Six varieties of cottons were given certain chemical treatments, and the resulting changes in their fundamental physical properties were measured. This first report of a series describes the purpose of the work, the methods used to measure the properties, and the types of chemical treatments used. It also furnishes photomicrographs of cross sections of the cotton fibers and the values of the physical properties of the untreated cottons, which are the controls for samples receiving the chemical treatments. Data are given for yarns and fibers of these cottons, and comparisons are made between values of corresponding properties.