qua

Did you bother trying a dictionary? http://www.onelook.com/?w=Qua&ls=a

I did, but most of them say it's an adverb, but I can see how they reached that conclusion. What would you say it is, an adverb or a preposition?

The dictionary labelling of an item is not always well-justified, right?

A good dictionary will cite a variety of parts of speech and usage patterns for a given word, with examples. Then you have to determine which fits your context. Many times you cannot tell a part of speech without context.

I always bow to the queen. (verb)
I tied my lace in a bow. (noun)
He was born with bow legs. (adjective)

The OED used to list "qua" as an adverb, but I hear they changed their mind and called it a preposition.

AnonymousThe OED used to list "qua" as an adverb, but I hear they changed their mind and called it a preposition.

Entirely possible. But they would likely object to the characterization of their methodology as professional lexicographers as "changing their mind."

AlpheccaStars AnonymousThe OED used to list "qua" as an adverb, but I hear they changed their mind and called it a preposition.Entirely possible. But they would likely object to the characterization of their methodology as professional lexicographers as "changing their mind."

They might indeed, but I wasn't speaking to them. I was using casual style in a conve

In these contexts, what would you say the part-of-speech is?

For sleep qua sleep has no experiential content:
The President qua head of the party mediated the dispute.
The work of art qua art can be judged by aesthetic criteria only.

AnonymousIn these contexts, what would you say the part-of-speech is?

Hint: all are followed by a noun.

The word is of extremely low frequency; one of those inkhorn words that is marginally assimilated into English from Latin.
All of your contexts are quoted in dictionary references, so I recommend that you take advantage of these resources.

http://dictionary.reference.com/browse/qua

adverb