1822.] Dr. Clarke on Cadmium. 195 



Article VIII. 



On the Presence and Proportion 0/ Cadmium in the Metallic 

 Sheet Zinc of Commerce. By E. D. Clarke, LL.D. Professor 

 of Mineralogy in the University of Cambridge, &c. 



(To the Editor of the Annals of Philosophy/.) 



DEAR SIR, Cambridge, Feb. 6, 1822. 



The phaenomena exhibited by burning metaUic zinc upon a 

 disk of platinian, having excited in my mind a suspicion of the 

 presence of cadmium in the zinc used for the experiment, I con- 

 ceived that nothing would be easier than to have this matter 

 .put beyond doubt by a regular chemical examination of the;smc 

 itself. I might, however, have spared myself some trouble if I 

 had known, or rather had recollected, at the time that Professor 

 Stromeyer, in the account published of his own experiments, 

 mentions the fact of the presence o^ cadmium in metallic zin€.^ 

 This circumstance was so little heeded by other chemists, to 

 whom I had communicated my reasons for believing zinc contained 

 cadmium, that had I not accidentally referred to the publication 

 now cited, I might have continued in the belief that this circum- 

 stance had not hitherto been ascertained. It may, perhaps,^ 

 however, appear to your chemical readers that the pains I have 

 taken upon this subject have not been altogether nugatory, 

 if I shall succeed, as I hope to do, in making them acquainted 

 with some properties of cadmium which either were not before 

 observed, or respecting which the accounts before pubhshed 

 were in themselves erroneous. First, then, in the precipitation 

 of metallic bodies by iron^ previous to the examination of a salt 

 containing cadmium, it may be stated, as a doubtful point, whe- 

 ther, if the action of the iron be continued long enough, some, if 

 not all, of the cadmium may not be precipitated. I have the 

 greater reason to rely upon an experiment which I made with a 

 view to ascertain this point, because I used for the preparation 

 of the salt of cadmium, some oxide of cadmium from Professor 

 Stromei/er himself, which Dr. Wollaston had kindly presented 

 to me. Having dissolved this oxide in muriatic add, and 

 neutralized the solution by evaporation with a very gentle heat, 

 and the addition of distilled water, I suffered two cylinders of 

 polished iron to remain in the liquid during 24 hours. Previously 

 to the placing of the iron in the liquid, it yielded an orange- 

 yellow precipitate to sulphuretted hydrogen ; and a white preci- 

 pitate to carbonate of ammonia , which had all the characters of 

 the carbonate of cadmium. But no change of colour was caused 



See Annals 0/ Philosophy, vol. xUi. p. 108. 1819. 



o2 



