_Bergamot oil_ is quite durable; in well-closed bottles stored in a cool cellar it keeps quite well for 3 to 4 years. _Oil of lemons_ is, however, very sensitive, and has to be especially protected against heat, by which it is readily decomposed and, so to say, turns sour. Freshly-distilled _neroli oil_ should never be used, it acquiring its proper aroma only after being stored for about 2 years; on the other hand, it should not be too old. When 6 to 8 years old, it shows a tendency to rancidity, which can, however, be prevented by mixing it at the proper time with an equal quantity of alcohol of the best quality. _Petit-grain oil_ is apt to spoil when kept for several years, and hence it is not advisable to have too large a supply of it on hand. Besides the French variety of this volatile oil, there has existed for several years past another kind, namely the _Paraguay petit-grain oil_, which is about one-half cheaper than the French. While some consider both oils as equally good, the French product no doubt deserves the preference. Of _lavender oil_ only the best French oil, especially made in France for the preparation of _Eau de Cologne_, should be used. The price of the English Mitcham lavender oil, being six times that of the French oil, is simply excessive. Of _rosemary oil_, an especially fine quality for Cologne water, which can be highly recommended, is also manufactured in France. Of _balm oil_ only the best German product should be taken. The three varieties of volatile oils last mentioned keep for years, especially when kept in hermetically-closed bottles in a cool place protected from the sun. Rose water and orange-blossom water also need careful treatment, the bottles containing them requiring to be well stoppered and kept in a cool place. These waters being liable to spoil, the supply of them should be renewed from year to year. As regards the compounding of the volatile oils, it is advisable to mix them in a capacious glass flask, add at least an equal weight of alcohol of the best quality, shake thoroughly, let the mixture stand about 14 days, and then in the apparatus incorporate it with the required quantity of alcohol. When the alcohol and volatile oils are intimately mixed, the mixture is allowed to stand quietly for about 14 days, when solution of the volatile oils will be complete. Now add, with vigorous agitation, the rose water and the orange-blossom water, and let the whole stand quietly to become clear. Cologne water thus carefully prepared answers all demands. Special attention is here called to the fact that all manipulation by the addition of fixing or conspicuous substances is injudicious. An addition of tincture of musk or civet should particularly be avoided. Nervous people immediately detect such additions, even if present only in very small quantities, and in most cases refuse the Cologne water containing them.