CHAPTER II. 



DUST-MAKERS FROST, HEAT, AIR, AND WATER. 



Dust-makers How Rocks are affected by Cold, Heat, Air, and Water 

 Expansion of Water and Minerals Dissolving Power of Water 

 Formation of Oxides and Carbonates. 



THE first of Nature's dust-makers whose manner of 

 working we are going to consider is frost. 



If a hollow ball of cast-iron be filled with water, care- 

 fully plugged, and then exposed to a temperature low 

 enough to freeze the water, what will be the result ? 



The water, as it congeals into ice, will require one- 

 fifteenth more space than it did before, and in the effort to 

 obtain it will exert so much, force as either to split the iron 

 or drive out the plug. Bombs measuring more than thirteen 

 inches in diameter have been thus burst in two ; while in 

 one experiment, an iron plug, weighing more than three 

 pounds, was hurled to a distance of 328 feet. 



Of course, if the iron expanded also, and in an equal 

 degree, there would be room enough for the ice ; but, like 

 most other bodies, iron shrinks under the influence of cold, 

 so that there is actually less space instead of more. 



We all know what frost can do in the way of cracking a 

 glass in which water has been left, or, worse still, in bursting 

 our water-pipes, though some people seem to imagine that 

 these latter are burst by the thaw, and not by the frost. 

 Like the iron ball, they are, however, cracked by the pres- 



