198 COMMON SUBSTANCES 



HC1. Heat the mixture. Cl gas is set free and flows into the jar, 

 driving out the lighter air. Do not breathe any of this gas. Note 

 the color of Cl. This is one of the few gases that have color and 

 can be seen. (If Cl is accidentally inhaled, pour alcohol on a 

 cloth and breathe through the cloth for a few moments.) 



Experiment 126. When the gas in the jar is very yellow, 

 remove the flame, wait a half minute, then remove the glass tube 

 from the jar, keeping the jar covered. Now moisten a small piece of 

 colored calico, drop it into the Cl, and quickly cover the jar again. 

 If no change is noticed soon, try another piece of a different color. 



A substance called bleaching powder is much used in bleaching 

 cloth and paper, because it contains Cl. 



229. Iron. Iron is the most important of metallic 

 elements in man's work. Its uses are too common to 

 need mention here. The element occurs in several ores, 

 usually combined with O or S. The sulphide, FeS 2 , 

 is commonly called pyrite. Iron is obtained from its 

 ores by heating them in a blast furnace. In this big 

 furnace coke or coal is mixed with the ore (usually an 

 oxide of iron) and burned. A blast of air is forced into 

 the furnace, and the fire (which burns all the time) gives 

 a very great degree of heat. In this heat the ore is 

 decomposed; its O unites with the C of the coke, and 

 the iron in a melted state collects at the bottom of the 

 furnace. From here it is drawn off into molds, and is 

 called pig iron or cast iron. It is very impure. 



Steel is a better grade of iron, which contains a fixed 

 amount of carbon. It is commonly made by blowing air 

 through a mass of highly heated pig iron. The impuri- 

 ties in the iron unite with the O of the air and are 

 thus burned off, and then a known amount of carbon 

 is mixed with the heated mass. 



