The first is one of the safety issues of dealing with the extremely cold: if it comes into contact with anything biological, from a bunch of flowers to the human body, it can very rapidly freeze the water inside and between the cells, thus killing them and also making the tissue very brittle. These four demonstrations are centred on three basic concepts relating to liquid nitrogen, and cryogenic liquids in general. Remove it, and tap it on a nearby surface to demonstrate that its properties have changed somewhat… When the spraying stops, the tube will be at the same temperature as the nitrogen.Liquid nitrogen will spray spectacularly out of the other end, so be careful where you point it! Take a length of rubber tube and place one end in a bucket of liquid nitrogen.The balloon will fill up with nitrogen gas, probably enough to explode it, or at least make it fly off comically around the room. Stretch a balloon over the neck of the bottle.Place a small volume of liquid nitrogen in the bottom of a glass bottle.Watch as a cloud of steam clears to leave a huge mass of bubbles.Give the second volunteer a polystyrene cup filled with nitrogen, and get them to throw it all into a bowl containing warm, soapy water.When the boiling stops, get them to pull the flowers out and smash them (hard!) onto a nearby surface.Give the first volunteer a bunch of flowers and encourage them to dunk them into a bucket of liquid nitrogen.The first two of these are done by audience volunteers, so get a couple down and kit them out with safety visors and cryogenic-safe non-porous gloves. Be sure to conduct a risk assessment in conjunction with your local safety office before using or transporting liquid nitrogen. The greatest risk from liquid nitrogen is probably asphyxiation, resulting from a large volume of nitrogen gas displacing oxygen in the room. Always be sure to wear appropriate clothing and use safety equipment when handling it. These demonstrations also illustrate why safety is of paramount importance when dealing with nitrogen in a science show.
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