CHAPTER XVIII 

 OILS 



THE oils of vegetable origin are obtained from seeds, nuts, 

 and beans, as well as from the leaves, fruit, trunk, and roots 

 of various plants. These oils are commonly classified in two 

 groups fixed oils and essential oils. The fixed oils do not 

 volatilize or evaporate upon exposure to air. The group of 

 fixed oils includes drying oils, semi-drying oils, nondrying oils, 

 and vegetable fats. Drying oils are characterized by their 

 power to absorb oxygen and dry into an elastic film. They 

 are therefore well adapted for utilization in paints and var- 

 nishes. Semi-drying oils are intermediate in character be- 

 tween drying oils and nondrying oils. They absorb oxygen 

 slowly and only to a limited extent. Nondrying oils do not 

 solidify on exposure to the air at ordinary temperatures. 

 Vegetable fats are solid at ordinary air temperatures, resem- 

 bling in this respect butter or tallow. Essential oils, as con- 

 trasted with this whole group of fixed oils, are volatile or 

 evaporate on exposure to air. They carry the characteristic 

 flavor or aroma of the plant from which they are derived. 

 Essential oils are obtained chiefly by distillation as contrasted 

 with fixed oils which are commonly extracted by pressure or 

 chemical solvents. In the preparation of essential oils the 

 material in which they are contained is finely ground, placed 

 in a copper still, and boiled. In the process of boiling the 

 essential oil is carried over into a condenser along with the 

 steam. Lemon oil and lime oil may be obtained by pricking 

 the skin of the fruit and applying gentle pressure. Distilled 

 lemon oil is considered to be of an inferior grade. Essential 



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