Extracts of Pyrethrum: Permanence of Toxicity and Stability of Emulsions

Abstract

Summary.1. Pyrethrum flowers (Chrysanthemum cineraraefolium) both as whole heads and as powder retain their insecticidal properties at ordinary temperatures and at 28°C. for considerable periods if stored in closed vessels. If exposed to the atmosphere in a thin layer as finely ground powder there is risk of loss of toxicity.2. Alcohol and petroleum extracts of pyrethrum retain their toxicity in temperate climates over many months. Alcohol extracts readily give permanent emulsions when added to water; petroleum extracts require the incorporation of an emulsifier.3. Water‐miscible petroleum extracts of pyrethrum can be prepared by the addition of certain materials, such as ammoniated Agral W.B. and neutral turkey‐red oil.4. A study has been made of the degree of permanence of the active principles in alcoholic and water‐miscible petroleum extracts at ordinary British temperatures and at 28°C. and also in emulsions of these extracts in alkaline spray fluids of varying PH. The active principles proved more permanent than has been usually supposed.5. The readiness with which water‐miscible petroleum extracts disperse in the aqueous phase and the stability of the emulsions formed under a variety of conditions have been investigated.