Atomic Weight of Cadmium, History

The atomic weight of cadmium has been determined by -

1. The Conversion of the Metal into the Oxide. - Stromeyer, from the ratio Cd:CdO, obtained an atomic weight for cadmium of 111.483, if O = 16.
   
   Morse and Jones dissolved the purified metal in nitric acid and obtained the ratio Cd:CdO = 100:114.27672 from ten ignitions of the nitrate into the oxide. The oxide was always tested for oxides of nitrogen. Cd = 112.0706.
   
   Morse and Arbuckle, in a repetition of this work, obtained from nine determinations 112.377 for the atomic weight of cadmium. Their calculations included corrections for gases occluded by the oxide.
   
   Between these two last determinations Bucher made five determinations by the same method. He carefully considered sources of error in his method, and, after applying various corrections, his results indicate an atomic weight for cadmium of 112.39.
   
   Lorimer and Smith had obtained a value of 112.055 that agreed more with the lower values of the earlier determinations. Their ratio of Cd:CdO = 100:114.27872 was obtained by depositing cadmium electrolytically from solutions of the oxide in potassium cyanide. They made nine determinations.
2. The Ignition of the Oxalate into the Oxide. - Lenssen obtained the ratio CdC₂O₄:CdO = 100:64.0059, giving cadmium as 112.043; Partridge the ratio 100:63.9649, making cadmium 111.816; Morse and Jones the ratio 100:64.00387, giving Cd = 112.032; Bucher the ratio 100:63.978, making cadmium 111.89.
3. The Conversion of the Oxalate into the Sulphide. - Partridge obtained the ratio CdC₂O₄:CdS = 100:71.973 ± 0.0007, and Bucher the ratio 100:72.052 from the sum of four determinations. Partridge's result was obtained from ten determinations. The former ratio makes cadmium 111.591 and the latter makes it 112.16.
4. The Reduction of Cadmium Carbonate to Metal in a Current of Hydrogen. - The sum of five determinations gave the ratio Cd:CdCO₃ = 100:153.417, from which the atomic weight of cadmium is 112.33.
5. The Analysis of Cadmium Sulphate. - Bucher obtained the ratio Cd:SO₄ by a conversion of the metal into the sulphate, and Baxter and Wilson by an electrolytic determination of cadmium in the sulphate. They made seven determinations. Bucher's ratio was 116.956:100 and the latter 117.019:100. The respective atomic weights for cadmium are 112.354 and 112.414.
   
   These determinations were made with the anhydrous sulphate. Perdue and Hulett found 43.799 per cent, of cadmium in the hydrated sulphate by estimating the metal electrolytically. Their figure was derived from seven determinations. If the salt is 3CdSO₄.8H₂O, the atomic weight of cadmium is 112.305.
   
   Some earlier methods converted the sulphate into the sulphide. Von Hauer, as the sum of nine determinations, obtained the ratio CdSO₄:CdS = 100:69.23, and Partridge, as the mean of ten experiments, the ratio 100:69.199 ± 0.0012. The atomic weights for cadmium are respectively 111.93 and 111.719.
6. The Analysis of the Chloride. - Stromeyer obtained the ratio Cd:Cl₂ = 100:62.89. Hardin obtained the ratio Cd:Cl₂ = 100:63.2808 directly by electrolysing the chloride and weighing the cadmium. This ratio, from the sum of ten determinations, gives 112.06 as the atomic weight of cadmium.
   
   Quinn and Hulett converted the chloride into the sulphate and estimated the cadmium by electrolysis. The ratio Cd:Cl₂ = 100:63.1375, obtained from seven determinations, makes the atomic weight of cadmium 112.32.
   
   Baxter and Hartmann obtained the ratio Cd:Cl₂ = 100:63.0795 from eighteen electrolytic determinations of cadmium in the chloride, but they preferred the ratio 100:63.0811 from five selected determinations. The former ratio gave Cd = 112.420 and the latter Cd = 112.417.
   
   Baxter, Grose, and Hartmann, from three electrolytic determinations of cadmium in the chloride, obtained the ratio Cd:Cl₂ = 100:63.0835, and this gave 112.413 for the atomic weight of cadmium.
   
   Dumas determined the ratio CdCl₂:2Ag = 100:117.813. He himself was uncertain about the accuracy of this ratio, which represents the sum of six experiments.
   
   Baxter and Hines obtained the ratio CdCl₂:2Ag = 100:117.6939. This ratio, obtained from six experiments, makes Cd = 112.409.
   
   Bucher obtained the ratio CdCl₂:2AgCl = 100:156.124. Cd = 112.71.
   
   Baxter and Hines, from three experiments, obtained the ratio CdCl₂:2AgCl = 100:156.3694. Cd = 112.417.
7. The Analysis of the Bromide. - Hardin obtained the ratio CdBr₂:Cd = 100:41.2031 from ten electrolytic determinations of cadmium in the bromide. Cd = 112.005.
   
   Quinn and Hulett converted the bromide into the sulphate and determined the cadmium by electrolysis. The ratio CdBr₂:Cd = 100:41.2569 was obtained from eight determinations. Cadmium is 112.25 from this ratio.
   
   Baxter, Grose, and Hartmann, by electrolysing the bromide, found that cadmium bromide contained 41.290 per cent, of cadmium as the mean of twelve determinations. From this figure CdBr₂:Cd = 100:41.290 and Cd = 112.407.
   
   Huntingdon and Cooke obtained the ratio CdBr₂:2Ag = 100:79.3179 from the sum of eight determinations, and Baxter, Hines, and Frevert the ratio CdBr₂:2Ag = 100:79.24958 from seven determinations. The former ratio gives Cd = 112.187 and the latter Cd = 112.325.
   
   Bucher, from the mean of five determinations, obtained the ratio CdBr₂:2AgBr = 100:138.005, and Baxter, Hines, and Frevert, from seven determinations, the ratio 100:137.9978. Cd is respectively 112.33 and 112.335. The sum of eight determinations by Huntingdon and Cooke had given the ratio 100:138.077.
8. Determination of the Ratio Cd:Ag by the simultaneous Electrolytic Deposition of the two Metals. - Hardin did not obtain satisfactory results, but Laird and Hulett, making sixteen determinations, obtained 112.31 for the atomic weight of cadmium.

The International atomic weight of cadmium is taken as

Cd = 112.41.

The atomic number is 48.