OSMOTIC PRESSURES OF SOME CONCENTRATED AQUEOUS SOLUTIONS. 505 
We think that, for the purpose of comparison, it may be of use to append a table 
of the results (some of which have already been published) of the determination of 
the osmotic pressures of cane-sugar solutions by way of their vapour pressures. For 
the discussion of the theoretical connection and the details of the method and apparatus, 
we would refer to the original paper,* but would mention that a slight modification 
m the apparatus has enabled us to obtain more concordant values. We hope to give 
full details on another occasion. 
Table XI. 
Concentration in 
grammes per litre 
solution. 
Temperature. 
Osmotic pressure 
in atmospheres derived 
from vapour pressure. 
Measured 
equilibrium pressure at 
0° C. in atmospheres. 
0 C. 
420 
12-6 
44-3 
43-97 
420 
14-2 
45-9 
420 
15-7 
46-6 
_ 
420 
19-5 
47-3 
_ 
660 
19-0 
105-7 
_ 
660 
19-4 
103-2 
_ 
660 
19-5 
107-0 
— 
Later Experiments. 
540 
0° C. 
69-4 
67-51 
660 
0 
101-9 
100-78 
750 
0 
136-0 
133-74 
We would draw attention to the fact that our results for cane sugar, where they 
overlap those obtained by Messrs. Morse and Fraser,! are somewhat higher. For 
instance, a solution containing 282 grammes in the litre is given by them as having 
an equilibrium pressure of 22-49 atmospheres, while we obtain 25 atmospheres, this 
value being taken from the curve. 
There seems to be no mention in Messrs. Morse and Fraser’s account of their 
work of any steps taken to determine the amount of solution which came through the 
membranes. A small “solution leak” would make a considerable difference to the 
pressure they obtained, not so much on account of “ back ” osmotic pressure, but 
because the passage of a small volume of solution would have a large effect, on the 
level of the mercury in the manometer, the more so as the diameter of the latter is 
only 0'5 millim. and it is a closed one. The general excellence of their work, however, 
makes it improbable that this hypothetical explanation is correct; it may be that 
future experiments will clear up the discrepancy. 
* ‘Roy. Soc. Proc.,’ A, vol. 77, 1906, and also ‘Nature,’ vol. 74, p. 6. 
t ‘American Chemical Journal,’ vol. 34, pp. 1-99. 
VOL. CCVI.-A. 3 T 
