to form dissolved zinc sulfate (Zn++ + SO4 =ZnSO4).Before the action starts, the sulfate and hydrogen ions cancel each otherelectrically in the solution. Once the hydrogen ions (2H+) are free, they seizeelectrons at the copper electrode, become normal hydrogen atoms (H), andform bubbles of gaseous hydrogen (H2). This allows the copper electrode todraw more electrons, which keeps the current flowing. In the process, acid andzinc are consumed. When either is used up, the battery fails. The simple voltaic cell cannot operate very long because the bubbles ofhydrogen gas that collect at the copper electrode act as an insulator, stoppingfurther electron flow. This blockage is called polarization. In 1836 John F. Daniell,an English chemist, produced a cell that was not subject to polarization. In theDaniell cell, the copper electrode forms the outer shell of the cell and containsa copper sulfate solution; the zinc electrode is immersed in a zinc sulfate orsulfuric acid solution. A porous cup keeps the two solutions apart. The cellproduces current just as the voltaic does, except that copper ions from thecopper sulfate seize electrons at the copper electrode. These ions are thendeposited as copper atoms on the electrode. No hydrogen bubbles appear. In about 1866 the French chemist Georges Leclanche created anothercell that prevented polarization. He used carbon and zinc for the positive andnegative electrodes and a solution of ammonium chloride (commonly calledsal ammoniac) for the electrolyte. Although this combination releaseshydrogen, the gas is absorbed in a mixture of carbon grains and manganesedioxide in the cell.Today's dry cell--the familiar battery used in flashlights, portable radios, andtoys--employs the same materials. The ammonium chloride electrolyte iscustomarily a jelly absorbed in a sheet of a porous substance. The zinc is formedinto a cup with the other materials inside. The top is sealed, making the cell "dry."Often a steel...
