Tofu

Tofu: also known as soybean curd, is a soft, cheese-like food made by curdling fresh hot soymilk with a coagulant. Traditionally, the curdling agent used to make tofu is nigari, a compound found in natural ocean water, or calcium sulfate, a naturally occurring mineral. Curds also can be produced by acidic foods like lemon juice or vinegar. The curds then are generally pressed into a solid block.

Tofu was first used in China around 200 B.C. Although the discovery of the process for making tofu is lost to the ages, Chinese legend has it that the first batch of tofu was created by accident. A Chinese cook added nigari to flavor a batch of pureéd, cooked soybeans; the nigari produced the curd that we know today as tofu.

Today, tofu is a dietary staple throughout Asia. This delicate food is made fresh daily in thousands of tofu shops and sold on the street.

In recipes, tofu acts like a sponge and has the miraculous ability to soak up any flavor that is added to it. Crumble it into a pot of spicy chili sauce and it tastes like chili. Blend it with cocoa and sweetener and it becomes a double for chocolate cream pie filling. Cubes of firm tofu can be added to any casserole or soup.

Types of Tofu

Three main types of tofu are available in American grocery stores.

Firm tofu is dense and solid and holds up well in stir fry dishes, soups, or on the grill... anywhere that you want the tofu to maintain its shape. Firm tofu also is higher in protein, fat and calcium than other forms of tofu.

Soft tofu is a good choice for recipes that call for blended tofu, or in Oriental soups.

Silken tofu is made by a slightly different process that results in a creamy, custard-like product. Silken tofu works well in pureed or blended dishes. In Japan, silken tofu is enjoyed "as is," with a touch of soy sauce and topped with chopped scallions.

Tofu Nutrition Facts

Tofu is rich in high-quality protein. It is also a good source of B-vitamins and iron. When the curdling agent used to make tofu is calcium salt, the tofu is an excellent source of calcium. While 50 percent of the calories in tofu come from fat, a 4-ounce serving of tofu contains just 6 grams of fat. It is low in saturated fat and contains no cholesterol. Generally, the softer the tofu, the lower the fat content. Tofu is also very low in sodium, making it a perfect food for people on sodium-restricted diets.

Nutrients in
4 ounces of:

Firm
Tofu


Soft
Tofu


Silken
Tofu
Calories

120


86


72
Protein (gm)

13


9


9.6
Carbohydrate (gm)

3


2


3.2
Fat (gm)

6


5


2.4
Saturated Fat (gm)

1


1


-
Cholesterol

0


0


0
Sodium (mg)

9


8


30
Fiber (gm)

1


-


-
Calcium (mg)

120


130


40
Iron (mg)

8


7


1

Source: Composition of Foods: Legumes and Legume Products. United States Department of Agriculture, Human Nutrition Information Service, Agriculture Handbook 8-16. Revised December 1986, and from product analysis.

Buying & Storing Tofu

Tofu most commonly is sold in water-filled tubs, vacuum packs, or in aseptic brick packages. Tofu is usually found in the produce section of the grocery store, although some stores sell tofu in the dairy or deli sections. Tofu is sometimes sold in bulk in food cooperatives or Asian markets. Unless it is aseptically packaged, tofu should be kept cold. As with any perishable food, check the expiration date on the package.

Once the tofu package is open, leftover tofu should be rinsed and covered with fresh water for storage. Change the water daily to keep it fresh, and use the tofu within a week.

Tofu can be frozen up to 5 months. Defrosted tofu has a pleasant caramel color and a chewy, spongy texture that soaks up marinade sauces and is great for the grill.

Tips For Using Tofu

Tofu is for everyone. The soft consistency of tofu and its mild taste make it a perfect food for anyone. It is a good source of protein for elderly people who prefer dishes that are easy to chew and digest. Soft tofu that has been pureed with fruits or vegetables is a good first protein food for infants. Toddlers can enjoy chunks of cooked tofu for snacks or meals.

Try some of these ideas for introducing tofu to your family.

* Add chunks of firm tofu to soups and stews.
* Mix crumbled tofu into a meatloaf for a pleasant light dish.
* Mash tofu with cottage cheese and seasoning to make a sandwich spread.
* Create your own tofu burgers with mashed tofu, bread crumbs, chopped onion and your favorite seasonings.
* Marinate tofu in barbecue sauce, char it on the grill and serve on crusty Italian bread.
* Add a package of taco seasoning to pan-fried, crumbled tofu, or a mixture of tofu and ground beef to tofu tacos.
* Blend dried onion soup mix into soft or silken tofu for a cholesterol-free onion dip.
* Stir silken tofu into sour cream for a reduced-fat baked potato topper.
* Blend tofu with melted chocolate chips and a little sweetener to make a chocolate cream pie.
* Replace all or part of the cream in creamed soups with silken tofu.
* Make missing egg salad with tofu chunks, diced celery, mayonnaise and a dab of prepared mustard.
* Substitute pureed silken tofu for part of the mayonnaise, sour cream, cream cheese or ricotta cheese in a recipe. Use it in dips and creamy salad dressings.

life on ice

: "New Scientist May 2,1998: 24-28 'Life on Ice' Various quoted snippets: 'Wood frogs, it turns out, only look frozen solid. In reality, the water in between their cells freezes, but not the water within them. To achieve this semi-frozen state, the frogs adopt two main strategies. First their blood contains ice nucleating proteins - molecules that actually encourage ice to grow by mimicking its crystal lattice. 'If you could fly over a nucleating protein in a miniature airplane,' story says, 'its surface would look like ice.' With so many nucleators in the blood, no one crystal ever gets big enough to damage tissue. Glucose is the second trick. Just as the extremities begin to get icy, the frog's liver starts churning out glucose, which circulates round its body. 'The frogs start out with the same amount of glucose we have,' says Storey, 'then go right to being diabetic.' Glucose in the cells has the same effect as antifreeze in a car radiator - it drives the freezing temperature down. Consequently, the cells' syrupy insides stay liquid even while the remaining 65 per cent of the water in the frog has turned to ice. Just as frogs use glucose, Arctic brine shrimp and many cold-tolerant insects use a sugar called trehalose, which forms a syrup as thick as stretchy toffee, is even better at lowering freezing points and stopping dehydration than glycerol or glucose. But just like glucose, it crosses membranes slowly. How then to get it into the cells so that it can work its magic? The answer, Beattie says, is to take advantage of the cold-induced leaky membranes. She and her UCSD colleague Alberto Hayek slowly cooled human insulin-producing cells in a trehalose solution, and just as the lipid membrane started to congeal at around 5 C, the trehalose leaked in. Then Beattie plunged the cells into liquid nitrogen to rapidly finish the freezing process. Given the progress that's been made, is there any hope of freezing and reviving a whole human? Barring some unforeseen breakthrough, such cryogenic time capsules will very likely remain impossible, according to most experts. Scaling up techniques that work on bits of humans won't work for the whole thing. high levels of sugar trigger diabetic shock, for instance, and glycerol would be toxic when you thawed out and started to metabolise it. And even if we could handle such chemicals, getting them inside all the cells in the body would be problematic. That's not to say that people like Storey don't wish they could freeze humans. 'If by magic I could fill you with high levels of sugar and put nucleating proteins in your blood,' says Storey, 'then I could freeze you.' unfortunately, the operative word, he says, is magic'.' Suggestion by poster: Try sorbitol instead. This sugar penetrates cell membranes much better than glucose or trehalose, and is nontoxic."

freezing and animals

Chapter 12.2

Freeze Tolerant Animals
For many animals that live in climates with extreme winter temperatures, the ability to survive freezing of body fluids is a necessary part of their existance. Natural freeze tolerance occurs in aquatic animals such as polar fishes and intertidal invertebrates, terrestrial amphibians and reptiles, and various polar and temperature insects. Various strategies have been worked out by these disparate animals to withstand the rigours associated with ice formation at low temperatures.

Freeze Tolerance in Amphibians and Reptiles
There are many examples of lower vertebrates that hibernate in temperature regions where ice growth in the extracellular fluid is tolerated within certain limits. For example, the wood frog, Rana sylvatica, is capable of withstanding temperatures as low as -8°C, with 65% of its body water converted to ice, or at temperatures of -2.5°C for periods of up to 2 weeks. Ice formation of this magnitude causes the cessation of all muscle movements (heart, breathing, vasoconstriction, skeletal), the onset of ischemia, and large changes in the volume of cells and organs. Other terrestrial frogs and some turtles display similarly advanced freeze tolerance while there are also many other reptiles and amphibians that are able to withstand short, mild freezing exposures typical of overnight frosts.

There are several factors that influence the ability of a vertebrate to survive extracellular ice formation (there are no examples of vertebrates that can withstand intracellular ice formation).

*
Assessment and Control of Ice Formation
It is essential that freeze tolerant animals initiate freezing within their body fluids at high sub-freezing temperatures, and that they can detect the presence of ice in their bodies. When ice forms in supercooled water, ice growth is rapid and the osmotic stresses that the cells face is severe. With no cryoprotectants present, the cells will be subjected to a high salt concentration and frozen into channels where no cryoprotectant is likely to appear, in order to mitigate this salt. If, on the other hand, ice growth is initiated near the freezing point, then the animal can take steps to minimize the physical damage by reacting to this ice growth.

Typically, wood frogs only supercool to -2°C or -3°C before ice growth begins. Spontaneous nucleation at such low degrees of supercooling is unlikely, thus there are probably ice nucleating proteins or bacteria on the surface of the frog that catalyze ice formation. Alternatively, contact with external ice will lead to ice growth inside the body cavity at the freezing temperature (-0.5°C). In addition to external ice nucleators, all freeze tolerant species generate ice nucleating proteins within their blood plasma during the hibernation season. These proteins are less efficient than the external ones, requiring supercooling to about -5°C to ensure ice nucleation. Because the plasma will freeze well before this temperature is reached, the function of these ice nucleators is uncertain. They may be involved in facilitating ice growth within capillaries, where the high curvature of the ice crystal would be inhibitory.

Ice growth through the organism is carefully controlled. Ice usually starts in the hind limbs and begins spreading throughout the body from there, taking several hours to grow throughout the body. Ice grows around the vital organs long before freezing occurs within the organs. Ice forms in the brain last, with the fluid portion freezing before the neural tissue. Melting does not occur with this same directional rigidity, but instead begins in the vital organs simultaneously, and then spreads outwards. Since the organs are the last to freeze, the cryoprotectant concentration is highest there, causing these regions to have the lowest melting point. The amount of ice that forms within the organs is limited by dehydration and ice formation in the fluid regions that surround the organs. At a temperature of -2.5°C, where 50% of the frog's body water is frozen, the eyes lose 3% of their water, the brain loses 9%, skeletal muscle loses 13%, the liver loses 20%, and the heart loses 24% of its water content.

Ice formation in the skin is detected virtually immediately by freeze tolerant frogs and the biological response, beginning in the liver, is fully active within two minutes.

*
Cryoprotection
The biological action that freeze tolerant species initiate, upon finding ice growing within their body, is the production and dissemination of enormous quantities of cryoprotectant. The cryoprotectants used are colligative in action, glucose and glycerol are two of the most common cryoprotectants (a particular species confines itself to the use of a single cryoprotectant).

When freezing is detected, a signal is transmitted to the liver where glycogenolysis, the conversion of glycogen to glucose, begins in earnest. Glucose levels within the liver will have risen by over six times within the first 4 minutes, and remain elevated for several hours. Blood flow distributes glucose throughout the body (there is no supplemental glucose production from other locations within the body) until freezing brings a halt to circulation. Thus the lowest concentration of glucose is in the skin and skeletal muscle (which freeze first) and the highest concentrations are in the vital organs (thereby depressing their freezing points the most).

The liver of freeze tolerant frogs is specialized for this task. It contains much higher levels of glycogen than is found in comparable non- freeze tolerant species. Likewise, the frogs' cells have much higher numbers of glucose transporters within the membranes to support cryoprotectant entry into the cells, the increase being seasonal as well. Animals that use glycerol as a cryoprotectant do not need to add transport proteins as cell membranes are naturally permeable to glycerol. It is not yet known whether aquaporins play a role in accelerating the large cellular water losses that must accompany freezing for colligative cryoprotection to be effective.

*
Lowered Metabolism and Limiting of Ischemia
The lowest temperature that freeze tolerant species are able to withstand is about -8°C. This is much too high to bring an effective halt to biochemical reactions; and indeed, the freeze concentration that occurs with ice formation may even accelerate some reactions. Thus these species must minimize ischemic damage while in the frozen state. There appears to be an active metabolic homeostasis that is maintained in the frozen state, along with significant production of antioxidant enzymes to combat reactive oxygen species.

*
Reanimation
All organ systems shut down during freezing with the heart being the last to stop (at about 12 hours after the onset of freezing). During thawing, the heartbeat is also the first physiological activity that is restored. Blood flow to the periphery is restored soon after, followed by breathing and then skeletal muscle activity. There are undoubtedly many biochemical event that must occur to reverse the process of cryoprotectant release and repair ischemic damage, but shortly after the ice melts, the freeze tolerant animal is able to hop (or walk or slither, as the case may be) away.

Aquatic Animals at Low Temperatures
There are many intertidal invertebrates that survive brief periods of extracellular ice formation. This occurs primarily by the mechanism of colligative cryoprotection, as in terrestrial animals. The real action here is the strategy that polar fishes have evolved for dealing with the freezing environment.

Seawater freezes at -1.9°C, a temperature that is reached during the winter in polar and temperature ocean regions. This is well below the melting point of the body fluids of marine fishes (-0.8°C). Although it is conceivable for an organism to exist with 1 degree of supercooling, the marine environment is one in which there are small ice crystals suspended throughout the seawater when it reaches the freezing point. Since it is necessary for fishes to live in this environment, and pass this water (with its ice crystals) through their gills, it is impossible for these organisms to avoid ice growth within their bodies. Yet they appear not to freeze until the temperature drops below -2°C, at which point they will freeze and die.

The melting point of the fluids within these polar fishes is -0.8°C, but the apparent freezing point (the temperature where ice begins to grow) is significantly lower. This freezing point depression is not colligative (although the depression of the melting point is) and is lost when the fluid is dialyzed through a molecular sieve with a cutoff of about 2500. The agents responsible for this freezing point depression are either glycoproteins (Antarctic and North-temperate fish) or proteins (Arctic fish). These compounds are generically referred to as antifreeze proteins.

*
Antifreeze Proteins
Antifreeze glycopeptides have a molecular weight between 2600 and 34000 while the antifreeze peptides range between 3200 and 14000. In solution these compounds form extended structures, usually helical rods. They are amphipathic molecules, with one side of the rod being composed of hydrophobic residues and the other side being composed of hydrophilic residues. On the hydrophilic side, there is a 4.5 Å separation between repeating threonine and aspartate residues that bind the protein to an ice lattice.

The thermal hysteresis, or the difference between the freezing point (crystal growth point) and the melting point is shown on the following graph for several of the antifreeze compounds.


Fig. 12.2.1 Freezing and Melting Points of Antifreeze Compounds.

Ice that grows in the presence of antifreeze proteins (AFP's) is spicular, forming long, thin structures with a hexagonal cross-section. The AFP's bind to ice steps along the a-axes of an ice crystal, so that spicular growth is growth that is restricted to the c-axis. The following diagram illustrates the structure of a hexagonal ice crystal.


Fig. 12.2.2 Hexagonal Ice Crystal.

When AFP binds to the a-axis steps, then water molecules cannot join the crystal between the AFP binding sites without introducing significant curvature to the growth along the a-axis.


Fig. 12.2.3 AFP binding to Hexagonal Ice Crystal.

At low degrees of supercooling, this increased curvature will completely impede ice growth along the a-axes. The basal plane will then get smaller with each step and the crystal will form a microscopic bi- pyramidal shape that is thermodynamically stable at temperatures below its melting point. Further cooling will lead to more rapid accumulations along the c-axis compared to the a-axes, leading to spicular crystals. Growth in the a-axes requires that the temperature be low enough to support the curvature between AFP molecules bound to the crystal. When this happens, the AFP's will be incorporated into the crystal as defects, rather than excluded as colligative solutes.

One consequence of the amphipathic nature of AFP's is that an ice crystal that has a surface coated with these molecules will present a hydrophobic exterior. This allows such ice crystals to grow through lipid bilayers without any thermodynamic exclusion. Once through the membrane and into the cytoplasm (that does not contain AFP's), the ice growth quickly spreads throughout the cell and leads to cell death.

Insect Adaptations to Low Temperatures
The ability of insects to adapt to diverse ecological conditions is legendary. This tremendous diversity is justly illustrated by their ability to withstand the intense cold of arctic and alpine environments. Indeed, the Arctic spring is accompanied by a veritable deluge of biting insects; a grim but unmistakable testament to their overwintering capabilities.

The adaptations that have evolved to allow insects to survive low temperatures are legion, but they can be classified along two general lines, freeze tolerance (the ability to survive following ice formation within the body cavity) and freeze avoidance (the prevention of ice formation within the body cavity at temperatures where such freezing would normall occur).

In addition to the problems posed by ice formation, there are also significant problems that must be solved for normal metabolism to occur at low temperatures. The maintenance of neural function, fluidity of cell membranes, pH control, activity of enzymes, adaptation to hypoxia, dehydration of body fluids, etc. all present obstacles to low temperature survival. Although these difficulties are formidable, they will not be discussed further here, as the adaptations to freezing temperatures are the focus of this chapter.

Very few insect species are actually exposed to the full rigors of winter temperatures as most choose an overwintering microhabitat that provides a buffered temperature. The habitats provided inside vegetation (logs, stumps, etc.) or under the soil provide thermal buffering, especially when covered with snow. In many climates, however, the organisms are still exposed to potentially lethal conditions throughout the winter. The particular adaptations associated with freeze tolerance and freeze avoidance allow these organisms to survive in such harsh environments.

#
Freeze Tolerance
Many species of insects have developed a tolerance for ice formation within their body fluids. The degree to which these species withstand freezing varies widely, from just a few degrees below freezing to -87°C for an Alaskan beetle. The strategies employed are legion, although the principle means for minimizing injury from ice formation is the use of cryoprotectants to reduce the amount of ice formed and the salt concentration at a given temperature.

*
Cryoprotectants
The cryoprotectants used by freeze tolerant species are similar (almost exactly so) to the compounds used by freeze avoidant insects to colligatively depress the freezing point. Glycerol is the most common cryoprotectant, followed by sorbitol and erythritol, ribitol, threitol, and sucrose. A multicomponent cryoprotection scheme is common, to reduce the concentrations of any given cryoprotectant to sub-toxic levels. The mechanism of cryoprotection appears to be simple colligative action, as in cryopreservation, with the additional benefit of stabilization of protein structure against low temperature denaturation.

*
Ice Nucleating Proteins
One strategy for mitigating the damaging effects of ice formation is to nucleate ice at a high sub-freezing temperature to avoid the high osmotic stresses associated with rapid freezing. Ice nucleators that have been found in insects are generally not too efficient, initiating ice growth at supercooling points between -7°C and -10°C, thus they are probably involved in avoiding intracellular ice growth rather than the directed ice growth seen in freeze-tolerant amphibians.

Some freeze tolerant insects have neither specialized ice nucleating proteins, nor an absence of ice nucleation sites (as in some freeze- avoidant insects). In a dry environment, they will supercool to near -20°C and then freeze and die. If they are inoculated with environmental ice at higher temperatures, however, they can survive. It seems, though, that most freeze tolerant insects produce ice nucleating proteins as part of their strategy for survival.

*
Stabilization of Bound Water
The water associated with macromolecules (bound water) is important for maintaining the tertiary structure of some molecules as well as the structure of membranes. It has been found that freeze tolerant organisms increase the amount of bound water in their systems during cold acclimation. That this confers additional tolerance to freezing is still a point of speculation.

*
Antifreeze Proteins
In many cases, damage from freezing has been linked to the rate of thawing, implicating the degree to which the ice undergoes recrystallization as a damaging mechanism. Since a few freeze tolerant insects produce antifreeze proteins, it has been speculated that these proteins minimize the injury associated with recrystallization of extracellular ice (AFP's are potent inhibitors of recrystallization). In fact, many of the freeze tolerant species that produce AFP's contain them in too low a concentration to produce thermal hysteresis; they are concentrated enough to inhibit recrystallization, however, since the thermodynamic driving force is much lower than for crystal growth in supercooled water.

*
Vitrification
It has been found that the hemolymph of a particular insect can be partially vitrified at cooling rates that are likely to occur in nature. Furthermore, the very low temperatures that some insects survive in the absence of ice indicate that vitrification could easily be achieved if the temperature went below the glass transition temperature. Thus it has been speculated that vitrification, or at least partial vitrification, may well be a strategy for freeze tolerance although direct evidence is thus far lacking.

#
Freeze Avoidance
Insects that are freeze-susceptible (ice formation in their body fluids is lethal) need to avoid freezing during the winter months. There are three basic strategies that insects employ to avoid ice formation within their body cavity: 1. Colligative depression of the freezing point through the concentration of a low molecular weight solute; 2. Production of an antifreeze protein (AFP) to lower the crystal-growth temperature non-colligatively; 3. Lowering of the nucleation temperature by removal of ice nucleation sites.

*
Colligative Freezing Point Depression
Colligative freezing point depression is simply the addition of low molecular weight solutes to the body fluids, exactly as occurs in normal cryoprotectant use. The solutes must be non-toxic in the concentrations required (molar), excluding many salts and small organic molecules. The polyhydroxy alcohols are the most common antifreeze solutes. Glycerol is undoubtedly the most prevalent polyol found in insects, but other compounds, such as ethylene glycol, sorbitol, and mannitol are also found in some species. There are other polyols that are found in elevated concentrations during the winter, but not in the molar quantities of an antifreeze solute (the combined effect, however, is to further reduce the freezing point of the solution); these include inositol, fucitol, arabitol, zylitol, rhamnitol, and ribitol. In conjunction with the polyols, elevated levels of the sugars trehalose, glucose and fructose are often found during the winter, as are elevated levels of the amino acid alanine. Such a multicomponent approach to freezing point depression allows a significant colligative action without bringing any one solute to the point of chemical toxicity.

*
Non-Colligative Freezing Point Depression
Thermal hysteresis producing antifreeze proteins (AFP's) have been found in many species of insects. The AFP's found in insects have, in some cases, been found to have a much higher activity than the AFP's isolated from polar fishes, primarily due to the increased concentration found in insects. Insect AFP activity has been found with a depression of the crystal growth temperature by as much as 6°C to 9°C below the melting point. None of the insect AFP's have been found to have carbohydrate moieties, in contrast to the antifreeze glycoproteins commonly found in antarctic fish.

The advantage of AFP's over colligative freezing point depression is in the much lower concentrations required and the ability to concentrate these molecules in the gut, where ice contamination is likely.

*
Supercooling
Pure water has a homogeneous nucleation temperature of -40°C, thus in the absence of any nucleation sites, it should be possible for an insect to survive very cold temperatures in a supercooled state if it could rid itself of all ice nucleators and prevent external ice from contacting its body fluids. It has been shown that some insects become much more susceptible to freeze injury if they are fed ice nucleating bacteria before exposure to cold temperatures, indicating that supercooling is a naturally occuring strategy for freeze-avoidant insects. In addition, insects have been found to have significantly lower supercooling points in winter, as compared with summer, without any lowering of their melting points or crystal growth temperatures. Some species remove ice nucleation sites seasonally whereas others have removed them permanently, over evolutionary time (a strategy that is evidently not compatible with all lifestyles).

There are some insect species found in the Canadian Rockies that have supercooling points of -60°C, combining colligative freezing point depression with an absence of ice nucleation sites to avoid ice formation at any terrestrial temperature (although these species are also freeze tolerant, there is simply no chance for them to experience temperatures of -60°C except in the laboratory).

BSCS | Bioinformatics

BCBS - High School

Main Surrealism Gallery page

how flour is made

how flour is made: "atching, rotating 'runner stone'. Each stone has special grooves or 'furrows' radiating out from the centre dividing the stone into 'lands' which are the areas of the stone which actually crush the grain. The grain is fed into the 'eye' at the centre of the horizontal stones and the 'furrows' distribute the grain out evenly to the lands across the stone while introducing air to cool the process. As the 'runner stone' rotates parallel to the stationary bedstone, the grain is crushed. The resulting meal is then carried further outwards along narrow furrows to be expelled at the circumference as flour.

The surface of the millstones, which must never touch, and the 'dress' of the furrows and lands are crucial to the quality of the flour are regularly maintained by skilled craftsmen."

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NETL's Cool Science

Play Putty Experiment

Play Putty Experiment


Play Putty Problem
by Mark J. Anderson, Stat-Ease, Inc.
(e-mail: mark@statease.com)

(This article is greatly expanded from a document contributed by Paul N. Sheldon of Honeywell International as an exercise for learning design of experiments (DOE).)

Description:
Mix ordinary white glue (Elmer's®) and a cross-linking agent: borax (20 MULE TEAM® brand from your local grocery store). Eureka! You've made play putty. To make things more interesting, add laundry starch (STA-FLO® concentrated liquid) to the mixture. See how well you can do with this home-made material in comparison to the real thing sold commercially as a toy: Silly Putty® (see note below).

Procedure:
These instructions leave plenty of room to be creative! Plan on taking at least two hours to complete the project. Have fun!

1. Brainstorm a list of desirable properties and how to quantify them. (Hints: consider bounciness (percent rebound), elongation (percent stretch) and possibly surface sheen and tackiness (ability to pick up printed copy from newspaper).)
2. Select at least two properties and decide exactly how you will measure them. Do your best with materials at hand. At the very least, establish ratings on a 1 to 9 scale, with 1 being worst :(, 9 being best :) and 5 so-so :|.
3. With the aid of Design-Expert® software, plan a mixture experiment. Here's a specific recipe modified from www.elmers.com:
a. Cover your work area with newspaper or paper towels.
b. In one bowl, combine 50 milliliters (ml) of glue and 25 ml cold water. Stir with a plastic spoon.
c. In another bowl combine 2.5 ml (1/2 teaspoon) of borax and 25 ml hot water. Mix with a straw.
d. Using the output from Design-Expert software for the recipe, add the borax/water (and/or the liquid starch) to the glue mixture. Stir with the spoon. Then knead it by hand when it forms a glob that's too stiff for the spoon. Lift the glob from the bowl and allow the moisture to drain off. You've got play putty!
e. Add food coloring if you wish (wear rubber gloves unless you want your hands the same color!). Let it dry for about an hour. It should become smooth and rubber like. Store the putty in an airtight container (such as a Ziploc® bag). It should last about 2 weeks before drying out.
4. Do the experiment and analyze the results.
5. Find the most desirable composition.

Other Things to Try:
· Does cooling improve the "bounceability"? If cooled too much, in a freezer for example, will the putty shatter when bounced?
· How does your putty deform with time? (Suggestion: Take a blob, roll it in a ball and stick it to the side of a metal cabinet or refrigerator. See how far it flows as days go by.) Does temperature affect the deformation?
· What happens if you hit a ball of putty with a heavy object, such as a hard-cover book? (Hint: Putty behaves as a "dilatant," which means it reacts differently to hard, fast pressure than it does to slow, even pressure. As the Zen proverb says: "Only when you can be extremely pliable and soft can you be extremely hard and strong.")"

Consider a second set of mixture experiments that incorporates a gas-producing reaction to reduce density of the putty. This can be done by adding a few spoonfuls of baking soda (Arm & Hammer®) to the borax solution and vinegar to the glue on a 1:1 basis. What will this do to the physical properties of the putty? Will it be putty, or something else altogether?

Scientific Details:
Play putty involves a reaction between polyvinylacetate in the white glue and borax (Na2B4O7-10H2O) to form a highly-flexible, cross-linked polymer. Two glue molecules (the monomer) become cross-linked by a borax molecule via reaction of alcohol end groups. Acetic acid is generated as the byproduct - two molecules per cross-link. Many borax cross-links occur, thus "glomming" together many polymer molecules to form a pliable putty material.

Adding commercially-produced starch in liquid form creates complications in the chemistry. For example, the STA-FLO brand lists not only water and corn starch as ingredients, but also (in order of concentration?) borax, "processing aids," preservative, "ironing aid" and perfume. As noted above, borax acts as a cross-linker, but the starch itself acts as a co-polymer or perhaps in some other way to modify the properties of the putty. (Sorry, I am a chemical engineer, not a chemist! Mark.)

Baking soda is sodium bicarbonate (NaHCO3) - a base. The vinegar, a weak form of acetic acid (CH3COOH), reacts with the baking soda to produce water and carbon dioxide (the gas).

The Story of Silly Putty:
During World War II, while looking for a cheap substitute for rubber, an engineer for General Electric, James Wright, accidentally developed Silly Putty®, now a famous toy.* Silly Putty is an organosiloxane polymer made from silicone oil and boric acid. Unlike home-made "play putty" it will not dry out, because it's not water based. Silly Putty has flexible molecules that, when 'smooshed' by fingers, slide over each other and cause the material to flow. For years, prominent physicists have pondered over the super bouncing properties of Silly Putty, which rebounds 80% or more. (For more fascinating facts on this incredible material, see www.sillyputty.com. They offer a short, but riveting, movie on how it's manufactured at http://www.sillyputty.com/silly_science/making.htm.)

According to the makers of Silly Putty and sources at Alfred University (Alfred, NY), Silly Putty has been put to many experiments in the past. Don't try these at home!

· It's flammable and when lit, the flame is a very bright white. Though it burns slowly, the left over ash from the putty crumbles very easily.
· When Silly Putty is microwaved in a drinking glass for about 3 minutes, it becomes very sticky. However, when cooled the putty returns to the same state it was in before.
· When it's baked at 450 degrees F for 15 minutes, it gives off very bad fumes.
· In 1989 a graduate student at Alfred University dropped a 100-pound ball of Silly Putty from the roof of the Engineering Building. It bounced about 8 feet into the air, returned to Earth, and shattered on the second impact.
· On Apollo 8, the astronauts used it to stabilize their tools in zero gravity.

One thing you should try at home, or better yet - the office, is using Silly Putty (or the like) as a stress reliever. According to the Wall Street Journal (see reference in footnote) "a nice, chunky handful, massaged and stretched and squeezed, is the perfect workplace stress-reliever. Some say ricocheting it off their office walls helps them think. Others spend hours sculpting characters, shapes and animals."

*An alternate story in the September 10, 2002 Wall Street Journal (WSJ) gives credit to a Dow Corning scientist, Earl Warrick, now 91 years old, for accidentally inventing this nontoxic substance while searching for a silicone-based rubber substitute during World War II. Dow Corning, who specializes in silicones, still makes the material under the brand-name "3179 Dilatant Compound." It's available only in 50-pound quantities. (For ideas on how to order the stuff in lesser quantities, but more than what's normally sold in stores, see http://www.hart.com/putty/ or http://www.puttyworld.com/.). According to WSJ, Dow-Corning sells most of its 100,000-pound annual production of dilatant compound to Crayola maker, Binney & Smith Inc., in Easton, PA, which processes it and sells it under its Silly Putty brand. (See the article Wall Street Journal article, entitled "Some Grown-Ups Go Silly for Buying Putty in Bulk," at http://online.wsj.com/article_email/0,,SB1031611692226887235,00.html).

Goop, Gloop, Glop, Flubber, and Fun

stdin: Goop, Gloop, Glop, Flubber, and Fun

Here are a bunch of recipes that are fun for summer, or any time.
Described as --- physics-defying "stuff" to make, play with and learn
from. I like the scientific explanations for some of them. Someone sent
these to me, and I don't know the authors, but the ideas are in many
books in one form or another...so hope you find something fun to try. I
haven't tried them all myself, but still...here they are!!
MaryAnn
maryann@brightring.com
==============

****FLUBBER
Borate solution:
2/3 cup warm water
1 1/2 teaspoon powdered Borax
3 drops food coloring
Mix together in a 1 cup measuring cup using a wooden spoon Glue Solution:
3/4 cup warm water
1 cup white school glue
Mix together in a mixing bowl using a wooden spoon. Pour the borate
solution into the bowl with glue solution. Use your hands to gently lift
and turn the mixture until only one tablespoon of liquid is left. Flubber
will be sticky for a moment or two. After the excess liquid has dripped
off, Flubber is ready. Store in a plastic bag in the refrigerator. When
you are through, discard in a waste can. DO NOT try to wash it down the
sink. If it dries on carpet or clothing, cover it with a cloth soaked in
vinegar to de-gel it, then wash the area with detergent and water.

**** GLARCH
Measure 1/2 cup liquid white school glue into bowl. I get the best
results with Elmer's School Glue. Measure 1/4 cup Sta Flo liquid starch
into the same bowl. Mix together with a wooden spoon. After the substance
becomes too thick to use the spoon, continue mixing with your hands. This
works quicker with warm hands. Glarch may be stored in a plastic bag.
Wash all supplies.

**** OOBLECK
Measure 1 1/2 cups of cornstarch and put in a pie pan or container If you
want a color of Oobleck add the coloring to the water first. Then
gradually add approximately 1/2 cup of water to the cornstarch. Stir well
(this will take some time). Add small amounts of more water or cornstarch
until you get a mixture which 'tears' when you quickly scrape your finger
through it AND THEN 'melts' back together again. Oobleck is often
referred to as a 'non-Newtonian' substance because it does not behave as
Newton's Third Law of Motion states; for every action, there is an equal
and opposite reaction. Applying this principle, you would expect Oobleck
to 'splash' when you 'smack' it with your hand. (Smacking is the action,
splashing is the reaction.) However, when you try this out. Oobleck does
not splash, in fact, it becomes a solid substance for a few moments. Why?
Scientists explain this as follows. Uncooked corn starch particles are
structured in both crystalline and noncrystalline arrangements. When
slowly mixed with water, the non crystalline
structures of corn starch absorb most of the water. When you smack or
stir it rapidly, you increase the temperature and pressure on the mixture
which causes more non crystalline structures to form. These new
noncrystalline structures absorb more water and the mixture becomes
thicker:hence the appearance of a solid. When you discontinue the
pressure, the number of noncrystalline structures decrease and water is
released, creating the 'soupy' mixture.

**** GUAR GUM SLIME
Put 1/3 cup warm water into a paper cup. Use a stirring stick and add 1/4
teaspoon guar gum into the water. Stir until mixed and the guar gum is
dissolved. Optional:add 2-5 drops of food color. Mix thoroughly. While
stirring, add about 2 tablespoons 4% borax solution to the guar gum
mixture. Once the mixture has jelled, remove the Slime from the cup and
knead it in your hands. Place the Slime in a zipper-type plastic bag to
prevent it from drying out. A few drops of Lysol can be added to the
Slime to minimize the formation of mold and extend the lifetime of the
Slime. You can get guar gum from Flinn Scientific.

**** POLYVINYL ALCOHOL SLIME
Put 2 tablespoons 4% polyvinyl alcohol solution into a paper cup. Add 2-3
drops of food color. Mix Pour in 4% borax solution into the cup of
polyvinyl alcohol solution. Stir constantly while the borax solution is
being added. Once the gel has formed, remove it from the cup and knead it
in your hands. Place the Slime in a zipper-type plastic bag to prevent it
from drying out. A few drops of Lysol can be added to the Slime to
minimize the formation of mold and extend the lifetime of the Slime.

**** SLIME OLYMPICS
Experiment with each of the Slimes by squeezing it; forming it into a
ball and throwing it onto a tile or linoleum floor; by pulling I gently
and then quickly; and by pressing the putty on top of your name written
with a water-soluable, felt-tip marker. Note: Differences: The Guar Gum
Slime is less viscous (more runny) and can be stretched further before
breaking than the Polyvinyl Alcohol Slime. Similarities: Both slimes are
clear and colorless (if food color is not added), can be molded into
different shapes, will flow from a funnel over a period of time, will
bounce (to a certain degree), and will become flat if left sitting on a
flat surface.

The following recipe is from Paula Lee pmlee@ties.k12.mn.us:
**** LOTION PLAYDOUGH
1 cup flour
1T vegetable oil
2T hand lotion
1/2cup salt
2 t. cream of tartar
1 c water
food coloring
Mix. For kids crafts.

The following recipe is from the Mudworks book.
**** FUN DOUGH
1 cup corn starch
1 1/2 cup baking soda
food coloring
water
Add water to dry ingredients to desired texture and consistency.
Color with food coloring.


======================

maryann@brightring.com
http://www.brightring.com

Strange fluids

Chemical and Process Engineering: "Some Strange Fluids

Not all fluids are the same. Some are thick and some are thin. Some get thicker when you stir them, some get thinner. The thickness of a fluid is referred to as its viscosity which has units of centipoise (cP). The viscosity tells us how hard we have to push the fluid to get it to move. Here's some typical viscosities:

* Water 1 cP
* Air 0.001 cP
* Golden Syrup 25000 cP
* Engine oil 200 cP

You can have fun with corn flour or custard powder (some of the cheaper brands don't work so well).

Put some dry corn flour or custard powder in a bowl. Add just enough water so that you can pour it out (into another bowl). You've probably alread found that it gets harder (more viscous) as you mix it. The hard you try the harder it becomes. If you want to create a mess try rolling some into a ball between your fingers and then between your hands. As soon as you stop rolling it, or when you pass it to someone else it will start to flow. Yuk. We refer to this fluid as a shear thickening, or dilatant, fluid.

The opposite behaviour is so common you don't even notice it. Think of thick yoghurt, for example. When you are not stirring it is hard to pour but when you stir it, it seems relatively thin. A lot of foods, or fluids that contain long molecules are like this. we call them shear thickening, or pseudoplastic, fluids.

What about toothpaste or mashed potato or putty? If you don't push them they don't flow. They are solid until you push hard enough and then they become liquid. Yes they are solid and liquid. We call them Bingham Plastic fluids.

Golden syrup is quite boring by comparison. It seems thick and it is thick. When you stir it, it stays just as thick. Its a normal, Newtonian, fluid."

Gak, Oobleck, Flubber Recipe

Gak Recipe - A to Z Home's Cool Homeschooling: "Gak Recipe
Ingredients:
# 1 cup white glue
# food coloring, your choice of color (optional: coloring can stain!)
# 1 cup liquid starch

Pour glue and coloring in plastic container.

Stir until color is thoroughly mixed in.

Add starch a little at a time, stirring with a spoon or kneading with your fingers as mixture thickens.

Keep stirring until mixture holds together like putty.

Test with your fingers: if too sticky, add more starch in small amounts until mass is smooth and rubbery.

Food Color stain removal information.

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Oobleck Recipe

Another interesting substance is called 'oobleck.' It also acts like a liquid until pressure is applied.
Ingredients:

* 4 parts cornstarch
* 1 part water
* food coloring is optional

Glorax (Flubber) Recipe

* Put 3 T. of water into a ziploc bag.
* Add 1 T. of white glue.
* Add 2 heaping T. of Borax (laundry detergent). It must be Borax.*

Shape into a ball. If the mixture is too sticky, roll the ball in a little bit of Borax. Enjoy stretching this elastic substance.

Silly Putty Recipe

This will bounce and pick up pictures from the paper just like the name-brand stuff.

* Add: 1/2 cup water to 1/2 cup Elmers Glue (Not School Glue!)
* Mix and add 3 drops of food coloring
* Make Borax solution: Take 2 tablespoons borax (You can buy this at a grocery store or online) and add to 1 cup of water and stir.
* Add 1/2 cup of borax solution to water and glue mixture
* Stir and store in a plastic bag

Mix well. Add food coloring if you wish. Let it dry about an hour. When ready, it will be smooth and rubber-like. Store in an airtight container."