ELECTROLYTES. 



217 



The pressures which were obtained are very large as compared with 

 the calculated gas pressure of molecular lithium chloride, the ratios 

 being (see table 75) 1.746, 1.816, 1.857, 1.899, 1.955, and 1.992, respec- 

 tively, for the 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 weight-normal solutions. 

 Such excessive pressures were, of course, to be expected from the 

 known considerable electrolytic dissociation of the salt ; but the ratios 

 cited above do not diminish with increasing concentration, as would 

 be expected, if the differences between the observed osmotic and the 

 calculated gas pressures were due solely to electrolytic dissociation. 

 On the contrary, the ratios in question increase in value with increasing 

 concentration. A similar increase in ratio of osmotic to calculated gas 

 pressure was observed in the case of cane-sugar solutions, and it was 

 tentatively ascribed to a hydration of the solute. It was presumed, in 

 other words, that any withdrawal of solvent molecules for the purpose 



Table 75. — Osmotic pressure of lithium chloride at SO . 



Observed pressures 



Mean pressures 



Calculated gas pressures* 



Ratio of osmotic to gas pressure 



Concentration. 



0.1 



4.325 

 4.311 

 4.317 

 2.472 

 1.746 



0.2 



8.946 

 9.005 

 8.976 

 4.943 

 1.816 



0.3 



13.809 



13.626 



13.768 



7.415 



1.857 



0.4 



18.755 



18.789 



18.772 



9.886 



1.899 



0.5 



24.162 



24.162 



12.358 



1.955 



0.6 



29.535 



29.535 



14.830 



1.992 



* For undissociated salt. 



of hydrating those of the solute would have the effect of concentrating a 

 solution, and that the result of such concentration would be an apparently 

 abnormally high osmotic pressure. Concentration through hydration of 

 the solute should manifest itself in the form of an increasing ratio of 

 osmotic to gas pressure, such as was observed in the case of lithium 

 chloride at 30° and in that of cane sugar at the lower temperatures. 



The electrolytic dissociation of the solutions of lithium chloride, 

 whose osmotic pressures were measured, have not yet been determined, 

 and the data available are insufficient for a safe estimation of the same. 

 It is, therefore, impossible to say at present what proportion of the 

 observed difference between osmotic and gas pressure is to be ascribed, 

 on the one hand, to dissociation; and, on the other, to a conjectured 

 concentration of the solution through hydration of the solute. If the 

 whole difference is ascribed to dissociation, the percentages of ionized 

 salt which must be presumed to exist in the 0.1, 0.2, 0.3, 0.4, 0.5, and 

 0.6 weight-normal solutions of lithium chloride are 74.6, 81.6, 85.7, 

 89.9, 95.5, and 99.2 respectively. Such relations of dissociation to 

 concentration are, of course, quite impossible. 



The effect which was produced upon the membranes by the lithium 

 chloride was very pronounced. They became at once exceedingly slug- 



