PROFESSOR GRAHAM ON OSMOTIC FORCE. 
181 
the osmometer throughout the whole experiment, so as to prevent inequality of hydro- 
static pressure. The volume of water in the jar was comparatively large, fifty to eighty 
ounces. The rise or fall of the liquid in the tube was noted hourly for five hours. 
This rise commenced immediately, and was pretty uniform in amount for each hour 
during the short period of the experiment. The object aimed at was to observe the 
osmose of the solution before its composition was materially altered by dilution and 
the escape of salt by diffusion. The quantity of salt diffused from the osmometer 
into the water-jar during the experiment was also observed. After every experiment 
the osmometer was washed out by distilled water, which was allowed to permeate the 
porous walls of the cylinder, under the pressure of a column of water of about 
30 inches in height, for eighteen hours. All the experiments were made at a tem- 
perature between 56° and 64°. The clay osmometer attained a considerable degree 
of uniformity in its action, when the same saline solution was diffused from it once 
in each of two or three successive days, with a washing between each experiment. A 
single observation is not much to be relied upon, as the first experiment often differs 
considerably from the others. One per cent, solutions were always used when the 
proportion of salt is not specified. Much larger proportions of salt have hitherto been 
generally employed, but it was early observed that the osmose absolutely greatest is 
obtained with small proportions of salts in solution. One part of salt to 400 water 
gives a higher osmose in earthenware than any other proportion for the great majo- 
rity of substances. Osmose appeared, indeed, to be peculiarly the phenomenon of 
dilute solutions. 
With the same proportion (1 per cent.) of different substances, the osmose varied 
from 0 to 80 degrees. Occasionally, instead of a rise of liquid in the tube, a fall was 
observed ; the fall may be spoken of as negative osmose, to distinguish it from the 
rise or positive osmose. 
Soluble substances of every description were tried, and find a place in the following 
classes : — 
1. Substances of small osmotic power in porous earthenware; osmose under 20 of 
the millimeter degrees (ms.). 
This class appears to include nearly all neutral organic substances, such as alcohol, 
pyroxylic spirit, sugar, glucose, mannite, salicin, amygdalin, salts of quinine and mor- 
phine, tannin, urea ; also certain active chemical substances, which are not salts nor 
acids ; chlorine water, bromine water. 
The great proportion of neutral salts of the earths and metals proper also, belong 
to the same class, such as chloride of sodium, of which the positive osmose was 
greatest in a solution containing no more than 0T25 per cent., being 19 ms. with 
that proportion of salt, but falling off and often becoming slightly negative with 1 per 
cent, and higher proportions of salt in solution. Chloride of potassium is similar. 
Nitrate of soda gave an osmose of 8, nitrate of silver of 18 ms. 
The salts of the magnesian oxides are all low and sometimes slightly negative. 
