obtained in the distillation of Wood, 'i^c. 9 



If turpentine, as it flows from the fir in a liquid state, be exposed 

 for a considerable time to the action of the atmosphere, it becomes 

 brittle, and is converted into resin, in consequence as it is supposed 

 of the absorption of oxygen. If the same turpentine be exposed to 

 the action of the fire, a colourless volatile oil is separated, and resin 

 remains in the retort. This however is not a mere case of the 

 separation of a more volatile from a fixed substance, for a decompo- 

 sition takes place, and acetic acid is generated. Nor can turpentine 

 be again reproduced by mixing together the essential oil and the 

 resin — it then forms a varnish. The essential oil is in fact a new 

 compound, produced from the vegetable elements by the action of 

 fire ; and although properly enough classed with those essential oils 

 which are vegetable secretions, differs from them in some of its 

 chemical properties. It is, for example, difficulty soluble in alcohol, 

 but on exposure to air it becomes thick and yellow, and is then easy 

 of solution in the same substance. 



If the resin, which is the residuum of this distillation be still fur- 

 ther heated, it gives over a thick and high coloured oil, gradually 

 increasing in weight, till it equals, and at length exceeds the specific 

 gravity of water. The residuum becomes ultimately black, and 

 very brittle, remaining soluble in ether and in lixivium of potash, 

 but refusing to dissolve in alcohol. 



Common tar differs from turpentine in containing a portion of 

 the vegetable tar now under review, mixed with common turpen- 

 tine and with the acetic acid which is formed in the distillation to 

 which the wood is subjected for the purpose of obtaining it. Eva- 

 poration converts this into pitch, by decomposing it. 



In this process, an essential oil, compounded of the oil of turpen- 

 tine and the oil of wood, together with a portion of acetic acid, is 

 separated, and the residuum or common pitch, is a compound of 



Vol. II. B 



