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Have pH papers or pH meter?

Possibilities:

1- For some reason it's a freebase. In that case, add a bit of vinegar to lower the pH, it should dissolve. If fails, try 2

2- It's DMT acetate, most/all of which already dissolved, and the undissolved stuff is other impurities. You can filter/decant the water with your alkaloids away from it. You could even save those undissolved parts in case something goes unexpected (low yield/effects) so you can come back to it and try to extract if necessary.

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Im not sure if the acetic acid bond can break off with normal warmth.. Try adding another 300ml vinegar, see if more dissolves.. If not, proceed to filtering and continuing your work, and just in case save the filtered solids for the future if yield is too low later on, you can try extracting from it again