148 RO\AL SOCIETY OF CANADA 



It may he doubted if physical chemistry wouhl now include the 

 concept of a semi-permeable membrane, were it not for the difficulty 

 experienced by botanists and physiologists in accounting for the capacity 

 of living cells to retain their organic constituents. There are, however^ 

 parallel physical phenomena which might in themselves have suggested a 

 different explanation, and one of these is manifest in the action of palla- 

 dium on hydrogen.^ At ordinary temperatures palladimn absorbs hydro- 

 gen, but gives it up again when heated in vacuo to temperatures above 

 100° C. Palladium does not so act towards any other gas, and in con- 

 sequence at about 200° C. it can be constituted as a membrane perme- 

 able, of course, to hydrogen, but impermeable to carbon monoxide, carbon 

 dioxide or nitrogen- 



If any of these gases be contained in a palladium tube surrounded 

 with hydrogen, the latter will pass through the palladium and cause an 

 ancrease in pressure in the tube equal to 90 per cent, or more of that of 

 the external hydrogen. Like palladium acts also platinum, a-ccording to 

 Kichardson, Nicol and Parnell.^ That we have in either palladium or 

 platinum material which would constitute a semi-permeable membrane 

 may at onoe be denied, for the absorptive power of palladium in regard 

 to hydrogen is due merely to solution of the hydrogen in tlie palladiimi, 

 while the semi-permeable membrane in the meaning of Pfeffer, van't 

 Iloff and others is practically a sieve, the meshes of wliich are Large 

 enough to allow molecules of water to pass through, but not those of 

 sugar. If, for a< moment, we admit that the membrane plays a more 

 than passive part in the exchange which takes place through it, we at 

 once practically alter fundamentally the concept of a semi-permeable 

 membrane. 



Even, however, when we are dealing with precipitate membranes, 

 we must abandon the sieve theory. Barlow ^ has pointed out that the 

 ferrocyanide membrane is more readily permeable under mechanical 

 pressure to alcohol than it is to water, that is the larger molecules pass 

 through more readily than the smaller. He found also tiliat when gutta 

 percha membrane separated pure alcohol and pure water, the alcohol 

 passed through to the water, the reverse of what happens when a copper 

 ferrocyanide membrane is used. Pringsheim ^ by varying this method 

 of forming the precipitated membrane, obtained some interesting results. 

 He took a U-shapcd tube into which he poured enough liquified gelatine 

 to fill the bottom and lower portion of each limb of the tube. On this 



1 Ramsay. Zeltschrift fur Physik. Chem., "Vol. 15, p. B18, 1894. 



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

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



* Observations published after his death, in 1895. 



