PROFESSOR GRAHAM ON OSMOTIC FORCE. 
197 
The mean diffusate of sugar also increases with the same change only from T020 
gramme to T585 gramme. 
In the second series of observations with the same membrane, given in the lower 
part of the same Table, both the osmose and diffusate fall off, to an extent which is 
perhaps pretty fairly represented by the 10 per cent, solution, which gives a mean 
osmose of 72 5 ms. against 96 3 ms. in the former series, and a diffusate of 0 /5 7 
gramme against T020 gramme in the former series. A rough proportionality between 
the two series of observations is sufficiently indicated. 
Two observations are recorded in the last series which must not be allowed to 
mislead. These are the comparatively high osmose of 19 ms. for the 1 per cent, 
solution, which is accidental, and arises from the 1 per cent, experiments having been 
immediately preceded by the high proportion of 20 per cent. The other observation 
referred to is the high diffusate of the last 20 per cent, solution at the bottom of 
the table, which has no doubt been occasioned by the sudden diminution in the 
hydrostatic resistance of the membrane from 8 to 3 in that which is the last expe- 
riment of the series. The membrane, indeed, appears to be giving way after its 
long use, for the osmometer had been exposed to the action of water for thirty-five 
days without intermission. 
The reason why the diffusion and osmose are smaller in the second series of expe- 
riments than in the first series (nearly as 3 to 4), is (I believe), that the membrane 
softens and swells somewhat by the protracted action of water ; a change in the 
structure of the membrane which impedes diffusion by increasing - the length of the 
channels through which the salt has to travel. 
It may now be interesting to discover the proportion between the water which enters 
and the sugar which leaves the osmometer in these experiments. That proportion 
appears not to vary greatly in the range from the 1 to the 10 per cent, solution. 
For a mean result, the sum of the eight diffusates between 1 and 10 per cent, inclu- 
sive, in the first series of observations of Table IV., may be taken, and the osmose 
belonging to the same experiments. There is so obtained 3 - 824 grammes of sugar 
diffused against an osmose of 17‘639 grammes of water. But this, the apparent 
osmose, has to be increased by the bulk of the sugar diffused, which may be esti- 
mated at ten-seventeenths of its weight of water, or 2 - 25 grammes. Adding the 
last quantity to 17'639 grammes, we obtain — 
Sugar or diffusate .... 3 - 824grm.= l 
Replacing water 19 - 889 grm. = 5‘2 
Hence the sugar appears to be replaced in osmose by rather more than five times 
its weight of water. The less complete experiments with alcohol, previously de- 
scribed, indicate a nearly similar relation to its replacing water. 
Calculating, in like manner, the observations made upon each of the five propor- 
tions of sugar in Table III., we obtain numbers for the replacing water which oscil- 
