My question is about the condenser used in a Soxhlet extractions. It's unusual looking compared to the rest of condensers, used in distillation for example, I've noticed it has a thin and short tube on top and my question is, do one leave it open when performing a Soxhlet extraction or should it be stopped with a stopper or something?
First thing, you should NEVER perform any heated reaction with a stoppered condenser. You shouldn't even be allowed to work independently in the lab if this rule is not coming automatic to you. I am not sure what you mean by a special condenser being used in Soxhlet extractions. You can use any condenser that fits. Since you don't do a distillation you can use a shorter condenser so your whole Soxhlet set-up has a reasonable height.