Sentence:  When the dipping is thus over, the next work is to "chip" or scarify the tree immediately over the box [...]. This is done by an instrument usually called a "<WSD>hacker</WSD>," sometimes "shave." Its form is somewhat like a "round shave," narrowing at the cutting place to the diameter of an inch, with a shank, to be fixed securely into a strong, heavy handle of about two feet in length, while the faces of the trees are low, but the handle is made longer as years advance the faces higher. 
Meaning of the word marked with <WSD> tags:  Something that hacks; a tool or device for hacking.