Green Book, 2nd ed.: IUPAC Quantities, Units and Symbols in Physical Chemistry. Second Edition, Blackwell Scientific Publications, Oxford, 1993.
PAC, 1994, 66, 533 (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994))
For a mixture of gases the contribution by each constituent is called the partial pressure p_i = x_i p, where x_i is the amount fraction of the ith constituent and p is the total pressure. [IUPAC]
For a mixture of gases the contribution by each constituent is called the partial pressure p_i = x_i p, where x_i is the amount fraction of the ith constituent and p is the total pressure. [IUPAC Gold Book]