9 



ENDOSMOSE. 217 



which permit the passage of liquids through them, are 

 interposed between two liquids, they present less hin- 

 drance to their mixture than difference in the specific 

 gravities. When two liquids are separated by such a 

 wall, the peculiar phenomenon is observed that the 

 liquids pass through the partition at unequal rates, and 

 that consequently the quantity of liquid on one side of 

 the wall increases, while that on the other side becomes 

 less. In general the heavier liquid passes through the 

 wall at a slower rate than the lighter, but this rule 

 by no means holds good in all cases. This phenomenon 

 is called endosmose. 



Kemove the bottom of a small glass bottle, of about 30 CC capacity, 

 by making a cut with the file about l cm> 5 from the bottom, and 

 carrying a crack all round with a pastille. Grind the lower end of 

 the bottle smooth, on the grindstone, or with emery powder on a glass 

 plate, and take off the sharp outer edge of the rim by holding the 

 bottle slantingly upon the stone or plate, and turning it slowly all 

 round ; a grindstone will serve for this operation better than emery 

 powder. A piece of calf's or pig's bladder, softened by soaking it 

 in moderately warm water, is stretched very tight across the 

 ground edge, tied very firmly by a piece of thin twine which is 

 wound in close turns six or eight times round the glass, and the 

 protruding points of the bladder are then cut away with a pair of 

 sharp scissors. A soft sound cork is fitted very tightly into the 

 eck of the bottle ; the cork is perforated for the reception of 



glass tube, as shown in fig. 153. The tube is open at both ends, 

 about 3 cm wide, from 10 to 20 cm long. 



The cork being removed, the bottle is filled with 

 a solution of 20 gr of sugar in 20 CC of water, again closed, 

 and the projecting glass-tube is clamped in the fork of 

 the retort-stand, the bottle being allowed to dip into a 

 larger vessel containing water, precisely in the manner 

 shown in fig. 153. When the cork is inserted, some of 

 the liquid in the bottle is pressed into the tube, and a 

 small quantity may even run out at the open end of it; 



