It is a phrase. Hope this helps
About being obdurate Douglass tells he was obdurate "enough to be insensible to the voice of a reproving conscience".
About being cruel Douglass mention "he committed the grossest and most savage deeds upon the slaves under his charge." being severe on his punishments.
About being artful Douglass says "He was one of those who could torture the slightest look, word, or gesture, on the part of the slave, into impudence, and would treat it accordingly" he was also very aware of it in other ways and he would not care about killing the slaves even as they were a property and in order to do not be condemned he would say "To be accused was to be convicted, and to be convicted was to be punished" so "It is better that a dozen slaves should suffer under the lash, than that the overseer should be convicted, in the presence of the slaves, of having been at fault.".
Answer:
It was an execution stand.
Explanation:
Based on the context of expression used in the Hangman poem such as "capping sill of the courthouse door" it portrays a court house scene.
Therefore, the scaffold changed in size when it fine to execute or hang the two persons (victims) sentence. This hanging would have warranted increasing the height of the scaffold.
