204 OILS. 



water and carbonic acid gas. Oils are found in all 

 parts of plants, but rather more abundantly in the 

 seeds and fruits than in other parts. The seeds of 

 some plants, such as the poppy, linseed, rape, and 

 mustard, contain frequently nearly half their weight 

 of oil. 



508. Fixed oils are divided into fat oils, and dry- 

 ing oils: the former remain fluid when exposed to 

 the air, like olive oil ; the latter gradually harden, 

 and dry up into a kind of varnish, like linseed oil. 

 Fat oils are used for soap-making, in wool-spinning, 

 to burn in lamps, and in diminishing friction ; those 

 like cocoa-nut and palm oil, which remain solid at 

 common temperature, are used for the manufacture 

 of candles. Drying oils are employed in preparing 

 paints and varnishes; for this purpose they are usually 

 boiled, which causes them to dry and harden even 

 more rapidly than in the fresh state. 



609. The odors of plants are for the most part oc- 

 casioned by the presence of volatile oil, in greater or 

 less quantity. The volatile oils are obtained by dis- 

 tilling the plants which contain them with water ; 

 fixed oils are procured by pressing the seeds in 

 which they are found, either cold or after a slight 

 roasting ; the former process gives the purest oil. 



610. The most important of the non-drying fat 

 oils, are those of the olive, cole-seed, rape, poppy, 

 almond, mustard, and till, or sesamum. The chief 

 drying oils are, linseed, hemp, nut, and castor. These 



