────────┬────────┬────────┬────────┬────────────┬────────┬──────────── No.│CdBr_{2}│ AgBr│ H_{2}O │Ex. AgNO_{3}│ At. Wt.│Remarks ────────┼────────┼────────┼────────┼────────────┼────────┼──────────── I│ 4.39941│ 6.07204│ │ │ 112.43│Distillate } II│ 3.18030│ 4.38831│ │ │ 112.42│Residue } III│ 3.60336│ 4.97150│ │ │ 112.45│Resublimed. IV│ 4.04240│ 5.58062│ │ │ 112.29│ V│ 3.60505│ 4.97519│ │ │ 112.38│ ────────┼────────┼────────┼────────┼────────────┼────────┼──────────── │ │ │ │ Average │ 112.394│ Discussion of the Results. The first three specimens were prepared under widely different conditions yet the results agree quite closely. The last two were prepared from the repurified hydrobromic acid. If chlorine had been removed during the second purification we should expect a higher result but the results are lower. There seems to be hardly any doubt that this is due to analytical errors rather than a change in the composition of the bromide. Whether this be true or not, the five determinations all fall within the limits obtained by the chloride method and confirms it as fully as can be expected. The errors of the method are the same as those of the bromide method, only they are probably less in most cases. One filtrate was examined for bromium, but none was found showing the method to be more perfect in this respect. Syntheses of Cadmium Sulphate. It was next thought of examining the method based on the conversion of cadmium sulphate into cadmium sulphide, which has been used by von Hauer whose result is 111.94 for the atomic weight of cadmium, and more recently by Partridge who obtained a much lower result, namely 111.73. They dried cadmium sulphate in porcelain boats, and then reduced it to sulphide by heating in a current of hydrogen sulphide. The reduction begins in the cold and is probably complete or at least nearly complete before the temperature is sufficiently high for cadmium sulphate to decompose into cadmium oxide, for the sulphate is very stable with respect to heat. This being the case, probably no error results from the formation of a silicate of cadmium in this method. The main difficulty in this method would be to prove that the cadmium sulphate used is free from water. Neither von Hauer nor Partridge has done this because drying a substance to a constant weight is not sufficient evidence of its anhydrous character, especially if the drying is done at a constant temperature. This has been shown very clearly in the case of copper sulphate, by Richards (Proc. Amer. Acad. Sci. 26. 263.) It was therefore decided to attempt the synthesis of cadmium sulphate, hoping to be able to fix a minimum value for the atomic weight of cadmium.