122 ANSWEES TO PRACTICAL QUESTIONS 



the most malleable of ordinary metals ; but, although it is 

 easy to hammer a mass of lead into a flat plate, or to 

 squeeze it between rollers, any attempt to reduce it to an 

 extremely thin sheet fails from its want of tenacity, which 

 causes it to be worn into holes by percussion or friction. 

 On the other hand, if malleability were entirely regulated 

 by tenacity, iron would occupy the first place, whereas, on 

 account of its hardness, it is the least malleable of metals 

 in ordinary use ; whilst gold, occupying an intermediate 

 position with respect to tenacity, is the most malleable, 

 which appears surprising to those who are only acquainted 

 with gold in its ordinary forms of coin and ornament, in 

 which it is hardened and rendered much less malleable 

 by the presence of copper and silver. 



I. Relative Malleability of the Metals. 



1. Gold. 4. Tin. 7. Zinc. 



2. Silver. 5. Platinum. 8. Iron. 



3. Copper. 6. Lead. 



II. Relative Tenacity of the Metals. 



III. Relative Ductility of the Metals. 



1. Gold. 5. Copper. 8. Zinc. 



2. Silver. 6. Palladium. 9. Tin. 



3. Platinum. 7. Aluminum. 10. Lead. 



4. Iron. BLOXAM. 



2. What is the cause of the changing color often seen in 

 the scum on standing water ? 



(See " Interference of Light," Philosophy, page 209.) 



The thin pellicles of iron-rust on standing H 2 O pro- 



