Discussion of the Oxalate Method 114 VIII. Other Methods 119 IX. Conclusion 122 Acknowledgement. The author wishes to acknowledge his indebtedness for advice and instruction to Professor Morse at whose suggestion and under whose guidance this work has been carried on. He also wishes to express his thanks for instruction to Professor Remsen in Chemistry, Professor Williams in Mineralogy, Dr. Ames in Physics and Mr. Hulburt in Mathematics. Introduction and Historical Statement. The atomic weight of cadmium has been investigated by a number of chemists but the results obtained vary between wide limits. The work described in this paper was undertaken with the object of finding the cause of the discrepancy in some of the methods employed. A complete historical statement has been given by Morse and Jones, (Amer. Chem. Jour., 14. 261.) and it is only necessary, here, to give a summary for the purpose of reference: Ratio. At. Wt. Cd. 1818, Stromeyer, Cd : CdO 111.483 (Schweiggers Jour. 22, 336.) 1857, Von Hauer, CdSO_{4} : CdS 111.935 (Jour. f. Prakt. Chemie 72, 338.) 1859, Dumas, 1st series. CdCl_{2} : Ag 112.416 2d „ CdCl_{2} : Ag 112.007 (Ann. Chim. Phys. [3], 55, 158.) 1860, Lenssen, CdC_{2}O_{4} : CdO 112.043 (Jour. f. Prakt. Chem. 79, 281) 1882, Huntington and Cooke, CdBr_{2} : AgBr 112.239 „ „ CdBr_{2} : Ag 112.245 (Proceedings Amer. Acad. 17, 28) 1890, Partridge, 1st Series CdC_{2}O_{4} : CdO 111.816 „ 2d „ CdSO_{4} : CdS 111.727 „ 3d „ CdC_{2}O_{4} : CdS 111.616 (Amer. Jour. Sci.[3], 40, 377) 1892, Morse and Jones, 1st Method, Cd : CdO 112.0766 2d „ CdC_{2}O_{4} : CdO 112.632 1892, Torimer and Smithy CdO : Cd 112.055 (Zeit. f. Anorg. Chem. I. 364) In this summary as well as in the rest of this paper the following atomic weights are used: Oxygen = 16.00 Sulphur = 32.059 Carbon = 12.003 Chlorine = 35.45 Bromine = 79.95 Silver = 107.93 The Oxalate Method Preparation of Pure Cadmium.