OCR Text |
Show 566 SPEARMINT. SPEARMINT. and the moreso in proportion to the continuance of the im. mersion and the heat: hence oils, distilled in the common man, ner, prove muchless agreeable in smell than the subjects them. selves. For the distillation of substances of this class, another method has been contrived ; instead of being immersed in water, 567 After the distillation of one oil, particular care should be had to clean the worm perfectly before it’be employed in the distil. lation of a different substance. Some oils, those of wormwood and aniseeds for instance, adhere to it so tenaciously as not to herbs orflowers are laid lightly in a basket, of such size that be melted out by heat, or washed off by water: the best way of removing these is to run a little spirit of wine throughit. Volatile oils, after they are distilled, should be stffered to stand for some days, in vessels loosely covered with paper, till it may enter into the still, and rest against its sides, just above the water. The head being then fitted on, and the water made they have lost their disagreeable fiery odour, and become limpid; then put them up in small bottles, which are to be kept quite to boil, the steam, percolating through the subject, imbibesthe oil, without impairing its fragrance, and carries it over intothe full, closely stopped in a cool place. With these cautions they will retain their virtues in perfection for many years. Most of the oils mentioned above are prepared by our cheinists in Britain, and are easily procurable in a tolerable degree of perfection; but the oils from the more expensive spices, though still introduced among the preparations in the foreign pharmacopeeias, are, when employed among us, usually im- they are exposed only to its vapour. A proper quantity of water being put into the bottom of the still, the odorifcrous receiver. Oils thus obtained, possess the odour of the subject in an exquisite degree, and have nothing of the disagreeable scent perceivable in those distilled by boiling them in waterin the common manner. Plants differ so much, according to the soil and season of which they are the produce, and likewise according to their own ages, that it is impossible to fix the quantity of water to he drawn from a certain weight of them to any invariable standard. The distillation may always be continued aslong astheliquor tuns well flavoured off the subject, but no longer. The mixture of water and oil, which comes over, may either be separated immediately, by means of a separatory, or afterit has beenput into large narrow-necked bottles, and placed in a cool place, that the portion of oil whichis not dissolved in the water mayrise to the top, or sink to the bottom, according to its specific gravity. It is then to be separated, either by a se- paratory (Plate I. fig. 10. of Duncan’s New Edinburgh Dispen, satory); or by means of a small glass syringe; or by means of a filter of paper; or, lastly, by means of a. woollen thread, one endof which is immersedin the oil, and the other lower endin a phial: the oil will thus pass over into the phial by capillary attraction ; and the threadis to be squeezed dry. The water employed in the distillation of volatile oils always imbibes some portion of the oil, as is evident from the smell, taste, and colour, which it acquires. ported from abroad. These are frequently so much adulterated, that it is not easy to theet with such as are at all fit for use: nor are these adulterdtions easily discoverable. ‘The grosser abuses, indeed, may be readily detected. Thus, if the oil be mixed with alcohol, it will turn milky on the addition of water; if with expressedoils, alcohol will dissolve the volatile, and leave the other behind ; if with oil of turpentine, on dipping a piece of paper in the mix- ture, and drying it with a gentle heat, the turpentine will be betrayed by its smell.. But the more subtle artists have contrived other methods of sophistication, which eludeall trials of this kind. Some have looked uponthe specific gravity of oils as a certain criterion of their genuineness. This, however, is not to be absolutely depended on; for the genuine oils, obtained from the same subjects, often differ in gravity as much as those drawn from different ones. Cinnamon and cloves, whose oils usually sink in water, yield, if slowly and carefully distilled, oils of great fragrancy, wh*ch are specifically lighter than the aqueous fluid employed in their distillation ; whilst, on the other hand, It cannot, however, Te the last runnings of some of the lighter oils prove sometimes so already used, and therefore almost saturated, may. be advan. tageously employed, instead of common water, ina second, ponderous as to sink in water. As all volatile oils agree in the general properties of solubility in spirit of wine, indissolubility in water, miscibility with water, by the intervention of certain intermedia, volatility in the heat tain above a certain quantity ; and therefore such as has been third, or any futuredistillation of the same subject. of boiling water, &c., it is plain that they may be variously |