Bubbles

Bubbles

In past columns, I”ve established my appreciation of classical

music, as well as discussing turbulent and laminar flow in

connection with the knuckleball. Now a reader, Dan from

Hawaii, e-mails me to say that I showed no appreciation for

Bernoulli”s Principle and its key role in the flight of pitched

spheroids. An experienced pilot, Dan tells me that B”s Principle

also explains why an airplane can fly. In particular, the faster a

volume of air moves, the lower its pressure. The airplane wing is

designed so the curvature of the wing causes air to move faster

over the top of the wing than under the wing. Hence, the

pressure is greater under the wing and the airplane is pushed up.

I confess that I still don”t see how that fully loaded 747 gets off

the ground! Dan also applies this reasoning to Nolan Ryan”s

curve ball. I”ll let the reader to figure out which way the ball

breaks.

Dan”s message from Hawaii prompts me to confess that my

musical tastes also run in an opposite vein from classical. In

particular, I”m a sucker for Hawaiian music, particularly that Don

Ho standard “Tiny Bubbles”. The coming millennium raises

questions not only about such serious matters as the Y2K

problem but also about holiday revelry and the availability of

champagne. Of course, a key difference between champagne and

wine, a more plebian libation, is tiny bubbles. Those bubbles

contain carbon dioxide. Why a little CO2 converts ordinary wine

into something worth over $100 a bottle (if you”re a Dom

Perignon devotee) is somewhat mystifying to me. The carbon

dioxide does lend an acidic touch to the concoction since it reacts

with water to give carbonic acid. This acid is one reason things

tend to corrode in humid environments whereas in desert areas

relics from thousands of years ago maintain a remarkable

faithfulness to their original condition.

One key to the proper enjoyment of champagne is the uniformity

of bubble formation and release, promoted by careful washing and

drying of the vessel in which it is served. Preservation of the

bubbly nature of the libation is also a factor for those who prefer

to savor the beverage as opposed to those who down it in one

gulp! Not too long ago, the custom was to serve champagne in a

wide, open glass and those not in the know (like myself) may still

employ these receptacles for festive occasions. However, in the

past couple of decades, the factors affecting the flow of bubbles

out of the host liquid have been recognized. It is now realized

that lowering the surface to volume ratio lowers the rate of loss

of bubbles. Hence, today”s sophisticates serve the bubbly in

relatively tall fluted glasses for a prolonged bubbly sensation.

Those who prefer beer also are acquainted with bubbles. Brian

Trumbore is certainly much more of an expert than I am

concerning this brew. However, I gather that there is a division

of opinion as to whether beer should be served in a manner to

promote a large head and whether the bubbles should be fine or

large. In any event, I”m sure that those imbibers will have noted

at some point, staring at their glasses, that steady streams of

bubbles tend to arise at certain points on the interface between

glass and liquid. Those in a more pensive mood may even

wonder why? The answer, I”m afraid, may show the different

approaches to cleanliness and attention to detail by those who

serve champagne versus your typical barkeep.

In the relatively few bars I”ve frequented over the years, I”ve

always been impressed by the rather casual approach to cleaning

used glasses. It seems that the process generally consists of a

rather cursory dip in some sort of cleaning fluid and perhaps a

quick rinse. Just the opposite of the fastidious champagne server,

as noted above. The origin of the steady stream of bubbles is a

case of nucleation. To form a bubble, the process has to start

somehow and it is common that in all kinds of chemical processes

that there is what is known as an “activation energy” for such

things as bubble formation, the growth of crystals, formation of

rain droplets (possibly from ice crystal), etc. I”ve probably

mentioned this term before but it bears repetition.

This activation energy can be illustrated by a rock sitting in a hole

on the side of a hill. The rock obviously would like to roll down

the hill but it has to get out of the hole to do so. Someone or

something has to use some energy, activation energy, to lift or

push the rock out of the hole, after which the rock rolls down the

hill on its own. Similarly, most processes need this push to get

started. In chemistry, catalysts are substances or things that can

lower this activation energy typically by providing attractive sites

for the process to get started on. A little bit of dirt or residue of

some sort is enough of a catalyst to promote the bubble stream

seen in the beer stein. This process could be called heterogeneous

nucleation; that is, it involves a foreign substance. In the

champagne glass, you may note that the bubbles tend to arise

within the liquid itself. This may be heterogeneous nucleation

involving fine particles not seen or homogeneous nucleation,

spontaneous growth of bubbles in the liquid. Ok, it is possible

that scratches in the glass or mug also provide nucleation sites.

Again, however, the champagne sophisticate will probably be

more inclined to treat his stemware more gently? Lest you think

this piece to be somewhat snobbish in nature, let me assure you

that my wife continually has to remind me to not put our good

stemware in the dishwasher.

We tend to think of bubbles as being innocuous, ephemeral

objects. I imagine most of you have fond memories of dipping a

wire contraption into a solution and wafting bubbles into the air.

In my day, we didn”t have such advanced technological devices

but relied on the bubble pipe. I remember mine as having three

bubble chambers! Actually, in certain circumstances, bubbles are

not at all gentle. The August issue of Discover magazine presents

some nice pictures of bubbles in action and credits Lord Raleigh

in England with showing how bubbles in the ocean can erode a

ship”s propellers. When I was a real chemist, I used to employ

ultrasonic cleaning to keep my glassware spotless. This process

employs bubbles to advantage. The Discover article also

mentions that surgeons use bubbles to liquefy the fat they deftly

suck out of certain portions of the anatomy. Yuk!

How does the bubble accomplish such tasks? When a bubble is

made to expand, perhaps to a hundred times its original size, the

pressure inside the bubble is lowered drastically. Then, when it

collapses back and it”s on a surface, a tiny jet of water is launched

through its center. This tiny jet can be going hundreds of miles an

hour, just the opposite of the old form of torture where a person

is held under a slow drip, drip, drip for hours or days. The fast

moving jet is more like a spear hitting a surface, say of a ship”s

propeller, and the cumulative effect of prolonged pounding by

millions of bubbles can be quite devastating.

Bubbles have even been touted as a means to achieve nuclear

fusion, the Holy Grail as an energy source when oil runs out.

This possibility is based on a phenomenon known as

“sonoluminescence”. When bubbles are exposed to high pitched

sound waves they glow, giving off light. The origin of this light is

the subject of debate in the scientific community. One school

believes that the ultrasound forms a shock wave so concentrated

that the local temperature is a couple million degrees Fahrenheit!

This strips electrons from the gas atoms to form a plasma, which

emits light. This purported high temperature is what leads to the

proposal that bubbles could produce nuclear fusion. Andrea

Prosperetti of Johns Hopkins University proposes instead that our

tiny jet of water slams into the wall of the bubble at 4,000 miles

an hour and “cracks” the water film as if it were a solid. This

energy is then released as light. Prosperetti thinks the

temperature is only about 10,000 degrees Fahrenheit, not

millions. If true, no nuclear fusion. Time will tell.

At Bell Labs many years ago, there was great interest in another

kind of bubble, the magnetic bubble. The magnetic bubble device

involved the magnetization of very small areas in a material.

These areas, known as magnetic domains could be oriented in an

up-and-down direction in thin films of certain garnets. Applying a

vertical magnetic field to these materials causes the areas of

opposite fields to shrink to circles or “bubbles”. By changing the

orientation and strength of the field in a small spot the bubble can

be created or destroyed. I don”t know if memories based on

magnetic bubble patterns are being used much these days. In the

old Bell System, one use was to record certain automated

messages. That voice you heard came from a garnet, a gemstone

in other settings such as on that charm bracelet you or your

spouse wears on special occasions.

Bubbles play a role in another kind of charm. I”m referring, of

course, to Lucky Charms. I myself have never knowingly eaten a

Lucky Charm. Yet, Lucky Charms have been one of General

Mills leading children”s cereals for 35 years. Another article in the

same issue of Discover magazines notes that the charming

component of this cereal is formed by extruding a foam (to me

this means lots of tiny bubbles) consisting of sugar, gelatin and

corn syrup. The extruded material is cut and, as we scientists

would say, heat-treated to form “marbits”, essentially bits of

marshmallow. Well, it appears that the control of the flow of this

compressible foam to engender the formation of a marbit is not a

simple matter. This is especially true for the more complex

marbits developed over the years through evolution. The original

pink hearts, yellow moons, orange stars and green clovers have

mutated into shapes such as blue diamonds, purple horseshoes

and even the Eiffel Tower! I don”t know if Bernoulli is relevant

here.

As I finish this column, I”m listening to what else? Don Ho and

“Tiny Bubbles” on my computer”s CD. Dan from Hawaii assures

me that Mr. Ho is still performing there. Mahalo, Dan. Aloha.

Allen F. Bortrum