These gases are difficult to combine with other substances, corresponding to less than 1% of air. They are not used by the body of living beings, they enter and leave unchanged during breathing.
Among the noble gases, the argon is the one that is present in the largest quantity (0.93%).
In ordinary (incandescent) lamps, argon is widely used as its production is cheap.
Other noble gases are:
- neon, used in bright signs (known as neon gas);
- xenon, used in camera flash lamps;
- heliuma low density gas used in certain types of bladder and airship balloons;
- radon, a radiative gas which is therefore dangerous in certain concentrations to living beings.
The steam of water
By pouring cold water into a glass and waiting a few moments, the outside of the glass becomes damp.
As the water inside the glass cannot pass through the glass, the water that formed came from the air around the glass. It was the water vapor from the air that condensed (turned into liquid state) in contact with the lowest cup temperature.
Water in the vapor state that exists in the atmosphere comes from the evaporation of water from rivers, seas, lakes and soils, as well as from the breathing and transpiration of living things.
You may have heard of relative humidity. It is the ratio between the amount of water that exists in the atmosphere at some point and the maximum amount it can contain (around 4%). When this amount is reached, we say that the air is saturated. The air is saturated in the clouds, in the fog and when it starts to rain. The higher the relative humidity, the greater the chance of rain.
There is a simple instrument that can be used to measure the relative humidity of the air: hair hygrometer.
What does a hygrometer measure?
A hygrometer indicates relative humidity. In the hair hygrometer a human hair, pressed into A, is wound on the B-axis and fixed to the spring C that extends it. When air humidity increases, the hair absorbs water from the air and expands, rolling the pointer shaft as it is extended by the spring. The pointer indicates relative humidity on a graduated scale.