How to prove presence of aspirin?

Some pills were bought as an agent that for the metter of confidentiality I will name "xyz#3". However to my suspicion and intuition I questionned the truth about its nature and tasted a tiny bit which was so similar to the very taste that : "only aspirin tastes like that". However I do wish to proove it "ex cathedra" and by an objective observable mean that is evident to anybody who would try to oppose the fact. I read about sulphuric acid and or ferric chloride and also chloroform all of these being not easy to access espacially not to me. There must be a basic "home-kitchen-trick" that whatever it may be can at least sustain 80 % of my argument. Please anyone ? It is so important here for it relates also with a matter of trust in a person whom I doubt more and more of being a con artist but I just cannot attack without evidence, as little as the proof may be . PLEASE ?