( 972 ) 
begins to turn its convex side downwards, gets at a greater La 
point of inflection and then turns the coneave side downwards, 
forming a more or less S-shaped line. 
So great an agreement with compounds so different chemically is 
somewhat surprising *). 
Apparently different from this are some of the results obtained by 
vay Bemmenen. When experimenting with silicie acid freshly preeipi- 
tated from soluble glass by hydrochloric acid and with ferric bydrox- 
ide recently precipitated by alkali from ferric chloride he obtained 
lines much more complicated, with three points of inflection. If, however, 
we examine the curves which he obtained from o/d silicic acid *) 
and ferrie hydroxide *) more closely, they appear to possess the 
same form as I have found. 
In the case of mixtures both experiment and theory lead to the 
conclusion that the line which indicates how the aqueous vapour 
pressure depends on 7, can have two types which gradually pass 
into each other. With some substances, for instance with propionic 
and acetic acids, the concave side is, from the commencement, 
turned downwards and the point of inflection has disappeared. Glycerm 
appears to lie exactly on the border line, the curve represented 
still just shows the point of inflection. 
The swelling bodies have, therefore, lines which agree with those 
of the miscible substances of the first group and bear, indeed, a close 
resemblance to these. 
This analogy goes still further: miscible substances of the first 
eroup have a strong heat of mixing and contraction of volume ; in 
those of the second group these properties are mostly but feebly 
positive or even negative. In all the imbibing substances, as yet 
investigated, they are strongly positive. 
The theory of the mixtures makes one suspect ') that the initial 
2) Curves of the same form were obtained by TrovroN with flannel and cotton 
wool, by Orme Masson and RicHarps with cotlon wool, by LÖWENSTEIN with 
cupric ferroeyanide, zine ferrocyanide and silicic acid formed by the action of dilute 
acid on silicates at the temperature ef the room. I myself, have examined more 
than thirty other swelling substances, among those being the majority of tbe 
known physiologico-chemical substances and a few other products such as tannins 
and soaps ; the curves invariably exhibited the S-shaped character. 
3) Zeitschr. f. Anorgan. Chem. 13, p. 354 (fig. 17). 
4) Zeitschr. f. Anorgan. Chem. 20, p. 207. The line of the jelly which has been 
kept under water for seven years is meant. 
1) This follows from the approximative formulae for concentrated mixtures 
described by Nerysr as the formulae of the “ideal concentrated solutions” and also 
from the expression derived by Van Laar from Van perk Waat’s theory of 
