374 
It is clear that if the reverse happens in the quadruple point g, 
fhe condition must have become different in so far that the homo- 
geneous gaseous resp. liquid phases, which were before saturate with 
regard to FeC and unsaturate with regard to C, must be saturate 
again in g with respect to both the solid phases, and infinitely little 
above the temperature of the quadruple point g the gaseous and 
liquid phases in contact with solid FeC must become unsaturate with 
respect to FeC, and supersaturate with respect to graphite, so that 
solid FeC is dissolved, and graphite is deposited, till all the carbide 
is gone. 
So in the quadruple point g we get for the transformation on 
supply of heat the symbol 
C+ Fe Fel) in the homogeneous gas- 
I f and liquid phases. he ee 
C FeC 
solid solid 
So the transformation given here must be endothermic in the 
direction of the arrows. We have to call attention to the fact that 
we assumed for shortness’sake that the formation of FeC in the 
coexisting gas and liquid phases is endothermic along the three phase 
line for C+L+G from a to 6. Now, however, we know only 
with certainty that the total transformation (1) is attended with 
absorption of heat. 
When in the process of condensation resp. solidification of FeC 
from the coexisting phases more heat was developed than was absorbed 
in the process of evaporation resp. melting of graphite *), the process 
in the homogeneous phases would undoubtedly be endothermic, but 
in the opposite case the total transformation (1) could be endothermic, 
whereas the reaction in the homogeneous gas and liquid phases was 
exothermic. But in this case we should have to inquire how it is 
possible that the gas and liquid phases, which were unsaturate with 
respect to FeC on the three-phase lines between the points a and 4, 
have become saturate with respect to this compound at 5. This is 
easy to see. We must namely consider two influences here which 
can displace the equilibrium : in the first place the temperature, and 
in the second place the concentration of the reacting components. 
On rise of temperature in the absence of graphite the equilibrium 
in the homogeneous gas and liquid phases would shift to the left, 
but in the presence of graphite just the reverse would take place, 
when namely the increase of solubility of graphite predominates over 
t) The heat of mixing included. 
