CHEMICAL SCIENCE. 207 



chiefly two, the white oxide, dry or ground in oil, and of several 

 grades of quality, and the colored pigments formed mainly by grind- 

 ing the raw ore. The zinc white is made in large oven-shapen retorts 

 of brick, around which the heat of an anthracite fire is conducted 

 both above and below. These ovens are very low, but of large superfi- 

 cial area. A wide pipe of sheet iron connects each with a very large 

 horizontal tube in which a current of air is kept moving by the 

 revolution of a fan-wheel. This current flows first through the 

 retorts, furnishing air to burn the zinc and means of transportation to 

 the oxyde formed, which is delivered by the current in large cooling 

 chambers. The charge in the ovens is one thousand pounds of 

 crushed red zinc and Franklinite mixed with its own bulk of the dust 

 of anthracite coal. The heat is raised to full redness and so managed 

 as to be hottest on the upper surface of the charge. Reduction of the 

 zinc is probably effected by the action of the hot carbon, but the 

 metal is immediately burned by the atmospheric oxygen drawn in by 

 the mechanical action of the blower before named. All the volatile 

 products of this chemical action are drawn through the long tubes 

 and partly delivered into capacious sacks of closely woven muslin 

 suspended in well ventillated apartments. The heat retained by 

 the oxide is not sufficient to scorch the muslin. From the proper 

 openings in the sack the material is collected in casks. In the retorts 

 the residue consists of undecomposed Franklinite and of metallic iron 

 mingled with unchanged carbon. When the best results are obtained 

 the ore yields half its weight of oxide. This oxide is never quite pure, 

 as a small quantity of dust and foreign materials are drawn in with 

 the current of air. Dissolved in acetic acid this residue remains on 

 the filter and perfectly pure carbonate of zinc may be precipitated 

 from the acetate. Chemists will regard this as an important means of 

 procuring chemically pure zinc. 



It is curious that the carbonate of zinc obtained by precipitation 

 when mingled with oil has no " body," or does not cover the surface 

 on which it is laid, while the anhydrous oxide obtained in the furnace 

 process covers very well. Water added even in small quantity to the 

 zinc oxide ground in oil, will cause the whole mass to solidify. The 

 greater cheapness of zinc oxide, its freedom from poisonous quality, and 

 the fact that sulphuretted hydrogen does not discolor it, are causes 

 which must - lead to the general use of this material in place of 

 lead. The New Jersey Zinc Co. are at present manufacturing about 

 5,000 pounds of zinc oxide daily, from 18 furnaces or retorts, only 

 one-half of which are usually in operation at the same time. The 

 colored paints formed by grinding the crude ore, are sold at very 

 cheap rates and found to possess remarkable power to prevent the 

 oxidation of metallic iron. Silliman's Journal. 



