64 Mr. W. Sutherland on Weak Electrolytes and 



them. This is in other words the hypothesis which I 

 suggested in discussing strong electrolytes, namely that 

 water dissociates a certain number of double molecules into 

 single molecules, which as strong electrolytes are immediately 

 completely ionized, so that the solute is present only as 

 double molecules and ions. 



It is usually assumed that the molecular lowering of the 

 freezing-point of water caused by acetic acid proves that 

 the acid is present as single molecules. In 100 grammes of 

 water 0*00571 of acetic acid give a molecular lowering of the 

 freezing-point of 2 o, 05, the normal being l c, 85, 1*66 grammes 

 give l°-86, 13-45 gr. l°-75, 25 gr. l°-63, 116-6 gr. 1°T5. 

 It is usually assumed that when 25 grammes of acetic acid 

 are mixed with 100 of water, the greater part of the acid is 

 dissociated into single molecules of which only a minute 

 fraction are ionized. But in our examination of the physical 

 properties of mixtures of water and acetic acid we have 

 found no phenomena indicating that nearly up to p 1 = 0'25 

 the greater part of the acetic acid undergoes one simple 

 change. Almost all the evidence pointed to change in the 

 water. The facts for the other fatty acids are similar. In 

 the case of ethyl alcohol §6 grammes mixed with 100 of 

 water give a molecular lowering of the freezing-point 

 1*81 degrees. We found no evidence in the physical pro- 

 perties of mixtures of water and alcohol to support the 

 hypothesis that all the alcohol undergoes a simple change to 

 the state of single molecules. The method of the molecular 

 lowering of freezing-point for determining absolute mole- 

 cular weights (masses) breaks down completely when applied 

 to the delicate problem of the double molecules we are 

 considering. This being so, there is no valid ground for 

 assuming the existence of single molecules of the fatty acids 

 in their aqueous solutions, and the current theory of weak 

 electrolytes becomes virtually untenable. Its chief fault is 

 that it draws attention away from the vastly important 

 electric fields betw T een an ion and its neighbour and therefore 

 from the even more important ones in and around atoms. 

 In Nernst's theory of the concentration cell one aspect of 

 these fields is considered. In ' k Ionization in Solutions and 

 Two New Types of Viscosity " and in " The Molecular 

 Constitution of Aqueous Solutions" (Phil. Mag. [6] xiv. 

 p. 1, 1907, xii. p. 1, 1906) I have sought to give due 

 prominence to molecular and atomic electiic fields. The two 

 new types of viscosity have not made their appearance in the 

 present discussion because with weak electrolytes the con- 

 centration of the ions is too small to bring in the viscosity 



