1822.] Dr. Clarke on Cadmium. 197 



oxide and carbojiate, and of metallic Cadmium in muriatic acid^ 

 The oxide obtained from this solution by heat and alkaUes has 

 a yellowish-brown colour. The murictte, as before mentioned, is 

 precipitated white by carbonate of ammonia^ and is redissolved 

 by adding an excess of that carbonate. It is moreover precipi- 

 tated white by potass,^" ammonia, and sulphate of soda ; yellow by 

 sulphuretted hydrogen, and w^hite hy prnssiate of' potass. 



To these characters may now be added the striking phseno- 

 mena observed in the combustion of Cadmium, by Dr. Wollas- 

 toHf and by Berzelins. 



According to Dr. WoUaston the oxide of cadmium is white ; 

 •when fixed at the point of the blue fame, before the blowpipe, 

 supported upon a platinum disk, the carbonaceous matter of the 

 flame reduces the oxide, so that the metal, being revived, burns, 

 and deposits during its combustion, di protoxide of cadmium, of a 

 reddish-brown, or copper colour, easily to be recognized by those 

 who have once seen it. According to Berxelius, whose obser- 

 vations in point of time succeeded those of Dr. WoUaston, sub- 

 stances containing Cadmium, when exposed to the action of the 

 blowpipe, and supported upon charcoal, yield a yellow oxide^ 

 which is deposited in the form of " a ring ^' around the body 

 exposed to trial. He calls it *' un anneau jaune, ou orange, 

 dioxide de cadmium ;" and such, he maintains, is the subtlety of 

 this test, that the carbonates of zinc which do not contain more 

 than one per cent, of the carbonate of cadmium, exhibit this 

 appearance ; insomuch, he adds, that if there be no manifesta^ 

 tion of this " anneau jaune,^' it is a proof that the substance 

 under examination does not contain Cadmium. 



Your readers will thus be put in the possession of a few facts, 

 within a small compass, which will be found useful in judging of 

 the validity of the following observations. 



Having exposed some fihngs of zinc upon a platinum disk 

 before the blue flame of a wax candle, urged by the common 

 blowpipe, I perceived that the pohshed surface of the platinum 

 was altered by the experiment, and that an appearance resem- 

 bling that of the protoxide of cadmium, produced under similar 

 circumstances, was apparent upon the metal. To see whether 

 this appearance was owing to the lead which is contained in the 

 metallic zinc of commerce, I exposed some white oxide of lead to 

 the same trial, and obtained nearly a similar result ; but with 

 marks of a fine blue colour mixed with hues of yellow and of 

 reddish-brown. I, therefore, resolved to submit the ziric to a 

 chemical examination. For this purpose having dissolved it in 

 muriatic acid, and neutrahzed the solution, adding distilled 

 water, I suffered iron to precipitate as many of the raetaUic 

 impurities as that metal would throw down during some hours 

 that it remained immersed in the liquid, which was then filtered, 



* Liquid caustic potast precipitates cadmium white, in the form of a hydrmtCy whidfc 

 U not redigfolved by aa exceM of the precipitank ; and thia diatinguishes it from einc 



