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Mr. J. A. Craw. Oa the Filtration of [Dec. 1, 



2. Under constant pressure the gelatine of the filter absorbs water, and its 

 porosity gradually decreases ; on decompression this water is expressed, and 

 the original porosity is rapidly regained. 



3. Gelatine of a definite concentration apparently has a specific permea- 

 bility for different crystalloids and colloids ; the value is high but not 

 complete for the crystalloids sodium chloride, potassium iodide, and butyric 

 acid, and it is low, but not zero, for the colloids ferric hydrate, serum and 

 soluble starch. 



4. As filtration proceeds the crystalloids pass through in increasing con- 

 centration, whereas the colloids rapidly decrease to zero. 



5. The simultaneous filtration of two substances may influence their 

 specific permeabilities, thus butyric acid alters the permeability to sodium 

 chloride, and iodine that of potassium iodide. 



6. Variations in the gelatine influence the permeability, e.g., formalised 

 gelatine is less permeable to sodium chloride than ordinary gelatine, and 

 15 per cent, gelatine is less permeable to megatherium lysin than 7"5 

 per cent. 



7. Variation in the pressure causes remarkable changes in permeability. 

 A sudden diminution of pressure gives highly concentrated filtrates of both 

 crystalloids and colloids, whereas a gradual diminution has practically no 

 effect. 



8. Substances which stain the gelatine, e.g., neutral red and iodine, give 

 filtrates with lower concentrations on diminishing the pressure. 



9. The rate of filtration is accelerated by amylic alcohol and butyric acid, 

 which accelerate the rate of sedimentation of silts in a similar way. 



10. Part of the phenomena may be explicable on the mechanical view 

 of a blocking of the gelatine pores, but chemical relations between the 

 gelatine and substances filtered must be taken into consideration, and 

 probably the most satisfactory view is that the action of gelatine on the 

 solutions tested is essentially an adsorption phenomenon. 



