What are you trying to slow down?
How would slowing down hashtables be an experiment?
You might be able to slow down hashtable operations by filling it with millions of values.
Seriously, like Maker said, what exactly are you trying to do?
I almost consider this a troll post, that's how little information you've give as to what you're asking for. There are a lot of things you need to clarify for us before we know what you want us to help you with.