maleic, definitely, as it is the isomer of fumaric.
Tartrate is also a solid salt. Nothing wrong with it compared to fumaric. Both should work equally as well.
From what I know DMT HCl is not a solid, or at least extremely difficult to prepare as a solid, because of its hydroscopic properties perhaps. (shulgin couldn't prepare the HCl salt)
I am not sure about sulphate, perhaps it is a solid, but im guessing its not for some reason.
also, these concentrated acids are obviously not 'food safe' (well there is concentrated HCl in your stomach, but im sure it would hurt going down...) The salts are most definitely food safe, or at least in the tiny amounts consumed they will not harm you.
Much more 'toxic' acids are approved by the FDA for use as a salt. For instance, HBr salt, is used in medicine. Where you not want to get near hydrobromic acid.
It is completely safe to consume these salts as long as there is no excess acid.
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