ANALYTICAL CHEMISTRY The specific purpose of analytical chemistry is the resolution of a compound or mixture into its constituent parts or elements by methods which are qualitative when the nature only of these con stituents is determined, or quantitative when their actual quantity or proportion is ascertained. The methods of chemical analysis may be classified as dry, consisting of the examination of the substance in the dry state, and wet, in which a solution of the sub stance is treated with other substances of known character, termed reagents, to promote a chemical change or reaction whereby a new compound of distinctive properties is produced. In quantitative work the methods of analysis may be subdivided into (a) gravi metric, in which the constituent to be determined is either isolated as such, as in the case of electrolysis, or as a compound of defi nite chemical composition; (b) volumetric, in which the volume of a reagent solution of known strength required to produce a cer tain definite reaction is measured. Colorimetric and gasometric methods are, strictly speaking, branches of volumetric analysis, as indeed is gas analysis (see below). Microchemical methods, which, however, involve a special technique, have been developed both on the qualitative and quantitative sides.