The Parkes process, patented in 1850 uses molten zinc. Zinc is not miscible with lead and when the two molten metals are mixed the zinc separates and floats to the top carrying only some 2% lead. However silver preferentially dissolves in zinc, so the zinc that floats to the top carries a significant proportion of the silver. The melt is then cooled until the zinc solidifies and the zinc crust is skimmed off.  The silver is then recovered by volatalising the zinc. The Parkes process largely replaced the Pattinson process, except where the lead contained insufficient silver, in which case the Pattinson process provided a method to enrich it in silver to about 40 to 60 ounces per ton, at which concentration it could be treated using the Parkes' process.