CAUSES OF THE MOTION OF JUICES. 307 
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 
effect 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 osinose of the carbonate, as well as of all other salts, 
acid or alkaline, may be due to their effect in modifying 
the hydration* 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. 
“Tt is well known that fibrin, albumin and animal mem- 
brane,swell much morein 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. 
