Glad that you got it, Michael (mishum).
Honestly, I am not such a great grammar teacher. :o I have a rather stupid way of testing whether a sentence is grammatically right. I just test sentences for their sound. If the sound is not quite right, I focus on the part which is wrong. So essentially I don't know the semantics of grammar that well.
BTW, I think we may both be right. Chemical is a noun as well as an adjective.
Noun here:
Acetic acid is a chemical.
Adjective here:
The scientists in the eleventh century were unaware of the chemical nature of vinegar.
As I am not very sure now, I appeal to wasleys or Erin for clarification!
EDIT: Michael (Wasleys), do you read minds!?? I think you do.
