194 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS perfume may benefit from slight oxidation effects during the maturing period. With regard to solubilised perfumes which will include some aqueous medium, the situation may be different. If the solubilising agent is based on an unsaturated fatty acid more antioxidant may be needed. Supplementary Question: Arising out of the above, is there any value in the use of sequestering agents in perfumes ? Answer: Use is made of sequestering agents to inhibit iron and copper ions from acting as oxidation catalysts in perfume raw materials. The addition of sequestering agents to perfumed soaps has not been very successful. A better approach is to remove iron and copper during pre- paration of the raw materials--natural and synthetic perfume materials are stringently tested for metal content nowadays. The so-called sequestering of metal ions is not always effective. The metal may still have some reactivity even when complexed. For example, patchouli travels all over the world in iron drums and usually contains some iron. By adding amyl salicylate to patchouli the mixture quickly turns from pale yellow to purple. If an iron sequestering agent is added to the original sample, subsequent admixture with amyl salicylate will give less strong colour development, but the colour reaction cannot be entirely eliminated. On the other hand, if the test is repeated after removal of the iron by distillation of the patchouli, no colour development occurs even on boiling. Question $: Can the panel give any views on applications of the H.L.B. system in emulsion technology ? Answer: The system represents a real first step in classifying emulsifying agents. But many combinations of emulsifiers give a recommended H.L.B. number so that much painstaking work is still required in order to find the best combination for a particular purpose. It must also be remembered that, in the academic approach in general, very simple oil-water systems are used in order to avoid complicated side-issues. The cosmetic chemist has to deal with more complicated systems at the very start of an investi- gation. The oil phase may be liquids of varying viscosity or even solid, polar or non-polar the system may be complicated by the inclusion of solid powders of various types the aqueous phase may contain a number of ingredients some emulsifying agents have other effects in addition to keeping an emulsion reasonab!y stable. Perhaps the H.L.B. system has suffered from the early impression (albeit accidental) that it was the quantitative answer to all emulsion problems. W. C. Griffin certainly would not claim this. It is the only system yet devised and is qualitatively

QUESTION AND ANSWER 195 useful. However it must be used with caution--after all, many emulsions are required to be less than perfectly stable in conditions of use. Question 4: What is the present position with regard to polypropylene for containers and is this material expected to be superior in any way to polyethylene ? Answer: It is important to remember that polypropylene is not a new wonder plastic which can be universally applied. It does not differ in character from polyethylene, but only in degree. It has a little more resistance to vapour transmission than high-density polyethylene (and even more resistance than low-density polyethylene). It has a higher surface hardness, can be moulded with a better gloss and cast into film of greater clarity. These properties could lead to pro- duction of decorative containers to compete in clarity with glass. It is more expensive than glass but is less dense and unbreakable, and will probably become cheap in time. The material may compete with cello- phane film. Its rigidity will prevent competition with normal polyethylene in squeeze-bottle packs and in laminate materials. It is stable to higher temperatures than is polyethylene. It does become brittle at very low temperatures but should be satisfactory over the normal range of terrestrial temperatures. Polypropylene is free from environmental stress cracking and should prove much more satisfactory in this respect than polyethylene for wadless caps, etc. The long-standing problem of adhesion, say of labels, to polyethylene will be accentuated in polypropylene and similarly there are difficulties in screen printing. Question 5: Is there a known reason for perfume deterioration in powder products, such as tinted face creams and talcum powders ? Answer and Comment: There are some known and some unlmown reasons. The deterioration of perfumes in tinted make-up preparations and powders is well known to perfumers and presents some baffling aspects. For instance, for many normal perfumes, particularly aldehydic ones, incorporation in face powders containing light-shade iron oxides may be reasonably satisfactory whilst in powders containing dark iron oxides, deterioration may occur at an alarming rate. Another feature is the effect of various powders on perfumes. In a series of powders, say kaolin, talc and chalk, a standard amount of perfume gives completely different impressions from the different powders. This is probably due to preferential absorption and adsorption. It is not deteriora- tion in the previous sense but the effect can be very unpleasant. Remark- able differences are noticeable over a series of talcs. For example, a per- fume which gives a full unchanged fragrance with Indian talc may give a