98 NATURE STUDY 



power of the microscope, the crystals will be seen to shoot 

 rapidly across the field. Sal ammoniac is excellent for this 

 experiment. 



Indications have already been made of the possible application 

 of these facts. In nature the water dissolves certain substances 

 from the soil or rocks which are carried to greater or less distances 

 and in the new situations by evaporation the substances take the 

 form of crystals, of quartz, limestone crystals, and the various 

 other beautiful crystals and gems found in the earth's crust. In 

 making solutions of all those substances which produce the crys- 

 tals in the rocks, water is aided by other substances mixed with 

 it, such as carbonic acid and other acids and alkalis. 



To show that water always dissolves something from the soil, 

 soak a jar of earth a day or so in distilled or rain water. Filter 

 off the water and evaporate it in a clean vessel and when all the 

 water has disappeared the vessel will be coated with a thin crust 

 of the substances which were dissolved in the water. For com- 

 parison boil down in the same way an equal amount of distilled 

 or rain water and no crust will be found to remain. The inside 

 of a tea-kettle long in use becomes coated with a thick crust of the 

 substances dissolved in the water used, which are left behind by 

 the evaporation of a large amount of water from the kettle. 



In the lessons on the foods of plants it was shown that car- 

 bonic acid and water are the main foods, but in addition the plants 

 obtain other substances from the soil. These come into the plant 

 dissolved in water. In burning a plant in open air those parts 

 made out of the carbonic acicl and water disappear in gases, the 

 product of the burning. There is left behind some ashes. These 

 ashes represent mainly what the plant had received from the soil 

 dissolved in water. While this is proportionally small in amount 

 it contains important and essential elements of the plant's food. 

 Thus it is seen that water is not only itself food for plants, but it 



