Wikipedia:Reference desk/Archives/Science/2013 December 1
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December 1
[edit]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)
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- 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
[edit]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 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
- 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)
- It is standard practice to attribute one water to a proton. I don't suppose that [AuCl
[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)
- Your mistake is that you assume that in the hypothetical H[AuCl
- 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)
- Yes, the acid is known as matter of fact to contain discrete [AuCl
- 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)
- Even if H[AuCl
- 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)