Mr. W. Horopatli 07i CaJmiiim. 167 



siich as'wax, oil, paper, &c. to de&troy the oxygen of the at- 

 mosphere in which the subhiuation takes place, otherwise the 

 cadmium is found as a bi'own oxide. Paper is the best, 

 because it prevents the metal from falling aniongst that from 

 which it has been separated. All the cadmium is not yet out 

 of the powder; to procure the remainder, dissolve in muriatic 

 acid and precipitate with a plate of zinc: this precipitate, which 

 c-onsists of iron and cadmium, may be submitted to the subli- 

 ming process ; or if a pure salt of the metal is I'ecjuired, it may 

 be dissolved in nitric acid and evaporated to dryness in the 

 proper way to peroxidize the iron, which remains behind 

 when the nitrate of cadmium is dissolved in water. 



Another pi'operty of the pure metal, besides those published 

 by Stromeyer and myself, is, that it makes a cracking noise like 

 tin when bent; and, although not to the same extent, yet, from 

 its general similarity ta that metal, it is likely to be mistaken 

 for it by those nnacquainted with chemistry : it may therefore 

 be advisable to have a ready test, by which they may be di- 

 •stuiguished. If a piece of tin be placed in nitric acid, it is 

 quickly converted into white oxide, but not dissolved ; whereas 

 the soluiiofi of cadmium goes on with rapidity in the same 

 acid. 



The late Professor Clarke was considerably embarrassed in 

 consequence of operating upon precipitates which contained 

 other metals ; in the mode above laid down, in which its vola- 

 tility is made use of to purify it, there is very little danger of 

 not succeeding; but as it is possible that accident may inU'oduce 

 a minute quantity of extraneous matter, I shall point out modes 

 by which it may be detected. When cadmium is perfectly 

 pure, if the button is cut through with wire-nijspers, it cuts sott 

 like lead, and leaves a sharp edge : but if not pure, it offers con- 

 siderable resistance, the nijipers get through it with a snap, 

 and the edge left is rough, from the metal breaking before the 

 instrument has completed the cut. This is almost as good a 

 test of its freedom from zinc (the metal it is most frequently 

 alloyed with) as the following: dissolve a little of the metal in 

 nitric or muriatic acid to saturation, drop in chromate of 

 potiish: if it contains the least particle of zinc, a yellow precipi- 

 tate will appear, but none at all if it is pure. 



Messrs. P. George and Co., zinc smelters, of Bristol, have 

 kindly thrown eveiy facility in my way; and, anxious lor the 

 extension of useful knowledge, they mean, if possible, to reduce 

 a quantity to the metallic state. As a sample of its utility in 

 the arts, I am induced to think that its sulphuret (not oxide, 

 as erroneously stated by Dr. Clarke) would produce a i)igment 

 but little, if at all, inferior in beauty to chromate of lead. 



While 



