The topic of substance identification is very complex.
Since I can't describe it in full on this board, I recommend some reading for those who what to really investigate what works and what does not work.
The science is called 'spectroscopy'. Here are two books I have been reading on the matter this year:
Organic structural Spectroscopy (1998) version.
Spectrometric Identification of Organic Compounds 1991 version.
These two books cover the issue of uniqueness of organic properties which are more complex than non-organic materials. Organic materials include plastics, foods, oils, plants, etc. Organics basically include everything with some form of Carbon molecule bonding to other molecules such as Oxygen, Hydrogen, Nitrogen, etc.
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