1904.] on Developnent of the Theory of Electrolytic Dissociation. 559 



pressure of a dissolved body could mucli easier be determined by- 

 help of a measurement of the freezing point of the solution than 

 directly. Now both the direct measurements made by De Vries, as 

 also the freezing points of electrolytic solutions, showed a much 

 higher osmotic pressure than might be expected from the chemical 

 formula. As for instance the solution of 1 gram-molecule of ethylic 

 alcohol — CoHgOH = 46 grammes — in one litre gives the freezing- 

 point —1 • 85°C., calculated by van'tHoff the solution of 1 gram-molecule 

 of sodium chloride — NaCl = 58*5 grammes — in one litre gives the 

 freezing-point — 3 • 26 ' = — 1 • 75 X 1 • 85^ C. This peculiarity may be 

 explained in the same manner as the " abnormal " density of gaseous 

 sal-ammoniac, viz. by assuming a partial dissociation — to 75 per cent. 

 — of the molecules of sodium chloride. For then the solution con- 

 tains 0*25 gram-molecules of NaCl, 0*75 gram-molecules of CI and 

 • 75 gram -molecules of Na, in all 1 • 75 gram-molecules. Now we have 

 seen before how we may calculate the number of active molecules in 

 the same solution of sodium chloride, and we find by Kohlrausch's 

 measurements precisely the number • 75. From this I was led to 

 suppose that the active molecules of the salts are divided into their 

 ions. These are wholly free and behave just as other molecules in the 

 solutions. In the same manner I calculated the degree of dissociation 

 of all the electrolytes that were determined at that time — they were 

 about eighty — and I found in general a very good agreement be- 

 tween the two methods of calculation. In a few instances the 

 agreement was not so good, I therefore made new determinations for 

 these bodies and some others ; the new determinations were all in 

 good conformity with the theoretical prevision. 



The next figure (Fig. 6) shows the freezing-points of some solution 

 of salts, and of non-conductors. As abscissa is used the molecular con- 

 centration of the bodies, as ordinates the molecular depression of the 

 freezing-point, divided by 1 * 85, that should be expected if no disso- 

 ciation took place. As the figure shows, all the curves for the 

 non-conductors — in this case cane-sugar, propyl-alcohol and phenol 

 — converge towards unity with diminishing concentration. At higher 

 concentrations there occur deviations from the simple law. As 

 examples of binary electrolytes are chosen LiOH, NaCl and LiCl — 

 their curves all converge towards the number 2. As ternary electro- 

 lytes are chosen K'SO^, Na.SO^, MgCls, and SrCL, they are decom- 

 posed into three ions, and their curves therefore all converge towards 

 the number 3. 



As I had taken a step that seemed most adventurous to chemists, 

 there remained to investigate its chemical and physical consequences. 

 The most general and wide-reaching of these is that the properties 

 of a highly attenuated solution of an electrolyte ought to be additive, 

 that is composed of the properties of the different ions into which the 

 electrolyte is decomposed. This was already known to be the case in 

 many instances, and Valson had to this end tabulated his " modules " 

 by the addition of the one value for the negative to the other for 



