1905.] Crystalloids and Colloids through Gelatine. 327 



tration of the filtrate is neither so marked nor so long continued as has been 

 imagined, for the following reasons. In the first place, the filtrates from 

 saline through gelatine containing the same concentration of saline are at first 

 only about half as concentrated as the original saline. Secondly, on decom- 

 pression, and again filtering, the filtrate may contain a higher concentration 

 of salt than the original saline. This seems conclusively to show that much 

 of the dilution of the filtrate is due not to the water of the filter, but to the 

 retention of the salt by the gelatine. Further, Reid found the quantity of 

 water in freshly prepared filters to vary between 2 and 13 grammes — i.e., pre- 

 sumably, the amount which can be removed by dry air. It is probable that 

 only a small part of this water will be removed by the passage of a slow 

 current of liquid through the gelatine, the remainder being retained by 

 adsorption or inhibition forces, etc. In this connection an observation which 

 was made with all the filtrations given in this paper may not be unimportant. 

 It was found that the sum of the volumes of the filtrate fractions and residual 

 fluid in any one filtration experiment was less than the volume of the 

 original fluid introduced into the wetted apparatus. It is a well-known 

 fact that water can be forced into gelatine by. pressure, and as a large part of 

 the gelatine in the pores of the filter, during filtration at 100 atmospheres, 

 must be under considerable pressure, it seems reasonable to assume that part 

 of the original water of the wet filter is more firmly bound, and that about 

 5 c.c. are imbibed partly from the water of the filter and partly from the fluid 

 filtered. The rapid passage of iodine, neutral red, and colloidal ferric hydrate 

 into the filtrate also point to a considerable percentage of the first fractions 

 of filtrate being contributed by the fluid filtered. It seems, on the whole, as 

 if the free water of the filter is almost wholly removed in the first fraction of 

 5 c.c. filtrate. 



The Application of Mechanical and Adsorption Hypotheses to the Filtration 



Phenomena of Gelatine. 



Mechanical Hypotheses.—- The most obvious explanation of the retention of 

 colloidal substances by the gelatine filter is that the colloidal molecule or 

 grain is too large to pass through the pores. Martin* has advanced the view 

 that the non-filtration may be due either to the size of the molecules or to 

 some interaction between the colloidal membranes and the dissolved colloidal 

 molecules. It has, however, been shown by E. W. Eeid (1904), Gatin- 

 Grazewska (1904), and others that proteids, glycogen, and other typically 

 colloidal substances, exert no measurable osmotic pressure in solution, do not 

 influence the freezing point of the aqueous medium, and in general diffuse 



* Loc. dt. 



VOL. LXXVII. — B. 2 B 



