898 ESSENTIAL OILS. 



alcohol, from which it precipitates on cooling in silky crys- 

 talline needles. The density of its vapour is by experi- 

 ment 8400; by calculation 8100, allowing its combining measure 

 to be 4 volumes. 



When the concrete essence is distilled with anhydrous phos- 

 phoric acid, the latter being added in a gradual manner to pre- 

 vent great elevation of temperature, a liquid is obtained, cedrene 

 C 32 H 26 , which appears to be the hydrocarbon of the essence. Its 

 odour is aromatic and quite peculiar, its density 0.984, its 

 boiling point 478.4 (248 centig.) ; the density of its vapour 

 7900 by experiment, and 7500 by calculation, supposing its 

 combining measure to be 4 volumes. Sulphuric acid and per- 

 chloride of phosphorus act upon cedrene as upon menthene. 

 The liquid essence of cedar, obtained from the crude essence by 

 expression, has the same density and composition as cedrene. 

 (P. Walter, An. de Chim. 3 ser. i. 498). 



Oil of roses, otto or attar of roses, is colourless, of a most 

 intense rose odour, lighter than water. Its stearopten, which 

 is inodorous, separates at the usual temperature in large 

 plates ; it fuses at 95, is very slightly soluble in alcohol, and 

 contains no oxygen, but is a polymeric variety of CH. 



Oil ofmentha viridis is, according to the analysis of Dr. Kane, 

 C M H M 0. 



Oil of valerian, extracted from the Valeriana qfficinalis, con- 

 sists of a hydrocarbon and oxidated oil, the last giving, when 

 treated with potash in fusion, valerianic acid, the same acid as is 

 extracted from the root of valerian, and obtained artificially by 

 the action of potash upon the oil of potatoes. 



Oil of chamomile is extracted from the flowers of the Matri- 

 caria chamomilla its colour is deep blue. It contains a hydro- 

 carbon and an oxidated oil, the last of which treated with 

 potash in fusion gives valerianic acid. (Gerhardt and Ca- 

 hours.) The Anthemis nobilis, Arnica montana and Archillea 

 millefolium, yield also blue coloured oils. 



Oil of rue, C 28 H 14 O 3 ; obtained by distilling fresh plants of 

 the Rut a graveolens-, is yellowish green, of density 0.837 at 64.4 

 (18 centig.) ; density of vapour by experiment 7892, by calcu- 

 lation 7^90, the combining measure being 4 volumes. This oil 

 is soluble in sulphuric acid, and is precipitated by water ; hydro- 

 chloric acid has no action upon it. (Dr. H. Will in Liebig's 

 Annalen, xxxv. 235). 



