448 
This curve begins almost horizontally (the first one vertically !) and 
then has its converity below; with larger abscissae it has its concd- 
vity below. 
The curve still shows however something 
y 
a minimum. Trouton aseribes this to the fact, that a part of the 
like a maximum and 
glasswool -is really dry, which means in our conception that a part 
of it has lost its adherent layer of fluid water. Two different pheno- 
mena are thus measured t gether. 
It would be very interesting to know how the curve would be 
in the other extreme case, viz. when it is certain, that all the glass- 
wool is covered with a layer of fluid water, because, as we shall 
see, just in this case it can be predicted by approximate calculation 
how the shape of the curve will be. 
Description of my own experiments. 
In order to be sure, that a layer of fluid water covers the par- 
ticles of the powder, weighed quantities of the powder were placed 
during several days in a bellglass above a 1°/, solution of sulphuric 
acid in water (vapourtension '’/,,, of the maximum tension of water) !). 
Then the dishes were placed over the different mixtures of acid- 
water till they were of constant weight, in a room which (situated 
on the north and provided with double windows) had variations of 
temperature as small as possible. 
The following was found as the relation between vapourtension 
'!) Pure water would have given too irregular condensations. 
