E. A. Partridge — Atomic Weight of Cadmium. 381 



tubes. The second was shown to be groundless, as in some 

 experiments the hydrogen sulphide used was prepared from 

 antimony trisulphide and in others from ferrous sulphide with 

 perfect agreement of results. The third objection was dis- 

 proved experimentally, as the highest heat that hard Bohemian 

 glass will withstand did not cause any volatilization of cadmium 

 sulphide. That there was no volatilization of sulphide was 

 proved by the weight of a sample of the same which was 

 heated in a stream of hydrogen sulphide to the extent just 

 mentioned, remaining absolutely constant, and also by the fact 

 that there was not the slightest sublimate on the tube. 



The hydrogen sulphide employed in this and in the follow- 

 ing series of experiments was washed by passing it through 

 water and dried hy passing through a long calcium chloride 

 tube. The carbon dioxide was dried by passing through a 

 wash bottle containing sulphuric acid and then over calcium 

 chloride By means of a three-way cock the carbon dioxide 

 could be run into the apparatus without changing the connec- 

 tions. 



The cadmium sulphate was prepared in the following man- 

 ner : Cadmium nitrate, prepared as above described, was dis- 

 solved in water and a slight excess of pure sulphuric acid added. 

 Five c. c. of this acid were evaporated in a platinum dish, leav- 

 ing a visible but imponderable residue. 



The solution was evaporated to dryness in a platinum dish 

 and heated long after fumes of sulphuric acid ceased to come 

 off. The sulphate was dissolved in water, recrystallized and 

 dried for six hours at 200° C. . 



The following is a description in detail of the method used 

 in the experiments, the results of which are tabulated below. 

 (Series II.) 



The dry cadmium sulphate was placed in a porcelain boat 

 and heated for some time in an air bath to about 300° C. 

 While still warm the boat was placed in the weighing tube, 

 allowed to cool and weighed. Cadmium sulphate parts with 

 its hygroscopic moisture very readily at 300° C. After weigh- 

 ing, the boat containing the cadmium sulphate was placed in a 

 hard glass tube, 50 cm in length, supported over a small combus- 

 tion furnace. A stream of pure dry hydrogen sulphide was 

 then passed through the tube and heat applied. It was heated 

 moderately for 45 minutes and to dull redness for as much 

 longer. By this time its reduction to sulphide was always com- 

 plete. It was then allowed to cool to about 200° C. in a slow 

 stream of the gas. When the temperature had fallen to this 

 degree the hydrogen sulphide was displaced by a stream of 

 pure dry carbon dioxide, and while still warm the boat contain- 

 ing the cadmium sulphide was placed in the weighing tube, 



