ERRORS IN THE ANALYSING OF PERFUMERY RAW MATERIALS 37 of non-volatile inhibitors in the liquid phase. Ester interchange reactions between hydroxyl- or carbonyl-containing components and ester type liquid phases are readily observed at elevated temperatures, and can be eliminated by the use of another liquid phase or by a significantly lower operating temperature as. It is essential that the support is and remains correctly impregnated. It is almost beyond doubt that alterations in the substance being analysed, where new columns are in use, are attributable to faulty impregnation. When the support is not completely saturated by the liquid phase, it results in tailing of the peaks TM. Suitable pre-treatment of the support reduces the presence of active centres, de-activating it and reducing the importance of this effect 4ø. Some catalytic reactions of substances with hydrogen on the platinum resistance wire of catharometers have been observed, resulting in a modifi- cation of the effluents and also in an alteration of the signal by virtue of thermal effects. If the alterations are accentuated by an increase in tem- perature, isomerisations of purely thermal origin can also take place (for example, ocimenes into allo-ocimenes, citrals into isocitrals, pulegone into isopulegone, carvone into spicatone). With fragile substances, it can be advantageous and at times even necessary, to transform them into products which are stable or more easily vaporised. One can, for example, acetylate alcohols, or convert acids into methyl esters. The remarks made here could discourage some of the users of gas chro- matography who are impatient to utilise an apparently simple analytical technique, and who are encouraged by apparatus suppliers and by publica- tions, which in reality are superficial and misleading. Provided the above remarks are taken into account, gas chromatography can be transformed into an analytical routine of accepted reliability and precision that lends itself to such a degree of automatic operation that work becomes rapid and does not require highly skilled operators. The acquisition and renewal of complicated and costly apparatus, its maintenance in good condition for use, keeping in touch with progress, and the study of the diversity of original problems which are particular to the perfumery raw material industries, are hardly within the reach of analysts of small concerns or of small laboratories. It is these who must be par- ticular!y careful to formulate their conclusions with the necessary reserve. It is useless and wrong to suppose that operational skill, which is often accompanied by a persistent error, can suffice 4•. Knowledge of all the phenomena that apply, attention to all accomplished progress, notably to all newly revealed causes of error, and incessant research are indispensable. The gas chromatography abstracts •2 are useful sources of reference.

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