THE USE OF LIQUID AMMONIA AS A SOLVENT 119 



was supposed to be a very close connection between the 

 dielectric constant and the ionising power of a solvent. 

 Goodwin and Thompson measured the dielectric constant of 

 ammonia and found it to be only about a quarter that of water ; 

 they therefore considered that the high conductivity of ammonia 

 solutions was due to the great mobility of the ions and not to 

 the high ionising power of the solvent. 



The problem which then arose was to find out for certain 

 which of these two factors — mobility or ionising power — was 

 the cause of the high conductivity of liquid ammonia solutions. 

 Frenzel endeavoured to settle this question 03' direct measure- 

 ments of the ionic velocity but owing to the numerous ex- 

 perimental difficulties the results were not of much value. 

 More decisive results were obtained by Franklin and Kraus (21) 

 from an extended series of conductivity measurements at 

 different dilutions. They found that the conductivity of pure 

 ammonia was as low as coi x io~ G , a result which made 

 possible the accurate measurements of the conductivity of very 

 dilute solutions. A large number of inorganic salts and also 

 some organic ammono-acids were used and measurements were 

 made up to very high dilutions. These showed that the limits 

 of the molecular conductivity were reached only at dilutions of 

 from 25,000 to 50,000 litres per gram equivalent, though with 

 water the limiting conductivity is usually met with at dilutions 

 of 1,000 to 5,000 litres. The following dilutions were found to 

 be necessary in order to produce a 50 per cent., 75 per cent, and 

 90 per cent, ionisation of the salt : 



Number of litres required to ionise 

 one gram molecule. 



90 per cent. 



KI 





In water 

 ammonia 



KN0 | In water 



l „ ammonia 



NaNO,( Inwater • 

 I „ ammonia 



AgNO,( Inwater • 

 I „ ammonia 



These numbers indicate that in moderately dilute solutions 

 the salts are far less ionised in ammonia than in water. The 



