The series of normal saturated dicarboxylic acids, their diethyl esters and mono-ethyl esters have been investigated by means of X-rays, and from the measurement of the principal spacings a definite chain structure has been assigned to each series. Mathematical formulæ derived by Shearer for similar series of compounds have been applied to these structures, and the intensity distribution among the several orders of reflection from the principal planes calculated. These calculated results have been compared with those actually observed from the plates, and the agreement was found to be good in every case, thus confirming the chain structures assigned by the authors to the above series of compounds.