Chap. 5.] Compofit'ion of Fat Oils. 49 



oils are burned in pure air, one of their component 

 , principles, hydrogen, is combined with pure air, and 

 forms water j while charcoal, its other component part, 

 combines with pure air allb, and forms fixed air. 



The denfe animal oils, fuch as butter, tallow, fat, 

 and the oil of the whale, exceedingly refemble vegeta- 

 ble fixed oils. They appear, however, to contain a 

 proportion of azotic air and animalized matter, pro- 

 bably in the ftate of ferum or jelly. 



Agitation in water feparates a mucilaginous matter 

 from fat vegetable oils, which feems to be the caufe of 

 their becoming rancid. They combine with pure fixed 

 alkalies into foap, and they alfo unite with magnefia 

 and lime, which form with them foapy compounds. 



IV. ESSENTIAL OILS are remarkable for a ftrong 

 aromatic fmell, and are fufficiently volatile to rife with 

 the heat of boiling water. They are in general foluble 

 in fpirit of wine, and their tafte is very acrid. They are 

 much more inflammable than the fat oils. 



Effential or volatile oils exift in moft fragrant vege- 

 tables, and in various plants are found in different parts; 

 thus the oil of cinnamon is found in the bark ; of balm, 

 peppermint, and wormwood, in the leaves ; of the rofe 

 and lavender, in the flower j of nutmegs, anife, and 

 fennel, in the feeds. They are obtained either by ex^- 

 preflion, as from the peel of oranges and lemons, or by 

 diftillation with water. For the latter purpofe, the plant 

 is put into a copper alembic, with water , the water 

 being made to boil, comes over together with the oil 

 into the receiver, and is obtained feparate by decanta- 

 tion. Some of the eflential oils are fluid, as that of laven- 

 der ; others congeal by cold, as that ofannifeed; others 

 are always concrete or folid, as thofe of rofes and parfley. 

 They differ much with refpe6t to colours : thus, oil of 



VOL. III. E lavender 



