Notes the speed at which to put the gas in (6)
I believe the answer is:
aerate
'which to put the gas in' is the definition.
I can't judge whether this definition defines the answer.
'notes the speed' is the wordplay.
'notes' becomes 'ae' ().
'the speed' becomes 'rate' (both can mean pace).
'ae'+'rate'='AERATE'
'at' is the link.
Can you help me to learn more?
(Other definitions for aerate that I've seen before include "get excited" , "Send out, broadcast" , "Supply with oxygen" , "Expose to fresh air" , "Make effervescent" .)