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First, plant matter is placed in the body of the still with water. Beneath the body is a chamber where fire or coal are placed to heat the water. (Remember the Bunsen burner you used in 10th grade chemistry class? Same principle.) Above or to the side of the body is the still head, where condensation takes place. Connecting the body and the head is the "gooseneck" (the col de cygne in French). The essential oil gases and water vapor rise up the gooseneck and are then cooled in the head. The cooled gases condense and funnel out a leadoff pipe and into a collecting flask (sometimes called a Florentine flask—named after Florence, the city which led production of essential oil during the Renaissance). In the flask, the oil and water separate. Although most oils will float on the top, clove oil and anise oil will drop to the bottom of the flask. Voilà! Pas très difficile, n'est-ce pas? |
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| Just dying to learn more about chemistry? Well here's an interesting fact: even though the boiling points of most essential oils in plants range from 150º C to 300º C, when they are distilled with water, they will boil at a temperature much lower—less than 100º C. This is an example of a phenomenon known as Dalton's Law of Partial Pressure, and has important significance in perfume making. If plant essential oils were allowed to boil until they reach their normal boiling points (150º C to 300º C as stated earlier), the result would be a gross sticky mess; the plants would decompose into disgusting goop. Goop is not good for perfume making. However, Dalton's law states that when two volatile liquids that are not mutually soluble, are boiled together, their collective boiling point is one that is lower than were either to be boiled separately. This means that when the plants are distilled in water (boiling point 100º C), the essential oils in the plant will boil at less than 100º C, and thus not decompose. La chimie, c'est chouette, non? |
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Distillation doesn't just stop here, mes amies. There are actually three types of plant distillation, though each is simply a variation on the amount of contact between the plant and the water. Some plants can handle the water immersion that normal distillation requires; others are more delicate and can handle only limited contact with water or water vapor. Earlier, we described the most common form of distillation, in which the plant is directly immersed in the water. This is called water distillation. The disadvantage of this method is that it is slow and some plants may decompose due to prolonged boiling. A second method is water/steam distillation, which is similar to the method you might use for steaming broccoli for dinner: Water is placed in the body of the still, as in the water distillation method, but instead of directly immersing the plant materials in the water, they are placed on a rack just above the water and are steamed directly in the still. The third method is called steam distillation. In this method, there is no water in the still body, just steam. The plant matter is again placed on a rack above the steam source. The steam condenses on the plant matter, both extracting and condensing the oil. If done properly, this distillation method has the highest success rate for oil extraction. The distillation process is often repeated so that every single drop of a plant's oil can be removed. Considering that the oils from some plants cost as high as $40,000 per pound, the extra step is worth it! |
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