\vbox{\line{\hfill
\diagram{\xaxis7truecm,0.,1.0,0.2,$x_{\rm Al_2O_3}$;\nogrid
\yaxis7truecm,-6.0,0.0,1.0,${\mit\Delta}_{mix}G$ %
[kJmol$^{-1}$];}
{\connect{\point1.0,-6.0;\point1.0,0.0;}
\curve{\vpoint0.,0.;\point0.1,-3.687;
\point0.2,-4.527;\point0.3,-4.676;\point0.4,-4.426;
\point0.5,-3.929;\point0.6,-3.322;\point0.7,-2.723;
\point0.8,-2.183;\point0.9,-1.597;\vpoint1.,0.;}
\values{\ownsymbol{1473\enspace K}\point0.37,-4.;}
\curve{\vpoint0.,0.;\point0.1,-3.993;
\point0.2,-4.886;\point0.3,-5.046;\point0.4,-4.743;
\point0.5,-4.248;\point0.6,-3.605;\point0.7,-2.963;
\point0.8,-2.360;\point0.9,-1.698;\vpoint1.,0.;}
\values{\ownsymbol{1513\enspace K}\point0.64,-4.;}}
\hfill}
\medskip
\noindent{\bf Figure~19. \rm Integral Gibbs energy of solution 
of the $\alpha$-Cr$_2$O$_3-\alpha$-Al$_2$O$_3$
system at 1473 and 1513~K.}}