1905.] Crystalloids and Colloids through Gelatine. 329 



the intensity of the adsorption depends not only on the physical condition 

 but also on the chemical nature of the active surface. Gelatine being, 

 probably, a porous substance, presents a large surface to the enclosed fluid, 

 and it seems highly probable that when this fluid contains crystalloids or 

 colloids adsorption will take place. Thus, gelatine containing 0'8 per cent, 

 saline apparently retains about one-half of its content in sodium chloride, 

 and the retention of crystalloids and colloids on filtration through gelatine at 

 constant pressure seems to admit of explanation on the basis of adsorption. 

 The results obtained in the investigation of the adsorption phenomena of the 

 sedimentation of silts through aqueous solutions may therefore be applied to 

 what apparently is the converse of that process, viz., the passage of aqueous 

 solutions through porous solids or powders, under pressure. This is rendered 

 highly probable from the fact that the rate of sedimentation of a silt through 

 saline is generally accelerated by the presence of butyric acid, arnylic alcohol, 

 and other substances influencing surface tension, and similarly the rate of 

 filtration through the porous gelatine is accelerated by the same substances. 

 An additional factor may, however, come into play in gelatine filtration. The 

 effect of pressure on gelatine containing a solution of salt will be to cause the 

 absorption of water. It seems permissible to assume, in view of Hardy's 

 work on the structure of gelatine, that this additional water will be taken 

 up by the web mass and will probably lead to a diminution in dimensions 

 of the pores or web spaces. This view would account for the continued 

 diminution in rate of filtration at constant pressure. The process should 

 show some similarity to the passage of a solution into filter paper, where the 

 water passes in more readily than the substance in solution. 



A sudden diminution in pressure will lead to the rapid expulsion of the 

 imbibed fluid, which will sweep the adsorbed matter into the widening pores. 

 The gelatine itself will thus express part of this concentrated fluid, and at 

 low pressures highly concentrated filtrates will be obtained. This will take 

 place markedly when the adsorption is easily reversible, but the less reversible 

 adsorptions of certain staining substances, e.g., neutral red and iodine will not 

 give this effect. Further compression and decompression would presumably 

 lead to a more uniform distribution of the adsorbed substance throughout the 

 gelatine, and as the filter is now also more saturated, the effect of variation of 

 pressure on the concentration of the filtrate would be less marked. 



Summary of Conclusions. 



1. Wet gelatine filters are to be preferred to those which have been 

 partially dried, as the former have more uniform rates of filtration, and dilu- 

 tion of the filtrate by the water of the gelatine can be largely eliminated. 



2 B 2 



