356 HOW CROPS GROW. 



Water is imbibed by the membrane of bladder much 

 more freely than alcohol ; on the other hand, a film of 

 collodion (nitre-cellulose left from the evaporation of its 

 solution in ether,) is penetrated much more easily by alco 

 hol than by water. If now these liquids be separated by 

 bladder, the apparent flow will be towards the alcohol; 

 but if a membrane of collodion divide them, the more 

 rapid motion will be into the water. 



When a vigorous chemical action is exerted upon the 

 membrane by the liquid or the dissolved matters, osmose 

 is greatly heightened. In experiments with a septum of 

 porous earthenware (porcelain biscuit,) Graham found 

 that in case of neutral organic bodies, as sugar and alco 

 hol, or neutral salts, like the alkali-chlorides and nitrates, 

 very little osmose is exhibited, i. e., the diffusion is not 

 perceptibly greater than it would be in absence of the 

 porous diaphragm. 



The acids, oxalic, nitric, and chlorhydric, manifest a 

 sensible but still moderate osmose. Sulphuric and phos 

 phoric acids, and salts having a decided alkaline or acid 

 reaction, viz., acid oxalate of potash, phosphate of soda, 

 and carbonates of potash and soda, exhibit a still more 

 vigorous osmose. For example, a solution of one part of 

 carbonate of potash in 1,000 p:irts of water gains volume 

 rapidly, and to one part of the salt that passes into the 

 water 500 parts of water enter the solution. 



In all cases where diffusion is greatly modified by a 

 membrane, the membrane itself is strongly attacked and 

 altered, or dissolved, by the liquids. When animal mem 

 brane is used, it constantly undergoes decomposition and 

 its osmotic action is exhaustible. In case earthenware is 

 employed as a diaphragm, lime and alumina are always 

 found in the solutions upon which it exerts osmose. 



Graham asserts that to induce osmose in bladder, the 

 chemical action on the membrane must be different on the 

 two sides, and apparently not in degree only, but n)* in 



