SEE ALSO AIR - : Nitrogen is often used in place of air, for an oxygen-free atmosphere.
Some foil-wrapped foods such as butter have been found to have extended storage life if the small amount of air trapped within the foil is replaced by nitrogen with a very low oxygen and moisture content. Usual moisture: <-60°C.
The 'fizz' in bottled and cask beer is usually produced by Carbon Dioxide gas (see also Carbon Dioxide). This may be the result of fermentation - in naturally conditioned beer - or the gas may be injected after fermentation in cask or draught beer. Some beers - notably a well-known Irish brew are now using nitrogen gas instead of the CO2. It has the same effect of giving life to beer, but it helps to give the product a longer shelf life. While the moisture is not at all important in the beer (it's nearly all water anyway) the gas compressors will be damaged by moisture in the gas before it is injected into the beer, hence the need for measurement. Usual moisture: <-50°C.
MARINE VESSEL PURGING
Because of the risk of explosion, the tanks of oil and LPG carrying ships must be purged with inert gas. Nitrogen is most commonly used, and the gas is frequently produced by plant on the ship itself. The gas must be dry to avoid corrosion, and in the case of the LPG carriers, to avoid condensation in the refrigerated tanks and void spaces. Usual moisture: <-40°C.
SUBMARINE PERISCOPE PURGING
Although a rather limited application, the general principle is worth remembering: if the dewpoint temperature of the atmosphere within the periscope tube is above the temperature of the sea, condensation will form, misting the prisms, so the captain cannot see where he is going! Our instruments are used to automatically purge the tube with nitrogen if the moisture is too high. Usual moisture: <-10°C.
Nitrogen gas is often used, frequently mixed with Hydrogen, for the atmosphere in heat treatment furnaces. The moisture content varies with the application and is usually drier than -50°C dewpoint to avoid oxidation of the metal surface.