.0000936 gram per ampere per second ; (/) 0.0001929 gram 

 per ampere per second. 



4. A current which gives a steady reading of 10 amperes on 

 an ammeter is found to deposit 8.24 grams of copper in 40 min- 

 utes from a solution of CuSO 4 . What is the error of the ammeter 

 reading ? Ans. 0.42 ampere too low. 



