DECOMPOSITION (Fr. decomposition. from Lat. de, down. away + componcre. to put together, join. unite). A term employed to sig nify the breaking up of compounds into simpler compounds or altogether into their chemical ele ments. The number of substances that are being decomposed is as a rule smaller, of course. than the number of substances produced by the & composition. However, in the class of chemical transformations known as 'double decomposi tions.' the number remains unchanged. Thus, AB and CD. two compounds. made up each of two ele ments, may, on being brooght into contact, under go decomposition. the result of which would be again only two compounds. AC and BD. Exam ples of this class of reactions arc very numerous in chemistry. But the term decomposition. un qualified, is generally applied, as stated above, to transformations involving an increase in the number of substances. Such decompositions are usually caused by the influence of some physical factor, such as heat. electricity. etc. Ileat isone of the most common of decomposing agents: mer curic oxide (11g0), when heated, breaks up into the invisible gas oxygen (0,1 and the liquid metal mercury (HO ; limestone decom into quicklime (oxide of calcium. Cap),
and carbon dioxide (CO) : coal and woiel decom pose into a great variety of useful materials, in oh a won], illuminating gas, and coal-tar. Electricity is a potent decomposing agent : under its influence. water is broken up into oxy gen (0„) and hydrogen (ILL and metallic salts are broken up into their constituent metals and acids, electrolytic processes being consequently much used both for scientific and industrial pur poses. Light effects many decompositions. as of the silver salts used in photography, of nitric acid, of hydrogen peroxide, and a number of other substances. Percussion explodes nitroglycerin, and even a touch causes iodide of nitrogen to de compose violently. Ferments (minute vegetable and animal organisms) cause many decomposi such as the breaking up of dextrose in the presence of yeast, into alcohol