CAUSES OF THE MOTION OF JUICES. 357 



kind, viz., an alkaline action on the albuminoid substance 

 of the membrane on the one side, and an acid action on 

 the other. The water appears always to accumulate on 

 the alkaline or basic side of the membrane. Hence with 

 an alkaline salt, like carbonate of potash, in the osmometer, 

 and water outside, the flow is inwards ; but with an acid 

 in the osmometer, there is negative osmose or the flow is 

 outwards, the liquid then falling in the tube. 



Osmotic activity is most highly manifested in such salts 

 as easily admit of decomposition with the setting free of 

 a part of their acid, or alkali. 



Hydration of the membrane. It is remarkable that 

 the rapid osmose of carbonate of potash and other alkali- 

 salts is greatly interfered with by common salt, is, in fact, 

 reduced to almost nothing by an equal quantity of this 

 substance. In this case it is probable that the physical 

 eifect of the salt in diminishing the power of the membrane 

 to imbibe water (p. 348,) operates in a sense inverse to, and 

 neutralizes the chemical action of the carbonate. In fact, 

 the osmose of the carbonate, as well as of all other salts, 

 acid or alkaline, may be due to their effect in modifying 

 the hy drat ion* or power of the membrane to imbibe the 

 liquid which is the vehicle of their motion. Graham sug- 

 gests this view as an explanation of the osmotic influence 

 of colloid membranes, and it is not unlikely that in case 

 of earthenware, the chemical action may exert its effect 

 indirectly, viz., by producing hydrated silicates from the 

 burned clay, which are truly colloid and analogous to ani- 

 mal membranes in respect of imbibition. Graham has 

 shown a connection between the hydrating effect of acids 

 and alkalies on colloid membranes and their osmotic rate. 



"It is well known that fibrin, albumin and animal mem- 

 brane,swell much more in very dilute acids and alkalies, than 

 in pure water. On the other hand, when the proportion of 







* In case water is employed as the liquid. 



