<p>The metal pieces are introduced into a vapour area including a volatile solvent. After a set period, the vapours condense on the surface of the pieces and the latter are heated to the vapours' temp. The condensate dissolves the high b.pt. impurities on the piece's surface and is collected to recover the solvent. The contaminated condensate is sent on a heat exchanger whose temp. is above the solvent b.pt. The upper end of the heat exchanger freely connects with the vapour area and its lower end includes a trap which collects and removes the high b.pt. impurities.</p>
