The black/crystalline powder could very well be partially anything.

The pleasant dose is difficult to find, particularly if you are working with a product batch of unknown purity.
Thus it is beneficial to know your dose.

How can I theoretically go about: further purifying measuring out an accurate dose?

Step 1: Weigh it
Step 2: Eat it
Step 3: Wait about 45 mins to 2 hours
Step 4: Not profit you lame mother fucker!

You are the smart one aren't you?:)

*Considering you have a limited amount and varying purity.....
* a single personal experience is not exactly a good way of interpreting the actual dose consumed.
* What makes you think i have the time and energy to go through more then one dose. It is a special occasion, I find it most excellent to know exactly how much i am ingesting before i set of on my pre-planned spiritual exploration.

*Note: No, absolutely no profit is to be made from this.