FILTRATION. 
many hours before the observations are conducted, and the stage of 
relatively constant rapidity of nitration (a uniform rate is never actually 
attained) is reached quicker at higher than at lower pressure. This 
phenomenon is not due to any stopping of pores by particles suspended 
in the fluids, since it is not noted when filtration is effected through 
unglazed porcelain, and is probably simply a result of compression of 
tortuous channels. 
The quantity of filtrate rises with the pressure, but in lower ratio. 
Thus, in an experiment by Tigerstedt and Santesson 1 of filtration of 
distilled water through goldbeater's skin (serosa of ox-gut), which had 
previously been exposed for 95 hours to a pressure of 80 cms. of water, 
Pressure. 
Filtrate per Minute 
Observed. 
Filtrate per Minute if 
proportional to Pressure. 
20 cm. 
40 ,, 
60 ,, 
80 ,, 
•046 grni. 
•081 „ 
•110 „ 
•148 , ; 
•046 grm. 
•092 ,, 
•138 ,, 
•184 ,, 
The experiments of Wilibald Schmidt - showed a contrary result, 
i.e. that the filtration rapidity increased at a higher ratio than the 
pressure (possibly due to using dried membranes, the pores of which 
were opened during experiment), as also did those of v. Eegeczy. 3 
A period of rest, interpolated between two filtration experiments at 
the same pressure, is found to often cause an increase of the permeability 
of the membrane above the value it possessed at the time of dis- 
continuing the first experiment (Eckhard, Runeberg, Tigerstedt and 
Santesson). 
Thus Tigerstedt and Santesson, 4 in a nitration of distilled water 
through gold-beater's skin at 40 cm. pressure, observed a filtrate of 
•490 grm. per minute, but after a resting period of 530' the filtrate at 
the same pressure was "577 grm. per minute. But whether or not this 
phenomenon is observed, is probably due to whether or not the elastic 
limits of the fibres have been passed, " recovery " not being possible if 
the membrane has been excessively stretched. The interpolation of a 
period of filtration at lower pressure of course produces the same effect. 5 
The rapidity of filtration rises with the temperature, 6 and, according 
to Schmidt, the temperature coefficient is nearly that of Poiseuille, for 
the flow of fluids in capillary tubes. 
The nature of the solution to be filtered must obviously affect 
both the rapidity of filtration, from differences in viscosity, and also 
the quantitative composition of the filtrate in relation to that of the 
original solution. 
The following experiment from Tigerstedt and Santesson 7 may be 
quoted in evidence of the first point : — 
2 Ann. d'.Phys. v. Ohem., Leipzig, 1856, Bd. xcix. S. 337 ; 1861, Bd. cxiv. S. 337. 
3 Loc. cit. * Loc. <'it., p. 30. 5 Runeberg, loc. cit. 
6 Schmidt, loc. cit. ; Eekhard, loc. cit. ; Luwy, Ztschr. f. physiol. Chem., Strassburg, 
1885, Bd. ix. S. 507. 
7 Loc. cit., p. 42. 
