1223 
A. No phase reaction is possible. The three phases form the apexes 
of a three phase triangle such as, for instance, /aa,, in fig. 4 (I). 
We may further distinguish three other cases, namely 
1. K+ L is converted by a change of pressure jn the one direction 
into /+ LZ’ + G’ and by a change of pressure in the other direc- 
tion, into + L". Hence on change of pressure in the one direction 
vapour is formed, but not when in the other direction. 
2. F+ L is converted by a change of pressure in the one direc- 
tion into + L’+ G’, and by a change of pressure in the other 
direction into “+ L" + G". Hence, vapour is formed on increase 
as well as on decrease of pressure. 
3. f+ L is converted by a change of pressure in the one direc- 
tion into “+ L/ and by a change in the other direction into 
F+ L". Hence, no vapour is formed either on increase or on reduction 
of pressure. The case cited in 1 is the one generally occurring; 
those mentioned in 2 and 3 only occur exceptionally. 
B. A phase reaction is possible. The three phases are now repre- 
sented by three points situated on a straight line. The system / + 1 
can then be converted by a change in volume unaccompanied by a 
change of pressure, into the system £ + L + G. So long as these 
three phases are adjacent, neither the pressure nor the composition 
of liquid or vapour is altered by a change in volume; all that hap- 
pens is a reaction between the three phases. As regards this reaction, 
we can now distinguish three cases: 
Kee dl Gr: | 
In the graphic representation, the point # is situated between the 
points L and G. On a change in volume in the one direction solid 
matter is deposited; when in the other direction this disappears. 
2, F4+ L2G. 
In the graphic representation the point G is now situated between 
the points # and £. On change in volume in the one direction, gas 
is formed; when a change takes place in the other direction the gas 
disappears. 
BA Gk. 
In the graphie representation the point Z is now situated between 
the points # and G. On change in volume in the one direction, 
liquid is formed, when in the other direction this disappears. If, in 
one of the reactions sub A and £ vapour is formed, the volume 
will as a rule become larger and if vapour disappears it will become 
smaller. The reverse, however, may also occur as will be perceived 
in the following manner. In order to convert + L into /+L’+6" 
we first of all form from Z a little of the vapour G’; the liquid LZ 
