186 
PROFESSOR GRAHAM ON OSMOTIC FORCE. 
of the diameter of the mouth of the bulb, and it was divided into millimeters. 
The action of an osmometer depends chiefly upon the extent of membrane-surface 
exposed, and very little upon the capacity of the instrument. Hence the relation 
of diameters (or areas) between the bulb and tube was adopted in preference to 
the relation in capacity, the area of a section of the tube being 1 one-hundredth of the 
area of the disc of membrane, or rather it was reduced by calculation to this relation 
by means of a coefficient for each instrument. Hence a rise of liquid in the tube 
amounting- to 100 millimeters, indicates the admission into the bulb of a sheet of water 
of 1 millimeter (one twenty-fifth part of an inch) in depth, over the whole surface of 
the membrane, and so in proportion for any other rise in the tube. These millimeter 
divisions (ms.) of the tube mark therefore degrees of osmose which have an absolute 
and equal value in all instruments. The bulb of the instrument filled with the 
solution to be operated upon was placed within a cylindrical glass jar of distilled 
water, containing at least sixty ounces (fig. 4), and 
during the experiment inequalityof hydrostatic pressure 
was carefully avoided by maintaining the surface of the 
water in the jar at the level of the liquid in the tube. 
The osmometer was supported upon a tripod of perfo- 
rated and painted zinc, at a height of about 4 inches 
from the bottom of the glass cylinder. The osmose 
was observed hourly for five hours, during which time 
it advanced in general with considerable uniformity. 
In an experiment with fresh ox-bladder as the septum 
and a solution of 1 per cent, of carbonate of potash in 
the osmometer, the rise, in five consecutive hours, was 
10, 12, 11, 14, 13 millimeter degrees, and in five hours 
immediately following, 13, 12, 9, 1 1 and 12 millimeter 
degrees, making sixty degrees in the first, and fifty- 
seven degrees in the second period of five hours. The 
quantity of salt which diffused outwards during the 
experiment of five hours was also frequently deter- 
mined, usually by evaporating the liquid of the water- 
jar to dryness ; it rarely exceeded one-tenth part of the 
salt originally present in the osmometer. The membrane itself was also weighed 
before it was applied to the osmometer, and again when its use was discontinued, 
which was generally after six or eight experiments had been made with the mem- 
brane. A loss of the substance of the membrane was always observed, varying from 
20 to upwards of 40 per cent, of its original weight. 
The outer muscular coat of bladder soon becomes putrescent, and from changes in 
its consistence, and the large quantity of salts and other soluble substances which it 
yields by decomposition, gives occasion to much irregularity in the experiments. The 
great change in the amount of osmose often produced by merely turning the mem- 
Fig. 4. 
