Welcome to Eggs-periments!
(Warning: This page contains an awful lot of bad, bad puns.)
Fellow eggs-perimenters, rejoice! The kitchen is our laboratory, and the test subjects are plentiful: a dozen in every carton, and 18 in a flat! In Eggs-periments we delve into the myriad mysteries of the unfertilized chicken egg, from its unicellular singularity to the strength of its shell, from its outstanding albumen to the bulk of its yolk. Eggs are commonplace, but they’re uncommonly complex, as we’ll discover in a series of eggs-periments drawing from the fields of chemistry, biology, mechanical engineering, culinary science, and others. Simply incredible, eminently edible, eggs-emplary in every way, the egg is our eggs-position, and through it we shall become eggs-perts!
Lesson 1: Egg-spin
Take two unmarked eggs, one raw, one hard-boiled. Without cracking them open, how can you determine which is which? You spin them, of course!
Spin the eggs simultaneously, side by side on a flat surface. Observers may notice that one of the eggs spins in tight, quick rotations, while the other wobbles wildly. With the index fingers, try and stop the spinning motion of the eggs. One will stop immediately with a firm touch, while the other, once the finger is lifted away, will continue to wobble. What eggs-actly is going on here?
The hard-boiled egg has become solid within, due to the denaturing of the proteins in the yolk and albumen, or egg-white. The egg-white proteins are known as globular proteins, meaning that the chains of amino acids are looped in something approximating a spherical shape. When these proteins are agitated by heat (as is inevitable when one is boiling an egg), they bounce around, colliding with one another and dismantling the weak chemical bonds that link the amino acids to one another. This is called denaturing the protein. As the egg remains suspended in the boiling water, these collisions create new chemical bonds—but instead of acid-to-acid, these new bonds connect one protein strand to another. The end result is a lattice of protein strands, denatured and bonded anew into a solid mass.
Thus, the hard-boiled egg spins with denatured efficiency, while the raw egg, with its liquid contents sloshing about, wobbles in a haphazard fashion. The hard-boiled egg stops spinning when touched, because there is no countervailing motion from the solidified contents. The raw egg, on the other hand, keeps gyrating about after being stopped, due to the egg white’s continuous rotation within the shell.
Lesson 2: Sink or Swim
Does an egg float in fresh water, or sink? What about in salt water? This eggs-periment works best with two large, clear glass jars filled halfway with warm water, placed side by side. Dropping an egg in each jar, what is immediately apparent? They sink.
Start pouring salt into one of the jars, a teaspoonful at a time. (Make sure the salt dissolves—stirring gently with a spoon helps.) Slowly, a remarkable thing starts to happen. The egg is being lifted from the bottom of the jar! As more salt is added, the egg eventually bobs to the surface, and the eggs-perimenter is aghast. What just transpired?
Because an egg is denser than fresh water, it sinks. (Remember, density is expressed as mass divided by volume.) But with the addition of salt, the water’s density increases, until it reaches a concentration at which the egg, being less dense than the water now, begins to float. To eggs-plore further, pour half of the salt water out and replace with fresh. Notice now that the water’s density has been altered, and the egg no longer floats at the top, but usually somewhere in the middle. And, because the salt water is denser, fresh water floats above it—so, provided that the water hasn’t been mixed too thoroughly, spooning off the water at the top should leave the remaining liquid with a higher salinity, causing the egg to again bob up to the surface.
Lesson 3: Structural Integg-rity
Cracking an egg against the edge of a pan doesn’t take much oomph. Neither, for that matter, can one toss an egg around for too long without making a mess. We English-speakers even have an expression to describe an emotionally fraught, fragile situation: walking on eggshells. But wild bird eggs, in order to be incubated successfully, need to be perched upon by the birds—some of which are rather hefty—or else buried under a substantial weight of self-heating compostable material. How do the eggs withstand this constant pressure?
The answer lies in the shape of the shell, and how the eggs are oriented relative to the pressure. The question we pose: Can six eggshells hold the weight of a dictionary? How about three dictionaries? Materials required: twelve large eggs (cracked in half, drained and cleaned, with the rounded ends cut off with scissors), masking tape, and some fat tomes.
The cleaned, dried eggshells should be arranged in two rafts, six shells apiece, held together with masking tape. One raft must be constructed of shells lying length-wise—that is, turned on their sides—while the other made of shells standing upright. Start piling on the dictionaries. What is the result?
The raft of sidelong-shells crumples easily under the weight of a dictionary, while the upstanding shells can withstand two, even three tomes. The reason is the shape: an egg’s load-bearing capability comes from the arch of its pointed end, intended to take on pressure from the top down. An egg on its side becomes compromised structurally; this is the weak point, and the reason why an eggshell offers very little resistance to pressure on its sides.
Lesson 4: Eggs, defrocked
Ever wondered what the inside of an egg looks like—without cracking the shell? Sure, breaking eggs is fun and easy and all that, but in order to fully appreciate the unicellular anatomy of an egg, a more subtle approach is required. (Also, the next lesson calls for raw, shell-less eggs, so we’d better figure out how to obtain them.) For this eggs-periment, we’ll need a large glass container (a Pyrex casserole dish works well), some white vinegar, plastic wrap, and a couple raw eggs.
Here’s the procedure:
1. Place the eggs in the container, taking care that they are not touching one another.
2. Add enough vinegar to cover the eggs. (Notice bubbles forming on the shells? We’ll eggs-plain later!) Cover the container, put it in the refrigerator, and let the eggs sit in the vinegar for a day or so.
3. Use a big spoon to scoop the eggs out of the vinegar. Be careful—since the eggshell has been dissolving, the egg membrane may be the only thing holding the egg together. The membrane is not nearly as durable as the shell.
4. Carefully dump out the vinegar. Put the eggs back in the container and cover them with fresh vinegar. Leave the eggs in the refrigerator for another 24 hours.
5. Scoop the eggs out again and rinse them carefully. If any of the membranes have broken, letting the contents ooze out, throw those eggs away.
6. When you’re done, you’ll have an egg without a shell. It looks like an egg, but it’s translucent—and the membrane flexes when you squeeze it. Very cool, no?
So here’s the scoop: When you submerge an egg in vinegar, the shell—composed of calcium carbonate crystals—slowly dissolves. (Remember those bubbles on the shell’s surface?) Vinegar contains about five percent acetic acid, which dissolves the eggshell into its calcium and carbonate parts. The calcium ions float free (calcium ions are atoms that are missing electrons), while the carbonate goes to make carbon dioxide, a buoyant gas—those bubbles you saw floating up from the shell.
Lesson 5: Osmosis!
Osmosis is the process by which water enters our tissues. All of our cells are surrounded by membranes that selectively allow in substances that the cells need but prevents unwanted molecules from entering. These membranes contain multitudes of infinitesimally tiny holes that allow the passage of small molecules, while keeping larger ones out. Water, being composed of very small molecules, enters cells by a process called diffusion, in which molecules travel from an area of high concentration to an area of lower concentration. This is called moving down the concentration gradient, and when the concentration of a given molecule equal both inside and outside the cell, the solution is referred to as isotonic. Because an egg has both an inner and outer membrane just beneath the shell, it serves well as a large-scale representation of the osmotic processes occurring in every living cell.
This eggs-periment puts those naked eggs to instructive use. If placed in water, the shell-less egg swells, due to the larger concentration gradient across the membrane. Because there are more water molecules outside the egg than within, the water diffuses in. Pure water is hypotonic relative to the egg, meaning that due to its dilution it contains more water molecules than the egg.
If placed in corn syrup, the opposite occurs: Because there is a much higher water concentration in the egg than in the syrup, water will pass through the membrane in the other direction, shrinking the egg. Corn syrup is hypertonic relative to the egg, meaning that it is highly concentrated, with little water compared to the egg’s aqueous contents.
Lesson 6: Eggs-treme pressure
For this mildly eggs-citing test, the eggs-perimenters will need a glass bottle with a mouth slightly smaller than a peeled, hardboiled egg. By merely placing the egg on the bottle’s mouth, it’s clear that the diameter of the egg is too large for it to slip inside. At this stage, the pressure of the air inside and outside the bottle is the same, so the only force that could cause the egg to enter the bottle is gravity. Gravity, alas, isn’t sufficient to pull the egg inside.
When the temperature of the air within the bottle is changed, the pressure also changes. If a constant volume of air is heated, the pressure of the air is increased. If the air is cooled, the pressure decreases. If the pressure inside the bottle is sufficiently lowered, the higher air pressure outside the bottle will push the egg inside.
Light a scrap of paper with a match and drop it into the bottle, and re-cover the mouth with the egg. As the paper combusts, oxygen is used until exhausted, and the fire runs out of fuel. Combustion heats the air inside, increasing the air pressure. The heated air rises, pushing the egg out of the way—the egg appears to hop on the bottle’s mouth—and, as the air within cools slightly, the increased pressure outside the bottle pushes on the egg, sealing the mouth. Now there is less air in the bottle than before the combustion, and this reduced volume exerts less pressure. When the temperature inside and outside the bottle are the same, there is enough positive pressure outside the bottle to push the egg inside.
To get the egg out, increase the air pressure within the bottle so that it is greater than that outside. Turn the bottle upside down, with the small end of the egg sitting in the mouth. Tilt the bottle just enough to blow air in around the egg, roll it over the mouth before removing lips, and step back to allow the egg to shoot out.