EMPYREUMATIC OILS. 239 



off, the rest of the tree is cut up into billets of tolera- 

 bly equal size. An oven is built of stone or brick in 

 the form of an egg standing on its small end. On 

 one side, about five inches from the lowest point, an 

 aperture is made into which a tube is inserted. A 

 large iron grating is laid at the bottom just above 

 the opening for the tube, and on this the billets of 

 wood are piled. This grating prevents the passage 

 of any pieces of wood or other impurities, which 

 would otherwise run out together and mix with the 

 tar. The oven being filled with wood, a layer of 

 dry chips is placed at the top, and the whole is 

 enclosed, leaving only an aperture at the summit to 

 act as a chimney : the chips are then kindled, and 

 when the fire has spread downwards, and the whole 

 is sufficiently ignited, the chimney is entirely closed 

 with a large stone, and wet earth is heaped on this, 

 more being thrown on whenever the smoke bursts 

 out too strongly. 



The general average product thus obtained is 

 about ten or twelve per cent, of the weight of the 

 whole charge. 



The common method, as pursued in the north of 

 Europe, though the least expensive of all, is attended, 

 however, with great inconveniences. The manage- 

 ment of the fire is extremely difficult and precarious, 

 so that scarcely any workmen, who have not been 

 long used to conducting the process, can be safely 

 trusted with its superintendence, and the success 

 even of these does not always answer their expecta- 

 tion. A much smaller quantity of tar is always 

 extracted in this manner than that produced from an 

 equal quantity of wood distilled in furnaces. The 

 process by furnace is therefore always preferred by 

 those tar-burners who ha\e the means of pursuing 

 it*. 



* Description de la Mauiere dont on fait le Goudron en Suede. 



