198 Dr, Clarke on Cadmium, [March, 



^and received into a platinum capsule containing a piece of clean. 

 xinc. In a short time both the interior of the platinum capsule 

 and the surface of the zinc vvere coated over with a precipitate 

 of a dull leaden hue ; and this, being washed, exhibited before 

 the blowpipe, and also after solution in muriatic acid, all the 

 characters before mentioned as peculiar to cadmium, with this 

 exception, that the precipitate yielded by the muriate to sulphur- 

 'etted hydrogen was somewhat darker than the precipitate caused 

 when cadmium is precipitated by tlie same reagent, which made 

 me suspect that it was still contaminated with lead, I, therefore, 

 •went to work in another way, and dissolved the zinc in dilute 

 sulphuric acid, following Stromeyer's process when obtaining 

 cadmium from the sulphurels of zinc, which contain sulphuret 

 of lead. As soon as all the zinc had been dissolved, I took 

 care to have a great excess of acid present in the solution 

 by adding fresh sulplniric acid to the liquid, which was afterwards 

 filtered. I then sent a stream of sulphuretted hydrogen gas 

 through it, which in the space of a few minutes comnmnicated to 

 the solution the fine orange-yellow colour, which characterizes the 

 precipitation of cad?Jiium by means of that reagent ; but many 

 nours elapsed before the precipitate was sufficiently disengaged 

 to subside. As soon as it had subsided, it was of dingy yellow 

 colour. The supernatant fluid being then decanted, muriatic 

 acid was poured upon the precipitate, and slowly evaporated. 

 Afterwards distilled water being added to the dry muriate, the 

 liquid was filtered, and it exhibits the following properties : 



1. Carbonate of atnmonia causes a ichite precipitate which, by 

 excess of the carbonate, is redissolved. The solution evaporated 

 to dryness, and the residue exposed to a smart red heat in a 

 porcelain crucible, affords an oxide,* similar to that mentioned 

 by Stromeyer. He says Cadmium forms only a single oxide, 

 100 parts of the metal combining with 14'352 of oxygen. 

 ** The colour of this oxide varies according to the circum- 

 stances in which it is formed. It is brownish-yellow, light- 

 brown, dark- brown, and even blackish. It is quite fixed, and 

 infusible in the strongest white heat, and does not lose its 



oxygen." t 



The oxide I obtained by exposing the carbonate to a vio- 

 lent heat agrees with Stromeyer's oxide ; but, in one instance, 

 instead of turning to the brown colour of snuflj which that 

 does, it remained scarcely altered by heat. In this respect, 

 it could not be considered as agreeing with Stromeyer's own 



" This would, perhaps, afford the finest yellow pigment known ; and when it is con- 

 sidered that a very powerful temperature is necessary to produce it, perhaps it is of all 

 <X>loitr:S the least likely to be affected by atmospherical changes of temperature after- 

 wards; neither would it be blackened by exhalations from the coal fires of our apart, 

 menis ; but the colour is rarely in two instances alike ; it is sometimes of a fine orpimenU 

 jeUoitr, and at others of a darker hue. 



f .^ AntuiU ofPhilusophy, vol. xiv. p. 270. 1819. 



