186 CHEMICAL DISCOVERY AND INVENTION 



theory assumes that the molecules of the electrolyte, though 

 moving about in the liquid, are all complete and entire until the 

 moment when the electro-motive force is applied, and that then, 

 and not sooner, they are separated by the opposite electrical 

 attraction of the cathode and anode respectively. 



In such operations if the same current passes successively 

 through solutions of different electrolytes the quantities of 

 substance liberated at each pole is in proportion to the chemical 

 equivalents of these substances. That is if 1 part by weight of 

 hydrogen is liberated in the cell charged with hydrochloric acid ; 

 108 parts of silver would be deposited from a solution of a silver 

 salt included in the same circuit. Similarly 32J parts of zinc, 

 103J parts of lead, 31| parts of copper would be liberated for 

 1 part of hydrogen. At the anode where the chlorine appears 

 for every 35 J parts of that element set free, 8 parts of oxygen, 

 or 80 parts of bromine, or 49 parts of sulphuric acid would 

 appear at the same surface. This is in accordance with 

 Faraday's law. It appears that all soluble or fusible compounds 

 are decomposed by the same current in chemically equivalent 

 quantities, however different they may be in chemical constitu- 

 tion. It is also a fact that the smallest current sent through 

 an electrolyte produces chemical decomposition in proportion to 

 its strength in accordance with Faraday's first law (p. 110). If 

 molecules, in the fluid state of a substance, are broken up by 

 the current it might be expected that while some would be 

 easily decomposed, others would be broken up with greater 

 difficulty, and one or other of Faraday's laws would not be valid. 



In one of his lectures on " Theories of Chemistry," given in 

 1904, Professor Arrhenius refers to the beginning of his own 

 work on the subject in the following words : " In the year 1883 

 I carried out an investigation on the conductivities of different 

 electrolytes, and was thereby led to the conclusion that all the 

 molecules of an electrolyte do not conduct the electric current. 

 The molecules were therefore divided into two classes, active 

 and inactive. At high dilutions all the molecules were sup- 

 posed to be transformed into the active state. The number of 

 electrically active molecules in a solution (e.g. of an acid) was 

 measured by its conductivity. 



" Now the order of different acids, as regards their power of 

 displacing one another from their salts, was known from thermo- 

 chemical measurements. This order was exactly the same as 



