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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



lighting companies, six dollars would operate Davy's arc light about 

 500 hours or 30,000 times as long. 



DANIELl's BATTERY 



It was soon discovered that if the zinc electrode were rubbed with 

 mercury (amalgamated), the local action would practically cease, 

 and if the hydrogen bubbles were removed, the operating voltage of 

 the cell would be increased. John Frederic Daniell, an English 

 chemist, invented a cell in 1836 to overcome these difficulties. His 



Daniell's Cell, 1836. 



Daniell invented a battery consisting of zinc, copper and copper sul- 

 phate. Later the porous cup was dispensed with, which was used to 

 keep the sulphuric acid formed separate from the solution of copper 

 sulphate, the two liquids then being kept apart by their difference in 

 specific gravity. It was then called the Gravity Battery and for years 

 was used in telegraphy. 



cell consisted of a glass jar containing a saturated solution of copper 

 sulphate (CUSO4). A copper cyHnder, open at both ends and per- 

 forated with holes, was put into this solution. On the outside of the 

 copper cylinder there was a copper ring, located below the surface of 

 the solution, acting as a shelf to support crystals of copper sulphate. 

 Inside the cylinder there was a porous earthenware jar containing 

 dilute sulphuric acid and an amalgamated zinc rod. The two liquids 

 were therefore kept apart but in contact with each other through the 

 pores of the jar. The hydrogen gas given off by the action of the 



