A 'chemical substance' is a material with a specific chemical composition. It is
a concept that became firmly established in the late eighteenth century after
work by the chemist Joseph Proust on the composition of some pure chemical
compounds such as basic copper carbonate.[ Hill, J.
W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry, 4th ed.,
p37, Pearson Prentice Hall, Upper Saddle River, New Jersey, 2005.] He
deduced that, "All samples of a compound have the same composition; that is, all
samples have the same proportions, by mass, of the elements present in the
compound." This is now known as the law of constant composition.[[http://db-
hs.wvusd.k12.ca.us/webdocs/AtomicStructure/LawofDefiniteProportion.html Law of
Definite Proportions]] Later with the advancement of methods for chemical
synthesis particularly in the realm of organic chemistry; the discovery of many
more chemical elements and new techniques in the realm of analytical chemistry
used for isolation and purification of elements and compounds from chemicals
that led to the establishment of modern chemistry, the concept was defined as is
found in most chemistry textbooks. However, there are some controversies
regarding this definition mainly because the large number of chemical substances
reported in chemistry literature need to be indexed. A common example of a chemical substance is pure water; it has the same
properties and the same ratio of hydrogen to oxygen whether it is isolated from
a river or made in a laboratory. Some typical chemical substances are diamond,
gold, salt (sodium chloride) and sugar (sucrose). Generally, chemical substances
exist as a solid, liquid, or gas, and may change between these phases of matter
with changes in temperature or pressure. Chemical reactions convert one chemical
substance into another. Forms of energy, such as light and heat, are not considered to be matter, and
thus they are not "substances" in this regard.
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