THE VALUES OF THE CONSTANTS. 9 



THE VALUES OF THE CONSTANTS. 



To introduce the subject of potential measurement, the quantities deter- 

 mining it in the simple formula iwF = RTln -Mnay be discussed, with a view 



to discovering how closely the numerical values selected for them may be 

 identified with absolute physical conceptions. In future the symbol ir will be 

 used instead of E to designate electromotive force, in accord with the more 

 general modern usage. 



By the derivation of the equation for monatomic metals, v is the valence 

 of the metallic ion in the electrolyte connecting the two amalgams. Cady's 2a 

 results are consistent with this premise, within the limit of error of his ex- 

 periments, for the two valences of tin. It is hard to imagine how the 

 valence of the zinc or cadmium ion in a sulphate solution could be anything 

 else but 2 ; therefore, in all calculations involving v, this number will be 

 used. 



Richards and Heimrod 2T have corrected four of the best determinations of 



the electrochemical equivalent of silver for small chemical errors. The new 



values were practically identical, in spite of a great variety of methods for 



referring the strength of the current observed to absolute units. Guthe ^ has 



recently come to the same conclusion. Hence, great confidence is placed in 



the conclusion that 96,580 coulombs are associated with a gram equivalent 



of silver. Richards, Collins and Heimrod, 29 and Richards and Stull 30 have 



established the universality of Faraday's law upon a firmer basis than ever. 



Hence, the same value, F = 96,580, is used for a gram equivalent of zinc 



with reasonable certainty. This value is based upon the usually accepted 



value 107.93 f r tne atomic weight of silver, and must be diminished by 0.04 



per cent if silver is taken as 107.89. 



P V 

 The constant R is defined as the quantity -= , expressed in mayers, for a 



gram molecule of a perfect gas at any temperature. The recent work of 

 Daniel Berthelot 31 makes it probable that the value of V under 760.00 mm. at 

 45 of latitude on the sea level is 22.412 liters, and that o A = 273.08 C. 

 Therefore these values will be used in the computations concerning a perfect 

 gas, realizing that an error of 0.1 per cent, while improbable, is still possible. 



26 Journ. Phys. Chem. 2, 558 (1898). 



27 Proceedings of American Academy, 37, 415 (1902). 



28 Physical Review, 19, 138 (1904). 



28 Proceedings of American Academy, 35, 123 (1899). 

 30 Ibid., 38, 409 (1902). 



81 Daniel Berthelot, Trav. et Mem. du Bureau internat. des poids et Mesures, 13, 

 113 (1903). Also Zeitschr. Electrochem., 10, 621 (1904). 



