Chemistry being defined as the study of the nature and properties of the various elements; of the laws according to which these elements enter into combination with each other and of the nature and properties of the compounds formed by their union 3 organic chemistry may be generally defined as the chemistry of carbon and its compounds, since carbon is the one essential element in all organic com pounds. The separation of chemical science into the two branches of inorganic and organic chemistry is in reality arbitrary, but it is convenient, simply on account of the enormous number, and special importance, of the compounds in cluded in the latter division 5 not that they are in any way subject to different laws from those which govern inorganic compounds.