Tag Archives: water

Do Eggs Gain Weight?

A second grade classroom at my school incubated chicken eggs until they hatched. When their feathers had dried, the fluffy chicks looked too big to have been enclosed within the broken shells still lying in the incubator.

One of the eggs did not hatch. For some reason, the chick inside had gone lifeless and would never break out into the wide world. Mr. Watts, the teacher who had run the whole project, handed it to me. “Feel this,” he said. “It seems heavier than it was in the beginning.”

I gently shook the egg from side to side, feeling the dead weight shift within the shell. Truly, it felt heavier than the eggs I buy for omelets. Was it because this egg had been fertilized and transformed into a nearly-finished young bird? Is it possible for an egg to gain weight while the chick grows inside?

My first thought was that it could not have gained any mass, because it had not eaten anything from outside the shell. Everything inside an egg until it hatches was in there since the moment it was laid. The chick forms from a small part of the material, and absorbs most of the rest as it grows. Since it does not eat or absorb anything from outside the egg, it seemed unlikely that it would actually weigh more at the end of incubation than it had at the beginning.

Since I am not an expert in birds or their eggs, I decided to do some research. The best article I found was on the Poultry Club of Great Britain website, which you can read here if you like. According to the article, a healthy chicken egg loses about 13% of its mass during incubation. Otherwise, the chick does not have room to move around enough to break the shell with its egg tooth, and dies inside the egg as a result. Maybe that is what happened to the egg that inspired this article.

EggTooth

There was one other thing I was unsure of. A chicken breathes oxygen and wastes carbon dioxide, like all animals on Earth. Would it not have to breathe through the shell? If so, there might be gases coming into the egg from outside, which might add mass.

It turns out that there is an exchange of oxygen and carbon dioxide through the shell, but since carbon dioxide is heavier than oxygen, this would reduce, rather than increase, the egg’s mass; indeed, this is one of the reasons – humidity being the other – that the egg loses weight.

Why did the egg feel heavy? Probably because an unfertilized egg – like the ones I get at the grocery store for my omelets – is all liquid inside. The egg with the unhatched chick had much less liquid, a larger amount of air, and a solid mass shifting around, which gave an illusion of added weight. I am reminded of when my children were small. When they would fall asleep and I carried them to bed, they felt heavier than when I would give them a piggyback ride. Their limp and sleeping bodies felt heavier, even though their weight had not changed.

My sons are much too big and heavy for me to carry anymore. But getting old has nothing to do with the weight of chicken eggs, so I suppose this post is done.

How Do Ice Cubes Work?

It seems like a simple question, with a simple answer: “The water gets colder!” But why? And what do we mean by “colder?”

Water (like just about everything else) can exist as a solid, a liquid, or a gas. The difference is its level of energy. If you add thermal energy – also known as “heat” – to an ice cube, it will melt into a liquid and you can drink it. But if your thirst for knowledge exceeds your thirst for water, you could keep on adding energy to the water just to see what happens. Of course you know what will happen – after adding enough energy, the liquid water will boil and turn into a gas. These phase changes – melting and boiling – happen to pure water at 0°C/32°F and 100°C/212°F.

If you are a student like most of my readers, you may be wondering why the amount of energy in a substance determines its state of matter – solid, liquid, or gas. This is because energy makes the molecules in a substance vibrate. If they have less energy, they will not vibrate very much, and the substance will be in a solid state. More energy means more vibration; at some point the substance will be vibrating too strongly for it to keep its shape, and it will melt. Likewise, the boiling point is the amount of energy at which the vibration is too strong for the substance to stick together, and it becomes a gas.

We measure the amount of thermal energy in units called “degrees”. When we talk about cooking food at 350°, or about the temperature outside being 45°, we are describing the amount of thermal energy in the food, or in the air.

Now we can deal with the question of how an ice cube cools a glass of water. The water in the ice cube is a solid, so it has less energy than the liquid water in the glass. When you drop a few ice cubes into the glass of water, they absorb some of the energy in the water. The ice gets the same amount of energy that the liquid water loses. As the ice melts, the water cools. Putting a little ice in a large glass of water will melt the ice quickly without cooling the water much; but adding a cupful of ice to a small amount of water might freeze the water. It depends on how much or how little energy is in either substance.

If you perform this experiment at home, try putting a thermometer in the glass before you begin. Measure the water temperature before adding the ice, and again after the ice melts. The change in degrees is the amount of thermal energy absorbed by the ice!

Cool.

Does Water Evaporate When the Sun Isn't Shining?

Everybody knows how quickly a puddle of water evaporates from the sidewalk on a hot summer day. But does water evaporate at night, or when it’s cool and cloudy?

Let’s look at what evaporation is. Liquids can change states of matter and become gases by absorbing energy. This can happen in two ways. If the entire liquid is heated (like a pot of water on the stove, the molecules throughout the liquid move faster and separate, forming bubbles of gas. If you watch water heating in a pot, you will notice that the bubbles come from the bottom of the pot because that is the part closest to the heat source. We call this “boiling”.

Evaporation is different. It only happens at the surface, where the liquid comes into contact with air; being a gas, the air has a higher level of energy, which the liquid can absorb. This happens not because of the presence of air, but because of the higher energy level at the surface. On the Moon, for example, there is no liquid water. There is water ice in some of the deep craters where the Sun never shines; the temperature here is about -249°C (-416°F), far below the freezing point of water (and most other substances as well). But if you could stand in such a crater and kick a lump of ice into the sunlight, it would not melt; the strong radiation from the Sun – without any atmosphere to reduce its glare – would vaporize the ice immediately.

So water evaporates at night, and in the shade, as long as the temperature is above freezing (0°C / 32°F). But it evaporates faster the higher the temperature is, and very slowly if it is cold.