The spectrophotometric determination of copper in sea water has been studied with sodium diethyldithiocarbamate as the color forming reagent. This reagent, compared with the frequently used dithizone, affords simpler operation, less interference from other metallic ions, higher sensitivity, and greater accuracy. Xylene has been found to be most desirable for extracting the copper diethyldithiocarbamate. Factors studied in some detail include the effects of varying the extracting time, concentration as it affects the coefficient of extraction, amount of reagent, hydrogen ion concentration, salinity, concentration of oxidizing and reducing agents, and the stabilities of the diethyldithiocarbamate reagent and the colored copper diethyldithiocarbamate....