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Suit Yourself™ International Magazine #30: Soap Bubbles Part 2 of 2

  

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Suit Yourself™ International Magazine #30 Soap Bubbles, Part 2 of 2: Bubbles

 

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SOAP & BUBBLES, Part 2 of 2: BUBBLES

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This is the 30th in our articles series and I hope this information is helpful!

All previous articles in the series can be found in our Library and in the Magazine Archives.  If you are experiencing problems viewing this newsletter in email, please use one of these links. Upon request, reprint permission and an addendum of substantiating resources are available for all magazine articles. When requesting reprint permission or addenda, please include the issue date and full issue title. All magazine articles are copyright © Debra Spencer, Suit Yourself ™ International. All rights reserved. ISSN 2474-820X. 

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Are you still feeling adventurous? I hope so! The familiar things around us seem so simple that they scarcely need explaining.  Yet even a mild curiosity about them reveals they're more than they seem, and always leads to surprises. 

This is the second of two parts:  SOAP was part one, and BUBBLES is part two. At the end of this article, I include recipes for making your own bubble mixture, links for large and unusual wand constructions, and other useful resources. 

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        Les bulles du savon; Magicien et chatons.

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SOAP BUBBLE REQUIREMENTS

RECIPES, wand constructions, and resources, are at the end of this article. Here are the most important points to consider when blowing large bubbles and using various bubble mixtures.

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Bulles de savon, Bande de Praxinoscope, Emile Reynaud, 1876.

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LOCAL CONDITIONS:  Many factors influence being able to make bubbles!  There is no one-size-fits-all-locations bubble mix, nor one-size-fits-all-locations-on-all-days.  The larger the bubble, the more vulnerable it is.  

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Two children conducting an effervescence bubbling experiment.

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Whether or not a bubble forms, or lasts, depends on lots of variables, including but not limited to surface and height humidity, altitude, pressure, wind, smoke, ambient temperature, ground cover, and air particulates. 

Bubble solutions may work well in all sorts of conditions, and then inexplicably to you, not work on a day when conditions seem ideal. The mixture may be unable to form a bubble, or the bubbles may be short-lived, even when the humidity and temperature seem conducive. Don't throw out your bubble mixture!  Try it again in a few days. It may well work just fine later, and you could get great results. If you're at all serious about this as a hobby, you will want to keep a log and take good notes, so you can track variables, results, and conditions over time. 

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Lana Del Rey faire des bulles de savon.

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UNLESS IT'S YOURS, KEEP OFF THE GRASS.  It's generally agreed that blowing big bubbles over grass tends to work better than over pavement or dry ground.  On hot and dry days, big bubbles can sometimes be made in a grassy area even when nothing at all happens on a paved area a few hundred feet away. 

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Even a 3-year-old can make giant bubbles with a tri-string wand.

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You should not, however, blow large bubbles, or even lots of little bubbles, over any lawn grass unless you want to kill the grass. Soap bubbles landing on grass kills grass, and leaves a bare patch, even if you hose down the area with water when you're done. This is always a tell-tale sign; you've been there, making bubbles.  I've not seen this possibly undesirable side-effect mentioned anywhere else but here.  

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Home Improvement by a tiny girl with a giant bubble on her yard lawn.

 

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Humidity is required for bubble blowing, and if you blow bubbles in a dry climate, the air humidity may be more conducive to bubbling while standing on vegetation than on concrete or dry ground.  However true this may be, be mindful of the trade-offs, and the consequences of your actions. Tree cover is problematic due to all the variables; meadows are better.

High humidity is great for blowing big bubbles. High temperatures and winds are not. Even with high humidity, if the temperature is too hot, bubbles might not last more than an instant. Winds are self-explanatory.  

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Blowing bubbles whilst submerged under water. Apnéiste David Helder fait des Bulles sous -marines, Parfaites!

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By "giant bubbles" I mean bubbles that are two meters in diameter or larger.  The general conditions required to make bubbles that size are cool temperatures between 45F to 60F or 7C to 15C, and 80% RH high humidity, or higher. 

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 Bubble freezing at 26 Centigrade as soon as it is blown. Une bulle de savon qui gèle avec etoiles; une bulle de savon glacée.

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With these conditions, a bubble two meters in diameter or larger might last 30 seconds or longer, while the same bubble mixture blowing a bubble under less humidity, or at a higher temperature, might last only 10 seconds. Under 20% humidity, it's very difficult to bubble anything large.  Once the humidity is over 50%, large bubble stability improves.

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La formation d'une énorme bulle de savon Bulle de savon gigantesque

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SURFACE TENSION

Nature searches continuously for the most efficient use of energy, the lowest energy configuration. One way this evinces is via surface tension; a fluid surface has an elastic tendency helping it spread over the least possible surface area. Being 'elastic' means having the ability to recover an original configuration, size, or shape after having been stretched, bumped, bounced,  tackled, tossed, deformed, flexed, strained, or otherwise altered. One synonym for 'elastic' is 'flexible'. 

We've had bubbles at home ever since the 1940's when the Chicago company Chemtoy began selling bubble solution to the public. 

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Une bulle de savon sur cactus. Ouch!

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What is really going on is that a fluid surface, like soapy water, is sensitive to any interaction; it's variable. And as a variable itself, it's sensitive to, and responds to, changes in any other variable with which it interacts.  J. Willard Gibbs showed that when the surface of a soap-water film is disturbed, the concentration of soap changes, in just such a way that the change in surface tension acts to stabilize the surface. This happens in different amounts with different substances and concentrations, of course. In favorable cases, a water film becomes quite stable and permanent, so that bubbles will persist. Surface action to stabilize them is important.

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Bouncing droplet: watch how a drop of water, dancing on a water surface, is subjected to vibrations.

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Neither a strengthening of surface tension, nor the formation of an actual surface film, is responsible for soap bubbles. Remember, there is a reason alkaline solutions are effective at removing grease. All soaps have a charged end that attracts water molecules strongly, and a hydrocarbon end that attracts molecules similar to itself which are not soluble in water. Hydrophilic water-loving molecules bind to one end, and hydrophobic water-fearing molecules (such as those of grease, oil, and dirt in general) will bind to the other end. 

When a soap molecule migrates to the surface of water, it finds itself in a low-free-energy environment with its' charged end held tightly by water molecules, while its' hydrocarbon end is bristling outwards. The presence of these soap molecules at the surface changes the surface tension; they're usually reducing it. For soap in water, J. Calvert states that the surface tension is reduced to about 38% of its' value in pure water! 

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A charming animation illustrating a gravity fed pet water cooler, incidentally also illustrating static pressure, barometers, and fluid mechanics.

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Static pressure chicken barometer, the same principle as the gravity fed pet water cooler, demonstrating fluid mechanics.

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The ability to make a foam (suds) is often used as a criteria for judging the effectiveness of a washing solution. However, some materials are effective detergents without being able to make stable films, and they're used where foam would be a nuisance, for example, in a dishwasher. 

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Cascade dishwasher detergent, advertisment.

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SURFACE TENSION SHAPES

A soap bubble floating in air forms a sphere.
A ring dipped in a soapy solution will create a plane surface soap film inside the ring.
A soap bubble between 2 rings can be stretched apart until it takes the shape of a cylinder.
The cylindrical form of the soap bubble is stretched still further to give the shape of a catenoid.
A bubble of oil stretched a proper distance between two rings will cause the lower portion of the cylindrical shape to bulge (due to gravity, surface tension, etc.) thereby forming the unduloid structure.

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Drawing showing five of the six surfaces of revolution formed by a film of oil or soap. The nodoid is not shown because only sections of it exist in nature.

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A soap plane film can be studied easily, when made suspended on a wire frame, as C. V. Boys explains (in Soap Bubbles; Their Colours and the Forces that Mould Them (New York: Dover, 1959)). This film consists of two surfaces, with water between. 

If the film is held vertical, the water will drain under the force of gravity from top to bottom, but only very slowly, since the film is thin, and viscous forces are dominant. This demonstrates Gibbs's explanation very well (that when the surface of a soap-water film is disturbed, the concentration of soap changes in just such a way that the change in surface tension acts to stabilize the surface). 

If the surface tension were not affected, but constant instead, a small element of film would have equal forces acting at top and bottom, and so would fall with the acceleration of gravity, which is certainly not what we observe. Therefore, the total surface force in the upper parts of the film is enough greater than that in the lower parts to overcome the weight of the film. This is a very small difference, but it's essential to the stability of the film.

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Iridescence in a soap film that is held within a frame creating a plane field, courtesy of Wikipedia.

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GLYCEROL

Of course, the water does drain out by gravity, thinning the film. Slowing this action is the reason we usually add glycerol when making bubble mixtures, to increase the viscosity.  Glycerine makes the bubbles last longer. Evaporation is what kills "em. You can buy 16 oz. bottle of vegetable glycerine at the health food store for a reasonable cost and one should be enough. See the recipes in the References at the end of this article.

Glycerol is also called glycerine or glycerin; it's a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic.

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Glycerine product, labeled "Pure vegetable glycerine is an outstanding moisturizer and skin cleanser that also provides softening and lubrication; it's easily soluble in water and has a long shelf life, and is an all-natural product derived from palm or vegetable oil."

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COLORS

One of the beautiful aspects of soap bubbles are their iridescent colors.

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Macro-photograph of a soap bubble, courtesy of Wikipedia.

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The colors first begin to appear when the film thickness is less than about 1 μm; first green and magenta, then the brighter colours of lower orders, including reds, blues and one good yellow (or 'straw')  color. 

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Colorful interference on a soap film, with commentary, courtesy of Wikipedia. Une lame d'eau savonneuse.

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At about 0.1 μm, there is a white, but for films thinner than  0.1 μ,  the color approaches black (film invisible) as the light from front and back cancel. 

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Susan Scwartzenberg, Exploratorium image of soap film and light interference.

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These colors make soap bubbles attractive but they also serve to indicate the thickness of the films. 

There is a difference of π (pi, 3.14159...) in the phase of the reflected light, between rare-to-dense and dense-to-rare reflection, just as in the case of Newton's Rings (which, in white light, show the same colors).  As a soap bubble thins as the water drains and evaporates, the colors appear first on the upper parts, and a drop of water grows at the bottom. A black film is very fragile; soon after this appears, the bubble bursts, as the two sides of the film cannot be held apart.

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Soap film showing light interference as a function of membrane thickness. When the frame holding the bubble is held in a vertical position, you'll see the colors change as the film grows thinner. Usually, shortly before bursting, a part of the film will become black. As the light from front and back cancel, the color approaches black (film invisible).

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Newton's rings occur when an interference pattern is created by the reflection of light between two surfaces: a spherical surface and an adjacent touching flat surface. You can read more about them here:  
https://en.wikipedia.org/wiki/Newton%27s_rings  
and in the wonderful book " Light and Colour In The Open Air"  by Marcel Minnaert (London: Bell and Sons, 1940, Reissued by Dover, 1954 and by Bell, 1959). English translation by Kremer-Priest of De Natuurkunde van het Vrije Veld (Zutphen: 1937). Dewey Classification: 535.

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SHAPES

A soap film will find its minimum surface, taking the most efficient shape that it can. In the References below, I've included links to instructions for making your own weird and wonderful bubbles using shaped bubble wands.

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Diagram from Columbia University Engineering, labeld "Double Bubbles Sans Toil and Trouble Discrete Circulation-Preserving Vortex Sheets For Soap Films and Foams."

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A cylindrical bubble with no ends, so that the pressures on the two sides of the film are equal, assumes the shape of a catenoid of revolution. 

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Electrical towers jumping robe with a catenoid power cable.

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The curvature of a catenary is equal to the reciprocal of the distance from an axis. This distance will be the radius of curvature of the film in a horizontal plane, and also the radius of curvature in the vertical plane, so that the net curvature will be zero. A film on a spiral frame with a central axis is a particularly attractive surface of zero curvature.

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A shaped soap film, attached to twin circular rings, will take the shape of a catenoid of revolution.

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Soap films will intersect along lines with three films making equal angles of 120° with each other, adjusting themselves so that this occurs.  This is rather like a caltrop.

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Diagram, bulles de savon jointives croisement de trois nappes, vers un univers non homogène.

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If four films happen to intersect at a line, they will move so that only three meet on any line. 

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Bulles de savon jointives animé.  Surface tension in soap bubbles.

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If two bubbles intersect, they meet along a circle. The centres of curvature of the two bubbles and of the surface separating them lie on a straight line, and obey the relation 1/r + 1/r' = 1/r", where r is the radius of the larger bubble, r" the radius of the smaller, and r' the radius of the common film. Relations like this are also familiar from optics and from electric circuits, as well as from projective geometry.

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Bulles de savon jointives; micro delle bolle al macro delle schiume. Various surface tension combinations in soap bubbles.

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When two bubbles collide, they often remain separate and bounce off one another. This demonstrates that only the hydrocarbon tails of the surface soap molecules come into contact, which does not break the film, not the strongly attracting water molecules.

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Elastic collision of masses in a system with a moving frame of reference, courtesy of Wikipedia.

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There is also a thin air film that must be squeezed out. Such air films often protect a water droplet from a hydrophilic surface, and it rolls like a ball bearing.

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A round bar of soap, rolling. Le pain de savon fait son grand retour et devient en un tour de main.

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BUBBLES UP YOUR NOSE:  Effervescence and Beer

Bubbles in an effervescent drink or boiling liquid have only one surface layer and either break when reaching the surface, or form an actual bubble there. These are the bubbles of the "bubble chamber" in which ionizing radiation triggers the evolution of gas in a supersaturated solution. When you move a glass of beer suddenly, the drops seem to have negative mass, like the holes in a semiconductor. 

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Effervescence in a stein of beer.

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Lava lamps contain a bubble of coloured material that is immiscible with its surroundings, and slightly heavier (more dense) than the surrounding liquid when cool. It sinks to the bottom, where it is heated by the illuminating lamp, making it become lighter, whereupon it languidly makes its' way upwards. 

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Diagram of lava lamp liquid motion.

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Bubbles and froths are used in the separation of minerals. The surface-active agents are specially tailored to attract the minerals of interest, either the ores or the gangue. The froth, carrying the mineral of interest, is then easily separated by skimming it off.

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ADDITIONAL RESOURCES 

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BOOKS & ARTICLES

Encyclopedia Brittanica, 14th Edition, 1929.

Calvert, J.B., Introduction to Boron http://mysite.du.edu/~jcalvert/phys/boron.htm

Wikipedia Borax: https://en.wikipedia.org/wiki/Borax

C. V. Boys, Soap Bubbles; Their Colours and the Forces that Mould Them (New York: Dover, 1959).

Marcel Minnaert, Light and Colour In The Open Air (London: Bell and Sons, 1940, Reissued by Dover, 1954 and by Bell, 1959). English translation by Kremer-Priest of De Natuurkunde van het Vrije Veld (Zutphen: 1937). Dewey Classification: 535.

Cyril Isenberg; The Science of Soap Films and Soap Bubbles

J. R. Partington, A History of Greek Fire and Gunpowder (Cambridge: Heffer & Sons, 1960). pp. 306-309.

E. F. Degering, ed., Organic Chemistry (New York: Barnes & Noble College Outline Series, 1951). Chapter XXX, pp. 280-284. 

R. L. Bates, Geology of the Industrial Rocks and Minerals (New York: Dover, 1969). pp. 393-401.

L. Pauling and R. Hayward, The Architecture of Molecules (San Francisco: W. H. Freeman, 1964). Illustrations 32-36.

Oil Paint Saponification
https://www.thoughtco.com/definition-of-saponification-605959

Saponification,  Anne Marie Helmenstine, Ph.D
https://en.wikipedia.org/wiki/Saponification

Silvia A. Centeno; Dorothy Mahon (Summer 2009). Macro Leona, ed. "The Chemistry of Aging in Oil Paintings: Metal Soaps and Visual Changes". The Metropolitan Museum of Art Bulletin. Metropolitan Museum of Art. 67 (1): 12–19. JSTOR 40588562. Pages 12-19.

Fleury, Paul (1912). "Manufacture And Treatments Of White Zinc". The Preparation and Uses of White Zinc Paints (1st ed.). London: London, Scott, Greenwood & son. "and although Petit declares this theory false, it is none the less on it and on its data that he bases his system of manufacture of hydrated white zinc, of which he is the inventor that is to say, the saponification of the oil, or the formation of metallic salts, dissolved therein"

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WANDS


    
    Making giant bubbles.
       

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    Results of using a flower wand with 6 concentric openings.

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    Constructing joined minimal surface configurations by using two bubble wands. Bulles de savon jointives. 

Instructions for making a tetrahedron dipping wand:
http://www.m2solids.com/stirtet.html

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How to make soap bubble WANDS in all the platonic solid shapes:
http://www.m2solids.com/wb/geo/geo_frames.html

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        Diagram of minimal surfaces for the various shapes of soap films.

 

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APPENDIX I: SOAP BUBBLE RECIPES


A recipe I've tried and used, from http://www.m2solids.com/soap/soapdemo.html

"The solution for our demonstrations consists of dishwashing soap, glycerine and distilled water (especially if your local water is hard). This will help to make the bubbles last longer. To dip the models, hold by the wire nuts. Keep fingers out of the solution. Otherwise, after a while the oil from the skin will tend to ruin it."
"For every gallon of distilled water (distilled is best):
add 6 tablespoons of dishwashing liquid (regular Dawn or Joy work well).
Glycerine makes the bubbles last longer. Evaporation is what kills "em. 
I get a 16 oz. bottle of vegetable glycerine at the health food store for a reasonable cost. One should be enough."

MY NOTE: I find Dawn works a little better than Joy but these really are the best brands for this job.

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    Soap bubbles on a triangular prism frame.

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J. Calvert's recipe from http://mysite.du.edu/~jcalvert/phys/surftens.htm


A recommended bubble mixture is 19 ml of sodium oleate (soap) in 750 ml of water, made up to 1000 ml with glycerol. For a good bubble mixture, the water should be clean distilled or at least deionized water.

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    Soap bubbles on a cubic frame by Paul Rapson. 

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Wikipedia recipe (I have not tried this one) from https://en.wikipedia.org/wiki/Soap_bubbles


The composition of soap bubbles' liquid has many recipes with slightly different ingredients. The most common one contains:
2/3 cup of dishwashing soap
1 gallon of water
2/3 tablespoon of glycerine
Because of the presence of dishwasher soap, it's not so uncommon for children to contract dermatitis on face, hands with consequences as rashes, swelling of the eyes, vomiting and dizziness. 

MY NOTE:  This is only true if anyone, not just children, is not instructed in how to carefully and properly handle any substance, including what they usually eat for breakfast. It can happen to anyone paying insufficient attention while doing anything at all.  Anyone who does not know how to properly wash their hands, and touches their face constantly, especially while playing outside, will very likely get contact dermatitis, and unless they are a toddler, it will be entirely their own fault. This is just a stupid warning. 

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    Bébé qui connait sa première douche de bulles de savon.

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APPENDIX II: FORMULA FOR THE PRESSURE IN A BUBBLE

 

J. Calvert's article on bubbles and soap derives a formula for the pressure in a bubble from statics. For the sake of completeness here, and because one doesn't know the future stability of online links, I'm quoting his 3 succinct paragraphs here.  He also points out that bubbles can have positive buoyancy if filled with a light gas, and explains that since surface tension acts like a surface film, a jet of water is subject to the same pressure instability, and breaks into droplets.  

This is available at http://mysite.du.edu/~jcalvert/phys/bubbles.htm

Wikipedia's article on surface tension derives this differently, in the sub-section titled "Thermodynamics of soap bubbles". There the writer states "The pressure inside an ideal (one surface) soap bubble can be derived from thermodynamic free energy considerations."

For that approach, see  https://en.wikipedia.org/wiki/surface_tension.


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    The pressure inside a soap bubble is greater than that surrounding the soap bubble due to surface tension in the soap film.


Calvert:
A formula for the pressure in a bubble can easily be derived from statics. The tension in the film, (2πr)(2γ), where γ is the surface tension, must equal the total force πr2p, where p is the difference in pressure on the two sides. Therefore, p = 4γ/r. For a sodium oleate solution, Rayleigh found γ = 25 dyne/cm. In the case of a nonspherical surface with principal radii of curvature r and r' (these are the maximum and minimum radii, which will be at right angles), p = 2γ(1/r + 1/r'). For a 1 cm radius bubble, p = 100 dy/cm2. If the film is 1 μm thick, the bubble will weigh about 1.2 dyne, or 1.3 mg. It is no wonder that such a light object can float on the slightest breeze. Bubbles can have positive buoyancy if filled with a light gas. Even methane, M = 16, will give a 1 cm radius bubble a lift of 3 mg, enough to float it. If a small bubble and a large one are connected, the small bubble will blow into the large one, so that large bubbles grow at the expense of small ones, something that is easily observed in foams.

A cylindrical bubble can be made by pulling on the ends of an originally spherical bubble and adjusting the pressure within it until the sides are cylindrical. The pressure inside a cylindrical bubble of radius r will be p = 2γr (since r' = ∞), the same as inside a spherical bubble of twice the radius. As long as the length of the cylindrical bubble is less than 2πr it is stable against small displacements. However, a longer bubble will break into two spherical bubbles, one on each support. Since the surface tension acts like a surface film, a jet of water is subject to the same instability, and breaks into droplets. Boys explains and illustrates these matters very well. Among other things, he shows how collisions between droplets cause the scattering of a water jet.

A cylindrical bubble with no ends, so that the pressures on the two sides of the film are equal, assumes the shape of a catenoid of revolution. The curvature of a catenary is equal to the reciprocal of the distance from an axis. This distance will be the radius of curvature of the film in a horizontal plane, and also the radius of curvature in the vertical plane, so that the net curvature will be zero. A film on a spiral frame with a central axis is a particularly attractive surface of zero curvature.

http://mysite.du.edu/~jcalvert/phys/bubbles.htm
 

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I sign our magazine articles "See Into The Invisible". Thanks for reading.

Best Wishes, 
Debra Spencer

All Content is © Debra Spencer, Suit Yourself™ International. Technical Library FAQ Index ISSN 2474-820X. All Rights Reserved. Please do not reproduce in part or in whole without express written consent. Thank you.
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All Content is ©2019 Debra Spencer, Appanage™at www.suityourself.international Suit Yourself ™ International, 120 Pendleton Point, Islesboro Island, Maine, 04848, USA 44n31 68w91 Technical Library FAQ Index ISSN 2474-820X. All Rights Reserved. Please do not reproduce in part or in whole without express written consent. Thank you.

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All Content is ©2019 Debra Spencer, Appanage™at www.suityourself.international Suit Yourself ™ International, 120 Pendleton Point, Islesboro Island, Maine, 04848, USA 44n31 68w91 Technical Library FAQ Index ISSN 2474-820X. All Rights Reserved. Please do not reproduce in part or in whole without express written consent. Thank you.
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