Acid: (1) Chemical that neutralizes alkalis. (2) Chemical that is corrosive to most metals and dissolves some metals. (3) Molecule or ion that can donate a proton or accept an electron pair in chemical reactions.

Azeotrope: Mixture of two or more liquids whose proportions cannot be altered by simple distillation. When boiled, the generated vapor has the same proportions of constituents as the liquid mixture.

Lethal Service: UW-2(a) - When a vessel is to contain fluids of such a nature that a very small amount mixed or unmixed with air is dangerous to life when inhaled. End Note 85 - By “lethal substances” are meant poisonous gases or liquids of such a nature that a very small amount of the gas or of the vapour of the liquid mixed or unmixed with air is dangerous to-life when inhaled. For purposes of this Division, this class includes substances of this nature which are stored under pressure or may generate a pressure if stored in a closed vessel.

Oxygen Service: Process in an oxygen rich environment. Thorough cleaning is required to remove combustible contaminants from the surfaces of all equipment in direct contact with an oxygen rich environment.

Reflux: The condensation of vapors and subsequent return of the condensate to the system from which the vapors originated.

Reflux Condenser: Typically a vertical shell and tube exchanger where vapor(s) enter the bottom channel and flow upward through the tubes counter-current to condensate flowing downward on tube walls. Commonly used in vent applications for tanks and distillation column overhead. Note: Properly designed reflux condensers can also be designed for horizontal installation.

Surfactant: A compound that lowers the surface (interfacial) tension between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may be use as detergents, dispersants, emulsifiers, foaming agents, and wetting agents.