269 



Hie Properties of Colloidal Systems. I. — The Osmotic Pressure 

 of Congo-red and of some other Dyes. 



By W. M. Bayliss, F.E.S., Physiological Laboratory, University College, 



London. 



(Received April 19— Read May 6, 1909.) 



Experiments made in 1895 by Linder and Picton* upon solutions of 

 arsenious sulphide indicated that colloidal solutions possess a real osmotic 

 pressure, although the authors themselves claim no quantitative value for 

 their results. In 1905f further experiments were made, but again great diffi- 

 culties were met with, and, although it seemed evident that osmotic pressure 

 was present, the numerical values obtained were irregular and small. 



The first definite proof that certain colloidal solutions are able to exert a 

 not inconsiderable osmotic pressure was given by Starling j in the case of the 

 colloids of blood-serum. When separated by a gelatin membrane from a 

 solution obtained by filtration of some of the same serum through Martin's 

 gelatin filter, the pressure rose to about 30 mm. of mercury. 



Waymouth Reid§ found that solutions of carefully purified haemoglobin 

 gave an undoubted osmotic pressure when separated from water by a 

 membrane of parchment-paper, but regards this fact as evidence .that 

 haemoglobin forms a true solution. 



Moore and Parker || determined the osmotic pressures of the colloids of 

 white of egg, of serum, and of soap solutions, while Moore and RoafU made 

 measurements of those of serum-proteins, of gelatin, and of gum-acacia. 



Hufner and Gansser** and, somewhat later, Roaf,ff independently of one 

 another, made careful determinations of the osmotic pressure of haemoglobin 

 solutions, to which reference will be made in a subsequent page. 



It will be noticed that, in all these cases, with the exception of arsenious 



sulphide and soaps, the chemical constitution of the body investigated is 



uncertain, although the molecular weight of haemoglobin has been calculated 



from its content in iron. The experience of those who had worked with 



arsenious sulphide and with soaps was not encouraging for further research, 



* ' Chem. Soc. Trans.,' vol. 67, p. 72, 1895. 

 + 'Chem. Soc. Trans.,' vol. 87, p. 1909, 1905. 



% 'Journ. Physiol.,' vol. 19, p. 322, 1896, and vol. 24, p. 318, 1899. 



§ 'Journ. Physiol.,' vol. 33, p. 12, 1905. 



|| ' Amer. Journ. Physiol.,' vol. 7, p. 261, 1902. 

 IT ' Biochem. Journ.,' vol. 2, p. 34, 1907. 

 ** ' Archiv f. Physiol.' (Engelmann), 1907, p. 209. 

 tt 'Physiol. Soc. Proc.,' 1908, p. i, in 'Journ. Physiol.,' vol. 39, 1909. 



