50 Ejfential Oils. [Book VUL 



lavender is yellow, that of cinnamon deep yellow, 

 that of parfley green, that of camomile blue. Some 

 of the eflential oils float in water, as moft of the 

 oils obtained from plants growing in temperate cli- 

 mates ; others, as thofe of faflafras and carraway- 

 feeds, and moft of the oils from hot countries, fmk 

 in that fluid. This property is not, however, invari- 

 able witlvrefpect to climate, as the efiential oils of 

 nutmeg, pepper, and mace, are lighter than water, ft 

 is remarkable, that eflential oils fometimes entirely 

 differ in their properties from the plant which affords 

 them ; thus, oil of pepper is mild, and oil of worm- 

 wood is not bitter. 



The perfume, or principle of fcent, in plants, to 

 whkh Boerhaave gave the name of Jpiritus rfffer, 

 feems in general to refide in the eflential oil. It 

 compofes an extremely fmall part of the weight of 

 vegetables, as may be inferred; from the lofs of fra- 

 grance fuftaincd by eflential oils with little or no 

 lofs of weight. It does not fcem improbable, that 

 the perfume, or principle of fcent, in plants, is a gas 

 of a peculiar nature. Its invifibility and volatility, 

 the manner in which it is expanded and difperfed m 

 the atmofphere, together with certain experiments 

 made by Dr. Ingenhouz, on the noxious gas af- 

 forded by flowers, render this opinion very pn> 

 bable, 



It is eafy to difcover the adulteration of volatile 

 oils, either by pouring ardent fpirit on them, which 

 will not diflblve the fat oil they may be contaminated 

 with ; or if they are dropped on paper, and held to 

 the fire, the eficntial oil evaporates, leaving the fat oil 

 behind, whkh makes a greafy fpot. If oil of tor- 

 pendne is fraudulently added to them, its fmell be- 

 ttays its prefence when treated in this manner. By 



cxpofurc 



