An elementary book on electricity and magnetism and their applications . up their negative chargesof electricity and react with the water (H20) to form sulphuricacid (H2SO4) and to set free oxygen (02). In this way thesulphuric acid, which is added to conduct the electricity, isnot used up, while the water (2 H20) is broken into hydrogen(2 H2) and oxygen (02). 180. Electrolytic cells in series. Suppose two electrolyticcells, one with copper plates in copper sulphate solution andthe other with silver platesin silver nitrate solution,are connected in series, asshown in figure 186, so thatthe sam
An elementary book on electricity and magnetism and their applications . up their negative chargesof electricity and react with the water (H20) to form sulphuricacid (H2SO4) and to set free oxygen (02). In this way thesulphuric acid, which is added to conduct the electricity, isnot used up, while the water (2 H20) is broken into hydrogen(2 H2) and oxygen (02). 180. Electrolytic cells in series. Suppose two electrolyticcells, one with copper plates in copper sulphate solution andthe other with silver platesin silver nitrate solution,are connected in series, asshown in figure 186, so thatthe same current will passthrough each of them. Onweighing the cathode platesin each cell before and afterthe current has been allowedto flow through, we find thatthe weight of silver depositedis a little over three times asgreat as that of copper. To explain this constant ratio between the weights of silverand copper deposited by the same current in the same time,we shall need the idea of chemical equivalent. The chem-ists have analyzed substances into about seventy simple. Copper Sulphate Silver Nitrate Fig. 186. — A current produces equivalentdecomposition in cells containing differ-ent electrolytes joined in series. 268 ELECTRICITY AND MAGNETISM substances, called the elements. For example, we have justseen that water may be decomposed into the two elements,oxygen and hydrogen. They also have assigned to each ele-ment a number, called its atomic weight, which expresses therelative weights of the atoms * of the different elements. Thusthe atomic weight of oxygen (0) is 16 and that of hydrogen(H) is approximately 1. In our discussion of ions (section178), we assumed that some ions, such as sodium (Na+),carried one unit charge of electricity, and others, such as copper(Cu++), two charges. An element which forms an ion withone unit charge of electricity is said to be univalent and one whichforms an ion with two is said to be bivalent. In electrolytes the valence of each ion is numer
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