Bubble Snouts

OK, not sure this is a demo so much as just a cool thing to do with bubbles. Simply use a rubber band to stretch terrycloth fabric over the wide part of a funnel made from the top of a 1 liter soda bottle.  Dip the fabric into bubble solution and blow into the narrow part of the funnel (do not inhale!).  The air pushes through the terrycloth to produce a stream or snout of many small bubbles. 

Geology Demo - Seltzer Popper Volcanoes

These demonstrations are a twist on the classic homemade volcano, in which vinegar and baking soda chemically react in a model of a volcano to produce sodium acetate, water, and carbon dioxide gas. The carbon dioxide bubbles up out of the model to produce bubbling “lava” which oozes out of the “volcano”.  The picture below shows the same reaction in a soda bottle (food coloring and dish soap have been added to make the lava flow more impressive).

But what about the volcanoes with more explosive eruptions?  Here we adapt another classic demonstration involving film canisters and Alka-Seltzer tablets. Wear eye protection.  First lay down a sheet of plastic to make cleanup easier. Place a film canister into a clay volcano, setting the lid aside for now.  Fill a milk cap with glitter. Fill the film canister halfway with water, with maybe a little dish soap and red and yellow food coloring for a “lava” effect.   Break a tablet of Alka-Seltzer in half (any more that is wasted).  Make sure everything is ready and the area is cleared out around the volcano.   

Then, QUICKLY add the half-tablet of Alka-Seltzer to the film canister, cover the canister tightly with the lid, place the milk cap full of glitter on top of the lid, and take a step back (NEVER stand over the lid).  The citric acid and baking soda in the tablet dissolve in the water and chemically react to produce sodium citrate, water, and carbon dioxide gas. The gas pressure builds up in the capped film canister until the lid pops off, scattering the glitter and sending reddish suds oozing down the side of the volcano. 

   
We can also use the Alka-Seltzer tablets to illustrate the effects that size has on processes.  If the half-tablet that is added to the film canister is first broken into small pieces, it will dissolve much more quickly in water to react and produce carbon dioxide gas.  The result is that, with all else equal, a popper volcano with the broken-up half-tablet will pop more quickly after loading than one with an intact half-tablet.  This illustrates how processes can proceed more quickly at smaller scales.  For example, many people are studying how making things really small (at the nanoscale) with lots of surface area can speed up chemical reactions.  

Another note:  We have also noticed that a film canister fits into the top of a milk jug with just a little widening (we also colored the jug piece with permanent markers).  This seems to be very inexpensive way to make a waterproof volcano cone without having to use modeling clay. 

Reference: Johnsen, N. V.  Nano Effervescence.  http://www.exo.net/~jillj/activities/nanoeffervescence.pdf (accessed January, 2012).

Geology Demo - Liquid Nitrogen Base Surge and Downburst

CAUTION: Liquid nitrogen is very cold and presents a serious frostbite hazard, especially if it gets trapped against your skin (e.g.in your clothing). Additionally, gaseous nitrogen occupies more volume than the same quantity of liquid nitrogen. Gaseous nitrogen produced quickly enough in sufficient quantities can displace oxygen from the air. Containers filled with liquid nitrogen could fail without warning due to thermal shock or gas pressure. Protect yourself accordingly.

Base surges and downbursts occur when dense gases sink rapidly down through less dense gases and spread outward upon impacting the ground. Base surges are clouds of gas and dust that move along the ground away from a volcanic eruption or a nuclear explosion. It is often produced when a column of these clouds collapses to the ground. Downbursts, and smaller microbursts, occur when cold air sinks to the ground from a thunderstorm. A similar phenomenon seems to occur during the filling of a typical 4 liter Dewar flask with a relatively narrow neck from a liquid nitrogen supply line. As the liquid nitrogen (boiling at 77 K) first passes through the supply line and into the flask at room temperature (about 298 K), the liquid nitrogen flashes into pressurized vapor. The vapor rushes out of the Dewar flask, creating a column of cool nitrogen vapor and condensed water droplets. As the supply line cools, liquid nitrogen actually makes it into the Dewar flask. The liquid nitrogen boils away less rapidly and the pressure forcing the nitrogen vapor up from the Dewar flask decreases. The cold dense vapor column then collapses down and spreads across the ground, resembling a base surge or a downburst.

References:

Clark Johnson. Base Surge. http://www.geology.wisc.edu/~g111/Terms/base_surge/base_surge.htm (accessed June, 2006).

Denton County, Texas. Downbursts. http://www.co.denton.tx.us/dept/main.asp?Parent=82&Link=84#Mistaken (accessed June, 2006).

BELOW: A liquid nitrogen base surge: (FIRST) Formation of the column of cool nitrogen vapor and condensed water and (MIDDLE) collapse of the column.  (LAST) Surge of air moving out from a thunderstorm rain column near Carlsbad, NM, in June, 2012.

Geology Demo - Liquid Nitrogen Geyser

CAUTION: Liquid nitrogen is very cold and presents a serious frostbite hazard, especially if it gets trapped against your skin (e.g.in your clothing). Additionally, gaseous nitrogen occupies more volume than the same quantity of liquid nitrogen. Gaseous nitrogen produced quickly enough in sufficient quantities can displace oxygen from the air. Containers filled with liquid nitrogen could fail without warning due to thermal shock or gas pressure. Protect yourself accordingly.

 

A geyser is a steam and water eruption (spring) water coming into contact with a very intense underground heat source. Certain geysers are periodic, but most of them occur in periods that vary from seconds to hours. For a geyser to occur there has to be heated rock underground, an abundant source of water, and a "plumbing" system consisting of channels in the ground that conduct water to and up away from the heated rock. Water flowing into the plumbing system is heated many degrees over its boiling point. Eventually the pressure of the heated water increases to the point that water and steam will be rapidly ejected into the air. Eventually, the plumbing system will restock itself with water and repeat the process again.
Liquid nitrogen geysers have been observed on Neptune's moon Triton (these are believed to erupt via a different mechanism than here on Earth). A small liquid nitrogen geyser can be made by placing a meter-long copper tube partially into a pool of liquid nitrogen. The tube at room temperature is inserted into the Dewar flask that contains some liquid nitrogen. Since the boiling point of liquid nitrogen is 77K and the tube is approximately room temperature (298 K), liquid nitrogen entering the tube will quickly vaporize, pushing vapor and liquid nitrogen up the tube into the air for a brief time.

Reference:

Wikipedia: Geyser. http://en.wikipedia.org/wiki/Geyser (accessed June, 2006).

BELOW: A liquid nitrogen geyser. The copper tube shown here is 120 cm long with an inner diameter of 1.4 cm.