64 BOTANY 
we are dealing only with liquids. The chief point 
to be noted is that the less dense liquid passes through 
the membrane more rapidly than the more dense, as the 
following experiments will show. 
Cover the mouth of a thistle funnel (Fig. 41) 
with vegetable parchment, fixed firmly to the 
rim and made absolutely air-tight with marine 
glue. Now fill the cup and part of the tube 
with strong bluestone solution, fix and _ stand 
the funnel with the parchment-covered end dip- 
ping into water. The liquid will soon begin to 
rise in the tube, showing that by osmosis the water 
is passing through the membrane into the funnel. At 
the same time the slightly bluish coloration of the 
liquid shows that some, though a lesser quantity, of 
the solution has passed out into the water. The liquid 
may not begin to rise in the tube immediately, since 
the parchment may continue to sag for a short time; 
but if left for a few hours a satisfactory result will 
always be obtained, provided that the parehment 
covering is air-tight. 
As there is some little difficulty in fixing this 
apparatus, the following simpler illustration may be 
employed. Chip the shell off the bottom of an egg 
(Fig. 42) in such a way as not to injure the delicate 
membrane within. Now open the top of the ege, 
remove the contents, and place inside the shell 
several teaspoonfuls of a strong solution of grape sugar. 
Stand the egg with the exposed membrane below just 
dipping into a dish of water. The water will enter 
the egg shell, and, if sugar be added to keep up the 
strength of the solution, will eventually fill the interior 
and overflow. By testing the water in the dish it will 
be found that some of the Sugar solution has passed 
through the membrane outwards. Ineidentally, by 
adding a little starch paste to the solution in the egg 
shell, it may be shown, by means of the F'ehling’s 
