1909.] 



The Properties of Colloidal Systems. 



275 



used above was a fairly good sample, having a conductivity of not more than 

 5 gemmhos at 18° while the purer water had a conductivity of 1*8 gemmhos. 

 If still better water had been used, no doubt the full theoretical value of 

 228 mm. for the osmotic pressure would have been reached. 



Since the ordinary distilled water presumably contained carbonic acid, 

 I tried the effect of water through winch carbon dioxide gas had been passed 

 until its conductivity was 23 gemmhos. By titration, this solution was 

 found to contain 0*19 gramme C0 2 per litre. The osmotic pressure fell from 

 207 to 120 mm. Hg. 



The powerful action of so weak an acid as carbonic is rather surprising, 

 and makes it unnecessary to subject stronger acids to detailed investigation. 



When the solution of carbonic acid in the above experiment was replaced 

 by a decinormal solution of sodium chloride, the osmotic pressure fell in the 

 course of 24 hours to 15 mm. Hg. When equilibrium was established, the 

 concentration of sodium chloride on both sides of the membrane would be 

 about one-twentieth normal. 



Linder and Picton* found that when aggregation of arsenious sulphide was 

 brought about by an electrolyte, it was impossible to reverse the process by 

 washing with distilled water. Similarly, although repeated changes of 

 distilled water were passed through the osmometer after the sodium chloride, 

 until the issuing water gave no reaction with silver nitrate, the osmotic 

 pressure only rose to about three-quarters of its initial value. It is possible 

 that very much more prolonged dialysis might have produced further effect, 

 but it seemed more important to use the apparatus for other experiments, 

 since all these experiments are of necessity of long duration. This washing 

 with water was, in one case, continued for three weeks, and, although after 

 this process the osmotic pressure had risen only to three-quarters of what it 

 was before the action of sodium chloride, no further rise was to be detected 

 on the mercurial manometer when a fresh change of water was added. If 

 a more delicate manometer had been used, it is quite possible that the 

 pressure would have been found to be still rising very slowly, since the 

 extreme slowness of removal of the last traces of electrolyte is characteristic 

 of adsorption phenomena.! 



In order to test the action of alkali, a solution of the blue free acid was 

 placed in the osmometer. Only a small pressure of a few millimetres was 

 obtained, too small to read accurately on the mercurial manometer. When 

 dilute sodium or ammonium hydroxide was run into the lower chamber, the 

 pressure rose rapidly as long as the alkali combined with the dye-acid. 



* ' Chem. Soc. Trans.,' vol. 87, p. 1911, 1905. 



t Bayliss, 'Biochem. Journ.,' vol. 1, p. 182, 1906. 



