ISO ROYAL SOCIETY OF CANADA 



of it.he substiince of tJie septum, and yet such axi-tivity may bo the only 

 factx>r in such osmosis as it certainly is in the case of hydrogen diffusing 

 through palladium into a uiediimi of nitrogen. Here there can be no 

 bombandmeiîit to explain how the hydrogen gets through the palladium. 

 Even in ordinaiy aqueous solutions, this bombardment must be ineffective, 

 for it has been estimated that to dnive one gram of urea through water 

 at the rate of 1 cm. a second, a pressure is required equivalent to 40,000 

 tons weight, and yet in a grtam molecuJar solution of urea the pressure, 

 according to the gas theory of solution is 22.4 atmoc-plieres or about 336 

 pounds to the square inch. 



The difficuJity of accounting for some of the phenomena of osmosis 

 on the postulates of a semi-permeable membrane and the gaseous con- 

 dition of the solutfe has led a number of physicists and physiologists to 

 reject both as quite inadequate and unsatisfactory. I. Traube^ explains 

 all the phenomena of osmosis as due to difference in surface tension on 

 opposite sides of the septum, the difference determining the direction and 

 velocity of the osmotic current, the direction being towards tlie liquid 

 having the greater surface tension. He claims, however, that " the 

 difference between the surface tensions cannot be considered as. equal to 

 the osmosis pressure, for this new pressure is quite different for isosmotic 

 solutions." That surface tension is tJie cause of osmosis is also the view 

 of Battelli and Stephanini,^ who, however, hold that the curnent does 

 not necessarily move toward tlie fluid having the higher surface tension, 

 but always in such a direction as to make the surface tensions on both 

 sides of the septum the same. Barlow ^ found in some of his experiments 

 that the current passed from the weaker solution, that is from the one 

 having the greater surface tension to tlie more concentrated solution, and 

 therefore, he does not support Traube's view. He suggests that the neces- 

 sary factor in osmosis is " that the membrane must absorb that liquid, 

 which, in going through, forms the osmotic current." 



That surface tension does play a very considerable part in osmosis 

 may be found on consideration of some elementary facts in connection 

 with solution. In cveiy vessel holding a fluid there are two tensions: 

 one at the surface known as the air tension, the other where the liquid 

 iti in contact with the wall of the vessel. Whenever the fonucr inci'eases 

 the latter diminishes. It has been olvserved that for most i^â\t solutions, 

 the air tension is greater than in the case of distilled water. Hence the 

 c-ther tension in such salt solutions, that between the liquid and tlie wall. 



1 Phil. Mag. (6), Vol. 8, p. 704, 1904. 



'Atti. Reale Acad, dei IJncei, Vol. 14, p. 3, 1905. 



•Phil. Mag. (6), Vol. 10, p. 1. 1905. 



