1511 
tible, would render the deviation of the lowest point still greater 
instead of smaller, because the specific heat of the products of 
dissociation NH, and HCl will certainly be greater than that of 
unsplit molecules of ammonium chloride; hence the heat of disso- 
ciation will increase at higher temperature; therefore the curve in 
fig. 4 will turn its convex side to the 7Z’~'-axis. The points for log p 
in fig. 5 can therefore undergo but little modification. 
There further remains an objection possible against the way of 
extrapolation. Decidedly the extrapolation can cause here pretty 
great inaccuracies, and the influence of this should therefore also 
be studied. 
In the extrapolation a straight line has been drawn through the 
points of fig. 5, whereas in reality the line will be curved, though 
probably exceedingly little also here. The straight line 
log p= — 7 + b 
supposes that the heat of evaporation (4.571 a) does not vary 
with the temperature. This is only the case when the specific 
heats of gas and solid are equal. The curvature is determined in 
the representation of fig. 5 by the difference in these specific heats, 
for: 
d log P Q 
dir R 
and 
d? log P T? dQ 
dU FR at 
When we bear in mind that Sp = Cas — solid, in Which C repre- 
sent specific heats, it is clear that the curvature will be positive, 
if Crolia << Chas. Now the specifie heat of solid ammonium chloride 
at the point of transition is 0.34 or molecularly about 18 according 
to table 7; this value will increase with the temperature. The 
specifie heat of HCl and NH, amounts about to 15 or 16 calories ; 
the specifie heat of gaseous NH, Cl will be smaller, hence the cur- 
vature, if it is perceptible, will lower the point of transition in 
tig. 5 instead of raising it. The point drawn therefore gives indeed 
the highest value for loy p at the transition point. 
Now the question remains whether we can draw a curve through 
the points of the dry ammoninm chloride (squares in fig. 5) with so 
great a curvature, that it attains the indicated value at the transition 
point. For this the curvature will have to be negative, hence in 
