VOLATILE OIL. TURPENTINE. 237 



very irritating to the eyes \ yet no evidence of its existence can 

 be obtained, without the addition of water ; so that the latter 

 probably occasions some change of composition, by which the 

 oil is produced. The volatile oil of Bitter Almonds seems 

 to be produced in a similar manner. Perhaps the increased 

 fragrance of our gardens after a shower of rain is due to a 

 similar cause. 



375. Into the particular uses of the foregoing oils, this would 

 not be the place to enter ; some of them will be noticed in the 

 description of the several orders, to which the plants that yield 

 them belong. There are other volatile oils, of much more im- 

 portance in the arts and manufactures, which must next be 

 noticed. One of the best-known of these is Oil of turpentine 

 (commonly termed Spirit of turpentine), which exists in com- 

 bination with resin, forming what is usually known as Tur- 

 pentine, in all the trees of the Pine and Fir tribe, as well 

 as in some others. The Turpentine is generally contained in 

 special receptacles in the substance of the wood ; but some- 

 times it collects in blisters underneath the bark, which appear 

 during the strong heats of summer. It flows from these as a 

 limpid juice, which thickens on exposure to the atmosphere, 

 when incisions are made into the stem. The common Turpentine 

 is obtained from the Scotch Fir, when growing in the South of 

 Europe, and the Southern part of North America ; but it cannot 

 be procured in any large quantity from the same tree when 

 growing in Great Britain. Superior kinds are drawn from the 

 Pistacia of Scio, and from the Larch in Southern Europe. Tur- 

 pentine is not itself applied to any important use ; but the two 

 substances which it contains, the volatile oil, and the resin, 

 both serve many purposes. They are separated by distilling the 

 Turpentine with water ; which causes the volatile oil to pass 

 over, leaving the resin behind. Oil of Turpentine is extremely 

 useful from its power of dissolving resins, which form the basis 

 of most varnishes ; and from its great volatility, it quickly flies 

 off or dries away, leaving a thin coat of the varnishing substance, 

 fixed to the surface on which it has been applied. The most 

 extensive use, however, to which it is put, is that of diluting oil 



