162 



HYDROGEN ION CONCENTRATION 



where p is the pressure of an ideal gas, v is the volume which con- 

 tains one mol of this gas at this pressure and at the absolute tem- 

 perature T; Po and Vo are the corresponding values for 0°C., and 

 273.09 is the absolute temperature value of 0°C. Taking Berthelot's 

 figure, at 0°C, at 1 atmosphere of pressure, Vo = 22,412 cc; Po = 1 

 atmosphere = 76 cm. mercury, which, at 0°C = 980,665 X 76 X 

 13,595 = 1,013,280 dynes per sq. cm. Therefore R = 83,157,720 

 ergs. 



10^ ergs = 1 absolute joule; 1 absolute joule = 0.99,966 inter- 

 national joules. Hence R = 8.313 international joules or volt 

 coulombs. 1 faraday, F = 96, 450 coulombs. Now by substituting 

 these numerical values in our equation we obtain for the E.M.F. 

 of a concentration chain: 



8.313 . (273 + t) , ci , 



ii< = 7:tt: in ~ volts 



96 540 Co 



Dividing the natural logarithm by 0.4343 we change to the Briggsian 

 logarithms (base 10) and obtain 



E = 0.000,1985 • (273 + t) log - 



C2 



= 6 • log — 



C2 



TABLE 22 



Table 22 gives the values of d (RT) for various temperatures. 



By applying these values and the proper experimental conditions, 

 Nernst's equation for concentration chains can be verified with great 

 accuracy. The experimental data of former years frequently did 

 not exceed in accuracy the difference of 2 to 3 millivolts between the 



