von Hauer. Lenssen. Work here described. 9 determinations. 3 determinations. 10 determinations. (O = 16) (O = 16) (O = 16) Mean 111.940 112.067 112.0705 Max. 112.121 112.304 112.086 Min. 111.796 111.911 112.053 Diff. .325 .393 .033 A difference of three or four tenths of a unit between the different results of a series leaves considerable doubt as to the accuracy of the method employed and to the value obtained. The figure selected by Ostwald,[5] as most probable for the atomic weight of cadmium is 112.08. This is the mean of the results on von Hauer and Huntington. My own work leads me to believe that this number is very close to the true value when oxygen is taken as 16. [5] Lehrb. d. Allg. Chem. I, 60. Objections to the method. Marignac[6] offered the objection to this method for determining the atomic weight of zinc that the zinc oxide dissociated when heated in platinum over the blast-lamp. The same objection might be urged against this method for determining the atomic weight of cadmium, had it not been shown that the objection does not hold for zinc[7]. What took place was a reduction of the zinc oxide by the highly heated hydrogen which passed through the hot platinum. [6] Archives des Sciences Phys. et Nat. (3) 10, 193. [7] Amer. Chem. Journ. X, 148. It was shown that zinc oxide can be heated in a platinum vessel in a muffle furnace, to the melting point of steel, without undergoing any dissociation, or in any wise losing in weight. This source of error was avoided by using porcelain vessels, which were not brought into contact with the free flame. The statement of Marignac that the oxide of zinc derived from the nitrate retains oxides of nitrogen even when heated to the temperature at which it begins to undergo dissociation, was shown by the same authors to be without foundation. The basis of this objection is doubtless to be found in the imperfect method of testing for such oxides. It might be urged as an objection to this method that the difference in weight between the metal and oxide is not very great, therefore any error in weighing would be multiplied in the result. At first sight this objection may appear valid, but since the substances weighed were so well adapted to that purpose and the weighings could be made with such a high degree of accuracy no appreciable error could have resulted from this source. A crucible with its contents was repeatedly weighed against its tare and weights to ascertain the difference between successive weighings under the conditions employed. A number of weighings agreed to .00002 gr. and in some instances to half this amount. Advantages of the Method.