Two elements lead and silver are completely miscible in all proportion in their molten state and give rise to a single homogenous phase containing two components lead and silver.

The co- existence of different phases in equilibrium at different set of conditions is as shown:

AREA ACB:

Within this area, a homogenous single phase of molten liquid of two components in aall proportions exists.

Applying the phase rule, P + F= C + 1

We have, P =1 and C = 2; which gives F = 2 (T and C)

MELTING POINT CURVES AC AND BC:

In phase diagram of lead and silver, A and b denotes the melting point of pure lead and silver respectively.

The curve AC denotes the variation of melting point of silver in Pb, while the curve BC indicates decrease in the melting point of silver with the addition of lead.

The curves AC and BC represent two phase equilibrium:

1. Solid lead ↔ molten liquid
2. Solid silver ↔ molten liquid

Eutectic point of lead and silver is denoted by point C in the diagram where all the three phases solid lead, solid silver and molten liquid coexist at a definite composition and temperature.

Applying reduced phase rule,

P = 3, C = 2, therefore, F = 2=1-3 = 0

Thus the eutectic point C of lead silver system is invariant.

which implies that a homogenous mixture of lead and silver of constant composition (2.6% Ag and 97.4% Pb) melts at a definite lowest temperature of 303 centigrade. This is known as the eutectic point of lead and silver.