Clear[xa];
DialogInput[A1=7.10179;B1=1244.951;C1=217.881;{Column[{"Antoine Constants for component 1 (P in mmHg and T in °C): ",Row[{"A1  ",InputField[Dynamic[A1],Number,FieldSize-> {6,1}],"  B1  ",InputField[Dynamic[B1],Number,FieldSize-> {6,1}],"  C1  ",InputField[Dynamic[C1],Number,FieldSize-> {6,1}]}],Button["Proceed",DialogReturn[""]]}]}];
DialogInput[A2=7.58670;B2=1281.590;C2=193.768;{Column[{"Antoine Constants for component 2 (P in mmHg and T in °C): ",Row[{"A2  ",InputField[Dynamic[A2],Number,FieldSize-> {6,1}],"  B2  ",InputField[Dynamic[B2],Number,FieldSize-> {6,1}],"  C2  ",InputField[Dynamic[C2],Number,FieldSize-> {6,1}]}],Button["Proceed",DialogReturn[""]]}]}];
DialogInput[A12=0.8552;A21=0.7526;{Column[{"Binary interaction parameters for the Van Laar Model: ",Row[{"A12  ",InputField[Dynamic[A12],Number,FieldSize-> {6,1}],"  A21  ",InputField[Dynamic[A21],Number,FieldSize-> {6,1}]}],Button["Proceed",DialogReturn[""]]}]}];
Psat1=10^(A1-B1/(T+C1)); 
Psat2=10^(A2-B2/(T+C2)) ;Gam1=Exp[A12 (A21 (1-xa)/(A12 xa+A21 (1-xa)))^2];
Gam2=Exp[A21 (A12 xa/(A21 (1-xa)+A12 xa))^2];
i=0;
P=760;
While[i<1001,{xa=i 0.001,
sol=FindRoot[Psat1 xa Gam1+Psat2 (1-xa) Gam2== P,{T,55,65}];xe[i]=xa,ye[i]=Psat1 xa Gam1/P/.sol,
Te[i]=T/.sol,i++}];
Tbl1=Table[{xe[i],Te[i]},{i,1,1000}];
Tbl2=Table[{ye[i],Te[i]},{i,1,1000}];
Tbl3=Table[{xe[i],ye[i]},{i,1,1000}];
Tx=Interpolation[Tbl1,InterpolationOrder-> 1];
Ty=Interpolation[Tbl2,InterpolationOrder-> 1];
xy=Interpolation[Tbl3,InterpolationOrder-> 1];
Quiet[Plot[{Tx[t],Ty[t]},{t,0,1},Frame-> True]]