86 



HARRY C. JONES 



solutions have of remaining homogeneous or standard, all volu- 

 metric methods in chemistry would be wiped out and experi- 

 mental biolog}' could not have hoped to achieve what has already 

 been done, or to advance as rapidly as we may reasonably expect 

 it to do in the near future. 



Perhaps this brief sketch may serve to give some faint concep- 

 tion of the importance of osmotic pressure as a property of 

 solutions, especially in maintaining solutions homogeneous for 

 the development, from the quantitative side, of not only chem- 

 istry but many other branches of natural science. 



And, again, consider the osmotic pressure of colloids or colloidal 

 solutions. This whole subject has come very much to the front 

 in the last few years, in connection with the tremendous develop- 

 ments in the field of colloidal chemistry. We all well remember 

 that it was only a few years ago that colloids were suspected of 

 having no osmotic pressure, and yet in many so-called colloidal 

 solutions we had phenomena manifesting themselves that were 

 at least analogous to diffusion; and how can we have diffusion 

 without osmotic pressure when the latter is the cause of the 

 former? 



More recent work indicates that these colloidal solutions, and 

 perhaps some of the colloidal suspensions in which the parts are 

 much larger than in colloidal solutions, actually have osmotic 

 pressure, and it would not be surprising if it should ultimately 

 be shown that the osmotic pressure of colloidal solutions obeys 

 the same general laws as the osmotic pressure of so-called true 

 solutions. In colloidal solutions we know that matter is much 

 less finely divided than in true solutions, and, consequently, the 

 number of physical units present for any given amount of sub- 

 stance in suspension is much smaller in the colloidal than in the 

 dissolved state. It is, therefore, not surprising that such colloids 

 should, in the presence of say water as a solvent, exert much 

 smaller osmotic pressure than equivalent concentrations of 

 crystalloids, in which we know the parts in the presence of the 

 solvent are in a much finer state of subdivision. The role of 

 osmotic pressure, and of surface tension, which is probably very 

 closeh^ connected with it, will, in my opinion, be very prominent 



