GALVANIC APPARATUS. 

 Fig. 398. 



335 



as may best answer the purpose ; three or four combined is 

 the usual number. They consist of cups of copper, four 

 inches wide and four and a half inches deep, having a lip at 

 the side connected with the inside of the cup by a number 

 of holes. To the rim of each cup there is attached a brass 

 cup with a binding screw. In the interior there is a zinc 

 cylinder, one in each set having a binding screw, and the 

 others, stout copper wires for connecting with the copper 

 cups of the next series ; between the zinc and copper cylin- 

 ders there is a cup of porous earthenware, entirely separat- 

 ing the two metals. To use, fill to within half an inch of 

 the top the outer space, with a saturated solution of blue 

 vitriol (which may be about one ounce to each cup), and put 

 some pieces of blue vitriol in the lip to keep the solution 

 saturated, and in the interior of the porous cup, put a table 

 spoon full of common salt, or Glauber's salt, and nearly fill 

 with Avater ; connect the zinc of the one with the copper of 

 the next throughout the series, the disconnected copper and 

 zinc being the poles of the battery. This battery will main- 

 tain nearly a constant action for a week (if properly supplied 

 with blue vitriol, and a little salt stirred in the interior once 

 a day), without disconnecting the series ; though when con- 

 venient, it is preferable to clean the zinc cylinders oftener. 

 In many cases a much weaker solution of blue vitriol may 

 be used than that described. Price, of a set of 3, $5.25. 



" 4, $7.00. 



Grove's batteries, of three different sizes of four cells 

 each, are conveniently arranged for gilding. 



Price, small size, $4.50. 

 " second " $5.50. 

 " large " $6.50. 



