PROFESSOR GRAHAM ON OSMOTIC FORCE. 
185 
the voluminous basylous molecule (H m+1 O m ) above described; which again breaks 
up at the negative pole into hydrogen and water, (H m+1 O m )=raHO and H. 
But even although such a representation of the circumstances of electrical endos- 
mose may not be fully admitted, the phenomenon itself is of great service to us, as 
showing that in the occurrence of chemical decompositions affecting ultimate parti- 
cles, sensible volumes of water may be involved and set in motion. 
Further, in considering the action of chemical affinity between bodies in solution, 
between an acid and alkali for instance, we are apt to confine our attention to the 
principal actors in the combination, and to neglect entirely their associated water of 
hydration. Yet both the acid and base may have large trains of water attached to 
them by the tie of chemical union. Sulphuric acid certainly evolves heat with the 
fiftieth equivalent of water that is added to it, and probably in dilute solution that 
acid is capable of having a still greater number, indeed an indefinitely large number 
of equivalents of water combined with it. In fine there is reason to believe that 
chemical affinity passes, in its lowest degrees, into the attraction of aggregation. 
The occurrence of chemical decomposition within the substance of a porous 
resisting septum may be calculated to bring into view the movement and disposal 
of the water chemically associated in large quantities with the combining substances ; 
as the interposition of a porous diaphragm in electrical endosmose makes sensible 
a translation of water in voltaic decompositions which is not otherwise observable. 
II. The osmose of liquids has hitherto been principally studied in septa of animal 
membrane, which from their thinness, their ready permeability combined with a 
sufficient power of resistance to the passage of liquids under pressure, have great 
advantages over mineral substances. 
The great proportion of the experiments of the pre - 
sent inquiry were also made with animal membrane. 
The membrane osmometer employed, which is 
only a modification of the classical instrument of 
Dutrochet, was prepared as follows : — 
The mouth of a little glass bell-jar A (fig. 2) had 
first loosely applied to it a plate of perforated zinc 
B slightly convex, and then the membrane was tied 
tightly over the latter for the sake of support (fig. 3). 
The quantity of metal removed in the perforations 
of the zinc plate amounted to 49 per cent, of the 
weight of the zinc. This plate was always varnished 
or painted to impede, if not entirely prevent, the 
solution of the metal by acid fluids. The usual 
diameter of the bulb was about 3 inches or 75 millimeters, and its capacity equal 
to 5 or 6 oz. of water. The tube C was usually not more than 6 inches in length, 
but comparatively wide, its diameter being about 7‘ 5 millimeters, that is one-tenth 
2 B 
Fig. 2. Fig. 3. 
B 
MDCCCLIV. 
