CONDUCTIVITY OF SODIUM HYDROXIDE IN AQUEOUS SOLUTION. 297 



conductivity-temperature curves, and not the product of some abnormal change in 

 the character of the solution. A series of measurements, made some years ago, had 

 shown that dilute solutions of the alkalies gave inflected curves. As there was no 

 reason to suspect the existence of any specfal complications in the case of such simple 

 substances, the conditions appeared to be particularly favourable for the investigation 

 of the nature of the point of inflexion and its dependence on the character of the 

 ulkali and the concentration of the solution. The experiments now described deal 

 exclusively with sodium hydroxide, but the few measurements that we have made 

 with other alkalies have shown that they all behave in a similar manner, as indeed 

 had been indicated by our earlier observations. 



Turning now to the specific case of sodium hydroxide, it may be noted that 

 although the linear temperature coefficient of conductivity has frequently been 

 noted, very few measurements have been made of its variation with temperature. 

 KOHLRAUSCH (loc. cit., 1885) investigated solutions containing 2'61 per cent, and 

 427 per cent. NaOH and gave the formulae 



NaOH 2-61 per cent, *, = 680(1 + 0'0295*+0'000016< 2 ) 

 427 / = 240(1 +0-0866<+0-00451U 2 ). 



He also noticed the great increase of conductivity with temperature in the case 

 of the more concentrated solutions, and recorded an increase of 100-fold in the 

 conductivity of a 40-per cent, solution between 10 C. and +80 C. His figures 

 are given below. 



The calculated values in this table are derived from the parabolic formula 



K, = 222(1+0'01059J+0-004459< 2 ). 



In neither case did the observations come within the range within which a point of 

 inflexion may occur. DtfouiSNE (' Dissertation, Strassburg,' 1895), working between 

 2 C. and 34 C., was also able to represent his measurements of the alkalies by 

 means of a flat parabola, and the existence of a point of inflexion in these curves 

 appears hitherto to have been entirely overlooked. This result is largely to be 

 attributed to the fact that the point of inflexion for solutions of caustic soda never 

 falls much below 50 C. and recedes above 100 C. both in dilute and in concentrated 

 solutions, and also to the fact that a parabolic curve has been assumed to express 

 universally the temperature-conductivity relation. 



VOL. cciv. A. 



2 Q 



