ES′SENCE

Syn. E entia , L. The active and characteristic portion of a substance, or that on which its most remarkable properties depend. The term has been very loosely applied to various preparations presumed to contain these e ential principles or qualities, disencumbered of gro er matter. Modern systematic writers generally restrict its application to the volatile oils obtained from vegetable substances by distillation, or to a strong solution of them in alcohol. In pharmacy and perfumery, the word ‘e ence’ is applied to concentrated preparations that differ vastly from each other. Thus, concentrated effusions, decoctions, liquors, solutions, and tinctures, are frequently called ‘e ences’ by those who vend them; but the term ‘fluid extracts’ would be more appropriate, if those already mentioned are not deemed sufficiently showy and attractive. We shall here confine ourselves to a brief notice of the principal compound e ences, or those that undergo some preparation beyond being merely extracted from vegetables by distillation along with water. The latter will be considered under the article Oil . The concentrated preparations of the pharmaceutist, termed ‘e ences,’ are mostly prepared by digesting the active ingredient or ingredients in rectified spirit of wine, either with or without the addition of a certain portion of water; or they are extemporaneously formed by di olving a portion of the e ential oil of such substances in the spirit. In this way are made the e ences of lavender, musk, ginger, . When it is desired only to obtain the aromatic and volatile portion of the ingredients, the latter are usually digested in the spirit for a few days, and then submitted to distillation, when the alcohol comes over loaded with aromatic e ential oil, or other volatile matter. In this way are prepared most of the fragrant e ences of the perfumer and druggist, when simple solution of the e ential oils in alcohol is not resorted to. In many cases the active principles of the ingredients are partly volatile and partly fixed, or at least do not readily volatilise at the temperature at which alcohol distils over. This is the case, for instance, with the active portion of ergot and Jamaica ginger. In such cases digestion alone should be adopted. When the principles of organic substances, of which it is desired to obtain a concentrated solution, are resinous or oily, or little soluble in weak spirit (which is mostly the case), the strongest rectified spirit of wine should alone be employed. In the preparation of e ences without distillation, the method by percolation or displacement is preferable to that of simple maceration and expre ion, when the nature of the ingredients and other circumstances render it applicable, as it is not only more economical, but a more concentrated solution may thereby be obtained. At the same time, however, the reader should remember, that this mode of operating requires much greater experience and skill to ensure succe than the former method. This clumsine of manipulation is the common cause of the failures which are so frequently met with in the preparation of these articles. The ingredients for the preparation of e ences must undergo the same operations of bruising, powdering, or slicing, as directed under ‘ Tincture ,’ previous to digestion in the spirit, or other menstruum; and the length of time they should be allowed to infuse, when this method alone is adopted, should not be le than ten days; but this time may be advantageously extended to a fortnight, or even longer. During the whole of this period frequent agitation should be employed, and when the ingredients are so bulky as to absorb the whole of the fluid, the ve el which contains them should be securely fastened by a bung or stopper covered with bladder, and inverted every alternate day. By this means every portion of the ingredients will be equally exposed to the action of the menstruum. In all such cases the method of displacement, or percolation, is preferable. For the e ences used as perfumes and for flavouring, not only must the spirit be perfectly tastele and scentle , but it must be also quite devoid of colour. The following formulæ embrace most of the e ences met with in the shops. Those not found among them may be readily prepared by applying the general directions given above, or by employing the formula given for the preparation of the e ence of some similar substance, merely varying the characteristic ingredient. Thus, were it desired to form an e ence of ambergris or of myrrh, and no formulæ could be found for these preparations, the tyro would consider in what menstruum the active principles of these substances were most soluble. This, he would immediately see by reference to their properties, is rectified spirit of wine. He would next have to decide on the proper strength of his e ence. In this he must be guided, either by the strength of the like preparations of other makers, or by his own judgment of what would be useful, novel, or convenient. Suppose he decided that his e ence should represent 1-10th of its weight of the solid ingredient. He would then take 2 oz. of ambergris or myrrh, and 20 oz. of rectified spirit, which he would digest together for 10 days or a fortnight in the manner described above. Had the required preparation been an e ence of senna (for example), he would probably recollect, or might easily ascertain by reference, that the active properties of senna are soluble in both water and weak spirit. Then, to make an e ence 4 times as strong as the tincture of the pharma copœia, 7 oz. of senna, and 1 pint of proof spirit, should be employed, with due digestion, as before. [280] The same applies to other preparations. See Concentration , Decoction , Infusion , Liquor , Spirit , Tincture , . [280] See directions given under Tincture .