144 FIRST BOOK OF FORESTRY 



of cold water. The greater part of these liquids is wood 

 vinegar, and a small portion pure acetic acid, wood alcohol, 

 and, toward the last of the heating, some creosote and tar. 

 The wood vinegar is employed in dye works ; the alcohol 

 by painters, hat makers, and in chemical works ; while the 

 acetic acid is largely used for vinegar. 



The retort usually holds about two thirds of a cord of 

 wood, and an ordinary factory of twenty-four retorts thus 

 requires about sixteen cords for each charge. They usu- 

 ally run night and day, refilling every twelve hours, so 

 that one of these factories uses eight thousand cords or 

 more per year. 



Posts. In former years, when most of our farms were 

 surrounded with rail fences, commonly of the " worm- 

 fence " type, enormous quantities of good oak, chestnut, 

 and other timber were converted into fence rails. Wher- 

 ever logs have a reasonably good market this wasteful 

 use of timber is disappearing, and wire or " wire-slat " 

 fences are taking the place of the old forms. This still 

 requires the use of posts, so that both for home use and, 

 in many localities, also for the market it pays to raise 

 timber for fence posts. 



Since durability is the first quality in a fence post, 

 only durable woods, like black locust, catalpa, chestnut, 

 white oak, cedar, redwood, and kindred woods should 

 be offered; and the post should always be large enough 

 so that the heartwood, the only durable part, is sufficient 



