OSMOTIC PRESSURES DERIVED FROM VAPOUR-PRESSURE MEASUREMENTS. 311 
On looking at the tables it will be seen that the values for piezometers 7 and 8 at 
0° C., although agreeing among themselves, are considerably lower than our previous 
results. We are, however, inclined to attach more weight to these experiments, for 
as may be seen by comparing the numbers for rising and for falling pressures, they 
are very concordant. In the experiments at 30° C., the earlier values with the Jena- 
glass piezometer are again higher. It is evident that the experiment with No. 7 at 
30°‘19 C. is somewhat faulty ; we are unable to give a reason for this. 
The Results for Cane Sugar. —The experiments at 0° C. are gathered together in 
Table III. where the columns have the same meaning as for water, except that the 
concentration of the solution is put under the number of the piezometer in column (l), 
and when the solution had been made up by weight, its approximate volume concen¬ 
tration (number of grammes per litre) is given in brackets. The numbers in column 
(4) for the experiments with the Jena-glass piezometers are generally the mean 
values obtained with a rising and a falling pressure; these, as already mentioned, are 
by no means concordant. In one or two cases even with No. 7 there were failures 
due to temperature troubles or to the mercury thread breaking. These remarks 
apply generally to all our observations. 
Again it will be noticed that the No. 7 results are lower on the whole than those 
for the other piezometers. 
The experiments at 30° C. are tabidated in the same way in Table IV., and again 
the values for piezometer 7 are lower. 
The Results for a-methyl Glucoside. —These, both for 0° C. and 30° C., are given in 
Table Y. All the observations are made with either piezometers 7 or 8 and they 
seem, except in one case, to be good. 
Final Values for the Compressibilities. —In this communication the com¬ 
pressibilities are only required for the purpose of calculating the s of Porter’s 
equation * The solutions themselves are very incompressible, so that even over the 
range of the highest osmotic pressure the effect on the volume is but small, and 
therefore the pressure effect on s will be that of a small correcting term. In these 
circumstances it will suffice to give the mean coefficients (over the range from one 
atmosphere to the osmotic pressure of each solution) that we will use later on. In 
the set of mean values entered in Table VI. greater importance was given to the best 
experiment with piezometers 7 and 8. 
The Calculation of s. —Although it is common knowledge that the quantity s, for 
the solutions with which we are concerned, differs but little from unity, yet it seems 
worth while to give the following analysis (due to Mr. G. W. W alker), as there are 
numerous cases in which a detailed statement may be important. 
Prof. Porter! defines s x as “ the reduction in a practically infinite volume of 
* ‘Roy. Soc. Proc.,’ A, vol. 80, 1908, p. 460. 
t Loc . cit . 
2 T 
VOL. COXVIII.-A. 
