58 ON THE IMPURITIES OF COMMERCIAL ZINC. 
In order to make the results obtained as general as possible, we have examined au- 
thentic specimens of all the commercial zincs which we were able to procure. These 
ac. 
by Proust, was most probably cadmium, — a metal not discovered till 1817. (See Gilbert’s Annalen der Phys., 
1819, LX. 193.) This consideration is important, as it may serve to explain the very loose statements about 
arsenic in zinc which have since prevailed. 
VAUQUELIN, in reporting on this memoir of Proust, says: “It has been, and still is generally thought that 
the black powder...... consists of carbide of iron.” Annales de Chimie, 1800, XXXV. 51. 
See also a remark by Proust, similar to that above quoted, on the impurities of zinc, in Annales de Chimie, 
1803, LI. 72. 
FourcroY. “In proportion as this solution (in sulphuric acid) takes place, we see a small quantity of 
very black powder in a state of extreme division floating in the liquid, which has long been mistaken by chem- 
ists, and which is nothing else than carburet of iron or plumbago, existing originally in the zinc.” Systéme 
des Connaiss. Ch., V. 377. See also the English translation, London, 1804, V. 533. 
Voce. “The black residue (from the sulphuric acid solution of commercial zinc) consists of carbon, iron, 
and sulphate of lead. French zine contains neither copper nor arsenic, but a small quantity of lead.” 
Schweigger’s Journal fiir Ch. u. Phys., 1814, XI. 418. This observer expressly contradicts the statements of 
Proust and Thomson [wide infra] in regard to copper and arsenic. 
BERZELIUS and DuLonG give the impurities of commercial zinc as follows : — lead, tin, copper, iron, cad- 
mium, and sulphur. Ann. de Ch. et Phys., 1820, XV. 388. 
Hovrton LABILLARDIBRE says: “ I have examined several times the residue which the zinc of commerce 
leaves when dissolved in weak sulphuric acid; I have always found that it was formed of tin and of traces of 
iron; I have never encountered lead, although it is possible that some sorts of zinc contain it.” Thenard’s 
Traité de Chimie, Paris, 1824, V. 307. 
Tomson. “It (the zinc of commerce) is never quite free from carbon; ..... it contains, likewise, small 
quantities of several metals.” First Principles of Chemistry, 1825, I. 52. 
W. Henry. “The zinc of commerce is never pure, but contains charcoal, lead, and sulphur...... Even 
after careful distillation, zinc is still liable to contain a small quantity of charcoal.” Elements of Exper- 
imental Chemistry, 11th edition, 1829, II. 16. 
These statements of the impurities of zinc have been extensively copied. “The common zinc of commerce 
generally contains a portion of lead, copper, iron, traces of arsenic and manganese, and a little plumbago : 
these impurities chiefly remain in the form of a black powder when it is dissolved in dilute sulphuric acid." 
BrANDE's Manual of Chemistry, 3d edition, 1830, II. 42. 
De La Rive and PLANCHE. “Commercial zinc contains traces of tin, lead, and sometimes more than one 
per cent of iron; also, a considerable amount of cadmium.” From the Bibliothèque Universelle, in Pogg. 
Ann., 1830, XIX. 234. See also Ann. de Ch. et Phys, XLII. 437. 
SCHLINDLER has found in commercial zinc, iron, lead, arsenic, copper, nickel, cobalt, manganese, carbon, 
and a small amount of uranium.  Berzelius's Jahres-Bericht, 1832, XI. 126. This determination of uranium 
has been doubted by all subsequent observers. : 
“The following impurities in commercial zinc occur : — lead, arsenic, iron, copper, cadmium, antimony, man- 
ganese, nickel, cobalt, sulphur, and carbon.” Brandes, in reporting on the prize essays of BONNET and others 
upon the oxide of zine. Ann. der Pharm., 1834, IX. 184. 
