886* ESSENTIAL OILS. 



over, and a resin remains behind. The oil met with in com- 

 merce generally contains some resin, produced by the oxidation 

 of the oil, from which it should be purified by rectification, that 

 is, a second distillation from water. The pure oil is a colour- 

 less, thin liquid, having a peculiar odour, of which the density 

 is 0.872 at 50, and boiling point 314.2 (156.8 centig.) The 

 specific heat of this liquid is 0.462, according to Despretz. that 

 of water being 1.000. The density of its vapour is 5010 by 

 experiment, 4763 by calculation. It abandons only half the 

 heat when condensed from the state of vapour at its boiling 

 point, that vapour of water does at 212; but a portion of that 

 heat is heat of temperature, for the latent heat of vapour of oil 

 of turpentine is to that of vapour of water only as 0.313 to 

 1.000. When cooled to 16.6, oil of turpentine deposits its 

 stearopten in white crystals, which are heavier than water, and 

 fuse at 19.4 (7 centig.) 



Oil of turpentine is certainly a mixture of two or more iso- 

 meric oils ; this appears in its forming two compounds with 

 hydrochloric acid, one of which has long been known as arti- 

 ficial camphor. To prepare this compound, well dried hydro- 

 chloric acid gas is made to pass slowly into the essence sur- 

 rounded by ice. Without this precaution, it becomes hot, a?td 

 the hydrochloric acid is not so completely absorbed. It is left 

 to itself for twenty-four hours, after which, a quantity of a white 

 crystalline substance is found deposited in a brown fuming 

 mother-liquor. The composition of the solid hydrochlorate is 

 represented by C 20 H 16 + HC1. The name camphene being applied 

 to the essence by Dumas,* this is the hydrochlorate of camphene. 

 When pure, it is a snow-white substance, of a peculiar odour, 

 suggesting that of common camphor, but very different in other 

 respects; fusible above 212, and volatile; alcohol of 0.806 

 dissolves at 57 one third of its weight of it. It is decomposed 

 completely when distilled rapidly by means of an oil-bath, with 

 two or three times its weight of quicklime, chloride of calcium 

 being formed, and a colourless oil, of the same composition and 

 density as oil of turpentine, which can be united again with 

 hydrochloric acid, and gives an entirely solid product. This 



* The essence of turpentine may be allowed, as the base of artificial camphor, 

 to retain this name. 



