Wikipedia:Reference desk/Archives/Science/2013 December 1

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December 1

Are deer "nearly blind by human standards" ?

This was the assertion by the Nature episode The Private Life of Deer. They said they only see blurry shapes, except when those shapes move. Deer have large enough eyes, so this assertion seems questionable to me. This program was focused on white-tailed deer, but I'm unclear if the comment applied to all deer of just that type. If true:

1) How do we know this ?

2) Why exactly can't they see stationary objects well ?

One thought I had is that they appear to lack the dilation/contraction response of humans and many other mammals, and therefore to be able to see at night they must get way too much light during the day, and perhaps this blinds them. I'd expect it to cause permanent eye damage, too. Is there some chemical change to alter the sensitivity of the receptors in daylight ? StuRat (talk) 01:51, 1 December 2013 (UTC)

This page seems to have some good information. --Onorem (talk) 02:04, 1 December 2013 (UTC)

Banned user
The following discussion has been closed. Please do not modify it.
I don't know much about deer, but the article cited above seems more than a bit suspect. Looking at several points about your query, StuRat:- 1. Birds see ultraviolet because they have, instead of three types of colour-sensing retina cells that humans have, they have four - an extra one that senses ultra violet light. In general mammals have only two type of cone sensor cells - thus their calour vison is no wher near as good as birds. Humans, as mammals, are an exception. We have three types of cone cell, so our colour vision is substantually better than other mammals. Mammals including humans, are blind to ultraviolet primarily not because of any filter, it's because mammals lack ultraviolet-sensing cone cells. 2. I suspect the pupil dilation/contraction resopnse works just fine in deer, but to answer your question, there are other ways that the eye can adjust for variation in scene brightness. The transduction of light energy into nerve signals depends on a substance called visual purple. Visual purple is consumed by the transduction - at a rate dependent on the intensity of light. Visual purple is continually manufactured in the eye. It happens that the rate of manufacture does not keep pace as light intensity increases, and the effect of this is to reduce percieved contrast and compensate for change in light level. 3. Throughout the animal kingdom, nerve systems react to change in stimulus not level of stimulus. This elvolved because it suits simple organisms well. For instance, a frog is completely blind to things that don't move. This economises on teh size of brain required. Flies and insect move - and the frog can detect them and gett them with its ballistic tongue. In more complex animals, eg crododiles, and probably birds, they move their head a lot. This causes the scene to move across their retina and thuis can be detected. The animal builds up a mental picture of the scene, including things that are not moving. So yes they are sort of blind to things that don't move, but that is misleading. Mammals, including humans, constantly move their eyes in tiny movements as well as moving their whole eyes. The movements are termed saccades. Saccades means that the retina cells are continually being re-triggered, so mammals can see non-moving objects without moving their head. 4. Not withstanding saccades, even for humans, detecting things that don't move remains difficult. When I was a boy scount, we received training, similar to army training, on how to survey natural scenes. As an exercise, conducted within a not particularly dense forest, one scout would be asked to hide himself behind a tree about 30 metres or so away, while other scounts were looking in the opposite direction and watching a lecture on knots or something. A tree with a trunk about 300 mm or so wide was chosen. This of course means that at least one shoulder was visible, and most likely a hip as well. He was instructed to remin motionless. The other scounts would then be told to turn around and put their hand up if they saw where he was. Usually it would take quite a while before anyone put their hand up, and some never did. Some people cannot see another 30 metres away if within a stand of trees but not hiding at all - just motionless. As a generally rule, herbivorous animals (eg deer) are less good at this than meat eaters (including humans). Good binoccular/stereo vision as meat eaters (and humans) have assist in seeing non-moving objects that are of interest, and partiall concealed behind trees etc, due to the additional depth cues. 5. We can't really know how animals see the world, but it is unlikely they see things in a blurry way similar to us trying to see through someone else's glasses, or as in a photograph that is out of focus. It is vastly more likely that they percieve things as perfectly clear or not at all, much as we cannot detect our own blind spots, unless by speciall trickery. 1.122.117.242 (talk) 15:17, 1 December 2013 (UTC)

A key thing to note is that deer don't have a fovea but a visual streak (mentioned briefly in retina, someone should start an article...) 20/200 is the threshold of legal blindness, which is what deer were rated at; macular degeneration can put people below that. However, I would be concerned that we may miss some of the tricks involved in having a visual streak, due to a lack of intuition about it. Hunters generally have a practical sense of what deer miss and see. [1] Wnt (talk) 21:15, 1 December 2013 (UTC)

That seems to explain the quote in question. Somehow I bet we are missing something, though. I understand that the image our eyes produce is also much worse than we think, and the reason is that our brain does a wonderful job of filling in the gaps. Perhaps a deer's brain is also able to make more out of the input from their eyes than we think. StuRat (talk) 12:53, 2 December 2013 (UTC)

Thanks all, for the answers so far. StuRat (talk) 12:53, 2 December 2013 (UTC)

Chloroauric acid

Where can I find information on the chemistry of anhydrous chloroauric acid, that is the substance with the formula H
₃O[AuCl
₄]? How is this substance obtained (not H
₃O[AuCl
₄(OH
₂)
₂] or [H
₅O
₂][AuCl
₄(OH
₂)
₂])? Plasmic Physics (talk) 07:07, 1 December 2013 (UTC)

Google suggests anhydrous chloroauric acid is crystallizeable from ethanol, but not clear how hydrated it begins. I see you made major changes to the article, including the very definition of the topic itself...need cites that the chemical named "chloroauric acid" and widely identified as just HAuCl₄ by formula is assumed to contain at least one water intrinsically as a hydronium (with then 2–3 more as the hydrated salt form). For example, VWR's catalog calls the chemical with 3 waters total in the formula the "trihydrate". DMacks (talk) 07:50, 1 December 2013 (UTC)

It is a well known fact within the chemistry domain, that no known compound contains free protons. By convention, salts purported to contain free protons, in actuality contain solvent coordinated protons. This case the common solvent is water. HAuCl
₄ is the canonical, but technically incorrect formula. Plasmic Physics (talk) 08:12, 1 December 2013 (UTC)

How do you know it's exactly *one* "water solvating the proton in the chemical? Some articles identify "HCl" as one of the ligands, which seems unlikely, but you seem to take for granted the opposite extreme, that [Cl₄Au] is completely non-coordinating/basic itself. You're the one making specific claims about a specific chemical that on their face contradict other information in the literature. WP:BURDEN's on you to make the specific case from the literature. DMacks (talk) 08:32, 1 December 2013 (UTC)

It is standard practice to attribute one water to a proton. I don't suppose that [AuCl
₄]⁻
is non-coordinating/basic itself, what I am supposing, is that it is the structurally irreducible anion that is participant to chloroauric acid. Furthermore, I suppose that it does coordinates very well, but not as strongly as a proton, hence why H
₃O[AuCl
₄(OH
₂)
₂] decomposes rather than dehydrate when subjected to elevated temperatures. Plasmic Physics (talk) 08:51, 1 December 2013 (UTC)

It may be standard practice to attribute one water molecule, but is it standard practice to write one water molecule. WP:BURDEN applies, the standard form as written should be written but it has been removed instead. Citation not explanation please. Dmcq (talk) 11:33, 1 December 2013 (UTC)

[H
₅O
₂][AuCl
₄(OH
₂)
₂] could also rather be H
₃O[AuCl
₄(OH
₂)
₂]•H
₂O, which contains genuine lattice water. Plasmic Physics (talk) 09:13, 1 December 2013 (UTC)

Oops, correction: the later two formulae should be

• [H
  ₅O
  ₂][AuCl
  ₄(OH
  ₂)] (or H
  ₃O[AuCl
  ₄(OH
  ₂)]•H
  ₂O) and
• [H
  ₇O
  ₃][AuCl
  ₄(OH
  ₂)] (or [H
  ₅O
  ₂][AuCl
  ₄(OH
  ₂)]•H
  ₂O, or H
  ₃O[AuCl
  ₄(OH
  ₂)]•2H
  ₂O).

Plasmic Physics (talk) 12:15, 1 December 2013 (UTC)

Sorry, I'm really suspicious of this. "oxonium tetrachloridoaurate" isn't getting me any hits at PubChem and only this article on Google. I think it is very standard practice to write HCl, HI, HF, etc. (and these do exist as molecules in gas phase, therefore exist in equilibrium in liquid phase, and I'd assume they can exist as pure solids if you catch some of those gas molecules where they have nothing to join up with. Whether those solids are ionized, covalent, polymerized, coordinated, whatever is another question). Show me a synthesis or purification procedure where somebody has actually shown that H3OAuCl4 has a discontinuity in its tendency for losing/gaining water at a 1:1 stoichiometry and I'll believe you. Wnt (talk) 21:04, 1 December 2013 (UTC)

Your mistake is that you assume that in the hypothetical H[AuCl
₄], the proton could be directly attached to the anion. It cannot, it is wholly unlike the hydrogen halides. Plasmic Physics (talk) 21:17, 1 December 2013 (UTC)

Are you sure? Chlorine can make more than four bonds if it wants. Wnt (talk) 21:43, 1 December 2013 (UTC)

Yes, the acid is known as matter of fact to contain discrete [AuCl
₄]⁻
ions. Plasmic Physics (talk) 22:37, 1 December 2013 (UTC)

That's a far cry from saying that HAuCl4 never occurs, or that having less than HAuCl4*1H2O would be impossible. I mean, my gut feeling is that "anhydrous" means "no H2O". It's like a sultan coming back to his hareem and finding his ninth wife with another man, but don't worry, he's her lover and he's the only one she can't do without. :) Wnt (talk) 23:20, 1 December 2013 (UTC)

Even if H[AuCl
₄] does occur as you suggest, it would do so for a vanishingly small time, before decomposing into AuCl
₃ and HCl. Plasmic Physics (talk) 23:42, 1 December 2013 (UTC)

Hmmm, then why doesn't H3O-AuCl4 decompose to H2O + AuCl3 + HCl...? Maybe that's not a valid comparison - in any case I shouldn't have taken your word for the H not having another way in. According to [2][3][4] the structure of AuCl4H is actually the gold in the center and all five ligands arrayed around it. (It's too easy for me to forget that transition metal chemistry is just different from the organic...) Wnt (talk) 08:39, 2 December 2013 (UTC)

One thing you'll learn with some experience, is that commercial catalogues are unreliable when it comes to structural information on compounds. Plasmic Physics (talk) 22:11, 2 December 2013 (UTC)

Actually, H
₃O[AuCl
₄] decomposes to AuCl, Cl
₂, HCl, and H
₂O. Plasmic Physics (talk) 22:14, 2 December 2013 (UTC)

May I suggest yet again that what should lead in the lead is the formula as normally written in reliable sources. All the argument above is irrelevant to that. Dmcq (talk) 09:35, 2 December 2013 (UTC)

I'll second that. --Jayron32 15:24, 2 December 2013 (UTC)