Wikipedia:Reference desk/Archives/Science/2018 December 25

= December 25 =

What's the boiling point of H2>C=N-H?
And if it's un-ionized and not a radical why is it so obscure? Is it unstable or something? Sagittarian Milky Way (talk) 00:25, 25 December 2018 (UTC)
 * Our article about methylene imine notes that it is unstable (and what happens to it when one tries to isolate enough of it to condense/boil (w00t--Two refs to Hexamethylenetetramine this week!)). DMacks (talk) 03:11, 25 December 2018 (UTC)
 * I suspect there's a bit of culture involved there, since formaldehyde (the precursor and oxygen analogue of methylene imine) produces polymers like metaformaldehyde, but as our article puts it these are considered "forms of formaldehyde" even though they're clearly not. But I think the reverse reaction for the formaldehyde polymers occurs more readily, as these are routinely used to make "formaldehyde" solutions for fixing tissues. Wnt (talk) 04:39, 25 December 2018 (UTC)
 * Two molecules of this imine can easily disproportionate to form dinitrogen and ethane, which are much more stable. 108.21.235.166 (talk) 09:42, 26 December 2018 (UTC)

Air in transport
I have found air in many forms of transport (coaches most of all) unpleasant to breathe for reasons I cannot explain. What feature of the air might be responsible for this? It is not the smell or the temperature. - - Leon (talk) 22:47, 25 December 2018 (UTC)
 * There are several reasons. Firstly, air travel. This is mostly pressurised, the pressure being supplied by tapping bleed air from compressor stages of the jet engines. This air is hot, so it needs to go through an aircon pack to cool it. Secondly, road travel.  This is simpler, but still has several problems. Most of these problems are largely avoidable, but are made worse (much worse!) by careless or cheapskate servicing.
 * Road travel has long ducts from the air inlet, to the passenger. These are rarely, if ever, cleaned. This becomes far worse if they're inhabited by moulds, which can release odours or even spores. Moulds favour damp conditions, which can arise from a humid climate or from the chilling effect of air conditioning acting as a dehumidifier and causing condensation. A poorly-drained or poorly cleaned dehumidifier often makes damp problems worse, not better. Many road vehicles nowadays have pollen filters in their air streams. These are great when they're fresh and can reduce pollen or dust loads, helping with allergies such as hay fever. However letting these get damp turns into a real hotbed for breeding mould!  I always change mine each Spring, after the damp Winter, and it's usually quite disgusting by then. Electrostatic filtration can help (and can be cleaned more often without needing replacement elements) but that's rare outside aircraft.
 * Fresh air supply is cheap, so is usually taken directly from the outside – but the inlets are near road level (even the top of a coach isn't that high) and are full of exhaust fumes and particulates: diesel exhaust particulates, brake dust, tyre dust. However when air conditioning is used, this costs energy to cool and so it's colder and less costly to recirculate this within the vehicle, rather than running it once-through. Recirculated air is often the cause of most 'bad air' problems in transport. Whatever goes wrong with it, it goes more wrong the more the air is recirculated around and around.
 * Aircraft suffer particularly badly from recirculation woes, as the cost of both bleed air and running the chiller packs costs fuel. Long haul flights especially, where fuel is not only expensive, but needs appreciable fuel to carry it for the first part of the flight. In some aircraft, there's even a difference in air quality between first and cattle classes – one reason why first is at the front. A few aircraft, infamously the BAe 146, suffered from fume events. The design of their engines (originally a helicopter turboshaft) made them more prone to releasing internal oil as a mist into the bleed air supply, and mineral oil mists are well known as hazards. Andy Dingley (talk) 23:15, 25 December 2018 (UTC)