Why do we use liquid nitrogen to cool down the experiment? Can't we use liquid helium or liquid hydrogen?

Recently, I saw some netizens discussing why liquid nitrogen is used in experiments to cool down the temperature. Why not use liquid helium or liquid hydrogen? After all, their temperature is more than 50 degrees lower than liquid nitrogen, so wouldn’t the effect be better?

Let me say a few words from a biological perspective, because liquid nitrogen is cheap.

01. Why do laboratories use liquid nitrogen?

Laboratories never choose the most expensive one, but the most balanced one, which is neither too expensive to be unaffordable nor too cheap to reduce the quality too much. That's enough. Anyway, the top laboratories I have seen do not buy things casually without considering the cost.

First of all, when doing biological experiments, most of the time it is enough to keep the temperature low enough . What is enough? It is about -60~-80℃, which is the storage temperature of our common laboratory refrigerators. It can store quite a lot of materials without worrying about spoilage.

Then materials with lower temperatures than this are naturally acceptable. Liquid nitrogen is generally -190℃, so it is completely sufficient and very good.

Secondly, liquid nitrogen is really abundant and easy to obtain.

What is the most easily available material in nature? Sunlight? No, there is no sunlight at night. Soil? In some places, the soil is not up to standard; water? Many places do not even have water. Of course, it is air.

As long as there is air on the surface of the earth, there is air everywhere, 24 hours a day, 365 days a year. Therefore, air is the best source of materials.

Look at the composition of the air:

78% nitrogen, it can be said that nitrogen is truly an inexhaustible source.

On the other hand, what about hydrogen? That percentage is too low. If you use water to generate hydrogen, you have to consider the source of water, right? Some places don't have water at all. The same is true for helium, which is far less abundant than nitrogen.

Third, nitrogen is very stable.

Compared to hydrogen, nitrogen is quite stable. Of course, it is not as stable as helium, but helium is in small quantities after all. In this case, liquid nitrogen is the best choice from the perspective of wide source, convenient use and stability.

02. How to make liquid nitrogen

The tools for making liquid nitrogen are also simple.

Build a small house, and then put a liquid nitrogen machine in it, and the liquid nitrogen will come continuously. I found a machine on the Internet, and it looks like this:

It is the size of a cabinet, and the liquid nitrogen produced is enough for one of us to use, and the price is not expensive. The main feature is economical.

Liquid nitrogen is now widely used. For example, it can ensure the quality of food, especially fresh food airlifted from abroad, which is preserved with liquid nitrogen.