724 PROPERTIES, HARVESTING AND DISPOSAL OF RESIN. 



dark-coloured and inferior in quality. From it, oil of turpen- 

 tine, the chemical formula for which is CioHi 6 , is distilled, 

 leaving deposited an oxidised suhstance which is solid at 

 ordinary temperatures, and is termed rosin, or colophany. 



These substances are separated from one another in the 

 following way : 



i. By melting and filtering the crude resin, so that the water, 

 sand, pieces of bark and other impurities* are separated from it. 



ii. By distilling the crude resin, the oil of turpentine and 

 colophany are separated from one another, as these substances 

 have different boiling-points. 



The crude resin, after being passed through straw filters, if 



Siphon 



Vat No. 1. 



Turpentine 

 tank. 



Straining tank. 

 Fig. 387. (After Hearle.) 



sufficiently fluid for this to be done, is placed in an uncovered 

 vat (Fig. 387, No. 1) and heated until it is completely liquefied. 

 This allows heavy substances, such as sand, etc., to fall to the 

 bottom of the vat, while light impurities, chips of wood, bark, 

 etc., float on the surface of the melted resin. This is a very 

 delicate operation, as if heated unequally, the resin is liable to 

 catch fire. 



The impurities are separated from the resin, either by 

 ladling it through straw-sieves, or passing it through a grating 

 into a second vat. The operation of heating and filtering goes 

 on a day in advance of the distillation, so that three vats are 

 required, No. 1 vat being always used for boiling and the other 

 two vats, alternately, as reservoirs from which the resin is 

 ladled into a small tank from which it is passed through a 

 tap to the retort shown in Fig. 387. 



This is the method employed late in the autumn, when the 



* Chiefly larvse of insects. This accounts for the flies in ambrr. fossil resin. 



