Why does Cody use Litharge?
Litharge is $\ce{PbO}$. It is probably introduced to save silver from compounds containing oxidized silver like $\ce{AgCl}$. If metallic silver powder is mixed with $\ce{AgCl}$, this compound will react with $\ce{PbO}$ according to $$\ce{2 AgCl + PbO -&gt; PbCl2 + Ag2O}$$ And $\ce{Ag2O}$ is an instable compound being easily transformed into $\ce{Ag + O2}$ at high temperature. So all metallic silver and silver from silver compounds are finally dissolved into lead, because lead dissolves metallic silver and not silver compounds. Without litharge, silver compounds like $\ce{AgCl}$ are lost.