Science Lab in the Supermarket (Illustrated)

by Bob Friedhoffer

  How many detergent manufacturers do you think there are? Dozens? Hundreds? Go to a supermarket and read the labels on all the packages of laundry detergent. Make a list of the manufacturers and write down how many brands each manufacturer makes. What does your research show? Are you surprised by the results?

  EXPERIMENT 14

  Materials

  1 tablespoon (15 mL) each of several laundry detergents

  A plastic bag for each sample

  Masking tape

  A permanent-marking pen

  One glass per detergent sample

  Warm water

  One spoon per detergent sample

  One 1-inch (2.5 cm) square of soiled cloth per detergent sample

  A sink

  Procedure

  1. Collect detergent samples from friends and neighbors.

  2. Put each sample in a plastic bag. Write the brand names of the detergents on separate pieces of tape and attach each label to the appropriate bag.

  3. Pour 4 ounces (120 mL) of warm water into each glass. Make labels for each glass.

  4. Add each detergent sample to the appropriate glass.

  5. Stir the contents of each glass for about 30 seconds. Do all detergents produce the same amount of foam?

  6. Place a cloth square stained with dirt or grease in each glass and stir for 30 seconds.

  7. Remove the cloth square from each glass and rinse it in clear water. (Keep track of which square came from each glass.)

  8. Allow the cloth squares to dry.

  Results

  Compare the cleanliness of each cloth square. Which detergent cleans the best? Compare the cloth squares washed in detergent to those washed in soap.

  THE LAUNDRY BLUES

  When white clothing is laundered, a yellowish residue is sometimes found on the fabric. Detergents with optical brighteners help to hide the yellow.

  In the not-too-distant past—before optical brighteners had been invented—a separate "blueing" agent, which contained blue dye, was added to the washing machine during the final rinse cycle to counteract the yellow residue. The blue dye was absorbed into the fabric's fibers. The blue dye reflected blue light more strongly than it did yellow light, so the yellow residue was not so noticeable. Unfortunately, the blueing caused the fabric to reflect less light than it received. As a result, clothing looked whiter, but not brighter.

  Today we use optical brighteners. They contain dyes that are absorbed by clothing during the wash cycle and are not removed during the rinse cycle. These brighteners transform ultraviolet light, which is ordinarily invisible, into visible light that is more blue than anything else. As a result, the yellowish residue is much less noticeable.

  CLEANING WITH SCRATCHY STUFF

  If you've ever washed dishes by hand, you know that using a sponge with a scrubbing pad on one side makes the process much easier. Steel wool can make cleaning dishes, pots, and pans even easier.

  What is steel wool? Steel wool does not come from steel sheep. It is made in factories—from thin strands of steel that are compressed. Some brands of steel wool are even filled with soap. Plastic wool is similar to steel wool, but it is made from strands of plastic.

  These products are more effective than a sponge because they are generally harder than the food they are meant to scrape off dishes, pots, and pans. Unfortunately, this hardness can be a disadvantage. Steel wool can scrape painted or enameled designs off dishes. It can also scratch Teflon™ pots and pans. Teflon—a low-friction, nonstick coating—is quite soft compared to steel wool. If you scour a Teflon-coated pot or pan with steel wool, you will scratch the Teflon and the nonstick surface will be damaged.

  THE MOHS' SCALE: WHAT DOES HARDER MEAN?

  German scientist Friedrich Mohs (1773-1839) developed a scale that tells us the relative hardness of materials. There are ten minerals in the original Mohs' scale. Each mineral listed can be scratched by the minerals with a higher number on the list. The softest material on the list is talc—the material chalk and talcum powder are made from. The hardest material on the scale is diamond. Your fingernails would measure about a 2 on the Mohs' scale.

  The Mohs' scale is very useful for scientists, but most people have probably never heard of many of the minerals included on the list. The information below describes some familiar items in terms of their hardness.

  * Your fingernail can scratch materials with a Mohs' scale rating of 1 or 2.

  * A copper penny can scratch materials with a rating of 3, if pressure is applied.

  * A steel knife can easily scratch materials with a rating of 4.

  * A steel knife can barely scratch materials with a rating of 5.

  * A steel knife can be scratched by materials with a rating of 6.

  * A piece of glass can be scratched by materials with a rating of 7.

  * A diamond can scratch any substance. It is the hardest naturally occurring material on Earth.

  Chapter Seven

  Getting Stuff Out of Bottles

  AEROSOL SPRAY CANS AND BOTTLES

  Many products in the supermarket come in self-dispensing spray bottles and cans. These containers make it possible to apply the contents directly to a surface. For example, the sprayer on window cleaner allows you to spray it directly on a window. You do not have to pour the cleaner on a cloth and then wipe the cloth on the window. The sprayer makes the job quicker and easier.

  The sprayer on a bottle of hair spray allows you to spray the aerosol directly on your hair. An aerosol is a suspension of fine drops of a liquid or solid in a gas. Many room deodorizers also come in the form of an aerosol. When you spray a room deodorizer in the air, the liquid comes out in tiny drops that stay suspended in the air for a short time. Before you read any further, try to answer two questions: "How do spray cans like Finesse® hair spray work?" and "How do spray bottles like Windex™ window cleaner work?"

  SPRAY CANS

  The contents of spray cans—room deodorizer, deodorant, hair spray, or other materials—exert a great deal of pressure against the sides and bottom of the can. As a result, these cans must be sturdy and have a concave bottom. If the bottom of the can were flat, the tremendous pressure inside the can would push against the bottom until it buckled and became convex. Spray cans, such as the kind that contain hair spray, usually have some sort of plastic button at the top. When you push the button, the seal between a washer and a flat disk inside the can is broken. As the disk moves downward, it pushes against a spring.

  At the same time, a tiny amount of liquid hair spray in the reservoir flows into the small gap that has been created between the flat disk and the plastic piece above it. The hair spray is forced through a hole in the center of the plastic piece and out through another small hole in the side of the button. The pressurized contents flow out of the can as a fine mist.

  A dip tube extends to the bottom of the can. A propellant inside the can forces the liquid up the dip tube and into the reservoir. To be a good propellant, a substance must be able to maintain a steady pressure as the amount of liquid in the can decreases. A propellant must also be able to work at as low a pressure as possible. If the gas pressure inside a spray can is too high, the can may burst.

  Air is not a good propellant. It cannot force liquid out of a half-empty spray can unless the pressure is so high that there is a chance of the can bursting. At one time, Freon™ was the propellant of choice. Freon is ordinarily a gas at room temperature and sea-level air pressure, but it transforms to a liquid when placed under a pressure roughly six times that of average atmospheric pressure.

  Inside the can, Freon initially exited as a liquid mixed with the product. As the product was used and the pressure inside the can decreased, the open space above the liquid was filled with Freon gas. Each time the button was pressed, the seal between the washer and the flat disk was broken, and Freon forced the product out of the can.

  Not all of the Freon in the can was converted to a gas. Some was released into the air along with the produ
ct. In the 1980s, scientists discovered that the small amounts of Freon that escaped from each can were carried to the upper regions of the atmosphere. Over time, the Freon from millions of spray cans had built up in the upper atmosphere. When the Freon came into contact with ozone molecules, a chemical reaction occurred. This reaction destroyed the ozone.

  Ozone is a very important part of the atmosphere. The molecules that make up the ozone layer, which surrounds Earth, protect humans and other living things from the sun's damaging ultraviolet rays. Scientists noticed that, at certain times of the year, a hole was developing in the ozone layer. Freon was very useful, but it was also putting us in danger. The United States and many other countries are no longer using Freon in spray cans. It has been replaced by less harmful gases.

  SPRAY BOTTLES

  Spray bottles, such as the ones that contain Windex and other window cleaners, work differently from spray cans. They are not pressurized, and the spray mechanism consists of a small pump. This pump uses air pressure to force the liquid out of the bottle.

  Air is constantly pushing against surfaces, including the surface of the liquid in a spray bottle. When you press the trigger of a spray bottle, a plastic piece inside the spray mechanism compresses a spring behind it. As the plastic piece moves backward, all of the air in the cylinder surrounding the plastic piece and the spring is pushed out of the cylinder.

  As the trigger returns to its starting position, so does the plastic piece inside the cylinder. The air pressure inside the cylinder decreases. Because the air pressure in the rest of the bottle is greater, liquid is forced up the dip tube, through the back of the cylinder, and into the tube at the top of the spray mechanism.

  When the trigger is pushed a second time, the fluid is forced out of the bottle and onto a window or other surface.

  Observation 9

  With your parent's permission, examine the mechanism inside an empty spray bottle.

  CAUTION: Do not do this with a spray can!

  After you have removed the mechanism, rinse it and take it apart. Can you see the parts shown in the illustration? If you need to cut part of the mechanism open, use scissors, or ask an adult for help.

  BABY BOTTLES

  Baby bottles have changed a lot over the years. At one time, all baby bottles were made of glass. To drink the formula, a baby would have had to create a fairly strong vacuum in his or her mouth. This would cause another vacuum to develop in the bottle. When the baby's mouth relaxed its grip on the nipple and swallowed formula, air entered the bottle to fill the vacuum. This air mixed with the formula and was also swallowed by the baby. The air built up in the baby's stomach and caused pain. To relieve this pain, the baby had to be burped. This involved gently tapping the baby's back until the air was forced out of the baby's stomach.

  Eventually, someone came up with a brilliant idea. That person designed a plastic bag that fit into a plastic bottle. The bag was filled with formula. As the baby sucks formula out of this bottle, the pressure inside the bag decreases, and atmospheric pressure collapses the bag. As a result, no additional air can enter the bag. This keeps the baby from taking in air along with his or her formula. This means no stomach pain for the baby. This makes everyone happier.

  Glass bottles are also a pain in the neck because they must be sterilized each time they are used. Another advantage of plastic bottles is that the inner plastic bag can be thrown away when the baby is done drinking. Before the bottle is reused, a new sterile bag is placed inside the bottle. When these bottles were introduced, parents rejoiced. They no longer had to sterilize bottles in boiling water.

  Chapter Eight

  The Cooler and the Freezer Aisles

  Much of a supermarket's space is taken up by refrigerators and freezers. The refrigerators contain cold cuts, chicken, beef, seafood, orange juice, cheese, butter, milk, and cream. The freezers hold a variety of frozen desserts, vegetables, pizzas, and TV dinners.

  SOME COOL QUESTIONS (AND ANSWERS)

  * Why do some supermarkets have long, vertical plastic strips covering doorways leading into the meat department's back room, instead of swinging doors?

  The meat department is kept cooler than the rest of the store to help prevent meat from spoiling. These strips of plastic help keep the warmer air in the store from mixing with the cooler air in the meat department. When someone moves from the store to the back room, a swinging door lets in more air than the plastic strips.

  * Why do your feet get cold when you open the door of an upright freezer?

  More expensive frozen foods are often displayed in upright freezers. When the door is opened, cold air escapes out of the bottom and is replaced with warm air coming in at the top. As the cold air flows out, it makes your feet cold. To be most efficient, this kind of freezer must be filled with many packages. When it is full of packages, there is less air to flow out.

  * Why do the doors of upright freezers get foggy?

  When upright freezers get all fogged up, it is difficult to see the tempting treats inside. As you know, whenever the door is opened, warm air full of water vapor rushes in, and cool air flows out. When the warm air comes into contact with the cool glass and sides of the freezer, the water vapor cools, condenses, and becomes a liquid. That liquid causes the "fog."

  * Why doesn't the cold air flow out of open-top freezers? Cold air is more dense, or heavier, than warm air. Because the cold air inside an open-top freezer is denser than the warmer air outside, it will not rise up and flow out of the freezer. As a result, customers can look down into the freezer and easily pull out what they want.

  * Why are boxes of frozen food sometimes covered with ice crystals?

  This ice forms when warm, moist air enters the freezer. The moisture in the air condenses and then freezes on the package, usually as a wispy-looking frost. There is nothing wrong with these packages of food.

  Ice may also form if packages thaw out and are subsequently refrozen. This ice usually forms in chunks, rather than as wispy-looking frost. This type of ice indicates that the package spent too much time outside a freezer or that the store's refrigeration system stopped working for a while.

  You shouldn't buy a package with this type of ice. There's no way to know how long it was thawed out. It is possible that large quantities of bacteria had a chance to grow inside. Eating the food could make you sick.

  Chapter Nine

  The Dairy Case

  Milk is a complicated mixture; it generally consists of 87 percent water, 5 percent lactose (a type of sugar), 4 percent fat, 3 percent protein, and 1 percent ash. Many nutritionists claim that milk is very close to being the perfect food—it is full of protein, minerals, vitamins, and amino acids.

  Where does the milk you buy in the supermarket come from? You probably know that it all starts with cows. Cows convert the food they eat into milk. It is important that farmers watch what their cows eat because certain foods can affect the taste of milk. If cows eat onions or cabbage, their milk will taste terrible. Most dairy farmers feed their cows hay, corn, or other grains.

  Farmers milk the cows and send the raw milk to be pasteurized. During this process, the milk is poured into huge vats and heated to destroy most of the bacteria and other microorganisms that could make you sick. In some cases, it is heated to a temperature of at least 145˚ F (63˚ C) for 30 minutes. In other cases, it is heated to 161•‹F (72˚ C) for 15 minutes. After the milk is heated, it is chilled and stored at a temperature of no more than 45˚ F (7˚ C).

  In some cases, milk undergoes a process called ultra-high-temperature sterilization (UHT) instead of pasteurization. In this process, milk is heated to 280˚ F (138˚ C) for 2 seconds to destroy all the pathogenic (disease-causing) microbes. This milk can be stored for a very long time at room temperature, so you will find it on supermarket shelves rather than in the refrigerated dairy case. One popular brand is Parmalat®. Once the package is opened, bacteria in the air can enter, so then it must be stored in the refrigerator.

  W
HERE DOES CREAM COME FROM?

  As you learned above, the normal fat content of milk is about 4 percent. Under normal conditions, the fat and the water in milk tend to separate. In the "olden days," when milk was delivered to the front door by a milkman, the cream (fatty portion) of the milk would separate and float on top of the rest of the milk.

  The milk you buy today does not have separate layers because it is homogenized. In this process, the fat globules in milk are broken down and evenly distributed throughout the milk. This prevents them from separating out of the solution and forming a separate layer of cream on top.

  Sometimes we want the fatty cream to separate from the rest of the milk. After all, without cream there would be no cheese sauces or whipped cream for ice cream sundaes.

  Cream and skim milk are partners. When all the fatty cream is removed from milk, the watery liquid left behind is skim milk. To remove all the cream, a machine called a separator must be used. A separator works just like a centrifuge or the spin cycle of a washing machine. The separator spins the milk until all the lightweight watery milk moves to the top and the heavier cream is left behind. The skimmed portion is poured out of the container and processed separately.