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The history of soapmaking

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[The Sumerians] used a slurry of ashes and water to remove grease from raw wool and cloth so that it could be dyed. Sumerian priests and temple attendants purified themselves before sacred rites, and in the absence of soap, they too probably used ashes and water.

The slippery solutions clean because the alkali reacts with some of the grease on an object and converts it into soap. The soap then dissolves the rest of the dirt and grease. The more grease and oil dissolved by the alkaline solution, the more soap there is and the better the mixture cleans.

People would inevitably notice this because they used the slippery solutions repeatedly until the solutions lost their potency. Thus, the Sumerians, realising that a little grease improved the performance of the alkali, proceeded to make soap solutions directly by boiling fats and oils in the alkali before using it for cleaning. Specific directions for making different kinds of soap solution have been found on cuneiform tablets.’

- H. W. Salzberg, From Caveman to Chemist , American Chemical Society, Washington DC, 1991

Soaps were not to be found in early Ancient Roman baths; even Cleopatra was confined to essential oils and fine white sand (as an abrasive) for cleansing.

Ancient Roman legend has it that the word ‘soap’ is derived from Mount Sapo, where animals were sacrificed, and from where rainwater washed a mixture of melted animal fats (tallow, a foul-smelling substance also used to make candles) and wood ashes into the River Tiber below. There, the soapy mixture was found to be useful for washing clothing and skin.

By contrast, Pliny the Elder, whose writings chronicle life in the First Century AD, describes soap as ‘an invention of the Gauls for giving a reddish tint to the hair’. He even gives recipes for making soap, indicating that it was used ‘to disperse scrofulous sores’. It’s difficult to imagine the smell and discomfort associated with its early use.

Exactly when soap arrived on British shores isn’t clear, although we probably learnt the art of soapmaking from the Gauls. In the Middle Ages, artisans independently worked away at crafts like dyeing and soapmaking. Secret recipes, refined by trial and error, were handed down from master to apprentice, and from father to son. Soap was largely developed for use in the cloth industry, to prepare wool for dyeing, and not for personal hygiene.

By the 13th century, soapmaking in Britain became centred in large towns like Bristol, Coventry and London, with each making its own variety. Large areas of British woodland were destroyed to meet the growing demand for wood ashes, causing a country-wide shortage of winter fuel. Italy, Spain and France also became early soap-producing centres.

Plentiful supplies of high quality olive oil and barilla ashes (from which they made their alkali) made regions like Castile in Spain and Marseilles in France renowned for the quality of the soap they produced. The method used throughout the Middle Ages and up to the 17th century consisted of boiling olive oil (in Mediterranean countries) or animal fats (in Northern Europe) with an extract of plant ashes and lime.

In the 16th century, three broad varieties of soap were available: coarse soap made from train oil (extracted from whale blubber), sweet soap from olive oil and speckled soap from tallow. For a while, the making of speckled soap was forbidden, not simply because it smelt so bad but because its manufacture would deplete the nation’s tallow reserves, thereby driving up the cost of candles beyond the reach of the poor.

As a result, soap was heavily taxed and became a luxury item only readily available to the rich. Eventually, market forces virtually eliminated sweet and speckled soaps, despite the difficulty of making an odourless coarse soap. Understandably, it wasn’t long before perfumed soaps were introduced from Italy.

In the early 17th century, chemists and soap manufacturers began to address the problems confronting the soap industry. Their combined efforts over the next 150 years produced an understanding of the chemistry involved, resulting in greater manufacturing efficiency, a wider variety of more fragrant and colourful solid (and liquid) soaps, and milder soaps for use on the finest lace and linens. The industry thrived.

The Industrial Revolution brought steam-power and mechanical energy, leading to economies of scale and even greater production efficiency under more readily controlled conditions. The combination of better soaps and advances in plumbing, including running water and drainable bathtubs, made bathing the social norm.

In 1853, Gladstone repealed the British tax on soap that had been imposed centuries earlier and the industry flourished. It was made even more profitable by Nobel’s invention of dynamite in the same year: dynamite was made from the explosive nitroglycerine, a chemical derived from glycerine, hitherto a waste product of soapmaking.

In the United States, one company, B. J. Johnson, produced a soap made entirely from palm and olive oils. The soap was popular enough to rename their company after it – ‘Palmolive’ (today’s Palmolive soap is not, however, the same as the original).

Today, soapmaking is a highly competitive, science-led, multibillion-pound industry whose product is a long way from the crude, evil-smelling soap of the Middle Ages – thank goodness!

In 1789, Cornish barber Andrew Pears opened premises in Soho, London (then a fashionable residential area), for the manufacture and sale of rouges, powders, and other preparations used by the rich to cover up the damage caused by the harsh soaps of the time. Pears was one of the first to recognise the potential of a purer, gentler soap that would be kinder to their fashionable but delicate alabaster complexions.

The upper classes associated tanned faces with the lower orders who worked outdoors. The manufacturing process he perfected, using purer ingredients, paying closer attention to each stage in the process, and adding a delicate perfume of flowers, remains substantially unchanged to this day.

In the 1880s, William Lever leased a chemical works in Warrington, where he experimented with different ingredients to manufacture soap. He settled on a formula of palm kernel oil, cottonseed oil, resin and tallow, and named it Sunlight soap.

It was an immediate success, forcing the company to move to a new and much larger factory by the river Mersey in Cheshire. People were now buying a particular make of soap rather than a type.

Like some other Victorian industrialists, Lever was a philanthropist. He built a model town to house his workers, calling it Port Sunlight after the soap it produced. Port Sunlight went on to develop other products like Lifebuoy carbolic soap, Sunlight soap flakes and Vim, each of which became a household name.

Book 3 of ST240, Our Chemical Environment , The Open University

Gibbs F.W., ‘The history of the manufacture of soap’ , Annals of Science, vol. 4, pp. 169–90, 1939

Lucock Wilson R., Soap through the Ages , a Progress Book published by Unilever Limited

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The History of Soap

Published April 15, 2020

That bar of soap you’re so rigorously scrubbing your hands with multiple times a day is one of the most ancient consumer products you use, with one caveat: A lot of modern soap isn’t soap at all.

Soap likely originated as a by-product of a long-ago cookout: meat, roasting over a fire; globs of fat, dripping into ashes. The result was a chemical reaction that created a slippery substance that turned out to be great at lifting dirt off skin and allowing it to be washed away.

Written recipes for soap date back nearly 5,000 years, with variations from Mesopotamia, Egypt, ancient Greece, and Rome. Here’s a method from an alchemist’s manual published sometime between the eighth and 10th centuries (even wizards who supposedly spent most of their time trying to turn lead into gold needed to do so with clean hands, apparently).

“Spread well burnt ashes from good logs over woven wickerwork … and gently pour hot water on them so it goes through drop by drop.… After it is clarified well, let it cook.… Add enough oil and stir very well.” The age-old soap recipe comes from an astonishing how-to guide called the Mappae Clavicula, which roughly translates from Latin as “A Little Key to Everything.” The alchemist’s recipe for soap calls for either olive oil or beef tallow. Tallow, or animal fat, along with lye, remains a basic ingredient of soap. Fat reacts with lye—a substance made in ashes that can be pretty toxic, which is why soap makers need to wear protective gear—in a process called saponification. The word possibly comes from the proto-German saipo, which means “to strain”; the Latin sebum, which translates as “grease”; or from Mount Sapo, an Italian mountain whose location is now lost to history. (The story is that the drippings and ashes from the cook fires of the gods rolled down the hill and were discovered by filth-encrusted Romans.)

Modern soap makers—at least those working in small, artisanal operations—use the same techniques. The saponification process yields a thick slurry. As it solidifies, fat neutralizes the caustic lye. “After 48 hours, you’ve got soap,” says Natalie Wong, of Vancouver, British Columbia’s Pep Soap, which offers both vegetable- and animal-fat-based bars.

The slipperiness of soap lowers the surface tension of the water you’re mixing it with. Rubbing your hands together while washing allows dirt to temporarily bond with the water and soap and get washed away. The same process occurs with most viruses and bacteria that might be lingering on your hands. Soap doesn’t kill these bugs—it slips them up, lifting them from your skin, mixing them with water, and sending them down the drain. This chemical and mechanical reaction makes soap and water more effective, in general, than waterless sanitizing gels.

In America, the soap industry got started because of bacon—and candles. Lighting is an integral part of the history of commercial cleansers, because both have traditionally been made from animal by-products. As the United States industrialized, people moved away from raising their own animals for slaughter, instead purchasing from butchers. In 1837, Cincinnati candlemaker William Procter expanded his attentions from lighting to soap, forming a company that would ultimately evolve—with partner James Gamble—into the world’s largest consumer products company. (A good move, since gas lamps were becoming popular , and Thomas Edison and others working with electricity would in a few short decades relegate candles to religious ceremonies and bathtime scene-setting.)

One of the first soaps to gain national distribution was Procter & Gamble’s Ivory. Originally introduced as a plain white soap, and designed to compete with Spanish castile soap (traditionally made from olive oil), the primary attribute of Ivory—the name was adopted in the 1870s, after a biblical passage—was that it floated, which the company claimed was an indicator of purity. A formal creation myth was manufactured for a product that was fundamentally the renderings of slaughtered livestock; the tale involved a mixing machine left on, an extended lunch break, and extra air accidentally pumped into a gooey agglomeration. In 2004, company archivists uncovered an 1863 diary entry, written by James Gamble, that seemed to dispel the legend of the buoyant accident: “I made floating soap today,” Gamble wrote. “I think we’ll make all of our stock that way.”

For most of the 19th century and into the early 20th century, soap companies made real soap. But in the early 1900s, German engineers discovered an alternate cleaning product: a synthetic called “detergent” (rough Latin translation: to wipe away). Detergents didn’t contain soap. Instead, they used enzymes that lifted stains off clothing and skin. American companies adopted and refined detergents, mixing ingredients to create surfactants, which, like soap, allowed dirt and grease to be pulled off the object being cleaned and into water. The reason for the move away from soap was simple, says Greg McCoy, Procter & Gamble’s corporate archivist: “Detergents clean better.”

The result is that what you’re calling soap today probably isn’t. At least not completely. “Most body cleansers, both liquid and solid, are actually synthetic detergent products,” states a Food & Drug Administration handout that provides the legal definition of soap. “Detergent cleansers are popular because they make suds easily in water and don't form gummy deposits. Some of these detergent products are actually marketed as ‘soap’ but are not true soap according to the regulatory definition of the word.”

Modern cleansers can also contain additional ingredients, including brighteners, water softeners, and antibacterials/antivirals like alcohol, benzalkonium chloride, and chloroxylenol. (Triclosan, one of the most effective bacteria-fighting additives, is no longer found in US consumer products; it was banned in 2016 in light of medical and environmental concerns.) These modern cleaning bars can contain some of the same ingredients as soap—animal fats, which appear on ingredient lists as sodium tallowate and sodium lardate, or vegetable fats like sodium palmitate and sodium cocoate—but they are not, in the legal/chemical/alchemical sense, really soap.

People in the Middle Ages faced disease and sickness, just as people do today. In the ancient alchemy manual, soap is described less as an object used in sanitation and more as an ingredient (gold solder can be made from a mixture of soap, copper, and a dyeing agent called calcothar). Riches from price-gouged bottles of hand sanitizers notwithstanding, it’s a good thing that today’s more complicated cleansers serve a more practical and urgent purpose.

Further reading

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History of Soap and Soap Interesting Facts

An excavation of ancient Babylon revealed evidence that Babylonians were making soap around 2800 B.C. Babylonians were the first one to master the art of soap making . They made soap from fats boiled with ashes. Soap was used in cleaning wool and cotton used in textile manufacture and was used medicinally for at least 5000 years.

The Ebers papyrus (Egypt, 1550 BC) reveals that the ancient Egyptians mixed animal and vegetable oils with alkaline salts to produce a soap-like substance.

According the Pliny the Elder, the Phoenicians used goat's tallow and wood ashes to create soap in 600BC. Early Romans made soaps in the first century A.D. from urine and soap was widely known in the Roman Empire

The Celts made their soap from animal fat and plant ashes and they named the product saipo, from which the word soap is derived.

Soap History

The first concrete evidence we have of soap-like substance is dated around 2800 BC., the first soap makers were Babylonians, Mesopotamians, Egyptians, as well as the ancient Greeks and Romans. All of them made soap by mixing fat, oils and salts. Soap wasn't made and use for bathing and personal hygiene but was rather produced for cleaning cooking utensils or goods or was used for medicine purposes.

Facts about Soap

Soap is a product for cleaning made from natural ingredients that may include both plant and animal products, including items as: animal fat, such as tallow or vegetable oil, such as castor, olive, or coconut oil. Soap supposedly got its name from Mount Sapo in Rome. The word sapo, Latin for soap, first appeared in Pliny the Elder's Historia Naturalis. The first soap was made by Babylonians around 2800 B.C. The early references to soap making were for the use of soap in the textile industry and medicinally.

Making Soap

Soap making history goes back many thousands years. The most basic supplies for soap making were those taken from animal and nature; many people made soap by mixing animal fats with lye. Today, soap is produce from fats and an alkali. The cold process method is the most popular soap making process today, while some soap makers use the historical hot process.

Detergent Facts and History

Did you ever wonder when the first detergent is made? How detergents are made? What are famous brands of detergents? Read about this useful cleaning substance that is used in cleaning dishes, laundry and other surfaces.

In the early beginnings of soap making, it was an exclusive technique used by small groups of soap makers. The demand for soap was high, but it was very expensive and there was a monopoly on soap production in many areas. Over time, recipes for soap making became more widely known, but soap was still expensive. Back then, plant byproducts and animal and vegetable oils were the main ingredients of soap. The price of soap was significantly reduced in 1791 when a Frenchman by the name of LeBlanc discovered a chemical process that allowed soap to be sold for significantly less money.

More than 20 years later, another Frenchman identified relationships between glycerin, fats and acid what marked the beginning of modern soap making. With the 1800 discovery of another method of making soap ingredients, soap became even less expensive. Since that time, there have been no major discoveries and the same processes are used for the soap making we use and enjoy today.

Advances came as the science of chemistry developed because more was understood about the ingredients. In the mid-nineteenth century, soap for bathing became a separate commodity from laundry soap, with milder soaps being packaged, sold and made available for personal use. Liquid hand soaps were invented in the 1970s and this invention keeps soaps in the public view.

Today, there are many different soaps made for a vast array of purposes. Soap is available for personal, commercial and industrial use. There is handmade, homemade and commercially produced soap, there is soap used to wash clothes, dishes and cars, there is soap used for your pet, soap for your carpet and soap for your child... but for many types of cleaning, soaps are a lesser used product these days, as alternatives to soap are the main choice.

International Conference on Multimedia Technology and Enhanced Learning

ICMTEL 2021: Multimedia Technology and Enhanced Learning pp 485–491 Cite as

A Comparative Study of REST with SOAP

• Usman Riaz 19 ,
• Samir Hussain 19 &
• Hemil Patel 19  
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Part of the book series: Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering ((LNICST,volume 387))

Currently most web services obtain REST architectural styles, which were originally founded by Roy Fielding in the year 2000. Alongside the styles, constraints and techniques were also discussed in Roys famous dissertation. In this research paper we will take a look at understanding the techniques used in the REST architecture style, covering the six constraints. Evaluating the testing techniques of REST and finally comparing REST with the SOAP standard. In order to remove the high latency, reduce network traffic and processing delays, which was being caused by SOAP, REST was introduced to overcome all of these issues. Furthermore, 70% of websites use REST architecture as many have found SOAP to be outdated.

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Riaz, U., Hussain, S., Patel, H. (2021). A Comparative Study of REST with SOAP. In: Fu, W., Xu, Y., Wang, SH., Zhang, Y. (eds) Multimedia Technology and Enhanced Learning. ICMTEL 2021. Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, vol 387. Springer, Cham. https://doi.org/10.1007/978-3-030-82562-1_47

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An Experimental Research on Making a Soap with Long-Lasting Fragrance

The researchers studied about making soap with long lasting fragrance in order to find its feasibility, which will also suffice the satisfaction of consumers through making its fragrance last in long period of time. This kind of product has not yet reached the demands in market, but through the study, researchers produced a soap that was different from other soap products. Such that, the study aimed to know if it’s possible to make a soap with long lasting fragrance, how long will that fragrance last, and how will it benefit consumers. Through these aims, the researchers hypothesized that the soap’s fragrance would reach 4-5 hours. The researchers made use of a true experimental research design because of having randomized selection of respondents. In the study, the respondents are divided into two groups: the control group and the experimental group, by which both groups will be tested to know how long will the scent of the soap would last. The control group were the regular students who doesn’t sweat that much while the experimental group were the varsity students who sweat more during their games. Thus, the researchers believed that the main factor to the duration of a soap’s fragrance is the sweat. The researchers created a proposed soap named Doux Aroma, which means sweet scent, which was used to test the respondents. It is shown that majority of the respondents had said that the duration of the soap reached 2-3 hours at normal cases while there are some who said that the duration reached 4-5 hours at rare cases. Based from the respondents, the soap benefited them because of the soap’s fragrance that would improve their hygiene and that they don’t need to buy expensive colognes and perfume anymore. Due to this, making a soap with long lasting fragrance is indeed possible.

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The purpose of this dissertation is to investigate the role of colour on the perception of odour by measuring the a) preference and b) intensity of 16 possible combinations of 4 coloured bottles and 4 odours as rated by 297 participants (130 males and 167 females). The two-way ANOVA for preference revealed that the role of both – colour and odour is significant for Czech participants, but the significance increases with the cultural homogeneity as for Slavic nationals, the colour and odour did not play a significant role in their preference ratings. In contrary to previous research, the effect of colour and odour on intensity ratings was not significant. Linear regression analysis then showed that gender is also a significant factor and males are generally more prone to give higher preference scores by 5.58 % than females to colour and odour interactions. On the other hand, a choice of preferred colour did not affect the preference scores. In addition, several types of congruencies between colour and odour were proposed. It is argued that one of these types (perceptual, semantic, mixed) reflect the decision-making about preference levels more precisely. As a result, it has been demonstrated that intuitive congruent pairings of colours and odours (such as lemon and yellow) do not increase the preference ratings among consumers. Instead, the mixed semantical-perceptual congruency corresponds significantly to the collected data. This approach could simplify product testing methods where the colour and odour are deemed to be selected variables.

Pascale Lemaire

This review describes the use of some natural products in cosmetic preparations, due to their low mammalian toxicity, with a brief description of the major use, plant parts used, the actives responsible for effect and the benefits of such products. Their use in skin care; such as dryness, eczema, acne, free-radical scavenging, antiinflammatory, antiaging and skin protection effects are explained, and also the use in hair care as hair growth stimulants, hair colorants, and for hair and scalp complaints such as dandruff. Essential oils when incorporated into finished products impart many benefits such as a pleasant aroma in perfumery, shine or conditioning effects in hair care products, emolliency and improving the elasticity of the skin.

Md. Zainal Abedin

Marketing is summation of all systematic and innovative functions which involve in value creation for customers and value capturing from customers inreturn. So Marketing is a continuous process of innovating products according to the exact need of customers. The marketers have to develop new products to keep pace with the continuous trend of changing culture and for technological advancement to fulfill modern customers' requirements. To survive from the decline demand of products and services, it is very essential and inevitable to develop new products or update existing products according to the exact demand of customers. The continuous process of innovating and updating products and services is very needed to survive as well as to make a competitive edge in the industry.The following Parachute brand is the example of continuous process of product innovation: Parachute Gold: Inner Strength, Parachute Gold: Nourishment, Parachute Gold: Sensorial Aroma, Parachute Gold: Nourishment + Sensorial, Parachute Gold: Sensorial – Non-Stickiness, Parachute Gold: Sensorial – Easy to Rinse. The study will help to develop a conceptual framework of innovating (Bath Soap) product as well as the innovative marketing process. The research or the conceptual framework developed through this research will help marketers to develop accurate strategies to develop new products as well as to market and launch the product successfully. The commercial or marketing success or failure of a product does not rest solely on the product itself. The launch strategy adopted also determines whether a product succeeds or fails in the market. The key to success in the marketing and launching process often rests in finding the proper strategies. The main purpose of the research is to survey the market and get a clear idea about the consumer behavior regarding new kind of soap which will hold both antiseptic and beauty care quality in a single soap. I. Scope and Rationale of the Study Launching a new product will require a large amount of planning, research, and investment of both time and financial resources. It requires problem identification, sample selection, market analysis, data analysis, data evaluation and interpretation through various numerical and statistical techniques and packages, and finally presents an understandable report to the audience. If it is planning on creating and marketing a new product, here are the most important tasks to complete before, during, and after launching. When launch a new product it can either be replacing or superseding an existing one or it may be a completely new product of a type that have never offered before. Even if the product is completely new to a company, there will be still information available about competing products and the market for them. If the new product is superseding an existing product, then will have information related to the sales of the product and its market. There can be many reasons for developing or adding a new product but most are the result of analyzing your product portfolio and either deciding that a product needs replacing and identifying a gap in the portfolio that presents with a potential opportunity. The new product launch phase is a critical part of the total new product development process. Developing a new product is an expensive and time-consuming process and its launch needs to be carefully planned. Technology development brings prosperity to nations, but the successful commercialization of this technology is the real meaning of innovation. For this reason, all companies have tried their best to launch maximum numbers of products to market. However, the commercial success or failure of a product does not rest solely on the product itself. The launch strategy adopted also determines whether a product succeeds or

Katherine Annett-Hitchcock

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• Proc Natl Acad Sci U S A
• v.114(10); 2017 Mar 7

On the shape of giant soap bubbles

Caroline cohen.

a Laboratoire d’Hydrodynamique de l’X, UMR 7646 CNRS, École Polytechnique, 91128 Palaiseau Cedex, France;

Baptiste Darbois Texier

Etienne reyssat.

b Laboratoire de Physique et Mécanique des Milieux Hétérogènes (PMMH), UMR 7636 du CNRS, ESPCI Paris/Paris Sciences et Lettres (PSL) Research University/Sorbonne Universités/Université Paris Diderot, 75005 Paris, France;

Jacco H. Snoeijer

c Physics of Fluids Group, University of Twente, 7500 AE Enschede, The Netherlands;

d MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands;

e Department of Applied Physics, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands

David Quéré

Christophe clanet.

Author contributions: C. Cohen, B.D.T., and C. Clanet designed research; C. Cohen, B.D.T., E.R., J.H.S., and C. Clanet performed research; C. Cohen, B.D.T., E.R., J.H.S., D.Q., and C. Clanet analyzed data; and C. Cohen, B.D.T., E.R., J.H.S., and C. Clanet wrote the paper.

Significance

Surface tension dictates the spherical cap shape of small sessile drops, whereas gravity flattens larger drops into millimeter-thick flat puddles. In contrast with drops, soap bubbles remain spherical at much larger sizes. However, we demonstrate experimentally and theoretically that meter-sized bubbles also flatten under their weight, and we compute their shapes. We find that mechanics does not impose a maximum height for large soap bubbles, but, in practice, the physicochemical properties of surfactants limit the access to this self-similar regime where the height grows as the radius to the power 2/3. An exact analogy shows that the shape of giant soap bubbles is nevertheless realized by large inflatable structures.

We study the effect of gravity on giant soap bubbles and show that it becomes dominant above the critical size ℓ =  a 2 / e 0 , where e 0 is the mean thickness of the soap film and a = γ b / ρ g is the capillary length ( γ b stands for vapor–liquid surface tension, and ρ stands for the liquid density). We first show experimentally that large soap bubbles do not retain a spherical shape but flatten when increasing their size. A theoretical model is then developed to account for this effect, predicting the shape based on mechanical equilibrium. In stark contrast to liquid drops, we show that there is no mechanical limit of the height of giant bubble shapes. In practice, the physicochemical constraints imposed by surfactant molecules limit the access to this large asymptotic domain. However, by an exact analogy, it is shown how the giant bubble shapes can be realized by large inflatable structures.

Soap films and soap bubbles have had a long scientific history since Robert Hooke ( 1 ) first called the attention of the Royal Society and of Newton to optical phenomena ( 2 ). They have been of assistance in the development of capillarity ( 3 ) and of minimal surface problems ( 4 ). Bubbles have also served as efficient sensors for detecting the magnetism of gases ( 5 ), as elegant 2D water channels ( 6 ), and as analog “computers” in solving torsion problems in elasticity ( 7 , 8 ), compressible problems in gas dynamics ( 9 ), and even heat conduction problems ( 10 ). Finally, in the last decades, the role of soap films and bubbles in the development of surface science has been crucial ( 11 – 13 ), and the ongoing activity in foams ( 14 , 15 ) and in the influence of menisci on the shapes of bubbles ( 16 ) are modern illustrations of their key role. The shape of a soap bubble is classically obtained by minimizing the surface energy for a given volume, hence resulting to a spherical shape. However, the weight of the liquid contained in the soap film is always neglected, and it is the purpose of this article to discuss this effect.

For liquid drops, the transition from a spherical cap drop to a puddle occurs when the gravitational energy, ρ g R 4 ( R is the typical size of the drop), becomes of the same order as its surface energy γ b R 2 . That is, for a drop size of the order of the capillary length a = γ b / ρ g ( γ b is the liquid–vapor surface tension, and ρ is the liquid density). Typically, this transition is observed at the millimetric scale: For a soap solution with γ b = 30 mN/m, a  ≃  1.7 mm. The two asymptotic regimes may be distinguished through the behavior of the drop height h 0 with volume: h 0  ≈  R for small spherical drops, while the height of large puddles saturates to a constant value h 0  ≈  a .

If we look for the same transition in soap bubbles, we expect the gravitational energy, ρ g R 3 e 0 , to become of the order of the surface energy, γ b R 2 , at the typical size R  ≈ ℓ, with ℓ =  a 2 / e 0 ( e 0 stands for the mean thickness of the film). Thanks to the iridescence, the mean thickness can be estimated to a few microns or less, and the light–heavy transition is thus expected at the metric scale (instead of the millimetric one for drops): For γ b = 30 mN/m and e 0 = 1 μ m, ℓ ≃ 3.1 m.

The experimental setup dedicated to the study of such large bubbles is presented in Experimental Setup , before information on Experimental Results and Model . The discussion on the asymptotic shape and the analogy with inflated structures is presented in Analogy with Inflatable Structures .

Experimental Setup

The soap solution is prepared by mixing two volumes of Dreft © dishwashing liquid, two volumes of water, and one volume of glycerol and was left aside for 10 h before experiments. The surface tension of the different mixtures was measured using the pendant drop method. It was found to be γ b = 26 ± 1 mN/m.

The bubbles are formed in a round inflated swimming pool of 4 m diameter ( Fig. 1 ), filled with 10 cm to 20 cm of soap solution. A large bubble wand was assembled with two wood sticks and two cotton strings. The strings were immersed in the soap solution. Two experimenters, located on opposite sides of the pool, slowly opened the loop in air and pulled the sticks above the water surface, before dipping the loop into the water to form the bubble.

Presentation of a “giant” soap bubble and definition of its radius, R , and height, h 0 . (Here, R = 1.09m, and h 0 = 0.97m.)

Once the bubble is at rest, the shape is analyzed by side view images as shown in Fig. 1 . In particular, we measure the diameter, 2 R , and the height, h 0 , of the giant bubble. The camera is placed 4m from the center of the pool, and the center of the lens is at the same height as the center of the bubble, to minimize parallax errors.

The film thickness e 0 is important when studying the effect of the bubble weight, as it determines the liquid mass. Following McEntee and Mysels ( 17 ), the thickness of the bubble is measured via the bursting technique: A hole in a punctured soap film grows because of unbalanced surface tension forces at the edge of the hole. The opening velocity v is constant and is given by the Dupré–Taylor–Culick law ( 18 – 20 ),

where γ b  ≃ 26mN/m, and ρ ≃  1 , 000 kg ⋅ m − 3 . Examples of thickness measurements are presented in Fig. 2 : In Fig. 2 A and Fig. 2 B , we present two sequences of four pictures showing the opening of a hole in two soap bubbles of different sizes. We use such sequences to extract the bursting velocity plotted as a function of time in Fig. 2 C . We observe that v is almost constant and takes the value of 8 m/s for sequence in Fig. 2 A and 2.8 m/s for sequence in Fig. 2 B . From the value of v , we deduce e 0  ≃ 0.81 μ m and ℓ ≈ 3.2m for Fig. 2 A and e 0  ≃ 6.6 μ m and ℓ ≈ 0.4m for Fig. 2 B , using Eq. 1 . Although it may seem surprising to find that the film thickness is homogeneous, earlier studies on the drainage of almost spherical liquid shells have shown that the thickness approaches a profile with little spatial variations ( 21 , 22 ).

Bursting of bubbles used to determine the soap film thickness. ( A ) Image sequence of bursting bubbles, with a time step of 60ms between images. Red arrows indicate the boundary of the opening hole on each image. (Scale bar, 50cm.) ( B ) Bursting sequence with a time step of 50ms between images. (Scale bar, 10cm.) ( C ) The bursting velocity corresponding to A and B is plotted versus time.

Experimental Results

Once ℓ is determined, we use it to rescale the experimental shapes. An example of a nonspherical bubble is presented in reduced scale in Fig. 3 A . A systematic analysis of the effect of gravity on the bubble shape is shown in Fig. 3 B , where we plot the reduced height h 0 /ℓ as a function of the bubble reduced radius R /ℓ for all experiments. Fig. 3 B reveals that the bubbles’ shapes remain approximately spherical ( h 0 /ℓ =  R /ℓ, black dashed line) only up to R /ℓ ≈ 0.3. For larger sizes, the bubble height is significantly lower than that of a sphere. The largest value of h 0 /ℓ reached experimentally is ∼1.2, with corresponding radius R /ℓ = 1.6. Two points must be underlined at this stage: ( i ) The experimental data in Fig. 3 B show no sign of a height saturation for increased bubble volumes, and ( ii ) despite our efforts, we never managed to make bubbles larger than R = 1m. Both observations will be explained in Model .

( A ) Example of flattened soap bubble of equatorial diameter 20 cm. The black dashed line is a circle, and the red solid line is the theoretical shape obtained through the numerical integration of Eq. 6 that gives the same aspect ratio h 0 / R as the experiment. ( B ) Flattening of soap bubbles due to gravity, quantified by the scaled height h 0 /ℓ as a function of the scaled radius R /ℓ, where ℓ =  a 2 / e 0 . Circles represent experimental data, the solid red line stands for the model prediction, and the dashed black line represents the spherical limit h 0 =  R .

We now consider the mechanical equilibrium of the soap film and predict how gravity affects the bubble shape. Bubbles are axisymmetric, and we assume a uniform film thickness e 0 . The bubble shape is described using the parametrization shown in Fig. 4 A and B : The local height of the soap film is h ( s ), and the local angle of the membrane relative to the horizontal is θ ( s ) (defined as positive everywhere). The height and angle are functions of the curvilinear coordinate s that measures the arclength starting from the top of the bubble; φ is the azimuthal angle around the vertical axis.

( A ) Sketch of a giant bubble of radius R and height h 0 . The local height is h . The gray area shows an infinitesimal surface element of the bubble. ( B ) Zoom on the infinitesimal part of the bubble located at distance r from the symmetry axis of the bubble. The surface area of this surface element is r d s d φ ; tan⁡ θ is the local slope of the soap film with respect to the horizontal. ( C ) Shapes of soap bubbles with dimensionless radius R /ℓ = 0.3, 1, 5, and 10. Although large bubbles tend to flatten (i.e., h 0 / R  → 0), the height of giant bubbles shows no sign of saturation. ( D ) Shapes of liquid drops with contact angle θ = 90 ∘ and dimensionless radius R / a = 0.3, 1, 5, and 10. The dimensionless height of large drops saturate to 2 . ( E ) Experimental dimensionless height of soap bubbles as a function of their dimensionless radius (circles). The theoretical dimensionless height h 0 /ℓ of bubbles (full line) is plotted as a function of their dimensionless radius R /ℓ. Small bubbles ( R /ℓ < 0.3) are insensitive to gravity and remain hemispherical, thus minimizing their surface area for the given volume. Giant bubbles flatten, but there is no saturation height as exists for drops larger than the capillary length: For large bubbles, one finds h 0  ≈  R 2/3 . The physical chemistry of surfactants, however, limits the range of accessible surface tension, setting the actual upper limit for the size of giant bubbles (dashed line): h m a x /ℓ = 2Δ γ / γ b .

The equilibrium of an infinitesimal part of the membrane of surface area r d s d φ is first considered along the s direction. To account for the experimentally observed slow draining and long bubble lifetimes, the air–liquid interface must strongly moderate the flow and behave as partially rigid, in contrast with the no-stress behavior of surfactant-free interfaces. The main effect is that gradients in surface tension γ ( s ), due to the presence of surfactants, have to balance viscous stresses applied by the flowing liquid along the interface. In reaction, viscous stresses balance the weight of the liquid in the film. Finally, the weight of liquid is fully transmitted to the walls through viscous stresses and balanced by surface tension gradients ( 15 ). The contribution due to surface tension on each side of the infinitesimal element gives a force 2 γ r d φ , where γ is a function of position s . The weight of the liquid inside the film is ρ g e 0 r d φ d s sin⁡ θ , when projected along the s direction. The balance of surface tension and weight thus gives

which, using d h /d s = −sin⁡ θ , yields

Here γ b is the surface tension of the soap solution at the base of the bubble ( h = 0), and the surface tension is found to increase with height ( 23 ). For a bubble of thickness e 0 = 1 μ m and height 1 m, the surface tension contrast between the base and top of the bubble is typically 5 mN/m.

A closed equation for the bubble shape is obtained when next considering the equilibrium normal to the membrane. The pressure difference Δ P between the inside and outside of the bubble, to balance the weight projected normal to the film ρ g e 0 cos⁡ θ and the Laplace pressure due to the two curved liquid–air interfaces. The balance of pressure and weight reads

where d θ /d s is the curvature along s and sin θ / r is other principal curvature for an axisymmetric surface. We remind that γ ( s ) is given by Eq. 3 . As a final step, it is convenient to eliminate Δ P by its value at the top of the bubble ( s = 0, θ = 0, and h =  h 0 ), where (d θ /d s +sin θ / r )| s →0  →  2d θ /d s | s =0 and γ ( s = 0) =  γ b + 1/2 ρ g e 0 h 0 . Combining Δ P ( s = 0) with Eqs. 3 and 4 gives the equation for the shape of the bubble,

Scaling all lengths with ℓ =  a 2 / e 0 , denoting scaled variables by a tilde, we obtain the shape equation in dimensionless form,

A unique bubble shape is found numerically for each value of the dimensionless height h ∼ 0 ; this is done by adjusting the value of d θ / d s ∼ ( s ∼ = 0 ) by a shooting algorithm to match the boundary conditions ( h ∼ = h ∼ 0 and θ = 0 at the top, with θ =  π /2 at h ∼ = 0 at the bath).

Fig. 4 C shows the corresponding bubble shapes for increasing volume. As expected, small bubbles are dominated by surface tension and are perfectly spherical. However, as bubbles get larger ( h ∼ 0 >  1 ), they show a tendency to flatten with respect to the spherical shape. A direct comparison of the theoretical shape with a real bubble is presented in Fig. 3 A , where we superimpose the picture of a 20-cm diameter bubble with the solution of Eq. 6 that has the same ratio h 0 / R . The two shapes cannot be distinguished. The model ( Eq. 6 ) also gives a quantitative prediction for the height h ∼ 0 = h 0 / ℓ versus R ∼ = R / ℓ that can be compared with the experimental data in Fig. 3 B (solid line). The result describes very well, without any adjustable parameter, the experimentally observed flattening due to gravity.

Unexpectedly, the numerical solution does not predict a saturation of the bubble height: h ∼ 0 continues to increase in the limit of large volume. This feature is highlighted in more detail in Fig. 4 E , showing the dimensionless bubble height on a log–log plot. For large volumes, we find that h ∼ 0 ≈ R ∼ 2 / 3 . This scaling law implies a decaying aspect ratio, i.e., h ∼ / R ∼ ≪ 1 , but, at the same time, there is no saturation of the bubble height. Interestingly, these asymptotic features cannot be derived on simple dimensional grounds. According to Eq. 3 , both surface tension and gravity scale with ρ g e 0 , which points to a scale invariance at large bubble heights. Indeed, as is shown in Supporting Information , the large bubble shapes in Fig. 4 C exhibit scale invariance and can be collapsed to a single, universal shape. The scaling of the universal shape near the edge reads h ∼ ≈ ( R ∼ − r ∼ ) 2 / 3 , as can be inferred from the dominant balance h ∼ d θ / d s = ( cos ⁡ θ − 1 ) ≃ h ′ 2 / 2 in Eq. 6 . The 2/3 scaling at the edge determines the horizontal and vertical scales for the bubble and leads to the scaling in Fig. 4 E (see Supporting Information for detailed analysis).

This scaling law for large bubbles, and, in particular, the lack of saturation, is in stark contrast with the classical result for liquid drops. The shape of droplets can be found from the classical hydrostatic pressure balance ( 13 ) and is different from Eq. 6 ,

Here, the lengths were made dimensionless using the capillarity length a = γ b / ρ g , and denoted by hatted variables. Fig. 4 D shows the corresponding numerical solutions: Large drops develop toward puddles, which, for θ =  π /2, saturate to the height h ^ 0 = 2 .

The height of soap bubbles may, however, be limited by physical chemistry of surfactants. The water that constitutes the bubble is prevented from draining quickly by gradients in the surface tension. The larger surface tension at the top of the bubble supports the weight of water in the liquid shell ( 15 ). In practice, the surface tension of a soap solution cannot be higher than that of pure water, γ ∗ ; γ also has a minimum, γ b , set by the surfactant concentration of the solution used in the experiments. Eq. 3 thus gives a criterion for the maximal height h m a x of the bubble,

where Δ γ =  γ ∗  −  γ b is the highest achievable surface tension contrast between the top and bottom of a bubble; γ ∗  ≃ 70 mN/m, and γ b may typically be as low as 20 mN/m, so that the expected maximal height of a bubble of thickness e 0 = 5 μ m is of order 2m, close to the size of the biggest bubbles we experimentally produced ( Fig. 1 ).

Analogy with Inflatable Structures

Interestingly, the shapes we have just discussed correspond to a minimization problem that is relevant in the context of large inflatable structures, such as shown in Fig. 5 . These structures consist of a thin sheet that we assume cannot be stretched, and which is inflated by a pressure difference Δ P . The mechanical analysis on an infinitesimal element of the thin sheet is strictly equivalent to that in Fig. 4 A and B : The role of surface tension is replaced by the tension that develops inside the membrane. It is interesting to confirm this analogy based on energy minimization, with the no-stretch condition imposed through a Lagrange multiplier λ . Characterizing the axisymmetric shape as h ( r ), and thus h ′ =  d h / d r , the functional ℱ[ h ] to be minimized reads

Festo’s Airquarium, 31 m in diameter.

The three terms respectively represent the gravitational free energy, the area constraint, and the work done by the pressure difference. The Euler–Lagrange equation for this functional gives (see Inflatable Structures ):

which is, indeed, strictly identical to the equation that dictates the bubble shapes ( Eq. 4 ). Designing the inflatable structures along these optimal shapes will naturally avoid stretching and compression of various parts of the sheets, avoiding wrinkles and reducing tensile stresses exerted in the sheets and on the seams that connect the various parts. This design should help increase the lifetime of such structures.

We study the shape of large soap bubbles and show that gravity becomes important at the scale ℓ =  a 2 / e 0 . We derive the equation for the shape and show that gravity matters in two distinct terms: the expected hydrostatic term and the evolution of surface tension via Marangoni stresses. A direct consequence is that there is a physicochemical limit to the size of soap bubbles, h m a x . Finally, we point out that, contrary to drops, the shape of giant soap bubbles is not characterized by a saturation of the height but by a self-similar behavior in which h 0 /ℓ ≈ ( R /ℓ) 2/3 .

Analyzing the Shape of Large Bubbles

For large volumes, the bubbles exhibit a universal shape; this can be seen in Fig. S1 , where we represent the numerical profiles ( Fig. 4 C ) after rescaling the height by h 0 and the width by R . The large bubble profiles collapse to universal shape that is close to (although not exactly) a circle. In Supporting Information , we explain this observation and use it to derive the scaling law h 0  ≈  R 2/3 as presented in Model .

Rescaling bubble profiles of large volume as h / h 0 and ξ =  r / R . The large-volume bubbles are self-similar and described by a similarity function G ( ξ ) defined by Eq. S6 (circles symbols).

We start from the dimensionless shape equation given in Eq. 6 ,

Throughout Supporting Information , we omit tildes for convenience. For analysis, it is convenient to use the connection to cylindrical coordinates,

where primes represent derivatives with respect to r . The bubble equation then reads

In Similarity Solution for the Global Shape and Near the Contact Line , we will analyze the limiting behaviors for large bubbles, by which we mean that the central height h 0  ≫ 1.

Similarity Solution for the Global Shape

Analyzing the profile at scales h ≫  1 , Eq. S3 simplifies to

Based on the collapse observed in the numerical solutions, we search for a similarity solution,

and we anticipate that large bubbles exhibit a small aspect ratio, i.e., ϵ ≡ h 0 / R ≪  1 . Inserting this form in Eq. S4 and expanding to leading order in ϵ , we indeed obtain an equation for the similarity function,

where we used 2 h 0 d θ /d s | s =0 =  ϵ 2 β . This second-order ordinary differential equation (ODE) is complemented by three boundary conditions,

which can only be satisfied for a unique value of β . Numerical integration of Eq. S6 gives β =  2.373 , and the corresponding similarity function G ( ξ ) is represented in Fig. S1 by closed symbols; it gives an excellent description of the collapsed profiles from direct integration of Eq. S1 .

For what follows, it is important to analyze the shape in the vicinity of the contact line. In terms of the similarity solution, this regime corresponds to G ≪  1 , for which the balance reduces to G G ″ +  G ′2 /2 ≃ 0; this gives the asymptotics

This equation is valid for 1 ≪  h  ≪  h 0 , because the similarity solution was derived from Eq. S4 . It is important to note that, up to this point, the scales h 0 and R are still completely undetermined. The problem will be closed by matching Eq. S8 to the contact line region for the full equation, Eq. S3 .

Near the Contact Line

At the scale h  ≈ 𝒪(1), we can neglect the axisymmetric contribution to the pressure as well as the integration constants in Eq. S3 . Then, the shape is described by

This equation has a first integral

where we used the boundary condition that the bubble has a 90 ∘ contact angle ( h ′2  → ∞ as h →  0 ). Eq. S10 is a first-order ODE that can be written as

Solving this equation by separation of variables, using h ( R ) =  0 , yields

This equation specifies the shape of the bubble in the vicinity of the contact line.

We are primarily interested in the large- h expansion of this result,

This expansion has an important consequence, as this “inner” solution has to match the form derived from the global bubble shape ( Eq. S8 ). Hence, the matching condition requires that

as is, indeed, observed in the numerical solution.

Inflatable Structures

The equilibrium of axisymmetric inflatable structures can be computed from the Euler–Lagrange equation,

Working out the derivatives for ℒ( h ,  h ′) given in Eq. 11 , this equation becomes

which can be recombined to the form

Using the geometric relations discussed at the start of Supporting Information , this equation indeed reduces to Eq. 4 .

Acknowledgments

We thank Tomas Bohr for organizing the 2013 Krogerup Summer School that initiated the collaboration between Paris and Twente. We also thank Isabelle Cantat for her input on the stability of soap films and for her constructive criticism of the initial version of our work.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1616904114/-/DCSupplemental .

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The production of paper soaps from coconut oil and Virgin Coconut Oil (VCO) with the addition of glycerine as plasticizer

Asri Widyasanti 1 , Anastasia Miracle Lenyta Ginting 1 , Elgina Asyifani 1 and Sarifah Nurjanah 1

Published under licence by IOP Publishing Ltd IOP Conference Series: Earth and Environmental Science , Volume 141 , 2nd International Conference on Biomass: Toward Sustainable Biomass Utilization for Industrial and Energy Applications 24–25 July 2017, Bogor, Indonesia Citation Asri Widyasanti et al 2018 IOP Conf. Ser.: Earth Environ. Sci. 141 012037 DOI 10.1088/1755-1315/141/1/012037

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1 Departement of Agricultural and Biosystem Engineering, Faculty of Agro-Industrial Technology, Padjadjaran University, Bandung Sumedang km 21 St., Jatinangor, Bandung 40600

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Hand washing with soap is important because it is proven to clean hands from germs and bacteria. The paper soapswere made from coconut oil and virgin coconut oil (VCO) with the addition of glycerin as a plasticizer. The aims of this research were to determine both formulation of paper soap using coconut oil and VCO based with addition of glycerin, and to determine the quality of the paper soapswhich is a disposable hand soap. This research used laboratory experimental method using descriptive analysis. The treatments of this research were treatment A (paper soap without the addition of glycerin), treatment B (paper soap with the addition of glycerin 10% (w/w)), treatment C (paper soap with the addition of glycerin 15% (w/w)), treatment D (paper soap with the addition of glycerin of 20% (w/w)). Parameters tested were moisture content, stability of foam, pH value, insoluble material in ethanol, free alkali content, unsaponified fat, antibacterial activity test, and organoleptic test. The result of physicochemical characteristics for bothcoconut oil-paper soap and VCO-paper soap revealed that treatment C (the addition of glycerin 15% (w/w) was the best soap formulation. Coconut Oil papersoap 15% w/w glicerin had water content 13.72%, the content of insoluble material in ethanol 3.93%, the content of free alkali 0.21%, and the content of unsaponified fat 4.06%, pH value 10.78, stability of foam 97.77%, and antibacterial activity against S. aureus 11.66 mm. Meanwhile, VCO paper soap 15% w/w glicerin had the value of water content of 18.47%, the value stability of foam of 96.7%, the pH value of 10.03, the value of insoluble material in ethanol of 3.49%, the value of free alkali content 0.17%, the value of unsaponified fat 4.91%, and the value of inhibition diameter on the antibacterial activity test 15.28 mm. Based on Mandatory Indonesian National Standard of solid soap SNI 3532:2016 showed that both of paper soap had not been accorded with SNI 3532:2016, unless the value of the insoluble material in ethanol. Moreover, organoleptic tests performed that both paper soap treatment D (20% w/w glicerine) were preferred by the most panelists.

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