alt=A large solid cylinder with a hole in its center and a rail attached to its side. While balloons are perhaps the best known use of<unk> , they are a minor part of all<unk>  use.<unk>  is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. Of the 2014 world<unk>  total production of about 32 million kg (180 million standard cubic meters)<unk>  per year, the largest use (about 32% of the total in 2014) is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners and NMR spectrometers. Other major uses were pressurizing and purging systems, welding, maintenance of controlled atmospheres, and leak detection. Other uses by category were relatively minor fractions. Controlled atmospheres<unk>  is used as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, and in gas chromatography, because it is inert. Because of its inertness, thermally and calorically perfect nature, high speed of sound, and high value of the heat capacity ratio, it is also useful in supersonic wind tunnels and impulse facilities. Gas tungsten arc welding<unk>  is used as a shielding gas in arc welding processes on materials that at welding temperatures are contaminated and weakened by air or nitrogen. A number of inert shielding gases are used in gas tungsten arc welding, but<unk>  is used instead of cheaper argon especially for welding materials that have higher heat conductivity, like aluminium or copper. Minor uses Industrial leak detection alt=Photo of a large, metal-framed device (about 3×1×1.5 m) standing in a room. One industrial application for<unk>  is leak detection. Because<unk>  diffuses through solids three times faster than air, it is used as a tracer gas to detect leaks in high-vacuum equipment (such as cryogenic tanks) and high-pressure containers. The tested object is placed in a chamber, which is then evacuated and filled with<unk> . The<unk>  that escapes through the leaks is detected by a sensitive device<unk>  mass spectrometer), even at the leak rates as small as 10−9 mbar·L/s (10−10 Pa·m3/s). The measurement procedure is normally automatic and is called<unk>  integral test. A simpler procedure is to fill the tested object with<unk>  and to manually search for leaks with a hand-held device.<unk>  leaks through cracks should not be confused with gas permeation through a bulk material. While<unk>  has documented permeation constants (thus a calculable permeation rate) through glasses, ceramics, and synthetic materials, inert gases such as<unk>  will not permeate most bulk metals. Flight Because of its low density and incombustibility,<unk>  is the gas of choice to fill airships such as the alt=The Good Year Blimp Because it is lighter than air, airships and balloons are inflated with<unk>  for lift. While hydrogen gas is more buoyant, and escapes permeating through a membrane at a lower rate,<unk>  has the advantage of being non-flammable, and indeed fire-retardant. Another minor use is in rocketry, where<unk>  is used as an ullage medium to displace fuel and oxidizers in storage tanks and to condense hydrogen and oxygen to make rocket fuel. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to pre-cool liquid hydrogen in space vehicles. For example, the Saturn V rocket used in the Apollo program needed about 370,000 m3 (13 million cubic feet) of<unk>  to launch. Minor commercial and recreational uses<unk>  as a breathing gas has no narcotic properties, so<unk>  mixtures such as trimix, heliox and heliair are used for deep diving to reduce the effects of narcosis, which worsen with increasing depth. As pressure increases with depth, the density of the breathing gas also increases, and the low molecular weight of<unk>  is found to considerably reduce the effort of breathing by lowering the density of the mixture. This reduces the Reynolds number of flow, leading to a reduction of turbulent flow and an increase in laminar flow, which requires less work of breathing. At depths below divers breathing<unk> –oxygen mixtures begin to experience tremors and a decrease in psychomotor function, symptoms of high-pressure nervous syndrome. This effect may be countered to some extent by adding an amount of narcotic gas such as hydrogen or nitrogen to a<unk> –oxygen mixture.<unk> –neon lasers, a type of low-powered gas laser producing a red beam, had various practical applications which included barcode readers and laser pointers, before they were almost universally replaced by cheaper diode lasers. For its inertness and high thermal conductivity, neutron transparency, and because it does not form radioactive isotopes under reactor conditions,<unk>  is used as a heat-transfer medium in some gas-cooled nuclear reactors.<unk> , mixed with a heavier gas such as xenon, is useful for thermoacoustic refrigeration due to the resulting high heat capacity ratio and low Prandtl number. The inertness of<unk>  has environmental advantages over conventional refrigeration systems which contribute to ozone depletion or global warming.<unk>  is also used in some hard disk drives. Scientific uses The use of<unk>  reduces the distorting effects of temperature variations in the space between lenses in some telescopes, due to its extremely low index of refraction. This method is especially used in solar telescopes where a vacuum tight telescope tube would be too heavy.<unk>  is a commonly used carrier gas for gas chromatography. The age of rocks and minerals that contain uranium and thorium can be estimated by measuring the level of<unk>  with a process known as<unk>  dating.<unk>  at low temperatures is used in cryogenics, and in certain cryogenics applications. As examples of applications, liquid<unk>  is used to cool certain metals to the extremely low temperatures required for superconductivity, such as in superconducting magnets for magnetic resonance imaging. The Large Hadron Collider at CERN uses 96 metric tons of liquid<unk>  to maintain the temperature at . Medical uses<unk>  was approved for medical use in the United States in April 2020 for humans and animals.
Helium
Milium 
Lead
Basilicon
Sybil 
Vinyl chloride
Chorus
Cerate