3 o THE MECHANISM OF LIFE 



Fio-. 1 represents an electrolytic vessel containing a solution 

 of sulphate of copper, the vertical line indicating a porous 

 partition separating the vessel into two parts. Fig. 2 shows 

 the same vessel after the passage of the current. The acid 

 radical has travelled twice as fast as the metal. For each 

 copper ion which has passed through the porous plate towards 

 the cathode two acid radicals have passed through it towards 

 the anode. Three ions have been liberated at either electrode, 

 but in consequence of the difference of velocity with which 

 the positive and the negative ions have travelled, the negative 

 side of the vessel contains only one molecule of copper sulphate 

 and has lost two-thirds of its molecular concentration, while 

 the positive side contains two molecules of copper sulphate 

 and lias only lost one-third of its concentration. This proves 

 clearly that the ions move in different directions with different 

 velocities. Let u be the velocity of the anions, and v the 

 velocity of the cations. Let n be the loss of concentration at 

 the cathode, and 1 — n the loss of concentration at the anode. 



Then-= " , i.e. the loss of concentration at the cathode is 



V 1—11 



to the loss of concentration at the anode as the velocity of 

 the anions is to that of the cations. Hence by measuring the 

 loss of concentration at the two electrodes, we have an easy 

 means of determining the comparative velocity of different ions. 

 In 1876, Kohlrausch compared the conductivity of the 

 chlorides, bromides, and iodides of potassium, sodium, and 

 ammonium respectively. He found that altering the cation 

 did not affect the differences of conductivity between the 

 three salts, thus showing that these differences of conductivity 

 were dependent on the nature of the anion only, and not on 

 the particular base with which it was combined. The difference 

 of conductivity between an iodide and a bromide, for example. 

 is the same whether potassium, sodium, or ammonium salts 

 are compared. A similar experiment has been made with a 

 series of cations combined with various anions. The difference 

 of conductivity of the salts in the series is the same whichever 

 anion is used. i.e. the difference of conductivity between potas- 

 sium chloride and sodium chloride is the same as that between 



