Science Buddies: "Ask an Expert"

We are wondering if water can enter an eggshell when hard boiling eggs? After reading the information on this science fair project we thought water would be able to enter the eggshell and replace the oxygen in the air cell. But after doing this experiment 3 times and seeing no weight change we have come to the conclusion that water cannot enter the pores of an
egg. Only oxygen and carbon dioxide can pass. Are we correct or do we need to find a better scale to see the weight changes?

Hi,

Congratulations on a completed science experiment! Repeating the experiment a couple of times was definitely a good idea.

You are right that there 'should' have been an increase in weight, but perhaps your scale was not sensitive enough to measure it. That's okay--that's part of doing science! Did the eggs release bubbles as they cooked? This is a good indication that air is being replaced by water (though it is also an indication of air expanding as it is heated and leaving the egg!).

Another thing you might do is peel the dried eggs after you let them cool a bit, and see if there appears to be water inside the shells. However, at this point, all your child needs to do is be able to discuss his/her experiment with judges and explain why they might have gotten the results they did (either the pores do not allow water, or your scale could not detect a change).

dear rocky3030,

I'm not sure if water will pass through the pores of an egg. Thinking about it: bird embryos do not die when it rains (if eggs absorbed water then when it rained the water would replace the oxygen in the egg and all the bird embryos would die, which doesn't happen). If water was to enter the egg your best bet would to look under the top part of an egg (http://www.aeb.org/LearnMore/images/egg ... _chart.gif the part that says "air cell") because there is an airspace there (this is used when birds hatched to give the chicks a boost of energy by taking in oxygen). Also, if you were to notice water at all then you would have to do it before the egg completely cooks because the egg expands to size of the shell while cooking. If you were to notice a difference in mass, resulting from water intake, the amount would be very small (about a gram or less), so you would need a scale that can measure that amount.

let me know if you have any more questions

good luck,
scienceexpert123

Actually, eggs can 'drown' (see, for example, here, at the end of the second page: https://fishandgame.idaho.gov/sites/Wil ... /grebe.pdf), and eggs normally lose ~5-10% of their weight during incubation due to water loss. Water doesn't pour into the egg, but small amounts can get in and out. Here, for example, is a study that manipulated the amount of water loss in chicken eggs (note that the 'control' eggs lost ~6% of their weight): http://www3.interscience.wiley.com/jour ... 1&SRETRY=0 .

Here's one that's really relevant to what you're looking at: http://www.springerlink.com/content/r4250q2284283741/ .

So water vapor CAN pass through the eggshell. Liquid water may have a more difficult time doing so because of its hydrogen bonds, which may make it more difficult to move through the pores. It may also have a hard time getting past the internal membranes of the eggs (as opposed to the shell itself).

So, the most likely explanation is that your scale simply couldn't measure the difference in the weight of the eggs before and after boiling.

Mellisa b and Science Expert 123,
Thank you for your answers on this topic. It is much appreciated and we will have fun exploring the web
links you gave us.

Has anyone tried this using water with food coloring in it? My kindergartner and I are getting ready to start this experiment and I would really love to have results he can see easily. If this works, then the boiled egg shall not only weigh a little bit more (I understand we will need a very sensitive scale) but the color should have moved to the egg inside when we peel it!

Hi,

Yes, when boiled eggs are dyed in Easter Egg dye, the color does penetrate the egg, especially with the dark colors and a prolonged soaking time in the dye. I don’t know about fresh eggs, but these should be more resistant to the dye.

Here’s a reference that reports dye penetration on fresh eggs. The authors used blue lake, an insoluble dye, and soaked eggs in 0.25% blue lake plus a small amount of nonionic detergent, and looked for blue specks on the shell membranes after breaking the eggs.

http://www3.interscience.wiley.com/jour ... 1&SRETRY=0

It looks like blue lake dye is available from garden and pool supply stores, and it is non-toxic, but I would not recommend purchasing this for a science fair project; use the food dye instead.

http://www.naturalenviro.com/productinf ... e-lake-dye


Donna Hardy