His gravity cell construction became very popular for telegraph applications. Fuller replaced the corrosive sulfuric acid in Daniell cell with the benign zinc sulfate to enhance the life of the battery. The carbon anode was surrounded by potassium dichromate crystals in sulfuric acid. John Fuller's ‘gravity cell’ (1852) had a zinc cathode, dipping in liquid mercury, in a porous cup filled with a diluted sulfuric acid. Owing to the shape of the zinc electrode in zinc sulfate or sulfuric acid, the cells were also called Crowfoot Cells. The gravity cell was used in a closed circuit with a slight drain on the cell. As soon as a continuous current was driven through the cell, diffusion, which normally would mix the two liquids, played no important role, because of the migration of the ions to the electrodes. To avoid mixing of the electrolytes, the battery had to be stored in an undisturbed locality. This construction did not require any separator between anode and cathode, thus reducing the internal resistance of the cell. Gravity cells, which were used in the early days of telegraphy and railway signaling, consisted of a lighter electrolyte floating on the top of a heavier electrolyte, e.g., a zinc sulfate solution over a copper sulfate solution. Kurzweil, in Encyclopedia of Electrochemical Power Sources, 2009 Gravity cells
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