CONDUCTIVITY OF SODIUM HYDROXIDK IN AQUEOUS SOLUTION. 



The solution volumes, V, of 1 gramme of sodium hydroxide at 1 8 C. are given in 

 the last column of Table VI., together with the total hydration, H, of the solution 

 expressed in molecules of water per molecule of soda. When these are plotted against 

 one another, they give the hyperbola-like curve of Diagram IV. The symmetry of 

 this curve, though not exact, is of interest because it appears to indicate that the 

 process of hydration, on which the contraction of volume depends, proceeds 

 continuously from the most concentrated to the most dilute solutions. From this 

 point of view it was of interest to inquire at what dilution the molecular volume 

 would reach its limiting value. A more careful study of the curve of Diagram FV., 

 in conjunction with a similar curve in which the molecular volume was plotted against 

 the logarithm of the hydration, revealed the fact that there was an alteration of 

 curvature at about 45 per cent. NaOH and a further change at about 5 per cent. It 

 was possible, however, to obtain remarkably concordant results for the limiting value 

 of the solution volume by two entirely different methods of extrapolating from the 

 densities between 1 and 5 per cent. The following table shows the agreement between 

 the observed densities and those calculated from the formulas 



(a.) p-p = 0-01141 P-0-000052P 4 , 

 (6.) Iog P/Po = 0-00496P 0-000049P 8 , 



where p is the density of water, p the density of the solution, and P the percentage 

 of sodium hydroxide. 



TABLE X. 



From formula (a) the solution volume is given by the expression 



y = -fl- 10 ,-!~^L , where a = O'OIHI, ft = 0'000052 ; 

 Pol Po+r(<*. F)J 



and from formula (6) by the expression 



y - I ' ~ ' ? ( 1 -~ < "~' II>> )~L where /t = 0'4343, a = 0-00496, =0'000049. 

 PoL J 



The limiting value deduced from formula (a) is 0-1423, and from formula (b) is 

 0-1427. 



The concordance between these figures renders it probable that they afford an 

 VOL. cciv. A. 2 o 



