( 328 ) 
Ty, 3 «EEE 
m,, >9 or oh amd ke, ¢) ana 0 “or a he k, 
a Pk a 
2, >0 or a>0 figs. 1 and 2) | hes. 7 and 8 | 
a | 
figs. 9, 10, 11 and 12. | 
m,, <0 or a<0 | figs. 3, 4, 5 and 6 
HARTMAN’s diagram represents at the lower limit the case m,, >0 
and m,, <0, at the superior m,, <0 and m,, >0. The case a >0 
will in general occur when the second is less volatile than the first 
substance; this for instance is the case when methyl chloride is 
added to carbon dioxide’). On the other hand we shall find the case 
«<0 when the second substance is the more volatile, when for 
instance hydrogen is added to carbon dioxide (comp. formulae 16) or 
carbon dioxide to methyl chloride *). 
A p, v, « diagram based on observations has, so far as | know, 
not yet been published. A diagram of this kind which I have drawn 
from my measurements on mixtures of carbon dioxide and hydrogen 
perfectly resembles the p, v, 7’ diagram after HARTMAN, so that in 
the neighbourhood of pure carbon dioxide we must have m,, >0 
-and m,, <0; according to formula (16) a is really negative, while 
with &,, —1,61 (comp. Kensom Joc. cit., p. 14) I find m,, = 454, 
and positive. For carbon dioxide with a small quantity of methyl chloride’) 
a — 0,378 and 8 = 0,088, and hence m,, <<. 0 and m,, > 0; and for 
methyl chloride with a small quantity of carbon dioxide, « = — 0,221 
and B= 0,281 so that m,,>Oand m,,< 0. At temperatures between 
the critical temperatures of the two pure substances, the p, v, « diagram 
for mixtures of carbon dioxide and methyl chloride will probably 
correspond to HarrMan’s drawing. 
While two neighbouring isothermals (7, 7 + dT) never intersect 
0p 
in the p,v, 7’ diagram (the | - never being zero) this may be 
Ps b o oT oO J 
the case in the p, v, « diagram for two neighbouring mixtures 
> 
1!) Figs. 1—13 represent diagrammatically p,v,« curves for infinitely small values 
of x and 7—T;, such as they appear in reality for finite values of x and T—T%. 
They are moreover theoretically extended into the imaginary region x < 0. All 
lines lying within the region of negative x are dotted; the isothermal =O is 
represented by a dot-dash line. The line # — xe: (erroneously marked zr in figs. 
1—12) would be the critical isotherm of the homogeneous mixture. 
2) Comp. KAMerLINGH Onnes and Reincanum, loc. cit., p. 35. 
3) Ibidem. 
*) Comp. Keesom, Comm. n°, 79, p. 8. 
