CHEMISTRY. The science that is concerned with the com position of bodies and with the changes of composition they undergo. Analytical chemistry deals with the methods of separa tion of purer substances from mixtures, of elements from com pounds, and with their estimation ; synthetic chemistry treats of the methods by which complex bodies may be built up from simpler substances. In each case it is the changes of composition that concern the chemist.
The combination of atoms, and the arrangement of atoms in a molecule, used to be regarded as the special province of the chemist ; while the physicist dealt with changes of state and with the motions of the molecules : but today this distinction cannot be maintained.
With the rapid growth of modern chemistry it has become the practice to divide the theoretical study of the science into three main branches, and this conventional division is adopted in the present article, which, in addition, contains sections dealing with the history of chemistry and the practice of chemical analysis:— History of Chemistry; Inorganic Chemistry; Organic Chemistry (Aliphatic Division, Heterocyclic Division, Homocyclic Division) : Physical Chemistry; Analytical Chemistry (Inorganic Analysis, Ultimate Organic Analysis, Gas Analysis).