218 Von Hauer on the Equivalents of Cadmium and Manganese. 



of several metals, and has published the results of his determina- 

 tions of cadmium and manganese. His method is based on the 

 fact that the sulphates of zinc, cadmium, lead, copper, manganese, 

 cobalt, and nickel, when heated in sulphuretted hydrogen gas, 

 yield their respective sulphides of perfectly definite composition. 

 The sulphates of all these metals, with the exception of that of 

 lead, crystallize readily, and may therefore easily be obtained 

 pure. They are also easily rendered anhydrous ; and although 

 they are then somewhat hygroscopic, the influence on the weigh- 

 ing may be avoided. The reduction is effected at a moderately 

 low temperature, the results are uniform ; there is no danger 

 from leaving the sulphide too long in contact with the gas, as it 

 is not altered thereby; there is no danger of mechanically carry- 

 ing away any of the substance, provided the operation be not 

 conducted too rapidly ; and further, sulphuretted hydrogen is a 

 gas which is readily obtained pure, and hence there is no fear of 

 introducing an impurity from that source. By the reduction of 

 the sulphate to sulphide, 4 equivalents of oxygen are carried off 

 in the form of water. This loss amounts to 30 or 40 per cent., 

 and hence in this important respect the determination is favour- 

 able. The determination is dependent on the purity of the sub- 

 stance ; and the only difficulty in execution lies in the reduction, 

 and the two weighings. 



For the determination of cadmium, a very pure sulphate was 

 prepared by frequent recrystallization : this was precipitated by 

 sulphuretted hydrogen ; the precipitate well washed out was 

 dissolved in hydrochloric acid, precipitated by carbonate of 

 ammonia, and after being well washed and dried, was ignited 

 to convert it into oxide. This was then repeatedly washed with 

 water to free it from accidentally adhering chloride of cadmium, 

 and then dissolved in dilute sulphuric acid, and the sulphate i-e- 

 peatedly recrystallized. In order to free it from excess of acid, 

 the sulphate was heated to dull redness each time before it was 

 dissolved. 



The reduction was effected in a glass tube heated by means of a 

 Bunsen's burner, and the salt was placed in small porcelain trays. 

 The reduction was commenced at a moderate temperature, which 

 was gradually raised; the operation was continued some hours, 

 although it was found that from 5 to 8 grammes were reduced 

 in two hours. The reduced sulphide was allowed to cool in the 

 current of sulphuretted hydrogen, and was then weighed. It 

 was found that the sulphide was not at all hygroscopic ; each 

 time it was tested for undecomposed sulphate. The mean of nine 

 experiments gave 55"9994 as the equivalent of cadmium, assum- 

 ing the equivalent of sulphur to be 16. Hence 56 is doubtless 

 the true number. 



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