OSMOTIC PRESSURES DERIVED FROM VAPOUR-PRESSURE MEASUREMENTS. .‘347 
Weight Concentration 
Diagram II. a-methyl glucoside. 
Note added by Lord Berkeley, April 5, 1919. 
[During the course of further work oil vapour pressures at 30° C., Mr. E. Stenhouse 
and I have found that with apparatus D when the 3rd and 4th vessels each contain 
water, # the latter always gives up a measurable quantity of vapour to the air stream. 
A number of experiments, which need not be detailed, have proved that the air on 
leaving 3 is saturated ; yet 4 loses, on the average 0'000235 gr. of water per gramme 
of total vapour carried to, and absorbed by, the sulphuric acid in vessel 5. 
Three explanations seem to me to be possible : 
(1) The current of air may not be fast enough to prevent an extra loss caused by 
diffusion to the sulphuric acid. (It is to be noted that when no air passes, about 
0’03 gr. of water diffuses in the time usually taken for an experiment.) f l his 
hypothesis is ruled out by the fact that in an experiment with water in 3, 4 and the 
first two branches at 5 (the other two containing sulphuric acid), 4 still showed the 
usual loss in weight. 
(2) Remembering that the vapour is practically all absorbed in the first branch 
of 5, it seemed possible that the sudden drop in pressure caused by this absorption 
* It is only with apparatus D, where the deposition of water in the quartz joining tubes is very small, 
that we have been able to put two water vessels in series. 
