COMPLETE FREEZING-POINT CURVES OF BINARY ALLOYS. 
27 
Jateiit heat of silver, the two curves will be found to intersect at a composition verj 
near that of the eutectic alloy. The intersection of the experimental curves in the 
eutectic point terminates the part of each curve which is generally realizable, 
although by utilizing phenomena of selective surfusion, both Lb Chateliee,'^' and 
DAHMst consider that they have, in one or two cases, traced the lower branches for a 
short distance. 
In a certain sense the phenomenon of the eutectic state gives rise to a horizontal 
branch of the freezing-point curve, passing through the eutectic point E, fig. 1 ; for 
if we take a mixture represented by the jioint X and allow it to cool, the changes 
in its state will be represented by points on the vertical XYZ. There will be a 
freezing point at Y followed by a slow fall in temperature until the temperature Z 
is reached, when the part still liquid will have the composition of the eutectic state 
E, and will solidify without further fall in temperature, thus giving a second very 
well marked freezing point. This phenomenon of double freezing points has long 
been known, and is well shown in the silver-copper curve given in this paper. 
B 
Let us now suppose that a comjDound C of A and B exists, whose composition and 
melting point in the pure state are given by the point P. Then, if P lies above the 
curve of fig. 1, and C is not completely dissociated by melting, we shall get a 
freezing-point curve such as fig, 2, with two eutectic points E and E'. This sort of 
curve is well illustrated by the copper-aluminium curve given by Le Chatflier 
Revue Generale des Sciences,’ 30 June, 1895), and in the work of Roozeboom on 
the equilibrium between water, hydrochloric acid, and ferric chloride (‘ Zeitsch. Phys. 
Chem., vol. 15, p. 588’). If more than one compound is possible, the main curves of 
fig. 1 may be interrupted by more than one such middle curve. 
If the compound C is not at ail dissociated by melting, then P may be an angle 
and will divide the figure into the two complete systems AC and CB, each corres¬ 
ponding to the case of fig. 1, and obeying the equations discussed above; but the 
* ‘ Comptes Rendus,’ April 9, 1894. 
t ‘ Ann. Pliys. Chem.,’ 1895, vol. 54, 386. 
E 2 
