34 DESCRIPTION OF GALVANIC BATTERIES. 



by a galvanic action upon the copper plate and the solution in the 

 battery. It generally begins at the lower edge of the copper plate, 

 and spreads upwards. This weakens the electric current, both by 

 inducing a galvanic action between the zinc and the copper, upon 

 which it is deposited, and by its tendency to send a current of elec- 

 tricity in an opposite direction to the main current, thereby neutra- 

 lizing to a great extent the original power of the circle. 



3d. When copper is used it becomes gradually covered over with 

 a thin, black, slimy coating of oxide and other impurities, which 

 materially affects the regularity and strength of the current : this is 

 a source of considerable annoyance in working, and necessitates a 

 regular cleaning of the coppers, which should be done immediately 

 on being taken out of the battery, by brushing with a hard hair brush 

 in water; but when the battery has been long in action, this mode of 

 cleaning is insufficient : the plates will then require to be rubbed 

 over with a little dilute nitric acid, and then washed. If the black 

 coating be allowed to dry upon the coppers, they must then be 

 dipped into strong nitric acid till their surfaces are acted upon ; or 

 they may be moistened with a little urine, then brought to a dull 

 red in the fire, and immediately plunged into water ; but in both 

 cases there is a loss of copper. A small quantity of the black matter, 

 upon being tested, gave oxide of copper, with a trace of iron, anti- 

 mony, and lead, which are the general impurities of sheet copper. 



Max, Duke of Leuchtenberg, 1 has. given the following results of 

 an analysis of the black matter found upon the copper plate forming 

 the positive electrode in a copper solution. 



An analysis of this sort invests the subject with great interest. 

 We wish there had also been given an analysis of the copper that 



1 Progress of General Science, vol. II. 



