TURPENTINE, ROSIN, PITCH, &C. 175 



close, and puts out the fire. Five barrels of green tar will make 

 two of pitch ; and it will take two barrels of other tar to make one 

 of pitch." 



The turpentine thus obtained is loaded with impurities, from 

 which it is freed by two distinct methods. One consists iu inclos- 

 ing it in a cask perforated at bottom, when, by exposure to a hot 

 sun, it becomes so fluid as to filter through, which gives the finest 

 and most valued turpentine. The other method consists in heating 

 it moderately in a large copper, till it is quite liquid, and then filter- 

 ing it through a strainer made of rows of straws laid close to each 

 other. This gives it a golden colour. 



The essential oil of turpentine is prepared largely both in the 

 countries where the turpentine is extracted, and from turpentine im- 

 ported to our own coasts. The process is as follows : An alembic 

 with a worm and cooler is used, precisely of the same construction 

 as what is employed for the distillation of spirits : this is filled with 

 turpentine and water in due proportions, and the volatile part, after 

 distillation, is found to consist of oil of turpentine swimming on the 

 water. This oil is perfectly limpid and colourless, has a very strong 

 smell, a bitterish taste, is extremely inflammable, and has all the 

 properties of the other essential oils. It is employed in immense 

 quantities in a variety of varnishes and similar preparations; but for 

 the finer purposes, such, for example, as that of dissolving gum 

 copal, it is necessary to rectify it by a second distillation with water 

 in a still, using a very gentle heat, and keeping apart the first pro- 

 duct, which is the best. From 250lb. of good turpentine the oil 

 obtained is about 60lb. 



Common, or yellow rosin, is the brittle and opaque residue from 

 the distillation of the oil of turpentine. It is called by the French 

 braisec ; who also obtain it from the hard concrete turpentine that 

 forms about the incisions of the fir-trees, while exsuding. When 

 common rosin is boiled in water for a time, it becomes yellow and 

 transparent; and is then the rosin used by musicians for the bows 

 and strings of violins. When common rosin is kept in fusion for a 

 considerable time it becomes of a browner colour; is still harder 

 and less adhesive to the fingers when cold, and is then called black 

 rosin, or colophony ; and this is the ultimate point to which the in- 

 spissation of turpentine is carried. 



A very fine essential oil is obtained in some parts of Germany by 



