166 Dr. Clarke on Cadmium, [Marci*, 



by sulphuretted hudrogen after the iron had been immersed for 

 the time specified ; nor could I any longer obtain a satisfactory 

 proof of the presence oi cadmium by the usual tests. 



The account which appeared in a volume of the Annals of 

 Pliilosophy* published in October, 1819, with the title of 'New 

 Details respcctifiiji; Cadmium, by M. Stromeyer, taken from the 

 Annalen der Fhi/sik, Ix. 193, mentions as a property o^cadmium, 

 that '* the precipitate formed by the carbonate oJ'ammo)iiah not 

 soluble in an excess of this solution, zinc exhibiting a different 

 property." This is certainly erroneous, if Prof. Strotnet/er's own 

 oxide of cadmium may be considered a proper substance for pre- 

 paring the salt necessary for the experiment. Having dissolved 

 a portion of this oxide in pure muriatic acid, and neutralized the 

 solution, as before, adding distilled water, carbonate of ammonia 

 yielded a white precipitate, which was wholly soluble in an 

 excess of the carbonate. The importance of attending to this 

 fact will be evident to all your readers who pursue the process 

 pointed out by Prof. Slromeyer for obtaining cadmium from its 

 ores. I think it also right to mention (with a view of putting 

 chemists upon their guard, who have not had more experience 

 in these matters than myself), that some of the pheenomena exhi- 

 bited by the combustion of cadmium, so nearly resemble those 

 exhibited by lead under the same circumstances, that the 

 absence of the last mentioned metal ought always to be carefully 

 ascertained. Before I proceed, therefore, to relate an account 

 of experiments which have enabled me to separate cadmium 

 from zinc, it will be proper to mention such characters of the 

 former metal as may serve to identify it under all circumstances. 

 For this purpose, owing to the brevity and perspicuity with 

 "which the present Regius Professor of Chemistry at Glasgow 

 has pointed out these properties, I shall quote two letters I had 

 the honour to receive from him upon this subject, when he 

 kindly undertook to examine some carbonate of cadmium whicli 

 I had obtained from an English ore of zinc, and when he con- 

 firmed by his own observations the fact of the presence of 

 cadmium in the mineral I had examined. According to Dr, 

 Thomi6on,f there are certain trials which may be considered as 

 affording the " experimentum crucis " with regard to this body, 

 especially in distinguishing Ca d m i u m from Zinc. ( 1 .) ''Phos*- 

 ^hate of soda precipitates zinc in small crystaUine scales ; it pre- 

 cipitates cadmium in a white pulverulent powder, f (2.) Sulphur^ 

 ettcd hydrogen throws down Zinc ichite, but Cadmium yellow, 

 which remains fixed at a red heat." Other chemical characters 

 of Cadmium are, the solution, with effervescence, both of its 



♦ See vol. xiv. p. 271. 



+ MS. Letters of Dr. llomsou, dated Gla$govo, Jan. 25, 1820, and Feb. 1, of the 

 same year . 



X It aUo precipitates lead in the same form, but lead precipitated bj carbonate »f 

 4unnmnia ii not rediiiolved by adding an excess of the carbonate^ or by liquid ammonia 



