Matter of constant composition best characterized by the entities (molecules, formula
units, atoms) it is composed of. Physical properties such as density, refractive index
, electric conductivity
point etc. characterize the chemical substance.
Physical Chemistry Division, unpublished
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook