v: What are similar to chemicals, in that closer analysis results in a worsening odour?
vii: What fragrance did the lovers inhale within Prince Eugen’s collection?
viii: What smell fills the air in the absence of the Electrician?
x: What is ubiquitous, invisible and odourless?
i: Fenton is not the deer-chasing dog of internet fame but a fellow in The Merry Wives of Windsor who "smells April and May" (googled by jeff_worrell)
ii: THE JACKDAW OF RHIEMS died in the "odour of sanctity": it stole a cardinal's ring and was made a saint in The Ingoldsby Legends (googled by jeff_worrell)
iii: is possibly the STINKING HELLEBORE aka BEAR'S FOOT (tho there seems to be controversy over its stinking nature) (googled controversy via jeff_worrell and braisedbywolves)
iv: GUESTS, according to BENJAMIN FRANKLIN (googled by belecrivain)
vi: REMBRANDT's Sense of Smell was recently rediscovered and reunited with three of the five senses: only Taste is still missing (googled by jeff_worrell)
ix: This refers to Betjeman's poem 'A Subaltern’s Love Song': "… nine-o’clock Camberley, heavy with bells/And mushroomy, pine-woody, evergreen smells" (googled by jeff_worrell)