Laboratory substance (8)

I think it could be either:

Which length description are you looking for?:

chemical

'laboratory substance' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for chemical that I've seen before include "Like 4 or 24 dn" , "Laboratory substance" , "substance produced in a lab" , "Of a substance such as ethanol" , "Substance derived from or used in molecular reaction" .)

I've seen this clue in The Times.

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