550 
raised by a new substance, when the volume increases on 
melting or conversion ; 
lowered, when the volume decreases on melting or conversion. 
This increase and decrease are at first approximation proportional 
to the quantity of the new substance. 
When we apply those rules to the melting of a simple substance, 
then follows the known rule of the decrease of melting or freezing 
point; the first formula (21) is then the known formula of Raovnt- 
VAN "T Horr. 
We may apply the previous deductions also when we substitute 
in (19) the liquid ZL by a gas G. In general AV is then positive 
and approximately equal to the volume V of the gas; by this we 
may give another form to the second formula (21) viz. 
GPP Pri NE BON (20) 
We may deduce the previous rules also in the following way. 
We take the equilibrium H= LFF... in which the new 
substance X is not yet present under constant pressure; then it is 
invariant (P) and it consists at a definite temperature, which we shall 
call 7. When we assume that reaction (22) takes place from left 
to right at addition of heat, then it follows: 
Pir Me ai J SO 
(L) (HEE CE ee cy 
towards lower 7 | towards higher 7. 
Consequently the equilibrium (D= F,+ F,+... consists at 
temperatures lower than 7,. When we add the new substance X, 
then # passes into #’ = L’+ F,+ F,+..., in which JZ, differs 
from ZL; this equilibrium £” exists at a temperature 7” which differs 
from 7. 
When we take away the liquid Z’ from H’, then it passes into 
FE, 4 F,+..., consequently in the equilibrium (Z) discussed above; 
as this exists at lower temperatures than 7,, it follows 7” < 7%. 
On addition of the new substance the common melting-point must 
fall, therefore. 
From reaction (23) we find the same for the common point of 
conversion. When we take at constant temperature the equilibrium 
E=L4+F,+ F,+..., in which the new substance is not yet 
present, it is invariant (7Z’); then it exists under a definite 
pressure P,. 
