1911.] 



The Properties of Colloidal Systems. 



239 



applies, the osmotic pressure should be a linear function of the conductivity. 

 Fig. 1 shows that this is not the case ; the departure, however, although 

 unquestionable, is not very great. The explanation may perhaps lie in the 

 fact that the part played by the non-dissociated molecules in the production 

 of osmotic pressure, and which would be relatively greater in the more 

 concentrated solutions, is not taken into account. That these molecules do 

 take part is shown by the fact that the increase of osmotic pressure for 

 a given rise in conductivity shows a steady increase from the more dilute 

 solutions upwards. For example, at 500 litres dilution, an increase of 

 50 recip. megohms in conductivity is associated with a rise in osmotic 

 pressure of about 5'5 mm. Hg. At 20 litres dilution the same increase in 

 conductivity gives a rise in osmotic pressure of 14 mm. Hg and there is a 

 fairly regular transition from one to the other. At higher concentrations the 

 rise per 50 recip. megohms falls to 10 again, but obvious precipitation 

 commences to appear. The curve representing these ratios has an S-shape 

 and is given in fig. 3, since it may turn out to be of some significance. 



Ordinates. — Rise of osmotic pressure in mm. Hg for each 50 recip. megohms in 



conductivity. 

 Abscissa. — Dilution in litres. 



It may perhaps be possible ultimately to arrive at some knowledge of 

 the relative parts played by the dissociated and non-dissociated molecules 



