IN CHEMISTRY. 121 



31. Why is lime placed in the bottom of a leach-tub I 



The potash of the ashes is generally in the form of a 

 carbonate, the acid neutralizing in part the strength of the 

 alkali. The lime combines with the CO 2 . 



32. Is saleratus a salt of K or of Na ? 



It should be a carbonate of K, but, on account of its 

 cheapness, the corresponding salt of Na is often sold in- 

 stead. 



33. Why will Na burst into a blaze when thrown on hot 

 water ? 



The heat of the water raises the hydrogen to the ignit- 

 ing point. This catches fire, and the volatilized Na colors 

 the flame. 



34. 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. 



35. Illustrate the force of chemical affinity. 



The tremendous force of chemical affinity forms with O 

 half the crust of the earth. Yet when the chemist sets the 

 O free from its prison-house, it comes before him a transpa- 

 rent, invisible gas, and he cannot condense it to a solid or 

 liquid state by any mechanical process. 



176. i. Pb is softer than Fe ; why is it not more mal- 

 leable? 



The facility with which a mass of metal can be ham- 

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

 depend partly upon its softness, and partly upon its tena- 

 city. If it depended upon softness alone, lead should be 



