( 773 ) 
here to the phenomena of retardation for so far they only appear 
token we work rapidly % 
If we consider first of all the phenomenon of undercooling and 
superheating of the solid, for so far as they are only observed with 
quick change of temperature, fig. 7 gives a satisfactory explanation. 
Starting from the inner liquid equilibrium p , not the curve of 
equilibrium pl„ but another curve e.g. pi, will be followed with 
rapid cooling, and when we get beyond l, the state is not only 
unarily, but also pseudo-binarily metastable. 
Let us assume for simplicity that in the pseudo-binary system no 
retardation worth mentioning appears, then the substance will solidify 
at l, and the solid substance S, is dej»osited. 
Now this two-phase equilibrium is metastable to a high degree 
in the pseudo-binary system. 
In the unary system equilibrium between liquid and solid sub¬ 
stance can only exist under constant pressure at one temperature, 
and now it is the rule that a metastahle state like that of the system 
h + S, is at once destroyed. Thus we see e.g. that a supersaturate 
solution in contact with the substance which this solution must 
deposit to pass to the stable condition, generally immediately deposits 
this substance. 
So the metastable two-phase equilibrium /, -f- S, is changed into 
the stable state l, -|- S„ and this being a process which generates 
heat, the temperature rises to the unary melting-point. - 
Starting from the solid inner equilibrium q we get just the reverse, 
because then the substance melts at too high a temperature if 
quickly heated, as has already been observed for rhombic sulphur. 
If now the curves of inner equilibrium run as in fig. 8, the 
liquid can solidify too early if cooled two rapidly, the solid sub¬ 
stance can melt too early if heated too rapidly, and then the result 
is that for a perfectly pure substance there is a range of temperature 
over which the solidification and the melting extends, which probably 
often occurs for organic .substances, in which the equilibrium sets 
in so slowly. 
With regard to the phenomena of retardation at the transition 
point I need only refer to fig. 9, which will now be clear without 
further elucidation. 
It is further hardly necessary to remark that when a substance 
is not M-, but tri-, or polymolecular , the phenomena discussed here 
remain es sentially the same. 
*) The peculiar phenomena, which will also appear for more complicated 
systems, as e.g. Fe f C when we work quickly, will have to be accounted for in 
