1322.] Dr, Clarke on Cadmium. 1^5 



i>jistion are among the most remarkable properties of the metal, 

 jmd they are those of which chemists have availed themselves in 

 detecting the presence of very minute portions of cadmium in 

 its various ores. Berzelius, in the inestimable volume which he 

 has recently published upon the *^ Use of the Bloivpipe/'^" seizes 

 with avidity this striking character, and makes it the prominent 

 and discriminating character of the ores of cadmium. f But 

 long before the publication of this work of Berzelius, and at the 

 time when Dr. Wollasiou, by his own experiments confirmed 

 the fact of the discovery o£ cadmium in the English ores of xiwc,J 

 this illustrious chemist had already availed himself of the same 

 atriking property in the metal. Speaking of the oxide of 

 cadmium as obtained from those ores, in a letter which I 

 received from him dated February 14, 1820, Dr. Wollaston 

 ^ays, " fixed at the tip of the blue flame, it is gradually reduced, 

 yolatihzes, and is carried along the shp of platina, coating it with 

 its peculiar reddish-brown protoxide in a way that cannot be 

 mistaken by one who has once seen it." Indeed so striking is 

 the manifestation of this character in ores containing the most 

 minute portions of cadmium that the fact of its presence in the 

 silicates and carbonates of zinc needs no other test. But there 

 is a method of putting those minerals to the trial of cadmium 

 which seems to me preferable to that mentioned by Berzelius, 

 who uses charcoal for a support. It is simply this : Triturate a 

 portion of the silicate or carbonate of zinc supposed or not to 

 contain cadmium, and place about the tenth of a grain of tlie 

 powder upon a slip of platinum foil. Then direct the blue fame 

 Qf a candle towards it by means of the blowpipe ; if any cad- 

 mium be present, its oxide will be reduced, volatilized, and 

 a protoxide will be deposited upon the surface of the platinum, 

 with the peculiar reddish-brown colour before mentioned. 



Another mode of showing the presence of cadmium in the 

 ores of zinc, remarkable for its simplicity and certainty, is also 

 dlie to Dr. Wollaston. This consists in dissolving the car- 

 honates of zinc, or gelatinizing the silicates in muriatic acid, 

 getting rid of the excess of acid, and adding distilled water ; 

 then removing any metals that ijvn wdll precipitate, and filter- 



* " De rEmploi du Chalumeau dans IcvS Analyses Chimiques," &c. a Paris, 1821. 



+ " Ce ph^nomene est si marqud dans I'oxide de cadmium, que les raineraux qui 

 comnie le carbonate dezinc, contiennent un ou deux pour cent de carbonate de cadmium, 

 ^tant exposes un seul instant au feu dc reduction, deposent i peu de distance de la 

 -matiere d'essai, un anneau jaune ou orange d'oxide de cadmium que Ton aper^oit d'au- 

 tant mieux que le charbon est plus refroidi. Cet anneau se forme bien avant le com- 

 mencement de la reduction de I'oxide de zinc, et si les flocons de zinc se montrent en 

 ineme temps, c'est une preuve que Ton a pousse I'insufflation trop loin; mais si Ton ne 

 peut decouvrir aucune trace jaune avant que la fumee de zinc commence a former un 

 depot sur le charbon, on doit en conclure que la matiere d'essai ne contient pas de cad- 

 mium."~(/6ij. p. 132.) 



J Dr. Clarke since writing this article has himself discovered cadmium in the metaJlic 

 . OT sheet zinc of commerce. A communication from him upon this subject wiE appear in 

 our next number. — Ed. 



