THE WATER OF SOILS. 



from 60% to 90% of liquid water, the temperature of which 

 can only be raised or lowered slowly ; a.nd the presence of the 

 sea tempers the climates of coasts and islands as compared w r ith 

 the heat or cold occurring in the interior of the continents. 



Ice. Again, it is shown in the table that the heat required 

 to melt ice is greater than in the case of any other substance, 

 especially the metals ; which when once heated to the fusing 

 point, require only a very little more heat to become liquid. 

 The fusion of salts (including silicate rocks) requires more 

 heat than does that of the pure metals. 



Vaporization. In the amount of heat required for its vapor- 

 ization water is also especially pre-eminent, and potent in its 

 influence upon organic life. The table shows that the evapor- 

 ation of water requires six hundred heat units 1 as compared 

 with alcohol, requiring only two hundred ; while spirits of 

 turpentine, the representative of a large proportion of vegetable 

 fluids, needs but sixty-seven. 



The practical result is that evaporation of \vater from the 

 surface of animals and the leaves of plants, is exceedingly 

 effective in preventing excessive rise of temperature, the heat 

 of the sun and air being spent in evaporating the perspiration 

 of animals and plants before an injurious rise of temperature, 

 such as would cause sunstroke in animals, and wilting or with- 

 ering in plants, can occur. But since evaporation is most rapid 

 in dry air, it follows that the cooling effect will be the greater 

 in the arid regions than in the humid. In the latter, therefore, 

 sunstroke is much more frequent than in the fervid regions of 

 the arid west, even though the temperature in the latter may be 

 higher by twenty or twenty-five degrees Fahrenheit. White 

 men who would soon succumb if they attempted to work in the 

 sun in Mississippi or Louisiana when the thermometer stands 

 at 95 F. will experience no inconvenience under the same con- 

 ditions in the dry atmosphere of the Great Valley of California. 



Solvent Power. To the exceptional properties of water dis- 

 cussed above, should be added another hardly less important 

 one, viz., that of being an almost universal solvent especially of 



1 A heat unit, or" calorie," is the amount of heat required to raise the tempera- 

 ture of a unit-weight (pound, kilogram, or gram) of water one thermometric degree. 

 According to the unit-weight and thermometric scale used, the figures will vary, 

 but in this text the basis is understood to be kilograms and the centigrade scale. 



