447 
That indeed different eurves are obtained in the ease of a solid 
which is covered with a thin laver of fluid or one by which this 
layer has been removed by intensive drying, is shown by the expe- 
riments of Trouton on the adsorption of water at glasswool '). When 
the glasswool had been dried during 70 hours at 160°C. in vacuo 
over phosphorpentoxide (so that we may presume that the adhering 
waterlayer had been removed) curves were obtained as shown in 
the subjoined figure. *) 
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Feeds 
ral 
The abscissae represent the amounts of water (in arbitrary units) 
which are adsorbed at the surface of the glass, the ordinates represent 
the vapourtension, which is in equilibrium with these. This curve was 
obtained when going from the driest towards the moister side. The 
curve rises quickly at the smaller values of the abscissae and 
turns its concavity downward, then shows a very curious Maximum 
and minimum and finally quite continuously becomes a line, which 
in the main seems to agree with the line obtained when a layer 
of fluid water covers the surface of the glass. 
Trouton has realised this last case only in an impure form, pro- 
bably because he had to meet the difficulty, that in his experimental 
technic the curves could only be followed from the driest to the 
moister side. As-driest substance he used glasswool dried at room- 
temperature over phosphorpentoxide until the vapourtension just 
had become zero. He then obtained the curve shown below. *) 
1) Proc. Roy. Soc. 79, p. 383—390. 
ay -LG. Poo: 
Mep: JS 
