146 CHYMISTRY APPLIED TO AGRICULTITKE. 



af all machinery is rendered more regular and easy, and 

 that friction is moderated ; and by it metals are pre- 

 served from rusting. 



The most important use to which oil has been applied is 

 that of lighting buildings ; but as it gives out, in burning, 

 more or less smoke, and a light inferior in brilliancy to 

 that of wax, the latter was preferred until the invention of 

 Argand's lamps : in these a current of air passes rapidly 

 through a circular wick surmounted by a cylindrical glass, 

 and thus the smoke is consumed and the light rendered 

 more clear and brilliant. 



The products of the combustion of the fixed oils are 

 water and carbonic acid ; this declares their constituent 

 principles to be carbon, oxygen, and hydrogen. Messrs. 

 Gay-Lussac and Thenard have found them in the follow- 

 ing proportions. 



Carbon 77.213 



Oxygen 9.427 . 



Hydrogen 15.360 



The volatile or essential oils are more easily volatilized 

 than the fixed oils ; they are inflammable at a lower tem- 

 perature, are soluble in alcohol, exhale a powerful odor by, 

 which they are distinguishable from each other, and have 

 a lively, acrid, and burning taste. 



The volatile oils do not belong exclusively to any one 

 part of plants : in some, as in the Bohemian Angelica, the 

 oil is distributed throughout the whole plant : sometimes,, 

 as in balm, mint, and wormwood, it is found in the leaves 

 and stalks: the elecampane, Florence iris, and bennet 

 contain it in their roots ; thyme and rosemary in their 

 leaves and flower buds; lavender and the rose in their 

 calyces ; camomile, lemon, and orange plants, in their 

 flowers ; the petals, and the rind of the fruit of the two 

 last abound in oil ; that of indigo and fennel is contained 

 in vessels forming the raised lines which may be perceived 

 on the bark. 



Volatile oils vary in color, consistency, and weight; 

 there are some, as that of sassafras, and the clove, for in- 

 stance, which are heavier than water ; and there are some, 

 as those of the rose and parsley, that remain in a concrete 

 state at the usual temperature of the air, &/C. 



The volatile oils are extracted either by distillation or 

 expression. When the oil is contained in vesicles upon 

 the surface of the rind, as is that of the lemon and berga- 



