zinc. 283 



nace, vaulted above. Through the bottom of each there passes a 

 tube of iron, the upper end of which terminates by an open mouth 

 near the top of the pot. The lower end goes through the floor of 

 the furnace into a vessel of water, situated in an apartment below. 

 The pots are left open for about two hours, till the flame begins to 

 assume a blue colour ; indicating that the zinc is beginning to be 

 reduced. They are then covered up on the top. The zinc is 

 reduced, and gradually escapes through the iron tube into the water, 

 where it is condensed in the form of globules. These are after- 

 wards melted and cast into ingots. 



Zinc is known in commerce by the name of Spelter ; but usually 

 contains an admixture of lead and sulphur. When purified from 

 these, it is of a brilliant white colour, inclining to blue. Its specific 

 gravity is about 6 # 8. It is brittle, except at a temperature between 

 200 and 300° of Fahrenheit, when it becomes both ductile and 

 malleable, and retains its tenacity when slowly cooled. It is the 

 most inflammable of the metals, burning with a brilliant flame 

 when heated to ignition. It melts at about 725° of Fahrenheit's 

 scale, and crystalizes on cooling. The principal use of zinc is in 

 the formation of galvanic apparatus, and in electrical experiments. 

 It has no sensible action on the system in its metallic state ; but 

 some of its compounds have been much used in medicine. 



Oxide of Zinc. Zhici Oxydum, L. E. D. — When zinc is 

 exposed to a temperature very little above its melting point, it 

 attracts oxygen from the atmosphere, and burns vividly with a daz- 

 zling flame of a blueish tint, producing an oxide in the form of 

 very light flocculi, formerly called flowers of zinc or philosophical 

 wool. It is directed to be prepared by throwing the metal into a 

 red hot crucible with another inverted over it to receive the oxide 

 as it forms. This oxide, which is the only one known, is of a 

 snow-white colour ; it is inodorous, insipid, insoluble in water and 

 alcohol, but entirely soluble in acids, and is not altered by exposure 

 to the air. According to Proust, it consists of 80 of zinc, and 20 

 of oxygen in 100 parts. The oxide of zinc is tonic and antispas- 

 modic, and has been employed in chorea and epilepsy in a dose of 

 from one to five grains. The TJnguenium Oxidi Zinci composed of 

 one ounce of oxide of zinc and six ounces of prepared lard, is used 



