Ice is considered dry ice

Try dry ice
This is frozen carbon dioxide or dry ice. At normal pressure (1013hPa) it has a temperature of -78.52 ° C and has the strange property of evaporating without changing to a liquid state. The technical term for this process is to sublimate. The resulting CO2 is then almost -79 ° C cold. At these temperatures, the water vapor condenses in the air, so that the gas is indirectly visible. In the picture it can be seen as thin strips of fog that spread out from the pieces of ice in a star shape.
Some material data on CO2
descriptionFormula symbolvalueunit
Critical pressurePk72.9bar
Saturation vapor pressure at 20 ° CPS56,56bar
Critical temperatureTk304,2K
Boiling temperature at 1.013barTs194,7K
Triple pointPT
K (0K = -273.15 ° C)
The critical temperature is the temperature above which the CO 2 cannot be liquefied under any pressure, however high. Since this is above room temperature (at 31 ° C), a CO2 cylinder under pressure can also contain liquid CO2. If this is led out of the bottle with a riser pipe, it cools down during relaxation according to the Joule-Thomson effect, and forms so-called carbon dioxide snow. This is then pressed into dry ice.
In a CO2 bottle there is a pressure of 56.56 bar at 20 ° C. This pressure is called the saturation vapor pressure. Once this pressure is reached, no more gas is formed. Liquid and gas are then in equilibrium.
The triple point is the point at which a substance appears in all three aggregate states. At lower pressures or lower temperatures, a substance changes directly from the solid to the gaseous state. Since this is 5.1 bar for CO2, it never becomes liquid at normal pressure. Hence the name dry ice. This strange effect can also occur with water when it is exposed to a vacuum.

Dry ice can be kept for a very long time in what is known as a dewar. Such a vessel is constructed like a large thermos flask. The thermal insulation takes place through an evacuated, double-walled glass vessel. The walls have an additional reflective coating to reflect as much heat radiation as possible. It is important that a small hole is drilled in the lid so that the gas can escape. Otherwise a very high pressure builds up, which can cause the vessel to explode. If you don't want to spend so much money on a dewar, you can also store dry ice in a cooler bag. When buying a Dewar, I would recommend choosing one that can also hold liquid nitrogen. It only has to have a second metal shell and a narrower neck and is therefore not significantly more expensive. For dry ice and Dewar vessels, see the list of sources of supply.

This video shows what happens when dry ice is tightly closed in a jar. After a short time, the stubble is catapulted out by the resulting pressure. Everyone can easily imagine what happens when a screwed container is used where the stubble cannot come off as easily as with this glass.

The gas that is constantly forming on the surface of the dry ice lifts every object that comes into contact with it. In this video, a warm coin is placed in a crack in a piece of dry ice. It begins to tremble and rattle. But not because of the cold.
When it comes into contact with the dry ice, a gas cushion is created that lifts the coin. Then the gas escapes and the coin falls back again. Of course, this only works as long as the coin is still warm. When it cools down, the movements become smaller.

Due to the gas cushion created, the pieces of dry ice slide very easily over a warm aluminum plate, as in this video. By tilting the plate slightly, the pieces accelerate very quickly, as the gas cushion underneath them makes the friction very small.

If you place a piece of dry ice on a suitable resonance body, in this video a cup from the Kelvin generator, very loud vibrations arise. The ice is stimulated to produce gas by the warm mug. A cushion of gas is created, which pushes it off the cup, causing it to vibrate. Then it falls back on the cup and the process begins again. If you press the dry ice with a little more force on a suitable piece of metal (e.g. aluminum conductor) and achieve mechanical resonance, the sound can sometimes be very loud.

If you put a piece of dry ice in a glass of water, you will immediately see clouds of fog. Much more gas is released from the piece of dry ice when it comes into contact with the water than in the air. This then rises to the surface of the water in the form of gas bubbles. Since the gas is still very cold, it allows the water vapor to condense in the air, which then becomes visible as a mist.
Tips and Tricks: Gas production can be increased by using warm water or breaking the dry ice into small pieces. In order not to impair fog formation, the water should not be too hot, otherwise the CO2 will heat up too much. A dish that is as flat as possible should also be used so that the cold CO2 does not have to rise in the water for too long and heat up in the process. The more humid and warmer the ambient air, the better the fog production.

This video shows how a piece of dry ice is thrown into a glass of hot water. The rising steam pulls the mist upwards very strongly. Only when it has cooled down a bit does it sink back to the ground.

Homemade mineral water:
The carbonic acid in mineral water is nothing else than CO2 dissolved in water. If you taste the water that was previously in contact with dry ice, you will notice a slightly sour taste. However, it does not contain as much carbonic acid as real mineral water. This is due to the fact that in mineral water the CO 2 is introduced under pressure. This works much better at around 5 bar than at normal pressure. That is also the reason why it always hisses when the bottle is opened. This is because the resulting CO2 is released from the water until an equilibrium is established due to the counter pressure. Under reduced pressure it is almost impossible to keep the gas in the water. A glass of mineral water in a vacuum bell will therefore smoke up after a short time. Ultrasound can also be used to drive the gas out of the water more quickly.
And here is another attempt, not recommended for imitation, with the delicious dry ice without words.

Danger: If larger amounts of dry ice are allowed to evaporate, sufficient ventilation of the room must be ensured. Since CO2 is heavier than air, it fills the space from below, thereby displacing the oxygen. CO2 is also produced during the fermentation of wine. Many accidents in cellars caused by fermentation gases have already resulted in death.
If dry ice is placed in acetone, it dissolves in it much faster than in water. However, there is still not so much fog or gas. On the one hand, this is due to the fact that acetone does not condense as easily as water and therefore a large part of the CO2 is not even visible and, on the other hand, the CO2 remains dissolved in very large quantities in acetone as long as it is cold. If a lot of dry ice is dissolved in acetone, its temperature drops to below -60 ° C. If it is then heated again, the CO 2 escapes again. If a warm object is brought into contact with the acetone, it looks like it is boiling. In reality, however, it is only the CO2 that is released.

Danger: In experiments with acetone. Fire danger !

If you light a candle in a glass and then put a piece of dry ice in the glass, the candle will go out for a short time.
When it comes into contact with the warm glass, a lot of dry ice evaporates and fills the glass with CO2 from below. This means that there is no more oxygen left in the candle. This is also the reason why winemakers often take a candle into the wine cellar. When it goes out, it is a sign that the lake of CO2 has already reached the candle. If you carry it in your hand, you will still have enough air to breathe above the candle.

It's even more impressive when you pour the heavy CO2 into the glass. To do this, you can put dry ice into a glass of water as in the first experiment to get more gas. The CO2 is so heavy that it falls down against the flow of heat from the candle.
Tips: This experiment works even better if you put the dry ice in a glass of the same size and let it evaporate completely. Then nothing can be seen at all that could be poured into the glass and the candle goes out anyway. When pouring out, you can even feel the CO2 flowing down if you hold your hand in front of the glass.

The CO2 lake can be made indirectly visible by dropping a soap bubble into a glass with dry ice. Since this is mostly filled with air, it floats on the much heavier CO2. It then looks like the soap bubble is floating freely in space. However, it slowly decreases over time. There are two reasons. Firstly, the air inside the soap bubble cools down on contact with the cold CO2 and, secondly, the CO2 diffuses through the soap skin into the interior.
For the patient: If you invest enough time, it is possible to make a frozen soap bubble this way. To do this, the bladder must be brought as close as possible to the cold dry ice until it finally freezes. Then you shouldn't make the mistake of trying to remove the bladder with your hand. The ice view is so thin that it breaks immediately with the lightest touch. In addition, the ice balls get a little wrinkled, because of course the air inside cools down and contracts.

With these low temperatures it is easy to freeze mercury. Because the reason why no mercury thermometer can display below -40 ° C is simply that it already solidifies at -38.8 ° C. If you have a tilt switch, you can see the otherwise unusual, solid shape of the metal for yourself.

An experiment on the Peltier element was also made with dry ice. To test whether the Peltier effect still works at -79 ° C, a Peltier element was placed between two pieces of dry ice. When it has cooled down after a while, the power is switched on. If the polarity is correct, the upper piece of ice freezes on the Peltier element and you can lift it up with the piece of ice. If the polarity of the current is reversed, the lower piece of ice freezes and the upper one loosens.
Danger: It is recommended that you only handle the dry ice with gloves. Because at -79 ° C the fingertips can freeze very quickly. However, normal woolen gloves are completely sufficient.
Tips: The other side of the Peltier element naturally becomes warm due to the current. Since this is no longer on the dry ice after being lifted, it heats up very quickly and the Peltier element detaches itself from the upper piece of ice. To delay this, the Peltier element should not be operated with full voltage. I operated a 12V element with only 5V. This is sufficient because only a very small temperature difference has to be generated. You should also make sure that the ice surface that is supposed to freeze is as flat as possible. But this is mostly the case when the Peltier element has been cooled down with the same piece of ice.

The opposite operating case is then of course also possible. The temperature difference between dry ice and the ambient air can be exploited through the thermal effect.
To do this, a piece of dry ice is placed on the Peltier element, which is located on a heat sink. The connected lamp lights up without any additional heat supply. The heat sink is cooled down and can absorb heat from the ambient air.
Even so, it is not entirely clear where the energy is ultimately obtained from. On the one hand, it could be extracted from the ambient heat, but on the other hand, it could also come from dry ice, which also requires energy to be produced. It looks like twice the amount of energy is available. In a way, this is true even when you consider that the ambient heat is generally not considered an energy source. Also read the thought experiment with the Peltier element.

In dry ice, the CO2 is trapped in a state from which it is very difficult to get out. When you consider the force with which a gas cylinder can explode, the calm state of dry ice, which also combines large amounts of CO2 in a small space, seems a bit strange.

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