OSMOTIC PRESSURES OF SOME CONCENTRATED AQUEOUS SOLUTIONS. 497 
Xli© solutions, both for cane sugar and for the other substances, were always made 
up the night before an experiment. 
The dextrose was purchased from Messrs. Kahlbaum, and was described by them 
as their purest anhydrous ; no tests as to purity were made except to determine the 
amount of moisture"' in the various quantities sent. The amount was found to be 
very small and practically constant. The galactose was also Kahlbaum’s purest 
anhydrous; the amount of moisture was found to be constant. Some of the galactose 
was lecoveied by crystallizing from a saturated solution and digesting with methyl 
alcohol for 10 days. Solutions of 500 grammes of this recovered galactose in the 
litre gave equilibrium pressures (see table of results) which were about 2 per cent, 
higher than those obtained with similar solutions of the original substance. As the 
purification of galactose is a very lengthy process, and our main object in making 
experiments with this substance was to see if it be suitable for osmotic pressure 
measurements, no further steps have yet been taken in the matter. The mannite 
came from Kahlbaum, and was only tested for moisture. 
A considerable number of organic substances which are not likely to be dissociated 
in aqueous solutions were tried, but without success, as they all passed through the 
membranes to a greater or less degree. 
Results. 
In the following tables we give all the experiments that we have made at 0° C., 
with the exception of those which were carried out merely for the purpose of testing 
the membranes. The concentration of the solution is placed at the head of each 
table; the numbers are the weights of the substance in one litre of solution made up 
at 15° C. :— 
Column (I.) gives the date of the experiments ; these are tabulated in chronological 
order. 
Column (II.) gives the name of the tube used. 
Column (III.) gives the apparent turning-point pressure, in atmospheres, as derived 
from the dead-weight standard pressure gauge. It is the pressure for which there 
would have been no movement of the water in the capillary gauge. 
A blank in the column means that the true turning-point pressure was exactly that 
on the solution, and therefore it was not necessary to take rates above and below it : 
in other words, this pressure gave a rate which exactly equalled the “ guard-ring 
leak ” rate. 
Column (IV.). In this and the other columns where rates are given it is to be 
noted that they all represent the movement of the level of the water in the capillary 
* The “moisture” was determined by the loss of weight of the substance on heating at 100° C.; but 
we have evidence that there were traces of methyl alcohol present. 
VOL. CCVI.—A. 3 g 
