Absolute Pressure A quantity of pressure measured with respect to total vacuum. Equal to the sum of a pressure gauge reading and atmospheric pressure (14.69 psia at sea level).

Absolute Zero The minimum point on thermodynamic temperature scale (-273.16°C or -459.69°F).

Absorption The condensation of gas, liquids or dissolved substances on the surface of solids.

Anhydrous A descriptive meaning without water.

Calibration Gas A gas of accurately known concentration which is used as a comparative standard in analytical instrumentation.

Compressed Gas Any material or mixture having in the container either an absolute pressure exceeding 40 psia at 70°F or an absolute pressure exceeding 104 psia at 130°F.

CGA Compressed Gas Association. Recommends cylinder valve outlet connections for specific gas services.

Corrosive Any gas which chemically attacks materials with which it comes in contact, such as metals or human tissue.

Critical Pressure The pressure at the critical temperture.

Critical Temperature The temperature above which a gas cannot be liquefied by pressure alone.

Density Concentration of matter, measured by the mass per unit volume.

Dew Point The temperature at which formation of a vapor begins. The term usually applies to a condensation of moisture from water vapor in the atmosphere.

DOT Department of Transportation. Regulates transportation of hazardous materials.

Filling Density The percent ratio of weight of a gas in a container to the weight of water that the container will hold at 60°F.

Flammable Limits The percent volume limits of concentration of a flammable gas at normal atmospheric pressure and temperature in air above and below which flame propagation does not occur on contact with a source of ignition.

Flash Point The temperature at which a liquid gives off vapor sufficient to form an ignitable mixture with air.

Inert Gases which do not react with other materials under normal temperature and pressure.

Liquefied Compressed Gas A gas which is partially liquid at its charging pressure and a temperature of 70°F.

Mole Mass numerically equal to its molecular weight. A gram mole is the weight in grams equal to the molecular weight.

Molecular Weight The sum of the atomic weights of all the constituent atoms in a molecule.

NTP Normal temperature and pressure, 20°C and 760 torr.

Oxidant A gas which supports combustion.

Partial Pressure In any gas mixture the total pressure is equal to the sum of the pressures (partial) which each gas would exert were it alone in the volume occupied by the mixture.

Safety Relief Device A safety device usually incorporated in a cylinder valve and actuated by excessive pressure or temperature, or both, at predetermined limits to avoid failure of the pressure vessel.

Specific Gravity The ratio of the weight of any volume to the weight of an equal volume of another substance taken as a standard. For solids or liquids the standards are usually water and for gases the standard is air.

Specific Heat The amount of heat required to raise the unit weight of a substance one degree of temperature at constant pressure.

Specific Volume The volume of a unit weight of a substance at a given temperature.

STP Standard temperature and pressure, 0°C and 760 torr.

Sublimation The process of passing from a solid state directly to a gaseous state.

SYNTAX Distribution and Manufacturing (SDM) Software The software package used by GTS Inc for functions such as Customer Definition, Product Definition, Inventory Control, Pricing, Order Processing, Counter Sales, Equipment Rental, Cylinder Lease & Rental, Purchasing, Manufacturing, and Accounts Receivable.

TLV Threshold Limit Value, the time weighted average concentration of an airborne substance that represents the condition under which it is believed nearly all workers may be exposed in a normal eight hour day, five day work week without suffering adverse effect.

Toxic Gases which may chemically produce injurious or lethal effects to humans.

Vapor Pressure The pressure exerted when a solid or a liquid is in equilibrium with its own vapor at a particular temperature.