All weighings were reduced to the vacuum standard on the assumption of 8.4 for the Sp. Gr. of brass, 21. for platinum, 3.31 for the oxalate and 8.15 for cadmium oxide. The results are: Cadmium Oxalate. Cadmium Oxide. At. Wt. Cd. I 1.97674 1.26414 111.73 II 1.94912 1.24682 111.82 III 1.96786 1.25886 111.77 IV 1.87099 1.19675 111.77 V 1.98941 1.27242 111.79 VI 1.37550 .87994 111.85 VII 1.33313 .85308 111.95 VIII 1.94450 1.24452 112.04 IX 2.01846 1.29210 112.09 A glance at these results shows that there is a variation of .36 of a unit and that the atomic weight in general increases with the number of determinations. In the first four determinations, there may have been loss of cadmium by reduction and subsequent volatilization, but in the later determinations this is not probable. It is believed that the greater part of the variation was due to imperfect dehydration of the oxalate. This and other sources of error in this method will be referred to later. The nickel crucible used gave a slight sublimate on heating, even after fifteen hours’ blasting. This condensed on the porcelain crucible as a brownish coating but, as both the crucible and its tare were blasted for the same length of time, it did not seem to change the difference of their weights. More than a dozen nickel crucibles were tried but none was found not to give a sublimate. The amount was so slight that no attempt was made to determine its nature. The Sulphide Method. This method is based on the conversion of cadmium oxalate into cadmium sulphide by heating in a current of hydrogen sulphide. The method has been used by Partridge. This result was 111.61 for the atomic weight of cadmium. Preparation of Hydrogen Sulphide In the present work this gas was always prepared from potassium hydrosulphide which was made from barium sulphide (commercial). Barium sulphide was treated with dilute hydrochloric acid and the resulting hydrogen sulphide washed thoroughly with a solution of potassium hydrosulphide and then with pure water. It was then passed into a strong solution of potassium hydroxide until the later was saturated. When it was required, it was set free from this solution by adding dilute sulphuric acid and again washing the resulting gas with a strong solution of potassium hydrosulphide. Preparation of Nitrogen.