The Properties of Colloidal Systems. 229 



down and rendered permeable by oxidation ; they may be repaired sub- 

 sequently, when assiinilatory processes become ascendant. 

 We are extending our observations to animal tissues. 



We have to thank Mr. Mummery for the assistance he has rendered to us 

 in carrying out a number of the experiments. 



The Properties of Colloidal Systems. HI.— The Osmotic Pressure 

 of Electrolytically Dissociated Colloids. 

 By W. M. BA.YLISS, F.B.S., Institute of Physiology, University College, 

 London. 



(Eeceived June 30, 1911.) 

 CONTENTS. 



PAGE 



Hydrolytic Dissociation 230 



Electrolytic Dissociation 230 



The Factors of the Osmotic Pressure 232 



Electrolysis of Congo Eed 240 



The Potential Difference at the Membrane 243 



The Distribution of Salts between Solutions of Congo Eed and 



"Water separated by a Membrane 249 



The Action of Carbon Dioxide 251 



The Temperature Coefficient of the Osmotic Pressure of Congo Eed 253 



Summary of Conclusions 253 



In a previous paper* I showed that the osmotic pressure of solutions of 

 Congo red, as measured directly in an osmometer with a membrane of 

 parchment-paper, is about 90 — 95 per cent, of that which they should have if 

 the dye were present as undissociated single molecules, such as those of glucose 

 or urea. Attention was chiefly directed, in tbe paper referred to, to the fact 

 that a body behaving as a colloid gives as high an osmotic pressure as if it 

 existed in solution as single molecules and not as aggregates. It is to be 

 remembered, however, that Congo red is the sodium salt of a fairly strong 

 acid and as such must be dissociated to a considerable degree in solutions of 

 the concentration employed. On this account, the interpretation of the 

 experimental results required further work. Subsequent investigations have 

 shown that there are many difficulties in the way of a satisfactory explanation. 



* 'Koy. Soc. Proa,' 1909, B, vol. 81, p. 269. 



