PROFESSOR GRAHAM ON OSMOTIC FORCE. 
189 
action of membrane, was excluded by the observation that similar large effects could 
be obtained from a septum of pure coagulated albumen. 
A convenient albumen osmometer is constructed by covering the opening of the 
bulb of the former instrument by ordinary thin cotton calico, which is best applied 
wet, and painting over the outer surface of the calico two or three times with undi- 
luted egg albumen, an hour being allowed to elapse between each application of the 
albumen. The instrument is then suspended in the steam rising from boiling water 
for a few minutes, so as to completely coagulate the albumen. The albuminated 
calico may then be macerated for twenty-four hours before use, by placing the 
osmometer in cold water, to dissolve out the soluble salts of the albumen. It should 
be preserved always in a humid state. Before application to the calico, the albumen 
in many cases was neutralized with acetic acid and filtered, the more completely 
to obliterate every trace of organic structure. 
The osmose in a particular instrument of this kind was, at 50°, for 
1 
per cent, carbonate of potash 
. . . 211 ms. 
1 
per cent, carbonate of potash 
... 367 ms. 
1 
per cent, carbonate of potash 
. . . 387 ms. 
0T 
per cent, carbonate of potash 
. . . 127 ms. 
0T 
per cent, carbonate of potash 
. . . 124 ms. 
The correct rate is rarely obtained in the first observation, as seen above, in osmo- 
meters of albumen as well as of other materials. 
The albumen plate has generally a greater thickness than prepared membrane, 
which appears to diminish proportionally the quantity of salt which escapes by dif- 
fusion. 
The diffusate in the three experiments above of 1 per cent, carbonate of potash 
was 0 f 024, 0’038 and 0'042 gramme of the salt. The largest proportion of car- 
bonate of potash (0‘042. gramme) which was obtained in the last of the three experi- 
ments was replaced by 23220 grammes of water, or 552 times the weight of the salt. 
An obvious and essential condition of osmose is difference of composition in the 
two fluids in contact with the opposite sides of the porous septum. With the same 
solution, or with pure water, in contact with both surfaces of a membrane there may 
be chemical action, but it will be equal on both sides, and although probably attended 
with movements of the fluids, yet nothing will be indicated, as the movements, being 
equal and in opposite directions, must neutralize each other. Difference of compo- 
sition in the two fluids is necessary in order that there may be inequality of action 
upon the two sides of the membrane. It is difficult however, with respect to the 
chemical action, to ascertain either its true sphere or its exact nature. No substance 
appears to be permanently deposited in the membrane during osmose, even by easily 
decomposed metallic salts, such as salts of lead and mercury. The action upon the 
membrane is probably of a solvent nature, and its seat may possibly be ascertainable 
