Essential oils are formed in the oil glands of plants and stored in plant tissues. They can be found in flowers, leaves, seeds, fruit peels, roots, resins, bark, or wood. Some plants produce essential oils from different parts, which can vary significantly in their chemical composition, such as cinnamon bark oil and cinnamon leaf oil. The most common method for extracting essential oils is steam distillation. In this process, hot steam is injected into a sealed boiler containing crushed plant material. The steam drives the essential oil out of the plant. In a cooled pipe, the oil-water mixture condenses, and the essential oil is separated from the water in a collecting vessel. The author describes the production of essential oils in this volume from 1876, illustrated with numerous images.