1822.] Mr. W. Herapath on Cadmium. 435 



Article XL 



On Cadmium, and the Sources of procuring it in Quantity, 

 By Mr. W. Herapath. 



(To the Editor of the Annals of Philosophy .) 



SIR, Bristol, 56, Old Market street ^ April 1 , 1822. 



When reasoning on the properties of cadmium, its volatility 

 in the metalHc state, and fixidity as an oxide, I expected to meet 

 with it in the subHmed products of the zinc smelting house. I 

 accordingly visited one in this neighbourhood, and brought av^^ay 

 some specimens, among which I have discovered the metal in 

 much larger quantity than it has hitherto been obtained, varying 

 from 12 to 20 per cent, being six times more plentiful than in 

 the richest substances examined by Stromeyer. 



It may be proper here to mention the exact situation in which 

 it is to be met with. I believe it is well known that zinc is 

 reduced from the ore by a sort of distillation, the calamine with 

 small coal as a flux being introduced into a pot closely covered 

 on the top, but having a tube leading from its bottom into a 

 vault below ; just under this, there is a vessel of water placed, 

 and a moveable tube is kept long enough to reach from the short 

 tube nearly to the surface of the water. 



The workmen are not in the habit of connecting the two 

 tubes until what they call the *' brown blaze" is over, and the " blue 

 blaze " begun : this brown flame is owing to cadmium absorbing 

 oxygen ; it subhmes, and is attached to the roof of the vault, 

 but in the greatest quantity immediately over the orifice froia 

 which it issues ; it is mixed with soot, sulphuret of cadmium, 

 and oxide of zinc. The colour is a compound of brown, yellow, 

 black, and white, varying with the quantities of the different 

 substances which enter into the mixture. 



To obtain the metal, I have used the following process : Add 

 to the subhmate an excess of muriatic acid ; filter and wash the 

 residue ; add the washings to the liquid ; evaporate to dryness 

 to get rid of the excess of acid ; redissolve in as Uttle water as 

 possible, filter again to separate the insoluble part ; introduce a 

 plate of zinc, and the cadmium is precipitated in the form of 

 small leaves. In reducing these to a mass without loss, I have 

 found considerable difficulty from the volatile nature of the 

 metal, &c. I followed Stromeyer's process, until I found that 

 the globules which sublimed into the cold part of the tube were 

 more malleable, and did not, as he describes, scale off when long 

 hammered ; I, therefore, put the spongy precipitate into a black 

 dass tube (closed at one end), together with a little lamp-black 

 ^ 2f2 



