126 Dr. Clarke on Cadmium. [Feb. 



ing the solution, which is to be received into a platinum 

 capsule, containing a piece of zinc. The cadmium, if any 

 be present, will coat over the interior surface of the capsule 

 with a precipitate of a dull leaden hue, and will adhere so 

 firmly as that it may be washed, and thereby freed from any 

 remaining solution of zinc. Muriatic acid being now poured 

 into the capsule will dissolve the lead-coloured coating with 

 effervescence, and either the carbonate of jiotass or caustic potass 

 will yield a white precipitate, which, by heat before the blue 

 Jiame of the blowpipe, will exhibit the remarkable character 

 already pointed out, as characteristic of Cadmium. 



As it will not I hope be long before some of the chemists of 

 Great Britain will obtain cadmium in the metallic state from the 

 ores which this country affords, I will mention the localities of 

 some of them, and give such a description of the minerals in 

 which I have myself detected the presence of this metal, that 

 there can be no difficulty in meeting with a supply of ore neces- 

 sary for the experiment. 



The Cumberland. Cave, near Matlock, contains both silicate 

 and carbonate of zinc, and both are cadiniferous. I have received 

 from Professor Sedgwick of this University, specimens of both 

 those minerals, which he himself brought from that cave. The 

 carbonate being the most abundant, 1 will describe this first. 

 All the carbonates and silicates of zinc found in the Cumberland 

 Cave go by the name of Calamine, and are promiscuously sold by 

 the dealers in minerals, either as electric or non-electric Calamine, 

 just as the name best answers the purposes of sale. Hence 

 arises that confusion in cabinets of mineralogy, whose owners, 

 trusting to the dealers, have not given themselves the trouble to 

 examine chemically the specimens they have bought. Nothing 

 can be more easy than to distinguish between a carbonate and a 

 silicate of zinc, even when they are not crystallized : both are 

 soluble in acids leaving no residue, but the first effervesces upon 

 the immediate action of the acid; while the second, exhibiting 

 no effervescence, forms, as the solution evaporates before a fire, 

 or over a lamp, in a watch glass, a transparent jelly. 



The carbonate of zi?ic of the Cumberland Cave is often sold as 

 a silicate. It is a veiy compound mineral, consisting of no less 

 than three distinct varieties of the carbonate aggregated into one 

 mass, besides galena, fuor, quartz, sulphate of barj/tes,* and 

 other bodies. To speak, therefore, of the specijic gravity of such 

 a mineral mass would be absurd. Of the three varieties of the 

 carbonate of zinc which it contains, all are cadmiferous. The 

 Jirst is of a honey colour, exhibiting a sparry fracture, and a 



* Small flattened acicular crystals of the sulphate of barytes are se€n in the cavities, 

 opaque, and of a white colour. Immersed in muriatic acid these crystals effervesce 

 owing to some earthy carbonate of zinc, by which they are covered; but they become 

 afterwards tran^arent, and remain insoluble, exhibiting their true characters before the 

 blowpipe. 



