92 ANSWERS TO PRACTICAL QUESTIONS 



32. Why iv ill Na burst into a Maze wJien thrown on 

 hot water, or put on wetted blotting paper ? 



The oxidation of the JSTa produces heat, part of which is 

 absorbed by the cold water, over which the pellet moves rap- 

 idly about, so that the kindling point of H i3 not quite reached. 

 If the water be previously heated, or if the Na is prevented 

 from moving abcut, by resting it on wetted blotting paper, the 

 H from the H 2 O is quickly raised to its kindling point. It 

 burns by taking O from the air, and its flame is colored yellow 

 by volatilizing some of the Na while the rest is taking O from 

 the water, and its hydrate is passing into solution. 



33. Why are certain Kinds of brick white ? 



They contain no iron, this being the substance which by its 

 oxidation gives the color to common brick. 



34. Illustrate the power of chemical affinity. 



Half the crust of the earth is made up of oxides, whose 

 constituents are held together by chemical affinity. To separate 

 the O from these elements, with which it is united, is exceed- 

 ingly difficult ; so much so that the attempt is but rarely ever 

 made. 



35. Why does not a candle lowered into a jar of Cl go 

 on burning indefinitely ? 



The Cl around it becomes mixed with HC1 fumes, which 

 stop the action. 



181 1. Pb is softer than Fe ; whij is it not wore 

 malleable ? 



The facility with which a mass of metal can be hammered 

 or rolled into a thin sheet without being torn, must depend 

 partly upon its softness, and partly upon its tenacity. If it 

 depended upon softness alone, lead should be 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 



