94 



The Origin of Osmotic Effects. II. — Differential Septa. 

 By Henry E. Armstrong, F.R.S. 

 (Received January 23, — Eead January 28, 1909.) 



I have had the privilege of following the progress of the inquiry of which 

 an account is given by Prof. A. J. Brown in the previous communication and 

 of watching the development of the exquisite and invaluable method of study- 

 ing the osmotic process which he has devised ; I trust that I shall not be 

 presuming if I discuss the results which he has arrived at and attempt to 

 interpret them in the light of views already placed before the Society in my 

 communication on " The Origin of Osmotic Effects "* and in the series of 

 " Studies of the Processes Operative in Solutions."! 



Prof. Brown's observations appear to be extraordinarily significant, as 

 affording the means of dividing substances broadly into two classes accord- 

 ing as they will or will not diffuse through a membrane such as that which 

 forms the outer covering of the seed of hax\ey\(Hordeum vulgare) and with the 

 aid of the classification thus secured of arriving at an explanation of the 

 selective process. 



Inasmuch as the barley grain contains but a small amount of soluble 

 crystalloids, the absorption of water by the grain may be regarded as mainly 

 conditioned by the extremely minute granules of starch enclosed within it ; 

 presumably these have great attraction for certain molecules in the liquid 

 and become coated superficially therewith. From this point of view the 

 method developed by Prof. Brown involves the study of a struggle for hydrone 

 between a mass of fine particles of solid and the solution of a substance 

 present in the liquid state in solution in water; the observations are the 

 first of their kind, I believe. 



It is clear, although the method affords only approximate results, that the 

 conclusions to be deduced as to the relative " concentrating " efficiencies of 

 the several solutes are in general accordance with those arrived at in other 

 ways. The observations made in my laboratory show that chlorides are more 

 active than nitrates in solution and that sodium salts are more active than 

 either potassium or ammonium salts — more active, that is to say, in the sense 

 that they exercise a greater concentrating effect ; this is precisely the result 

 arrived at by Prof. Brown. 



No division of the substances into electrolytes and non-electrolytes can be 

 made in any way corresponding to the extent to which water is absorbed 

 * ' Eoy. Soc. Proc.,' 1906, A, vol. 78, p. 264. 



+ Ibid., p. 272 (I); II— V, vol. 79. 1907, pp. 564—597 ; VI— X, vol. 81, 1908, 

 pp. 80—140. 



