504 
THE EARL OF BERKELEY AND MR. E. G. J. HARTLEY ON THE 
The number of grammes in the litre are, for the cane-sugar and dextrose solutions, 
reduced to a vacuum, the dextrose being further corrected for the small quantity of 
“moisture” found in the “anhydrous” substance. Neither of these corrections are 
applied to the galactose and mannite; in the former case because the substance is 
presumably slightly impure, and in the latter because the experiments are not very 
accurate. 
In the following set of curves the final values are plotted against concentrations, 
and it is interesting to observe that all four substances show considerable deviations 
from the straight lines which represent the theoretical osmotic pressures.* It is also 
o 125 250 375 500 
Concentrations in grammes per 
litre of solution. 
Cane sugar. 
Concentrations in grammes per 
litre of solution. 
Mannite. 
to be noticed that on extrapolating the various curves towards the origin they appear 
to merge in the straight lines before the origin is reached; this means that dilute 
solutions will give pressures corresponding to the Boyle-Avogadeo law, the gradients 
at the origin being inversely as the molecular weights of the dissolved substances.t 
* The straight lines are drawn on the usual assumption that 1 gramme molecular weight of solute per 
litre should give an osmotic pressure of 22 • 4 atmospheres. 
t Further consideration of the theoretical bearing of the forms of these curves is deferred. 
