THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 197 



the solvent by diffusion. The oxygen escapes and can be collected. The 

 amount of hydrogen and oxygen liberated are in the same proportion as in 

 water, and thus we have an explanation of the " decomposition of water by 

 electrolysis." 



When copper sulphate is electrolyzed metallic copper is deposited on the 

 negative electrode, and sulphuric acid and oxygen collect at the other. In the 

 case of sodium sulphate the sodium ion when discharged acts on water, result- 

 ing in the accumulation of sodium hydroxide and hydrogen around the nega- 

 tive electrode, and as before sulphuric acid and oxygen collect at the positive 

 electrode. 



Faraday's laws of electrolysis, Michael Faraday, of England, was the 

 first to make a careful quantitative study of electrolysis, and announced the 

 following two laws: 



I. The amount of a substance liberated in an electrolytic cell is proportional to 

 the quantity of electricity that has passed through it. 



II. Chemically equivalent quantities of ions are liberated by the passage of equal 

 quantities of electricity. Chemically equivalent quantities are determined by 

 valence. Thus for every divalent ion liberated, two univalent ions are liber- 

 ated, etc., by the same amount of electricity. 



The liberation of 1 gramme of hydrogen requires the passage of 96,540 units 

 (coulombs) of electricity. A current strength of 1 ampere is such that 1 cou- 

 lomb of electricity flows through a circuit in 1 second. Hence a current of 

 1 ampere will require 96,540 seconds (26 hours and 49 minutes) to liberate 

 1 gramme of hydrogen (nearly 11 liters). A current of 5 amperes would do the 

 same work in one-fifth of the time. 



One coulomb (a current of 1 ampere flowing 1 second) will liberate 0.0000104 

 gramme of hydrogen, 0.0000828 gramme of oxygen, 0.0003294 gramme of 

 copper, 0.001118 gramme of silver, etc. These quantities are proportional to 

 the chemical equivalents, and are called in electrical science, electro-chemical 

 equivalents. 



An instrument constructed for determining the amount of a substance as 

 silver or copper liberated by a current in a given time, and from this the cur- 

 rent strength, is called a voltameter (see page 77). Suppose a current flowing 

 for 1 hour through a voltameter liberates 0.59292 gramme of copper upon the 

 cathode, the current strength is 



0.59292 gm. copper = i ^ 



3600 seconds X 0.0003294 elect, chem. equiv. of copper 



Conductivity. Every solution of an electrolyte offers a certain resistance 

 to the flow of the current, which can be measured in ohms (see page 76). If 

 the resistance is small, the solution offers an easy passage for the current, hence 

 it is said to have a high conductivity. A solution of great resistance is said to 

 have a low conductivity. The numerical value for conductivity is the recip- 

 rocal of the resistance, thus: 



Conductivity = 



resistance 



In order that results may be compared, conductivity measurements are made 

 with electrodes 1 cm. apart. The algebraic character used to represent con- 



