Written by Aimee
Liquid nitrogen. It’s cool (minus 196 degrees Celsius), it’s fun, and it’s undoubtedly one of our very favourite chemicals here at Big Bang Education. Brett has presented hundreds of shows using liquid nitrogen, and over the years has answered many hundreds of questions about it from curious students and adults alike.
Some questions, however, seem to come up very often. So today, I thought I’d answer three of the most frequently-asked liquid nitrogen questions. (If you have another question about liquid nitrogen that is not featured here, please feel free to get in touch and we’d be happy to answer it!)
Frequently Asked Questions
1. Can I drink it?
Short answer: No.
Slightly longer answer: The answer to this question (and the closely related “Can I eat it?”) is almost*
always a no in a science lab. Although many chemicals we use, such as water, are safe to consume,
there are also a LOT of very undrinkable chemicals, such as liquid nitrogen, that look a LOT like
water. (And almost all of them are NOT water.) So as a general rule, no drinking allowed.
Outside of the lab, liquid nitrogen is often used in the food industry. It’s useful for freezing things
quickly and with a smooth consistency, and it is also used to make food and drinks look cool.
Watching your order arrive engulfed in a billowing cloud is quite exciting. However, even if your drink does arrive with a layer of liquid nitrogen floating on top, you should wait for it all to evaporate before taking a sip.
Liquid nitrogen expands up to 600 times in volume when it turns into gas. This means that even a 10ml sip of the liquid will expand into six litres of nitrogen gas. The average human stomach has a maximum stretching capacity of between two and four litres, so a lot of that gas will have nowhere to go. Sure, you might do the world’s most epic burp and impress everyone. But a more likely outcome is that your stomach will rupture, which is pretty bad news and can have lifelong implications. So to stay on the safe side, which is always the side we want to be on, don’t drink liquid nitrogen.
*The exception to this rule is our Vacation Care Edible Science program, in which eating things is very much encouraged.
2. Is it the same as dry ice?
Short answer: No.
Slightly longer answer: These two chemicals both share the property of being very cold, as well as being commonly used in our programs. There are even some demonstrations that work equally well with either chemical. This tends to lead people to guess that they’re the same thing. But the answer to this question should be clear from the common names of the two respective chemicals, along with some basic knowledge of states of matter (solid, liquid, and gas).
‘Liquid’ nitrogen is a LIQUID. This means it can pour between containers and it takes the shape of the container it’s in.
‘Dry’ ice is DRY. Unlike most liquids, which are famously wet. Unlike liquid ‘nitrogen’, dry ice is the solid form of carbon dioxide, which doesn’t have a liquid phase at normal atmospheric pressure and turns straight from a solid into a gas.
Dry ‘ice’ is also ICE. Which is solid, not liquid. It usually comes in pellets or blocks and can be picked up (with gloves or tongs), and will keep its shape.
(Side note: one time we got asked this question in an airport by a security guy curious about what our liquid nitrogen dewar was for. Unfortunately it was empty at the time – otherwise Brett could have educated him in the best way he knows…by doing a science show!)
3. What would happen if you put (insert thing) into liquid nitrogen?
Short answer: It would get cold.
Slightly longer answer: This depends a bit on what kind of thing you are inserting into liquid nitrogen.
For things made of cells (anything that is or once was living, such as body parts, fruits/vegetables, flowers etc): Cells, the building blocks of life, consist of a membrane (animal cells) or wall (plant cells) filled with water-based fluid. As we know, when water is cooled below zero degrees Celsius, it freezes solid. Unlike most other substances, which shrink as they cool, frozen water also expands a bit in volume. So the fluid in the cell will freeze, and as it expands, will rupture the membrane or wall enclosing it, causing irreversible damage to the cells. In the case of a plant, fruit, vegetable etc, this means that it will usually be very limp and soggy when it thaws, as the cell walls that gave the plant its structure have been broken apart. In the case of animal cells, such as your hand, this will mean really bad frostbite and ultimately the death of the cells. (This happens to explorers who venture into really cold places – they often lose extremities such as fingers, toes and noses to frostbite.)
For foods such as cream, custard, yoghurt etc: It would get cold and turn into a frozen version of the thing. This is actually a very good use for liquid nitrogen, but it’s easier to pour the liquid nitrogen into the bowl of cream, rather than the other way around. Frozen treats like ice cream and frozen yoghurt can of course be made in the freezer, but using liquid nitrogen makes it happen much more quickly, since it’s so much colder. Also, faster freezing means smaller ice crystals in the finished product, which results in a wonderfully smooth texture.
For things made of metal: They will get really cold and shrink a bit. This can be very useful – liquid nitrogen is used in plumbing to get metal pipes to fit tightly inside each other.
For things made of rubber (e.g. squash balls, rubber ducks): They will get really cold, shrink a bit, and also lose their stretchy, bouncy properties, becoming brittle like glass. This makes them easy and fun to smash with a hammer, if you are so inclined. However, this means no more rubber duck, and also a million tiny pieces of rubber duck to pick up from the surrounding area, which is less fun.
For other things: I don’t know, but they would probably just get cold, and possibly damaged.
So there you have it. Comprehensive answers to three of the most commonly-asked questions in our liquid nitrogen shows. And now that I’ve written this, I expect we will never be asked any of these questions ever again.
P.S. Liquid nitrogen has been a feature of our Big Bang Science Show since we began back in 2014, as well as our Year 3 Heat and States of Matter program and Edible Science vacation care program. For more information on these programs, get in touch today!
