Releasing gas including hydrogen (an amount you barely notice) (8)
I believe the answer is:
farthing
'barely notice' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'releasing gas including hydrogen an amount' is the wordplay.
I cannot quite understand how this works, but
'gas' could be 'fart' (I've seen this in another clue) and 'fart' is found within the answer.
'hydrogen' could be 'h' (H is the chemical symbol for hydrogen) and 'h' is found in the answer.
'an' could be 'i' (Roman numeral for one) and 'i' is located in the answer.
'amount' could be 'n' (N is an example) and 'n' is present in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'you' is the link.
Can you help me to learn more?
(Other definitions for farthing that I've seen before include "once of minimal value" , "Smallest coin once" , "Old piece" , "One quarter of an old penny: measure of land in old England" , "It used to be one quarter of a penny" .)