§§ 156 , 157-3 
HYDROCARBONS. 
143 
3. TERPENES—ESSENTIAL OILS—OIL OF TURPENTINE. 
§ 156. The terpenes are hydrocarbons of the general formula C n H 2n _ 4 . The 
natural terpenes are divided into three classes :— 
1. The true terpenes, formula (C 10 H 16 )—a large numbei of essential oils, such 
as those of turpentine, orange peel, nutmeg, caraway, anise., thyme, etc., are mainly 
composed of terpenes. 
2. The cedrenes, formula (C 15 H 24 )—the essential oil of cloves, rosewood, cubebs, 
calamus, cascarilla, and patchouli belong to this class. 
3. The colophene hydrocarbons, formula (C 20 H 32 ), represented by colophony. 
Of all these, oil of turpentine alone has any toxicological significance ; it is, 
however, true that all the essential oils, if taken in considerable doses, are 
poisonous, and cause, for the most part, vascular excitement and complex nervous 
phenomena; but their action has not been very completely studied. They may all 
be separated by distillation, but a more convenient process for recovering an 
essential oil from a liquid is to shake it up with petroleum ether, separating the 
petroleum and evaporating spontaneously; by this means the oil is left in a fair 
state of purity. 
4. OIL OF TURPENTINE—SPIRIT OF TURPENTINE—“ TURPS.” 
§ 157. Various species of pine yield a crude turpentine, holding in solution more 
or less resin. The turpentine may be obtained from this exudation by distillation, 
and when the first portion of the distillate is treated with alkali, and then redistilled, 
the final product is known under the name of “ rectified oil of turpentine,” and is 
sometimes called “ camphene.” It mainly consists of terebenthene. Terebenthene 
obtained from French turpentine differs in some respects from that obtained from 
English or American turpentine. They are both mobile, colourless liquids, having 
the well-known odour of turpentine and highly refractive ; but the French teie- 
benthene turns a ray of polarised light to the left —40-3° for the sodium ray, and 
the Enghsh to the right +21-5° ; the latter terebenthene is known scientifically as 
austra-terebenthene. This action on polarised light is retained in the various com¬ 
pounds and polymers of the two turpentine oils. 
The specific gravity of turpentine oil is -864 ; its boiling-point, when consisting of 
pure terebenthene, 156°, but impurities may raise it up to 160° ; it is combustible 
and burns with a smoky flame. Oil of turpentine is very soluble in ether, petroleum 
ether, carbon disulphide, chloroform, benzene, fixed and essential oils, and by the 
use of these solvents it is conveniently separated from the contents of the stomach. 
It is insoluble in water, glycerin, and dilute alkaline and acid solutions, and very 
soluble in absolute alcohol, from which it may be precipitated by the addition of 
water. 
It is polymerised by the action of strong sulphuric acid, the polymer, of couise, 
boiling at a higher temperature than the original oil. With water it forms a crystal¬ 
line hydrate (C 10 H 20 O 2 ,H 2 O). On passing nitrosyl chloride gas into the oil, either 
pure or diluted with chloroform or alcohol, the mixture being cooled by ice, a white 
crystalline body is deposited, of the formula C 10 H 16 (NOC1). By treating this com¬ 
pound with alcoholic potash, the substitution product (C 10 H 16 NO) is obtained. By 
treating turpentine with an equal bulk of warm water, and shaking it in a large 
bottle with air, camphoric acid and peroxide of hydrogen are formed. When tur¬ 
pentine oil is left in contact with concentrated hydrochloric acid, there is formed 
terebenthene dihydrochloride (C 10 H 16 2HC1), which forms rhombic plates, insoluble 
in water, and decomposable by boiling alcoholic potash, with formation of terpinol, 
(C 10 H 17 ) 2 O. The dihydrochloride gives a colour-reaction with ferric chloride. This 
is an excellent test—not, it is true, confined to oil of turpentine, but common to the 
dihydrochlorides of all the terpenes. A few drops of the oil are stirred in a porcelain 
capsule with a drop of hydrochloric acid, and one of ferric chloride solution ; on 
gently heating, there is produced first a rose colour, then a violet-rod, and lastly 
a blue. 
