60 Mr. W. Sutherland on Weak Electrolytes and 



degree of ionization of a weak electrolyte in the definition of 

 van 't Hoff, Arrhenius. and Ostwald is really a measure of the 

 dissociation of its double molecules and of the ionization of 

 the single molecules resulting therefrom. For these reasons 

 the electrical conductivity of solutions of the fatty acids will 

 receive special study in the next section. 



5. Electric Conductivity of Solutions of the Fatty Acids. 



The fatty acids will be investigated here as typical weak 

 electrolytes. Let a gramme-molecule (for a single molecule, 

 such as CH3COOH for acetic acid) be dissolved to make Y 

 litres of solution, and let the molecular conductivity of the 

 solution as hitherto defined be \, and its viscosity be ??, A, 

 and rj being the values when V is infinite. Then, according 

 to the usual notation of Ostvvald's theory for weak electro- 

 lytes X/\ ~oi or i the degree of ionization. As a rule the 

 investigation is confined to values of V so large that it may 

 be assumed that 7) = rjQ. It is better to provide for a 

 difference between rj and r) by writing \r)/\ r) Q = a or *. 

 The simple theory of Ostwald is that the non-ionized electro- 

 lyte 1 — a. is ionized at a rate k(l — a)/V, and that the two 

 sets of ions recombine at a rate k / u 2 /V 2 ) so that for equi- 

 librium 



k(l-cc)/V = k'* 2 /Y 2 .-. cc 2 /(l-*)Y=k/k' = K. (52) 



This is the equation which is in beautiful accord with the 

 experimental facts, 10 6 K having the following values near 

 15° C, those of X at 18° being added from the data of 

 Kohlrausch. 



Acid ... Formic. Acetic. Propionic. Butyric. Isobutyric. Valeric. Caproic. 

 10 6 K ... 214 18 13 15 14 16 14 

 A ... 365-2 353-4 349'8 346-3 ... 



For dilute solutions of the fatty acids, then, we have 



(X^/Ao^o) 2 = Ky(l-Av'X 7 7o ). . . . (53) 



I propose to give a different interpretation to this formula 

 from that current in the text-books of physical chemistry 

 after Ostwald, van 't Hon , and Arrhenius. It is important 

 then first to pass to the case of solutions which are not dilute. 

 With acetic acid between p 1 ~0A and j? i = 0'd, Grunmach 



{Ann. d. Phys. [4] xxviii. p. 217, 1909) noticed that X* 

 is nearly linear in the concentration pj9 1 /M 1 = l/10 3 V. With 

 this clue I have found that in not dilute solutions of the 

 first four fatty acids (Xrjy is linear in p l . To illustrate this 



