MANUFACTURE OF WOOD-VINEGAR. 221 



Cast-iron retorts are either cast in one piece, having in this case 

 a cylindrical form with a circular cross section, or flat pieces 

 are connected together by screws to parallelepiped boxes ; the lat- 

 ter form is preferable for the distillation of birch bark, which fills 

 up the room to the best advantage by placing it in flat, even pieces. 



Dimensions of the retorts. The size of the retorts varies greatly, 

 but the most suitable for horizontal cast-iron or wrought-iron re- 

 torts is a length of from 5J to 6 J feet with a diameter of from 2 J 

 to 3J feet. In England retorts of a still greater size are in use, 

 for instance, wrought-iron ones, which with a length of 6-J feet 

 have a diameter of 4J feet, and cast-iron ones with a length 

 of from 8f to 9J feet and a diameter of 3 feet. AVrought-iron 

 retorts are generally from 0.27 to 0.31 inch thick. 



For vertical wrought-iron retorts Vincent recommends a height 

 of 6 feet and a diameter of 4 feet, and Gillot, as well as Rothe, a 

 diameter of from 4 to 5 feet and a height of 7 \ feet. 



For rectangular wrought-iron boxes : length 4J feet, width 

 2.62 feet, height 3.28 feet. For rectangular cast-iron boxes : 

 length 8.85 to 9.18 feet, width 3.28 to 4 feet, height 4 to 4j- 

 feet. 



Position of the retorts. In France vertical wrought-iron cylin- 

 drical or rectangular boxes are most frequently used. This 

 arrangement allows of the vessel, when distillation is finished, 

 being lifted from its position by means of a crane and inserting a 

 new one in its place, so that the high temperature which the brick 

 work has acquired is utilized almost without loss. The disadvan- 

 tage is the inconvenient filling and emptying of such vessels, both 

 operations having to be executed from above. To facilitate the 

 emptying, an aperture is occasionally provided near the bottom, 

 but in this case it is difficult, on account of the high temperature, 

 to make the aperture tight by a clay luting. Further, the va- 

 pors escaping from the lower portion of the wood to be distilled, 

 especially those specifically heavier than tar, rise only with diffi- 

 culty to the discharge aperture, and having consequently to re- 

 main an unnecessarily long time in the hot space are partially 

 decomposed to permanent gases. Even with the best condensing 

 apparatus they carry along a certain quantity of acetic acid and 

 especially of wood spirit, and the non-condensing portion is then 



