An entrainment method has been used for the determination of the vapour pressure of Zn over the pure metal and over liquid Cu-Zn alloys. The results obtained with pure Zn show tjhc lnet,hod to br reliable, providing certain precautions are taken. The activities of Zn and Cu have been deduced anti show negative deviations from Raoult's law; the solution is approximately regular, with all illt,ercharlgc energy w of -630 cal per mole. L'ACTIVITI? DU ZIXC DSNS LES ALLIAGES LIQUlDES CIJIVKE-ZINC Une methode d'entrainernent a Btk utilisPe pout la dPtrrmination de la pression dc. vapeur dr zinc* SW le n&xl pur et sur des alliages liquides Cu.Zn. Les r$sultats obtenus avec du zinc pur rnontrant que la mbthodr rst, fidixle pourru que cvt~airws pr6cautions soient, prises. Les activitb du zinc et du cuivre ont & dbduites et montrent des d&iations nPgatives de I;] loi de Raoult; la solution est approximativement normale avtc une &wrgie d'interaction w de-630 c~II. alar mole. DIE AKTIVITXT VON ZIXK IN FL~SSIGEN KUPFER-ZINK-LEGIERUXGEN Zur Restimmung des Dampfdrucks van Zink iiber dam reinen Metal1 und iiber fliissigen Kupt;~ Zink-Lcgierungen wurde eine Mitfiihrungsmet,hode verwendrt. Die an reinem Zink erhaltonen Ergeb-r&se zeigen, dass dieses Verfahren bei Einhalt,ung bestimmter Vorsichtsmassnahmen zuverl&ssig arbeitet,. Aus den Ergebnissen wurden die Aktivitiiten van Zn und Cu abgeleitet,. Sic zoigen negativr: Abweichungon vom Raoultschen Gesetz. Die LBsung ist n8herungsweise rcgul8r mit, einer m'echs~~lwirkungsenergir w = ~ 630 cal/Mol. Although several determinations of the activity of zinc in solid copper-zinc alloys have been reported,(l) little attention has been paid to the liquid phase,c2) apart from measurements of boiling-paints.(3) In this paper new measurements of the vapour pressure of zinc over liquid alloys are recorded. These measurements, made by an entrainment method, covered a wide range of composition, so that it was possible to deduce a,lso the activity of copper. Apparatus EXPERIMENTAL The general layout of the apparatus used is shown diagrammatically in Fig. I, and details of the furnace and saturation vessel in Fig. 2. The main feature of this apparatus is the use of two gas streams entering the furnace tube at a and b (Fig. %). The former passes over the liquid alloy contained in the transparent silica saturator, c: the latter passes through the silica furnace tube, d, surrounding the saturator and then into the collector, e. The collector is a transparent silica tube of 8-mm diameter which fits loosely over the short capillary outlet (2-mm bore) of c. Vapour in equilibrium with t'he metal in c is entrained *