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Sci.chem FAQ - Part 4 of 7

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See reader questions & answers on this topic! - Help others by sharing your knowledge
Subject: 15. Chemical Demonstrations 

15.1  Are there any good compilations of demonstrations? 

Yes. Good places to start are the four volume "Chemical Demonstrations"
by B.Z.Shakhashiri [1], the two volume "Chemical Demonstrations - A
Sourcebook for teachers" by Summerlin and Ealy [2], or "Chemical Magic"
by Ford and Grundmeier [2a]. The Journal of Chemical Education is also an 
excellent on-going source of novel demonstrations and developments of 
traditional demonstrations. 

15.2  What are good outdoor demonstrations for under 12s?
15.3  What are good outdoor demonstrations for over 12s? 
15.4  What are good indoor demonstrations for under 12s?
15.5  What are good indoor demonstrations for over 12s? 

While waiting for a promised contribution, here is my only contribution,
and some from my sci.chem archives. Unfortunately, enthusiastic editing
by others allows some of the culprits to go uncredited :-).

The ability of water-miscible solvents to mask the hydrophobic nature of 
Goretex can be demonstrated. Goretex is just a porous PTFE, the same 
material as PTFE filters - such as Millipore HF. You can easily filter 
liquid water through porous PTFE, provided the filter is previously wetted
with a water-miscible solvent ( usually ethanol ). If a filter is set up on 
a vacuum flask, ensure the filter is completely wetted with ethanol, turn on 
the vacuum, and immediately add water - it rapidly filters through. Once it 
has stopped, it only takes about 15 seconds for the air to dry the filter, 
then ask a student to filter more water from the same flask. No chance. 
Pour off the water, surreptitiously add a few mls of ethanol, immediately 
followed by the same water - and watch it filter through again :-). 

This is the nearest equivalent our laboratory has to the workshop practice
of sending an apprentice out to purchase a spark plug for a diesel engine. 
It does relate slightly to the real world - indicating why "breathing"
fabrics like Goretex should not be used with solvents. 

From: brom@yoyo.cc.monash.edu.au (David Bromage) Date: Tue, 14 Sep 1993
Subj: Re: Need: A safe chemical display 

  The so-called "Blue Bottle Reaction" might be useful.

  Half fill a 1 litre flask with water and add 10g of NaOH, then add 10g
  of glucose and up to 1ml of 1% methylene blue. Stopper the flask and
  swirl gently to dissolve the contents. On standing for a few minutes the
  solution should turn colourless. When the flask is shaken the solution
  will turn blue then decolorise on standing.
  Methylene blue exists in solution as a reduced colourless form and an
  oxidised blur form. The initially blue dye is reduced by the alkaline
  form of glucose and re-oxidised by dissolved oxygen. When the solution
  is shaken, atmospheric oxygen enters into solution at a more rapid rate
  than when left standing. The dye acts here as a catalyst whose colour
  indicates the redox state.

[ This demonstration, and different coloured versions of it, have recently 
been discussed in the J.Chem.Ed.[3]. ]
  
  How about a chemical garden?

  Make up (or dilute a commercial preparation) of sodium silicate to
  1.1g/ml. Place this solution in a large glass container then add 'lumps'
  or large crystals of salts to be grown. Lumps should not be more than
  0.5cm in diameter. As a salt dissolves it forms an insoluble silicate
  which forms a membrane around the lump of salt. The membrane is
  permeable to water which enters and dissolves more salt. The resulting
  pressure bursts the membrane releasing more salt solution to form more
  membrane. As the salt solution is less dense than the silicate solution,
  the membrane grows as a convoluted vertical tube.

        Salt                     Colour        Growth time 
  Ferric chloride                brown           1 hour
  Ferrous sulphate             grey-green        3 hours
  Cobalt chloride                purple          5 hours
  Chromium chloride            grey-green        6 hours
  Nickel sulphate            yellow-green      ~24 hours
  Cupric sulphate                blue          ~24 hours
  Potassium aluminium sulphate   white          ~1 day

  To produce a "garden" which is not completely overgrown with the faster
  species it is necessary to take growth rates into account. Distilled
  water should be used as Ca and Fe in tap water can cause cloudiness.

  If you really want oscillating reactions, I know of two.

  A. Iodate reaction.
  Make up 3 solutions
  1) Dilute 200ml of 100 vol hydrogen peroxide to 500ml
  2) dissolve 21g of potassium iodate (KIO3) and 1.5ml of conc sulphuric
     acid in 500ml of water.
  3) Dissolve 7.8g of malonic acid and 1.4g of manganese sulphate in 400ml
     of water and add 1.5g of starch in 100ml of water.

  Add equal volumes (50-100ml) of each solution to a flask in any order.
  Colourless-blue oscillations should start within 2 minutes. If not, try
  10-20% variations in relative volumes. (try increasing 2 first).
  Oscillations should last up to 10 minutes but I my experience have lasted
  up to 3 hours.

  B. The Belusov reaction 
  Prepare 5 solutions.
  1) 58g of malonic acid on 500ml of water
  2) 6M sulphuric acid
  3) 21g of potassium bromate (KBrO3) in 500ml of water
  4) Dilute 5ml of solution 2 to 500ml then add 1.75g of cerous sulphate.
  5) 1.6g of 1,10-phenanthroline and 0.7g of ferrous sulphate in 100ml of
     water (or commercial ferroin solution to 0.025M)

  Mix together 50ml of 1 to 4 and 5ml of solution 5. Blue-pink oscillations
  should start within a few minutes.

  For either oscillating reaction the choice exists of complete mixing with
  uniform oscillations or waves of colour (eg in a measuring cylinder).
  Some interchange of reagents is possible. The Bray reaction omits
  malonic acid from the Iodate reaction. Malonic acid can be replaced by
  citric or succinic acids. 

[ There have been several good discussions [4,5], and recipe compilations 
[6], for many popular oscillating chemical reactions.]  

  A particularly dramatic 'trick' is not to burn paper. Make up a solution
  containing 57% v/v ethanol and 43% v/v water with 5% w/w sodium
  chloride. Soak a filter circle in the solution and hold it near a flame
  (with tongs) just long enough to ignite. After the flames die down the
  filter circle will still be intact. The ethanol burns but just enough
  water remains in the paper to prevent ignition. NaCl is added to provide
  a more convincing flame. To add drama, 'burn' a banknote - but ensure
  that all of the note, especially the corners, is soaked. 

From: lmartin@uclink.berkeley.edu (Lonnie C Martin) Date: 17 Feb 1993
Subj: Re: Growing a Silver Tree in Beaker?
 
  In article <...> xslkkk@oryx.com (kenneth k konvicka) writes:
  >Am trying to do a demo for elementary school kids.  How do you grow a tree 
  >of silver using copper wire(?) submerged in a solution of AgNO3?  Saw one 
  >in high school physics class about a thousand years ago at good ol' Reagan 
  >HS, Austin, Tx.  Was really beautiful.  The silver formed nice large 
  >plates.  Any demonstration books you could steer me toward? 

  What you have described is about all there is to it. I do this 
  demonstration for the chemistry classes here at Berkeley about twice a 
  year, or so. Just make a "tree" out of copper wire (you might clean it 
  with sandpaper or steel wool) so that it will fit into a beaker of your 
  choice (we use 4 litre here), and pour in the silver nitrate solution. 
  I think we use 0.1 molar, but as long as the concentration is fairly close 
  to that, it will work just fine.

  It is not necessary to make the tree very "bushy".  The silver will fill it
  out nicely with fuzzy thick hanging globs of crystals.  The solution will
  change from colourless to blue, as copper nitrate is formed. A very nice
  experiment.  You can expect this to take on the order of an hour to get
  fully developed.

From: flatter@rose-hulman.edu (Neil Flatter)   Date: Tue, 14 Sep 1993
Subj: Re: Need: A safe chemical display
                                                                         
  We use cobalt (II) chloride in a saturated sodium chloride solution to 
  demonstrate cooling coils.  It changes from red/pink to a blue/purple when 
  heated and reverses as it is cooled.  We cycle it through a condenser from 
  a distillation to illustrate that portion of a simple set-up.

Subject: Stupid lab tricks -Compiled-  VERY LONG   Date: 7 Jul 92

From: Nazman <nasadk@rpi.edu>

  Ever try taking an empty ditto fluid can, put some water in it, heat it 
  until steam is coming out, cap it back up and let it cool off?. You would
  be surprised what a little air pressure can do. That one amazed me when I 
  was young.

  I was amazed again when I saw a brief description on TV of how science 
  teachers are trying to make science fun again. Four teachers on stage, set 
  up a few ring stands and a few bunsen burners, and placed a 55 gallon oil 
  drum on top. Boiled the water, capped it. Put a hell of a dent in the drum 
  when it collapsed.

  A favourite of mine requires a little preparation, but is great fun. Try 
  tearing an aluminum can in half. Kinda difficult. Now, if you take an empty 
  can, gently score around the circumference on the inside, (the inside is 
  coated to prevent a reaction between the soda and the can) and fill the can 
  with a solution of warm water and Copper(II)Chloride (CuCl2) so that the 
  solution is just above the score mark. Let this sit for a few minutes.
  You are done with the solution when the outside of the can appears brownish
  (blackish) where the score mark is. Gently pour out the solution (keep it)
  and let the can sit. When ready, hold the top of the can in one hand and 
  the bottom in the other, and break like you are breaking a stick in half.

  Two bits of advice :
  BE CAREFUL!. You will end up with the sharp edge of the can, which can cut 
  severely!

  Try this ahead of time just to make sure you get it right. Wait too long,
  and when you pick up the can, it will split due to the weight of the 
  solution. Don't wait long enough and it won't work. My guess is about 
  5 minutes
  
  P.S. This is more of a demonstration of structure of an aluminum can, but
  if you want to demonstrate the "strength" before you rip it in half, place 
  the can on the floor, so it is sitting like it normally would, and balance 
  on one foot off the top of the can. It helps to have something nearby to 
  hold on to, and the can cannot have any dents. You would be surprised how 
  strong an empty can is. I weigh about 190 lbs, and have stood on an empty 
  soda can for 30 seconds, get off the can, and not have it collapse. This 
  takes some practice, so give it a try.

From: A_ROSATI@GUVAX.GEORGETOWN.EDU  <Anthony V. Rosati>      

  You can followup the bromophenol blue trick by brewing a cup of tea
  and, while they watch, add some lemon juice. The color will lighten.
  There is an indicator in tea that changes with the acidity of
  ascorbic acid.

  Another neat trick is to demonstrate the dehydration capacity of
  concentrated sulfuric acid. Take a 500 mL beaker about one third full
  of white table-sugar. Then add about a half-inch to one inches worth
  of concentrated sulfuric acid. (This demonstration _MUST_ be conducted
  in a hood) Let it sit for about five minutes. Within that time, the
  sulfuric acid will seep in, start turning the color of the sugar
  brown, and then black, followed by an intense, hot dehydration. The
  sugar will start to form a jet black, smelly, sticky column that rises
  out of the beaker. It is really impressive.....

  You might want to also look up "oscillating reactions" in your
  chemistry library. Many of these are simple to set up and generate
  neat color cycles that would impress the kids!

From: mfrancis@ucsd.edu < Lyn Francisco >
                          
  1.  Take a balloon, blow it up, tie it, then stick it in a vat of
  liquid nitrogen.  Wait until it shrinks (around 3 s or so), take it
  out, and then watch it inflate in your hands.  This will very nicely
  illustrate the relation between temperature and pressure.

  2.  We did this during a demonstration to let the world know about
  ACS on campus.  Take a large container (like one of those 10-gallon
  water containers, cut in half or something), fill it up with water,
  then put in one can of the original Coke and one can of diet Coke.
  Make sure that both cans are unopened.  Now, drop a few pieces of
  dry ice in the container.  The original Coke should drop to the
  bottom, and the diet Coke stay up toward the top.  It was cool, and
  attracted all the frat-types and non-science people to our table.
    
From: dfield@nike.calpoly.edu < Dan Field >

  If you really want to fire them up, my favorite has always been the 
  hydrogen balloons. Just fill up several balloons, one color with air or 
  He, another with H2, and another with 2H2 + O2. You can fill them ahead of 
  time, or better yet if demonstration time allows, use the products of one 
  of your demonstration reactions to fill the balloons.  Light a candle on 
  a  L O N G  stick, dim the lights, and pop!, boom!,  B  O  O  O  M !!.  
  You'll have instantly created little monsters, young pyromaniacs virtually 
  guaranteed to associate some excitement with chemistry. 

[ Warning - the sound level of such explosions has recently been found to  
 exceed health and safety guidelines, and people should read the article
 before demonstrating this experiment to students or children [7]. ]
  
From: edremy@d31ha0.Stanford.edu < Eric R.>
        
  There are lots of things you can do with liquid N2.  Try freezing a
  banana and using it as a hammer.  (Follow by using an unfrozen banana:
  kids love it!)  Simply adding some to a test tube and (lightly!) corking
  it is fun, provided you're careful with the cork.  Shattering a
  superball is also good.

  However, my personal favorite for spectacular demos is the HCl fountain.
  Ascii graphics follow


                        ---------
                        \       /  Top flask is filled with HCl gas
                         \     S   S=rubber stopper w/ hole for needle
                          \   /
                           -|-
                          / | \    Run tube from top into bottom
                         /--|--\   Bottom flask filled with water and
                        /   |   \  acid/base indicator.
                       -----------

  MAKE SURE THAT THESE FLASKS ARE VACUUM SAFE!!!

  To start this whole extravaganza, inject 20-30 cc of water into the top
  flask.  The HCl gas goes into solution, creating a partial vacuum, sucking
  the water up from the bottom.  As the water spurts out of the tube, it
  collects more HCl (And changes color as it becomes acid) and accelerates
  the reaction...  Quite impressive.

  We used to do this for our chemistry magic show every year.  The only
  problem is that the failure mode is somewhat dangerous: One year the
  top flask had a flaw and imploded, sending glass and HCl everywhere.
  Best to do behind a shield

From: Bill
  
  I believe that the same thing can be done with ammonia. 
  The same precautions apply.

From: ?

  Bubble H2 through a soap solution and you get bubbles that float up.
  Have them float through a bunsen burner flame suspended over the table and
  they explode. VERY NEAT effect.

From: joec@morgan.com <Joe>

  USUAL WARNINGS: many chemicals are poisonous and some reactions
                  may be difficult to control. Use your head.

  Best done indoors
  -----------------
  Dissolve silver nitrate in warm water. Get some copper wire
  and clean it with steel wool. Insert copper wire (preferably coiled
  at one end) in the solution and it will immediately dull. Some time later,
  silver crystals will be CLEARLY visibly growing on the copper.
  The best effect is to let it sit overnight. The resulting
  effect is downright beautiful

  Dissolve Cobalt Chloride in warm water. Put some Aluminum foil
  in it and watch it tarnish. Clean, polished Aluminum works
  best but household aluminum foil also works (just slower).
  The Aluminum slowly disappears and Cobalt metal shows up at the bottom.
  This is a slow one but it does work.

  Light an alcohol lamp, i.e. denatured alcohol and bring a magnet near
  the flame but not above it- to the side. Watch the flame get pulled in
  the direction of the magnet.

  Sprinkle iron filings over the same alcohol lamp and watch sparks fly!

  Ignite some Magnesium ribbon and drop into an atmosphere of CO2. It
  will continue to burn with lots of noise and sparks. Carbon dust will
  rain down as a byproduct.

  Mix water and household (3 in 1) oil. Note the phase boundary.
  Add soap and shake. Watch the phase boundary disappear.

  Heat up a piece of blackboard chalk with a propane torch. Chalk
  is CaCO3 - heating it up will drive off CO2, leaving CaO (also known
  as lime). Heating up lime will cause the it to emit a whitish light,
  which is where the phrase 'limelight' comes from. 
  [ Note - not all blackboard chalk is CaCO3 - test carefully first ]

  Do these outdoors:
  ------------------

  Get some KMnO4 and pour into a small pile. Depress the center of
  the pile slightly and add a drop or two of Glycerine and stand back.
  Something between 1-5 minutes later, it will burst into flame.
  When it dies down, drop some more glycerine on it to have it flare up
  again. Be careful disposing of the KMnO4 left over - its a powerful
  oxidizer.

  We also do THERMITE periodically (Aluminum powder and rust). Details for
  those who ask - it burns *BRIGHT* and *HOT*.

  Drop some dry ice chunks into a 2 liter PLASTIC soda bottle 1/2 full with
  warm water which is then quickly sealed. Get at least 50' ft back rather
  quickly. The pressure will build up and detonate with a LOUD *BOOM* after
  a brief and unpredictable time. The bottle will break into many hundreds
  of parts (don't use GLASS!) and you will get a mist cloud some 20-30'
  across. Note: It is quite LOUD and may scare a younger audience.

  Make Hydrogen soap bubbles and set them off. Get an erlenmeyer flask and
  fit a cork into the top and route a glass tube through the tube and
  have it bend down and into a jay of soapy water. Remove the cork and
  drop in Zinc metal and pour in somewhat dilute HCl. Put the
  cork back in and let the H2 bubble into the soapy water. This will
  make H2 soap bubbles. Let them break free and ignite them with a light
  match on long pole.

  Thermite reaction

  First of all....this is a fairly vigorous reaction so take the usual
  precautions:
  1-Do it outside, preferably on sand or dirt. Since it burns at 4000 degrees
    fahrenheit, it will melt most anything. By the way, a nuclear explosion
    burns at 8000 and the surface of our Sun burns at 10000. It will readily
    melt rock salt, beach sand, etc.  You get the idea.
  2-It can spray sparks around. Keep it away from combustible materials. The 
    burning sparks are either molten Aluminum or molten Iron.
  3-It is VERY bright so you shouldn't stare at it.
  4-It puts out lots of smoke.

  Here is how I do it.

  Ingredients:
  1-Aluminum powder
  2-Iron Rust (Red-Fe2O3).

  Grind carefully and separately into a powder-like consistency.
  Mix in roughly equal proportions, by volume with an excess of rust.
  Mix thoroughly to get an even color.
  Pour the powder mixture on the ground in a pile.
  Get magnesium ribbon and lay it on top of the pile, and press partially
  into the pile. Do not smother the Mg ribbon. Ignite the ribbon with a 
  propane torch and get back quickly.

  When done, be careful...it will leave molten, glowing red iron as a 
  byproduct.
  You can make rust by mixing household clorox with steel wool pads and let 
  sit overnight and then filtering out the rust.
  Have fun and be careful.

  Usual disclaimers apply

From: gallivan@after.math.uiuc.edu < Justin Gallivan >

  This works nicely with soap bubbles in a dish.  If you have the H2 and O2
  tanks available, Try a few with the H2 only which makes a nice quiet
  flame and add the O2 later for a little shock value.  You may want to
  try this first for safety's sake but it always went off without a hitch in
  my general chemistry days.

From: Rob 

  I hope I'm not too late.  An extremely simple trick is done with a chunk 
  of styrofoam (larger the better) and some acetone, which is an excellent
  theta-solvent for styrofoam.

  Simply spray the acetone out of a bottle onto the styrofoam, and the
  styrofoam rapidly decomposes, losing its structure, and appears to
  actually be melting.  It is quite a "dramatic" demonstration, and can be
  offset against how nicely styrofoam coffee cups hold water/coffee, but not
  acetone.

From: ?
  
  I thought this one was neat...

  Take a bottle (should be reasonable size, like a ketchup bottle)
  fill it to within 2" of the top, color light blue (not opaque!)
  with methylene blue.  Drop in a NaOH pellet and a few drops of
  Karo clear syrup.  Other reducing sugars might work; I just know
  it works with this syrup.  (Or did; the last time I tried it was
  almost 20 years ago, and they may have changed the formula since
  then.)

  Over a period of a few minutes, the blue color will fade.  Shake
  the bottle, and suddenly it's blue again.  Leave it, and it will
  slowly fade.  It'll last for a couple of days, until random
  microbes do in the sugar I suppose.

From: ? 

  A "Bottle of fire" for lighting bunsen burners and such:

  Get a dark, heat-resistant glass bottle, and put just enough pentane
  in it to wet the sides.  (i.e., rinse it with pentane and dump out
  the excess.)  Light the top of the bottle.  The flame will burn down
  into the neck of the bottle a little, but be almost invisible to the
  audience.  Pick up the bottle, turn it over, and flames will pour
  out.  Set it down, and the flames seem to go out.

  When Dr. Toffel did this, someone said "There's something in the
  bottle!" He said "Nope," poured some water from the faucet into the
  bottle, dumped fire and water into the sink, then showed that the
  bottle would still "pour fire".  (This probably takes some practice.)

From: mvp@hsv3.lsil.com < Mike Van Pelt >

  Portable bunsen burner:
  Bubble air through a test tube of pentane, and run this to
  your bunsen burner.  You can use a large balloon as your air source,
  or have a vict...  I mean, volunteer, blow through the tube.

From: Howard Clase.

  One experiment that I like was you make a solution of lead nitrate,
  which is clear, and a solution of some iodide salt (potassium iodide), 
  which is also clear.  When you mix the two of them together you form 
  a yellow solid - lead iodide.

  This is only half of it!   If you don't use too much of the chemicals
  to produce your "instant orange juice" - but DON'T let anyone drink it. 
  You will find that the lead iodide will dissolve if you heat the solution.
On
  Cooling it re-precipitates as beautiful golden spangles.

From: mgray1@metz.une.oz.au < Matthew Gray >

  Another exciting and easy impress all trick is to get two solutions, one
  of Ag(I) and another of Cu(I), usually both hexamine complexes. When 
  these two are mixed, a redox reaction takes place, producing a silver 
  mirror effect. Other reducing metals can be used, such as iron, but I 
  haven't tried these myself.

From: ?

  Grind some potassium permanganate to a fine powder (to speed up the 
  reaction). Put it in a small heap (1 teaspoon) on a tile, make a dent in 
  the top and pour one drop of glycerine in the hole.  After about 10-15 
  seconds the heap will catch fire.

From: torin.walker@rose.com

  Here are some that are rather interesting. All of these tests have been
  performed in my workshop and are all safe (with the exception of the 
  handling of HCl and the irritating effect of experiment #2). Experiment #3 
  is by far the most fascinating.

  1 Copper Sulfate couple grams in a test tube.
    Sodium Bicarbonate - same as above.

    These two liquids are transparent but when mixed, turn into a soft blue
    opaque suspension.

  2 Glycerin and HCl

    Takes a long time (couple of hours) to complete but when these two clear
    liquids are mixed together, it turns from clear to a deep transparent red
    and slowly goes brown. Warning - this is extremely irritating to the eyes 
    if you are exposed to it for a while - usually, an hour is enough to 
    really get you annoyed.

  3 (My favorite) Acetone (you can buy large tins of this stuff (1L) at a
    hardware store in the automotive section (usually with the bondo and 
    other body repair supplies) and styrofoam (a large bag of popcorn type 
    packaging filler will be needed.)

    When styrofoam is placed in acetone, the styrofoam ( large volume of 
    styrofoam for a small volume of acetone ) dissolves and becomes a wet, 
    play-dough like substance that feels cold to the touch.

    This experiment is harmless unless swallowed :-) and should prove to be
    quite interesting to the students.

    The coldness is due to the evaporation of the acetone from your skin 
    (ever use nail polish remover? That's acetone.) The acetone will 
    eventually all evaporate (a 2 inch sphere of this will take a day or two) 
    and the result will be a porous (trapped acetone bubbles) material that 
    can be molded to any shape you wish.

From; David O'Driscoll. University of Central Queensland...

  Hope someone hasn't already done this one, I have been studying for 
  exams so have not been reading all of them.

  The one we use at our high school demos are pH clocks....
  quite good as they are not static displays.

  First, take three or four large (1L) beakers and 3/4 fill them then
  take your favourite pH indicators (ones with good colours), and add a
  few drops to them, then add some dilute sodium hydroxide or something
  to make them slightly basic. Next add a handful of dry ice to each beaker.

  This creates a nice bubbling mixture with good visual effects, what happens
  is obvious (I hope!!!). Some of the CO2 is dissolved in the water, turning 
  the mixture acidic and when the end-point of the indicator is reached the 
  colour changes - sometimes quite dramatically. The kids seem to like it and 
  the chemistry is not too involved.

From:webbb@mbf.UUCP ( Bryan Webb )

  I didn't see the originating message of this thread, but from the
  responses that have made it here, I think this is the kind of stuff
  you might be looking for.  In earlier times, I've done these:

  1) Place a small pile (several grams) of powdered magnesium on a surface
     you don't care about in an environment provided with plenty of
     ventilation.  On top of this, place a couple of grams of powdered
     iodine (well, as close as you can get to it, though that might not
     be crucial).  Now, put a couple drops of water on the iodine ...
     enough to also contact the magnesium ... and stand back.  The heat
     of the reaction vaporizes some of the remaining iodine into a purple
     vapor.

  2) This is pretty dangerous, so be very careful.  Take a couple of grams
     of red phosphorous and place on top of a couple of grams of potassium
     iodate.  Rapidly stand back...  spontaneous combustion.  My experience
     was a time delay of a couple of seconds, but I wouldn't want to count
     on it...  I discovered this accidentally... boy was I surprised.  The
     speed of the reaction may be related to the humidity.

  3) Potassium dichromate is normally bright orange at room temperatures.  If
     it is cooled to liquid nitrogen temperatures, it becomes yellow.  If
     heated, it becomes a deeper red color.  I'm not aware of any other
     inorganics that have this range of color change when the temperature
     is varied.

  4) Ahhh, my favorite...  When I was in high school, I took the 2nd year
     chemistry class that was offered.  We had the resources of the
     school at our disposal, so long as the experiment we wanted to do
     was "in a book".  The book I had was "Chemistry Magic", and described
     an "experiment" where some cotton balls were placed on a fireproof
     surface, a few grams of Sodium Peroxide was placed on top, and then
     you put a drop or two of water that will wet at least a little bit
     of both the peroxide and the cotton.

     It's a long story, but I this experiment worked, at least on other
     cellulose objects like paper towels.  In fact, the fire in the
     metal trash basket was hot enough to melt/burn away the bottom,
     the linoleum underneath, and some of the concrete in the floor.
     The flames formed a "solid" yellow flame and lots of thick white
     smoke (containing NaOH dust).  You really don't want to breathe
     this stuff.  We didn't, anyway :-)

  5) Oh, another thing we did in that class was take the gas outlet used
     for the bunsen burners and direct it into a test tube that was
     partially submerged in liquid nitrogen.  (The whole system was
     sealed.)  The gas condenses into a liquid...  the only problem
     was safe disposal.  It helps to plan ahead! :-)

  [ Note that nuke@reed.edu subsequently supplied the following warning ] 
    " If you decide to try this be aware that liquid nitrogen will condense 
      liquid oxygen in a vessel open to the air immersed in it. Liquid O2 
      forms explosive mixtures with many organics. IF you still want to try 
      it, immerse the tube in the nitrogen and then immediately run the gas 
      in. only do a little bit. How much you get depends on what proportion 
      of weights of low hydrocarbons the gas contains ( I think methane 
      condenses at this temp, but not quantitatively like some stuff, unless 
      there is a large surface area)."

  6) One of my classmates made luciferin [sic].  It's a liquid that
     glows in the dark for about 12 hours.  That was fun too!

  Happy researching!              
  Standard disclaimers apply; I'm not sure my company would have hired
  me if they had the foregoing admissions before them.
  Non-standard disclaimers too: I don't recommend you do any of these things
  either.

From: fred@theory.chem.pitt.edu < fred >

  If you would like to condense out methane gas in a relatively safe way,
  fill a balloon with the gas and THEN condense the gas with liquid N2.
  You can use scissors to cut the balloon, and pour the liquid CH4 into
  a beaker with water in it (notice that it floats, forms ice, etc.) and
  light it.  Only the fumes burn as they mix with atmospheric oxygen.
  This makes a fair "olympic torch."  Wear goggles etc.

From: Larry (Call me "Lefty") C
  
  One that can be safely performed with a long enough spatula.
  Mix Calcium Carbide with any strong oxidizer (KMnO4, NaNO3, even MnO2
  works). Proportions aren't real important here.

  Using face shield, gloves, lab coat and long spatula, drop a SMALL
  amount (say, 1 gram or so) of this into common household bleach.
  Acetylene and chlorine are evolved, which immediately, uh... exploded
  Delightful chlorinated hydrocarbons result, unfortunately :(

15.6  How do I safely perform the Glowing Pickle experiment?

This experiment consists of electrically heating a vegetable that has been 
soaked in a brine solution to conduct electricity. Because this experiment 
involves electricity at dangerous voltages, the experiment should be 
performed on special apparatus under qualified supervision. I'm not going 
to detail the equipment and procedures, as they have been described in
an Journal of Chemical Education article [8]. The experiment has not just
been limited to table salt and pickles, many other vegetables and salts 
that produce different colours have been investigated and described in the
same issue of the Journal of Chemical Education [9]. People intending to 
perform the experiment should obtain both articles.

15.7  How do I make Slime?.

" Slime " is a trademarked commodity obtained by cross-linking guar gum and 
borax, and is marketed by the Mattel Toy Corporation. The slime produced for 
demonstrations is usually made by cross-linking a poly vinyl alcohol (PVA) 
product using borate. The normal method is to carefully prepare a 4% 
mass/volume aqueous solution of a hydrolysed high molecular weight PVA
( >100,000 ) - available from Eastman Kodak. Commercial PVA-based adhesives 
( such as Elmer's Glue ) will also produce a reasonable quality slime, as 
will polymeric materials that have multiple hydroxyl groups and can form
highly-hydrated gels, such as guar gum - but some experimentation may be 
required to ascertain optimum ratios. 

High MW polymers are difficult to dissolve in solvents ( including water ), 
and the best method is to carefully sprinkle the powder over a beaker of 
water that is being gently stirred, and continue gentle stirring until a 
uniform solution with no gelatinous lumps is obtained. 

Any grade of borax ( Na2B4O7.10H2O ) can be used to prepare a 4% mass/mass 
aqueous solution. The slime is made by vigorously mixing the two solutions 
in the ratio of 1-2 parts of the borax solution to 10 parts of the PVA
solution using a paddle stirrer. Details of a suitable procedure for use in
classrooms have been published [10]. A firmer, less messy, slime can be 
prepared from an 8% PVA solution - using equal ratios of the 4% borax 
solution [11].

The properties of slime indicate that the cross-linking mechanism does not 
consist of strong covalent bonds. Borax hydrolyses in water to form a boric 
acid-borate buffer with an approximate pH of 9.

  B(OH)3  +  2H2O  <==>  (B(OH)4)-  +  H3O+    pK = 9.2

The borate ion is tetrafunctional when interacting with the alcohol groups
of polyols, and thus builds the cross-linking structure. PVA has about 1-2% 
of 1,2 diols amongst the remaining 98-99% of 1,3 diols. To obtain the desired 
properties, the bonds between the borate and the PVA must be weak, and it is 
believed they are hydrogen bonds ( shown as ... below ). 

   PVA         Borate          PVA

             H              H
             |              |
       O-H...O        O-H...O
    \ /       \      /       \ /
   H-C         \    /         C-H
    /            B-            \
   CH2         /    \           CH2
    \         /      \         /
   H-C-O...H-O        O...H-O-C-H
    /  |              |        \
       H              H         

Although individual hydrogen bonds are weak, the large number of available
OH groups in highly-hydrolysed PVA will result in a hydrated, 3-dimensional, 
gel, rather than a borate precipitate. The continual breaking and reforming
of the bonds under low mechanical stress, and the large amount of water
incorporated into the gel, are responsible for the rheological properties of
the hydrated gel. Slime can be broken down by reducing the concentration of 
borate by titration with a strong acid, and details of such a procedure have 
been recently published [12].  

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