try this out...not even sure how well this will work..but...it 'should'
take 50g of root bark and grind into a fine powder(coffee grinder)
take 25g of sodium carbonate and mix it with the powdered root bark(not really sure how much sodium carbonate to use..but that should be enough)
add JUST ENOUGH water to make it DAMP..not wet..or soupy..but so its like the consistency of cookie dough or something
stir it up really good for 5 minutes...make sure everything mixes together...
now this is the part that sucks..
dry your mimosa-sodium carbonate mix...you dont want any water for the next step...so the best way to do this..is somehow get your mimosa mix up to about 100F and allow it to evaporate...it may take a day or three!! you want it to be dry..but you dont want the temp to go over...like 120F
once its dry...soak your mix in acetone..lets say start with 100ml..and do something like 3 of these...so you will use about 300ml of acetone...not sure if thats too much..but whatever..stir it up really good..and let each pull sit for a few hours..one hour would probably do it just fin
now that you have this acetone(300ml) put it in a container..with a wide moutha baking dish(glass) with a flat bottom should work...now you want to heat it up SLIGHTLY..like to 100 degrees F...but you dont want to use any flames for this...at all...and a fan blowing INDIRECTLY around the dish...this will evap the acetone and what SHOULD be left is some freebase spice..
this tek hasnt been perfected at all..and may not work that well..but it SHOULD get you something..not exactly sure..but you could try it out on 50g and see what you get...