980 
Now the important question is still left undecided, in how far 
b, ie Ce 
does the value of — differ for the different substances. We have 
lim 
already stated that it is not probable that there are substances for 
which this quantity = 1. These substances have sometimes been 
called perfectly hard substances, but then it should be borne in mind 
8 ; 
that since it has appeared that 7 >4 and s > = for monatomic sub- 
stances, even monatomic substances would not be perfectly hard. 
For all substances, with our present knowledge we may say without 
by 
: Y re . 
exception, — >1, and probably not very different from 2. Now 
lim 
we might account for about 2 by assuming quast-assoctation. In large 
volume 5, is the fourfold of the volume of the molecules; hence if 
the spherical shape is assumed and the diameter is put = 4, 
ot 
b, —4- o. The limiting volume of the substance is present when 
b 
the pressure is infinite at temperatures 7’>> 0. Then the molecules 
must touch, and the volume is only little smaller than 6° or 6 j,, <6’. 
Hence: 
or by Mb 
But on the other hand we should consider that often 
den 
Blin 
If not the spherical shape was assumed; but as extreme case, a 
b, 
g 
rectangular shape, 6, would be = 40°, and by = 0°, and =a 
et lim 
This will, probably, not be expected by anybody. For ellipsoidal 
shape we should again find a little more than 2. In this way it 
ze 
seems impossible to me to explain the value of —— < 2. But we 
lim 
shall possibly discuss this later. 
The original theorem of the corresponding states pronounced the 
equality of the z,u,r surface. In the form given here it states the 
Ane : Pp . 
superposition of the <7, m——— surfaces. These two forms would 
Iq 
Dim 
coincide, if there was only one single law for the course of 6. In 
