morganbw
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polarimeter
Are there any affordable for the amateur chemist?
I would love to have one.
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Sulaiman
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Isn't it just
Light source - polarising filter - object - polarising filter - eye
one of the two polarising filters needs to be rotatable with an angular scale
You could use 'polaroid' lenses, camera filters (durable, multi-coated and round shaped)
or a used/eBay polarising set for a microscope is quite cheap.
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morganbw
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That is exactly what it is.
It should be doable to make and I may go this route.
I would prefer to buy if available cheap. I already have too many unfinished projects laying around.
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Natures Natrium
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The light from a standard, modern LCD panel is polarized already.
To check glassware for stress, I bring up a blank notepad file and fullscreen it. Place glass object in front. Then using a cheap polarizing lens
for a 35mm camera like a monocle eye piece, I can rotate the lens with one hand and the object with the other to reveal internal stresses in the
glass.
As for the "meter" part of polarimeter, I don't have any advice as I have never used polarimetry. Now I am curious as to its utility, and will do a
bit of research on the subject.
\"The man who does not read good books has no advantage over the man who cannot read them.\" - Mark Twain (1835-1910)
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Crowfjord
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I think photographic filters are circularly polarized; make sure to get linearly polarized filter material to make a polarimeter. The "meter" can just
be a protractor. There are examples of home made polarimeters on the web, and I think member Smaerd made one and posted about it on sciencemadness. Polarization.com has decent prices on polarized film (I've been wanting to make a polarimeter for some time, but haven't gotten around to it).
[Edited on 27-3-2015 by Crowfjord]
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Magpie
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I picked up a polarimeter off eBay a number of years ago. It is a Cenco-Kern (Breda, Netherlands) excessed by Dekalb Community College. It is an old
style where you supply your own light and turn the analyzer wheel manually. I built my own sodium lamp using parts from Home Depot.
I have been playing with this lately just to refresh my rusty technique. I've been testing some sugars from my kitchen and the health food store. I
made no attempt to control temperature but feel it is likely close to 20°C. Here's what I found for specific rotations:
Sucrose from the kitchen: +63.5°; Wiki: + 66.3°
Fructose from the health food store: -90° (2dm tube)
-94° (1dm tube)
-92° (Wiki)
Dextrose (D-glucose) from the health food store: +45°
+52.7° (Wiki)
I'm satisfied with the results for the sucrose and fructose. However the discrepancy with the dextrose has me puzzled. I gave the dextrose plenty of
time to mutarotate. Do any of you have an explanation?
[Edited on 20-12-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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IrC
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Just search the word polarimeter in this very sub forum. 9 pages long, a thread by smaerd where he built one. Very good work, not too difficult to
build with a little effort, patience, and not too much money at all. He provides much in the way of time and work which after reading you will agree
is a great way to add yet another instrument to your lab.
http://www.sciencemadness.org/talk/viewthread.php?tid=18597
"Science is the belief in the ignorance of the experts" Richard Feynman
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nezza
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One thing worth bearing in mind is that it works much better with monochromatic light. Sodium vapour or a laser source with a diffuser are suitable.
If you're not part of the solution, you're part of the precipitate.
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IrC
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After looking at that old thread for the first time in over a year I realize the OP already knew of it for he posted in it. If just looking for
equipment I did find a couple items although I'm not sure how useful or within budget.
http://www.ebay.com/itm/Vintage-Precision-Polarimeter-Rudolp...
http://www.ebay.com/itm/Student-Polarimeter-Half-Shade-Labor...
"Science is the belief in the ignorance of the experts" Richard Feynman
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Magpie
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I have a further result to report:
Per Brewster sucrose was treated with HCl and heated for 20 minutes to hydrolyse it to D-(+)-glucose and D-(-)-fructose. The hydrolyzed product had a
specific rotation of -24°.
Taking my readings for D-(-)-fructose of -92° and for D-(+)-glucose of +45° the following predicted rotation of the hydrolyzed sucrose is:
[α] = (-92° + 45°)/2 = -23.5°
[Edited on 21-12-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Dr.Bob
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Quote: Originally posted by Magpie  |
Dextrose (D-glucose) from the health food store: +45°
+52.7° (Wiki)
I'm satisfied with the results for the sucrose and fructose. However the discrepancy with the dextrose has me puzzled. I gave the dextrose plenty of
time to mutarotate. Do any of you have an explanation? |
I would not be surprised if it is hydrated or maybe not pure dextrose. Many products from "health" food stores are not very pure and often are not
even what they are labeled. Same for many herbal supplements and other non-regulated drugs.
http://www.nytimes.com/2013/11/05/science/herbal-supplements...
https://www.washingtonpost.com/news/morning-mix/wp/2015/02/0...
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unionised
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The rotation of glucose isn't as well defined as you might think.
https://en.wikipedia.org/wiki/Mutarotation
So there's probabaly no real point maligning the supplier.
Also, did you get the anhydrous or monohydrate form?
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Magpie
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My health food store sells all the usual concoctions to provide the trace ingredients that sick people are grasping for a cure. It also sells quite a
lot of bulk food raw materials like various milled grains, vegetable oils, Medjool dates, Finnish licorice, 33% H2O2, activated charcoal, niacin, and
other such goodies. The dextrose and fructose I bought were in bulk and those were the only labels.
What I find really interesting is that the +45° I found for the dextrose (D-glucose) is consistent with the value of -24° I measured for hydrolyzed
sucrose. But it is always possible that this is mere coincidence.
Edit: the dextrose was subtitled: (corn sugar).
[Edited on 21-12-2015 by Magpie]
[Edited on 21-12-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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Here's another result of my polarimetry:
Per Brewster, p.119, I did the "1. Mutarotation of Glucose":
I added 1 drop of con NH4OH to 43ml of dextrose solution. This was in expectation of mutarotation of α-D-glucose to ß-D-glucose to an equilibrium
condition. However, there was no change after 20 minutes. It was still at [α] = +45°. I guess this shows that it was already partially
mutarotated as the pure α form is +112° and the pure ß form is +18.7° giving a mutarotated value of +52.7° at equilibrium.
http://www.ochempal.org/index.php/alphabetical/m-n/mutarotat...
[Edited on 21-12-2015 by Magpie]
[Edited on 21-12-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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The mp was tested today indicating I have the monohydrate. This will increase the rotation angle by about 10%. Therefore a corrected angle would be
+49.5°C. Better, but still short of the lit value of +52.7°
The single most important condition for a successful synthesis is good mixing - Nicodem
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