USE OF THE FOREST 



143 



This industry usually demands sound, split "body," or 

 log wood, fifty-two inches instead of forty-eight inches 

 long, so that the acid men get nearly one and a tenth 

 cords for each cord they buy. In making acid the wood 



FIG. 55. Rolling in Spruce Logs on Ampersand Creek 



is_heated for about ten hours in large steam-boiler-like 

 vessels called retorts. As the wood grows hotter and 

 hotter it gives off gases, part of which are cooled into 

 liquids in a " worm " or coiled tube, kept cool by a stream 



