Milk Bottle & Egg Demo

This demonstration is beneficial when discussing air pressure, how heated gases expand, atmosphere pressure, pressure always goes from high to low in an attempt to equalize, and how the number and/or velocity of molecules in a container influences the pressure exerted by the gas. In this demonstration, the boiled egg is placed on the top of the bottle. Nothing happens because the pressure inside the bottle is equal to the outside air pressure. When the gas inside the bottle is heated by the flaming material placed in the bottle, the gas expands escaping (due to the molecules having a greater velocity) from the bottle so there are fewer air molecules remaining in the bottle. This can be seen as the egg moves up and down. When the flame is extinguished, the egg seals the bottle so air cannot return into the bottle, thus you have fewer molecules than before. Since this can be viewed as a gas in a rigid container, the pressure decreases as the molecules inside slow down, reducing the inside pressure. The atmospheric pressure has not changed but is now greater than the inside pressure, pushing the egg into the bottle (not that the air is contracting, although it would if the air was in a flexible container such as a balloon. To get the egg out one must increase the amount of air in the bottle to where the pressure inside is now greater than the outside. This can be easily done by inverting the bottle so that the egg is in the neck of the bottle and then blowing air into the bottle while it is upside down, increasing the number of molecules, more pressure. I find that using a small amount of cotton dipped in a little bit of rubbing alcohol and set on fire reduces the amount of ash that remains. People are more likely to be volunteers to blow into the bottle if there is much less ash. If you have liquid nitrogen available, you can simply place the egg on top of the bottle and insert the bottle, upright, into the liquid nitrogen. Same reasoning as before. I've seen the egg in the bottle demo performed with a raw egg which has been pithed at both ends using. Ideally, the insides are pushed into the bottle while the egg shell remains at the top. I have not yet been successful with this, yet! We include this demonstration in our outreach programs dealing with the topics of pressure and/or properties of gases. You can easily purchase these bottles at the grocery filled with milk. Enjoy the milk, wash out the bottle (don't return for a refund), and then use them for this activity. The bottles are thick and a hard boiled egg sits perfectly on the mouth of the bottle.

It was this demonstration that my high school chemistry teacher performed and thus began my journey into falling in love with this science! Once I began my career as a chemistry teacher I searched hard to find this very same bottle that my chemistry teacher used. Thank you EI for having it!! Yours is perfect, great strength and length for excellent visibility of the egg being sucked into the bottle. And... if you're as daring as my high school teacher was, you can create enough pressure with your mouth to remove the egg!

I loved doing this demonstration on the first day of school to get my students talking about science. Many of them knew hot to get the egg INTO the bottle, but getting it out, was always a different story. You will get some pretty "creative" responses on how to do it. When the tried their ideas, it usually led to lots of laughs (something you need in middle school on the first day). When I led them to the answer on how to remove the egg from the bottle, they LOVED it!

I used the bottles to assist the students in setting up an experiment using all the steps of the Scientific Method. Using water and pebbles the students worked through the steps while causing water from the bottom to the top of the bottle. They loved identifying and going through the steps while learning about water displacement.

I've used these for several years now for the egg demo. It works better than a flask because it's heavier and sturdier, so it's less likely to tip over when the egg falls into the base. Not so easy to clean - you have to cut the egg into pieces while it's in the bottle to get it out - but well worth it.

Great for demonstration. Students enjoy tryign to determine the "why" and are even more intrigued in getting the egg out so easily.