It affords me great pleasure to express my sincere thanks to Professor Remsen for his instruction and personal supervision during my entire connection with the University; to Dr. Morse, under whose immediate guidance the work described in this dissertation was completed; to Dr. Renouf for valuable assistance in qualitative chemistry and to Dr. Williams, with whom the branches of mineralogy and geology were followed as subordinate subjects. Determination of the Atomic Weight of Cadmium. Introduction and Historical statement. A careful examination of the literature on the atomic weight of cadmium will convince any one that considerable uncertainty yet remains in reference to this constant. Six experimenters have worked on this problem but the results of no one of them can be accepted as being more accurate than those of all others. The value assigned to cadmium varies from 111.48 to 112.32 on the basis of oxygen = 16. The best work has apparently been done by von Hauer, Lenssen and Huntington. The results of these three seem entitled to about equal confidence, yet the figure obtained by von Hauer differs from that of Huntington by three tenths of a unit. The more prominent difficulties which have been encountered were: First. The preparation of cadmium compounds free from all impurities, and which at the same time were well adapted to weighing. Second. The lack of a thoroughly simple and exact method for the analysis of cadmium compounds. Third. Insufficient care in weighing in many cases whereby small errors were introduced into the results. The methods which have been employed are: 1 Conversion of the metal into the oxide. (Stromeyer). 2 Conversion of the sulphate into the sulphide. (von Hauer and Partridge). 3 Decomposition of the oxalate to the oxide. (Lenssen and Partridge). 4 Determination of the chlorine in cadmium chloride, by which the relation between the chloride and metallic silver was established. (Dumas.) 5 Precipitation of the bromine in cadmium bromide as silver bromide. (Huntington.) 6 The conversion of the oxalate into the sulphide. (Partridge.) The different pieces of work will be taken up in chronological order and briefly considered. Stromeyer, Schurigg Journ. 22, 366. 1818, determined the atomic weight of cadmium a short time after the discovery of the element. He does not describe his method in detail but established the relation between cadmium and oxygen to be: Cd : O = 100 : 14.352. If the atomic weight of oxygen = 16, ” ” ” ” cadmium = 111.483. The very low result as compared with all subsequent work was probably due to the presence of a small amount of zinc, since the cadmium used was obtained from zinc ores and no adequate means of separation from the zinc is described.