454 PROCEEDINGS OF THE AMERICAN ACADEMY 



The Battery. 



The needle of the electrometer was charged and kept at a constant 

 potential by being connected to the positive pole of a constant buttery, 

 while the negative pole was coiniected to the ground. 



At first, a zinc and copper distilled water battery of two hundred 

 cells was used. The number of cells was afterwards increased to 

 four hundred. The battery was placed in a large covered box to 

 keep out the dust. The zinc used was common commercial zinc, and, 

 became coated with an oxide which had to be scraped off every two 

 weeks. The evaporation of the water in a warm room was very 

 great, so that the battery required constant care. 



At the sugf^estion of Professor Trowbridge, we made a Beetz solid 

 battery.* The cells consisted of glass tubes 10 cm. long and 1.2 cm. 

 in diameter. One half of the tube was filled with white alabaster . 

 plaster of Paris mixed with a solution of copper sulphate. A copper 

 wire was placed in this, and the plaster allowed to harden. Then 

 the other half of the tube was filled with plaster of Paris mixed with 

 a solution of zinc sulphate. A zinc wire was placed in this, and the 

 plaster allowed to harden. The cells were connected in series. In 

 order to save the time and trouble required to solder the copper of each 

 cell to the zinc of the next, sheets of copper 10 cm. wide were soldered 

 to similar sheets of zinc. These were then cut into strips, which 

 were bent in the shape of a U. The copper end was placed in the 

 })laster of Paris containing copper sulphate, and the zinc end in the 

 plaster of Paris and zinc sul[)hate of the next cell. Care was taken 

 that the wires should not extend quite to the middle of the cell, to 

 prevent their coming in contact with the opposite sulphate. The 

 ends of the cells and the connecting wires were dipped in paraffine 

 to prevent the zinc and copper sulphates creeping along the wires. 

 A battery of two hundred cells was made and placed in a box 

 GO cm. long, 40 cm. wide, and 20 cm. deep, which could be moved 

 around easily. Care should be taken not to connect the terminals, 

 for the battery will ])olarize and soon destroy itself. Six cells were 

 experimented upon in November, 1884. to determine their electro- 

 motive force and internal resistance. They worked perfectly until 

 the latter part of February, 1885, when they gave out. Their 

 average electromotive force was LOG volts; their average internal 

 resistance, 1,600 ohms. The rest of the battery does not seem to 



* riiil. Mag., March, 1884. 



