148 CHILWELL AND HARTLEY : DETERMINATION OF RESIDUAL [Vol. 86 Determination of Residual Organo-phosphorus Insecticides inL Foodstuffs A Review* BY E. D. CHILWELL AND G. S. HARTLEY (Fisons Pest Control Ltd., Chesterford Park Research Station, nr. Saffron Walden, Essex) SUMMARY OF CONTENTS I. Introduction 11. Extrac