A technique devised for rapidly quenchin4] reactions oecurrimj in a rapid compressi{m machD., durimy the ignition de~y period is described and the results of preliminary studies made with it are presented. The quenc.hirud device was designed and adapted to the machine to extend its utility atul provide a means of studyin# the chemical reactions preceding auto ignition. With this devtce preJlume reactions can be arrested at any predetermined point during compression or ignition dela!l. Nuit~tble te~ehniquem may then be employed to analyse the partial oxidation products. An initial it~re,tiyqtio~Β’ with the device, was co~wlucted on the stoichiometric benzene-air system. These studies col,.fi~me,I the previousl!! known fact that on 0 a ne4lligible amount of benzene or oxygen is consumed dur&,g the early stages of the ignition delay. Based on this finding and ignition ~b, la:! time tt~egr*urement.,.. ,t global activation energy of ca. 11 kcal/gmole was txdeulated for the be;t'.ene--air reaction which muq apply t,o the ingtiating steps of the reaction mechanism. The derice described show.~ promL, e of being a powerful tool .for followim.! the chemical course of preflame retwt;ot,., which occur ~tt high pre,w,r,, and temperat,tre.