Lever rule
= Lever rule
{title2=$\phi=(\overline C-C_s)/(C_l-C_s)$}
{wiki}
The lever rule finds phase fractions from a horizontal tie line on a <phase diagram>. For solid and liquid <concentrations> $C_s,C_l$ and bulk <concentration> $\overline C$, conservation gives $\overline C=(1-\phi)C_s+\phi C_l$. Thus $\phi=(\overline C-C_s)/(C_l-C_s)$ is the <liquid fraction>, provided $C_s\le\overline C\le C_l$. For pure solid, $\phi=\overline C/C_l$.