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Sauron
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[*] posted on 10-7-2008 at 09:08


Yes to both. The positions of flame, prism and target (photo plate/film holder) would be fixed - I assume.



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[*] posted on 10-7-2008 at 09:26


There are some pretty simple beasts described here.

http://en.wikipedia.org/wiki/Spectroscope

I guess Curie et al would have used something along these lines.
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[*] posted on 10-7-2008 at 09:40


Interestingly there are instructions for building basic spectroscopes on the Internet.

http://sci-toys.com/scitoys/scitoys/light/cd_spectroscope/sp...

One of these pointed at a gas flame with a stick of salt held in it would have no problem picking out the sodium D lines
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Sauron
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[*] posted on 10-7-2008 at 09:47


In modern instruments liquid samples are more usual and the solution is nebulized (nebularized?) into the flame, sometimes the flame device and nebularizer are combined.

I have seen this technique in some HPLC detectors that use destructive detection (not the usual approach in LC).

I'll have a look at those links now, thanks.




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[*] posted on 11-7-2008 at 03:22


Quote:
Originally posted by jgourlay

Could point me in the direction of "diffraction grating from cd" suggestions? I'll check instructables and google, but I figure you might know a better source.



Here's an excellent site on CD based homemade spectroscopes, it's remarkably detailed and if you drill down a bit you'll find great information about spectroscopy and the actual spectra (w/ beautiful pix). The simplest versions of these spectroscopes take about 1 - 2 h to build. The author is a professional scientist.

Here's another one I like: solar spectrocope built from a cereal box, a piece of CD ROM and some gaffer tape...

Just comparing the spectrum of an incandescent light bulb (hot) with that of a compact saver bulb (much cooler) is in essence a corroboration of quantum mechanics....

Good luck!

[Edited on 11-7-2008 by blogfast25]
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[*] posted on 11-7-2008 at 09:58


Quote:
Originally posted by blogfast25
Quote:
Originally posted by jgourlay

Could point me in the direction of "diffraction grating from cd" suggestions? I'll check instructables and google, but I figure you might know a better source.



Here's an excellent site on CD based homemade spectroscopes, it's remarkably detailed and if you drill down a bit you'll find great information about spectroscopy and the actual spectra (w/ beautiful pix). The simplest versions of these spectroscopes take about 1 - 2 h to build. The author is a professional scientist.

Here's another one I like: solar spectrocope built from a cereal box, a piece of CD ROM and some gaffer tape...

Just comparing the spectrum of an incandescent light bulb (hot) with that of a compact saver bulb (much cooler) is in essence a corroboration of quantum mechanics....

Good luck!

[Edited on 11-7-2008 by blogfast25]


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Sauron
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[*] posted on 11-7-2008 at 10:11


Amazing what you can do with a CD as a diffraction grating and a cereal box as a camera obscura. These are great for demonstrating the principles involved.

However I would prefer something a wee bit more professional, if I can find one. Some company must have made them for educational labs etc. Or else they may be present in the used market.

The Chinese make a lot of relatively old fashioned optical instruments for labs like polarimeters (I have one) and Abbe refractometers (I am ordering one) Companies in Europe buy these on an OEM basis and mark them up horribly, but the Chinese factories sell them cheap. Maybe they make one of these older spectroscopes.




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[*] posted on 11-7-2008 at 10:14


Quote:
Originally posted by Sauron
Amazing what you can do with a CD as a diffraction grating and a cereal box as a camera obscura. These are great for demonstrating the principles involved.

However I would prefer something a wee bit more professional, if I can find one. Some company must have made them for educational labs etc. Or else they may be present in the used market.

The Chinese make a lot of relatively old fashioned optical instruments for labs like polarimeters (I have one) and Abbe refractometers (I am ordering one) Companies in Europe buy these on an OEM basis and mark them up horribly, but the Chinese factories sell them cheap. Maybe they make one of these older spectroscopes.


Actually, the CD version is outstandingly perfect. It will be my son's first self made scientific instrument. However, I have a large equilateral prism on order and I may wait for that because explaining the concept of the rainbow from the prism, which is the necessary precursor of the spectrograph conversation, is easier with a prism.

Actually, I'll admit my ignorance and tell you that it's easier because I think I understand that as opposed to knowing I don't understand how diffraction grating works.
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[*] posted on 11-7-2008 at 11:59


If you can understand how a prism works then spectra by diffraction gratings are also well within your grasp, even though the underlying phenomena are quite different.

I "built" (cut an' glued together is a more accurate description) two Mk II spectroscopes (from the Köppen site), one with a reflective grating, one with a transparent grating (both from pieces of CD ROM, the latter with the foil removed - see Mk IV). I've got all the materials and detailed plan for a Mk III, it's just that damn backyard chemistry keeps getting in the way of putting it all together... :o
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[*] posted on 11-7-2008 at 18:00


I found this on ebay and for 19 bucks (including S/H) it is hard to beat. Below I pasted some of the text from the auction. I believe this one is right up your alley as far as finding a cheap but very useful instrument in your teaching. While they mention US shipping, I am sure an email to the seller could get you one mailed to any other country very cheaply.

DIFFRACTION GRATING SPECTROMETER SPECTROSCOPE

"Offering for your consideration a new Diffraction Grating Spectrometer/Spectroscope. This spectrometer consists of a black plastic housing with a slit for incoming light and wavelength scale at the wide end, and a small replica diffraction grating at the eye (narrow) end (see photo). The spectrometer breaks down incoming light into color components and displays them against a scale showing wavelengths from 380 to 730 nanometers. The scale is marked every 10 nanometers allowing measurements to +/- 5 nm precision. Various light sources can be identified by the bright emission bands or dark absorption bands in their spectra at specific wavelengths.

This spectrometer is about 7.5" long, 4" wide (wide end) and 1" thick. The wavelength scale is 1.5" long. The spectroscope comes with an information/activity sheet to get you started viewing and measuring various spectra."

Here are two more types:

SPECTROSCOPE

SPECTROSCOPE

Which one of these seems to be the best choice?

----------------------------------------

While I know you guys hate sidetracking threads and this one is primarily talking about the spectroscope, I wanted to touch on the gravity subject mentioned within this same thread. Also, I squished the images for Sauron but the second one did not work well as it made me look like I am standing in Jupiters gravity.

"He's referring to the fact that a mass object, if separated by enough distance from other mass(es) has no gravitational force acting on it. The heaviest man on Earth would still be weightless in space. Mass, weight and gravitation are related, connected yet distinctly different things. Quite a challenge to explain that to a youngster: that's where the dancing comes in I guess..." quote from blogfast25.

I think it is important to be more specific, meaning even in space you are still affected by gravity. If you were floating between the earth and the sun (zero velocity) at the exact distance to balance the gravity between the earth and the sun you would feel weightless, but are still within several gravitational fields. In fact there is nowhere within this galaxy where you would not be subject to gravity, even though you were in effect "weightless". As to being in orbit, your weight is merely being masked by your angular velocity. I know it sounds nitpicky, but I thought it important to mention in regards to teaching young minds insofar as eliminating anything which must be unlearned later, if the child decides someday to go in depth in a given field of study. Having lived many years, I know from experience that it is much easier to learn something complex if there is no "unlearning" to do.

If we were being very picky we could say there is gravity between each particle of our makeup. To me mass is energy, while weight is closer in concept to potential energy relating mass, height, and a specific level of gravitational field. By this I mean the potential energy in terms of momentun unleashed if that weight were suddenly free to fall and then stop when it hit the surface of the attracting mass. I may be explaining this thought poorly but for what it's worth there it is.

From experience I know it is sometimes hard to explain the difference between what is weight and what is mass. While my post may not be very helpful, hopefully it gives a few more insights which may help jgourlay teach.
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[*] posted on 11-7-2008 at 20:27


I had a similar problem when homeschooling my kids (the education system here is tripe). Basically I can find two good answers

The old method: If matter A is a compound A = BC, then reactions of the type are possible

A + D -> DB + C

where A can not be obtained from D and C by any manipulation. This means essentially that something has split-off from A, and it doesnt rely on isolating an element chemically. If A were not a compound then only the following could obtain

A + D -> A_xD_y + A_mD_n

where clealy A can be ontained from C (=A_mD_n) and D.

New method: Mass spectroscopy - not ordinary low-T, where some bond might not be broken and look elementary, but plasma MS. At this temperature, as someone wrote, chemistry does not exist, and all matter becomes a mixture of ionised atoms 'elements'. Each element isotope creates a geometric series of M, M+, M++ mass to charge ratios, and a mixture looks like the direct sum of two such series. In this regard chlorine would look like a mixture of 35 and 37 isotopes.
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[*] posted on 11-7-2008 at 20:50


Fluorine NOT flourine.

And definitely not flourene.




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[*] posted on 12-7-2008 at 04:55


IrC:

The second one is definitely the most comprehensive one:

• Sturdy brass construction should beat plastic every time
• Adjustable optical path length allows some control over line-fineness, hence resolution. A longer optical path means the light waves will travel more parallel to each other, leading to higher resolution (but with the grating further away from the light source [at longer optical path length], lines will also be fainter at higher resolution)
• Adjustable slit-width allows to adjust resolution to object brightness: where detection is by the naked eye (and not by means of photosensitive pixels or something like that) being able to adjust the amount of incoming light can mean the difference between seeing a line and not seeing it at all

Never stopped to think to look in eBay. Still, I'll be building Mk III before considering any purchase: there's much to be learned from building one's own instrument.

On gravity: agreed; I was being generic as this thread isn't about gravity, mass, weight or inertia...

[Edited on 12-7-2008 by blogfast25]
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[*] posted on 12-7-2008 at 15:00


I agree, if jgourlay had not only started the thread but also asked the gravity question within it I would have felt like it deserved another thread of it's own. Actually, since SCM is about science of many varieties rather than just chemistry the subject may deserve it's own thread seeing as how there is a lot of confusion out there on the subject of gravity. But enough on that.

I thought about the one you mentioned and almost bought it myself but it lacked a scale (and the S/H was high). I don't know but it seems the scale would be so very useful, i.e. we can actually compare the real wavelengths numerically to say a chart of line spectra of the elements or something like that. On another note I saw the bulk of all the nicer looking instruments seemed to be about checking jewels for authenticity. Would this also be just as useful if say I wanted to know which element was involved by comparing real world numbers of various elements with where the lines are on the spectrascope at the time I am actually looking at a spectrum? The problem I have is other than ballpark guesses as to around where the color is in terms of frequency, how can you really tell the element if say there are several elements with lines very close to each other. Not being a master on the subject and having never actually used or owned a spectrometer would it not be better if you had an actual numbered scale to go by? Or is there something I am missing in all of this?
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[*] posted on 13-7-2008 at 04:51


Sure, the absence of a wavelength scale is a bit of a limitation, although it might be possible to add one yourself. It would not stop me from buying the instrument. Calibrating with two really easy lines is certainly possible: assuming the grating is of sufficient quality, the scale is linear and the wavelength of an "unknown" line depends only on the actual distance from the calibration lines. Photography obviously solved that problem, as it records accurately the position of the lines and will allow to determine the wavelength of any line precisely, relative to the position of calibrating lines...

But without a full scale automated ("CSI New York/Miami" style) piece of equipment that can identify lines both by wavelength AND relative intensity, spectroscopy for the identification of chemical elements is a bit of an art form, I guess. While many elements can be identified by means of 1 or 2 prominent lines, to separate the lines from multiple elements probably requires experience, as well as systems both upstream and downstream from the scope.

Upstream is the light generator. For element research typically a hot gas flame into which the sample is gradually fed. At our level that's easier said than done. Anyone with ideas/experience on that one, please do elaborate...

Downstream is the detector: unless you want to be peering into the ocular side of the tube for prolonged periods of time, some piece of photographic equipment and knowledge of required exposure times to bring out faint lines, separate doublets etc, will be a requisite. Digital photography really is the dream ticket here because the images can be inspected almost pixel by pixel for faint lines using some image manipulation software or other.

It makes one wonder what kind of hoops Bunsen and Kirchoff must have been jumping through to spectroscopically discover and later isolate Caesium in mineral water and allegedly following their progress in concentrating the Cs solution by studying the increasing intensity of the prominent blue line. Probably one of the first examples of successful quantitative spectrometry...
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[*] posted on 14-7-2008 at 04:36
Appreciate it gents, thoughts on spectroscopy


Gents,

I really appreciate the discussion. I'm adding this board to my list (now expanded to three) of "sites where people know stuff AND are helpful."

Spectroscope: I'm definitely going for build not buy, for a few reasons. First, "build not buy" and "recycle/repurpose before purchase" are two ethics I'm trying to teach the kids. Second, he and I will learn so much more building it ourselves. Remember that the purpose of this is to demonstrate element vs. compound.

For this we'll need a slit, scale, and something to break the light down. THIS provides me the excuse to buy one of those really nice prisms my parents would never let me have!

We'll make a board with depressions for the prism standing on end and for a glass dish. I'll come up with a slit--or maybe pinhole? I can use a laser to rough place the scale on a screen in the projection path of the prism.

In use, we'll put various metal salts in alchohol (or sterno or whatever) and put that sludge into the mortar. THis way the "light source" doesn't change position relative to the prism. As long as in that setup the same wavelength will always fall on the same spot on the scale (and it should), I should be able to prove the point. FURTHER, at least for things that will turn colors when they burn, it should be "analytical" in that I should be able to give him any powder and he should be able to tell me at least some of the constituents.

Moreover, we'll develop the list ourselves. For example, "strontium = 1.5", sodium equal 2.37", sulfur = 4", etc."
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[*] posted on 14-7-2008 at 13:48


Wanting something a little better than what I can build myself I went ahead and bought one to play with. I thought I would post this so I can mention the instructions have one very useful bit of help in calibration. They say to point the thing at a regular florescent light and reading the position of the two bright bands, which are 436 and 546 nanometers.
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[*] posted on 14-7-2008 at 15:54


You can go a step further by using a DVD instead of a CD, since it is a finer grating. You can go yet a step further by capturing images with a digital camera and analyzing the image with free software to determine numerical values. I don't know if I would suggest starting with this more advanced path, but here are two articles from J. Chem. Ed. about how to do it:

A DVD Spectroscope: A Simple, High-Resolution Classroom Spectroscope
Resolving Spectral Lines with a Periscope-Type DVD Spectroscope

[Edited on 7-14-2008 by Polverone]




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[*] posted on 16-7-2008 at 09:31


Very interesting. Never stopped to think that DVDs have finer gratings than CDs (according to the first *.pdf about twice as fine). That should be something that could be easily verified even without building the actual scope.
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[*] posted on 16-7-2008 at 09:47


Quote:
Originally posted by Polverone
You can go a step further by using a DVD instead of a CD, since it is a finer grating. You can go yet a step further by capturing images with a digital camera and analyzing the image with free software to determine numerical values. I don't know if I would suggest starting with this more advanced path, but here are two articles from J. Chem. Ed. about how to do it:

A DVD Spectroscope: A Simple, High-Resolution Classroom Spectroscope
Resolving Spectral Lines with a Periscope-Type DVD Spectroscope

[Edited on 7-14-2008 by Polverone]


Thanks, Polverone!

The first article gives me an error, but the second loaded fine. It mentions using NIH Image as an analysis tool. NIH Image has been largely superseded by ImageJ, a rewrite of NIH Image in Java. ImageJ is completely open-source and free, it runs on a wider variety of platforms, and it's got a very active community developing plugins, macros and other extensions. It's got a very active mailing list for users as well.

I use ImageJ for my day job (processing medical images), and I've even contributed back to the code base a little bit. It's a very capable package, and it can run on just about any machine, even an old and creaky Windows PC.
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[*] posted on 16-7-2008 at 11:41


Quote:
Originally posted by -jeffB
Thanks, Polverone!

The first article gives me an error, but the second loaded fine.

Oops, sorry about that. Permissions should be ok on the first article now.




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