Xerofoam gauze and glycerin-soaked cotton were placed in the umbilicus.

Xerofoam = not a noun or pronoun
gauze = noun
and = not a noun
glycerin = noun
soaked = not a noun
cotton = noun
were = not a noun or pronoun
placed = not a noun or pronoun
in = not a noun or pronoun
the = not a noun or pronoun
ubilicus = noun

3 answers

In this construction, "glycerin-soaked" is an adjective.

The others are correct.
Can you please explain why?
Glycerin-soaked is hyphenated -- making it one word. It's used as an adjective modifying cotton. It tells what kind of cotton is being used.

When the word "glycerin" stands alone, it is indeed a noun.

Example: Glycerine is a colorless, odorless, syrupy, sweet liquid.