ESSENTIAL OILS. 233 



screwed down. This is .digested during twenty-four 

 hours in a water-bath ; during that time the oil will 

 have imbibed the rich perfume of the flowers, and it 

 is then disengaged from the cotton by pressure. 

 Where ben oil is scarce, fine nut-oil is made to supply 

 its place, but Phuile antique so prepared is not consi- 

 dered genuine. 



Other essential oils maybe obtained by distillation, 

 water being added to the ingredients in sufficient 

 quantity to prevent their burning. 



In this manner essential oils are drawn from 

 flowers, leaves, barks, roots, woods, gums, and bal- 

 sams, with a slight alteration of circumstances, de- 

 pendent on the nature of the substance under pro- 

 cess. Lavender flowers and roses yield their oil by 

 these means. The former is much more rich in oil 

 than the latter. On being distilled with water, the 

 oil comes over with the aqueous vapour and con- 

 denses with it in the receiver; then rises to the surface 

 in a thin pellicle, which must be carefully separated 

 from the water. This oil forms an ingredient in 

 some varnishes, and is likewise used to dilute me- 

 tallic oxides for painting on porcelain. 



The use of the essential oils to the perfumer is too 

 well known to require explanation. Some of these 

 oils are employed in pharmacy and in chemistry 

 others are used in confectionary, but any particular 

 notice of them would be here misplaced. 



Empyreumatic oils obtained by dry distillation 

 partake of the nature of volatile oils. 



Birch oil is classed among these : it is prepared 

 by the Tartars from the white bark of the birch-tree. 

 For this purpose the bark is taken either from the 

 trees growing in a wild state, or from those which lie 

 rotting in the woods. The oil made from the bark 

 of the trees in a putrid state is the most esteemed, 



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