ELECTROLYSIS 189 



chlorine. There are, however, also the ions, hydrogen and 

 hydroxyl, resulting from an increased dissociation of water, the 

 latter interacting with chlorine to reproduce hydrogen chloride 

 and oxygen gas. Water seems to have a special power of inducing 

 ionisation, superior to that of other liquids which have been 

 tried as solvents. 



All these and many other facts are accounted for by the 

 doctrine of Arrhenius. The current passing through a dissolved 

 or melted electrolyte does not tear the molecules asunder, but 

 simply directs the ions according to the electrical charges with 

 which they are already invested, and causes them to be dis- 

 charged and so restored to the common molecular neutral state 

 at the surfaces of the electrodes where they appear. 



The laws of electrolysis indicate the relation of electrolytic 

 decomposition to the ordinary chemical doctrine of valency. 

 A molecule of hydrogen chloride, HC1, is resolved into 1 part by 

 weight of hydrogen and 35J parts by weight of chlorine. Accord- 

 ing to the law of electro-chemical equivalents, if the same current 

 passes through a solution of common salt, NaCl, and then 

 through solutions of calcium chloride, gold chloride, and tin 

 chloride, for every 35J parts of chlorine set free in the first cell, 

 the same amount of chlorine would be liberated in each of the 

 others. But while 35J parts of chlorine combine with 23 parts 

 of sodium, which is the atomic weight of that metal, the same 

 quantity combines with 20 parts of calcium, with 65f parts of 

 gold, and with 29f parts of tin, and these are respectively J, 

 J, and J the atomic weights of those metals. But since the 

 atomic weights are known from other considerations we must 

 suppose that an atom of calcium combines with twice as much 

 chlorine as an atom of sodium, an atom of gold with three times 

 as much, and an atom of tin with four times as much. And these 

 metals are respectively said to be univalent, bivalent, trivalent, 

 and quadrivalent. Chemically equivalent atoms carry in electro- 

 lysis the same electric charge, and the charge carried by one 

 atom of hydrogen or one atom of chlorine is called the unit 

 charge, and is represented by 96,500 coulombs of electricity for 

 1 gram of hydrogen. 1 The atom of calcium, therefore, carries 

 two such atomic charges, an atom of gold three, and an atom of 

 tin four atomic charges of electricity. 



1 No explanation can be given here of the electrical units, definitions ot 

 which will be found in every text-book of physics. 



