92 GENERAL SCIENCE 



of a few inches more or less annually. In the region just 

 east of the Rocky Mountains the rainfall is deficient, and 

 just east of the Sierra Nevadas in Nevada, Utah, and adja- 

 cent regions, it is scarcely five inches a year. On the north 

 Pacific Coast of the United States the rainfall is about 

 seventy inches per year. 



AVater vapor when cooled rapidly and to a sufficiently low 

 temperature forms beautiful crystals known as frost. These 

 may gather on window panes and other exposed surfaces, or 

 may float about in the air. Snow flakes may be considered 

 as masses of frost crystals. Ice and snow and frost form at 

 temperatures below 32 F. (o C.), and melt when above this 

 "freezing point." Ice melts at 32 F. as heat is added to it, 

 and water at 32 F. freezes as heat is abstracted from it. It 

 must be remembered, however, that vaporization of water 

 occurs at any temperature even from the frozen (solid) state. 



When melted iron is run into moulds, it is found when 

 solidified to have increased enough in volume to take any 

 markings that may have been on the sides of the mould. 

 Iron and steel castings are made in this way, and any desired 

 patterns may be had upon their surfaces. When cast iron 

 is broken a crystalline structure is easily noted by use of a 

 magnifying glass. The increase in volume is explained by 

 the added space required for the newly formed crystals 

 whose regular forms do not fit as closely together as did their 

 molecules before the crystals formed. The change of water 

 to ice is similar, and experiences with broken pipes are 

 common when water is allowed to freeze in them. A block 

 of ice is just a mass of more or less perfectly formed crystals 

 indistinguishable save when they are forming or when they 

 fall apart as the ice "honey-combs." 



The process of vaporizing solids, and then condensing the 

 vapor to the solid state once more without passing through 

 the liquid state in either case, is called sublimation. The 



