138 EXPERIMENTS WITH PL A XT S 



placed in the lower and upper pans and the whole 

 apparatus set on a stove. When the water in the 

 lower pan boils the steam rises until it strikes the 

 under surface of the upper pan, which is kept cool 

 by the water in it. The steam condenses in drops and 

 collects in the cake- tin. 



It is desirable to use graniteware utensils for this 

 apparatus, but tinw^are is equally good so long as it 

 is kept bright and free from rust. Distilled water may 

 be made in this apparatus at the rate of over a quart 

 an hour. The cost of the whole apparatus need not 

 exceed half a dollar. 



The purity of distilled water (like that of "rain- 

 water) depends on the fact that when water evaporates 

 it leaves behind any substances w^hich may be dis- 

 solved in it. (We may use, if necessary, freshly col- 

 lected rain-water in place of distilled water.) 



Wheat may be recommended for this experiment. 

 Place the seeds in boxes of sawdust; water one with 

 distilled water; the other w^ith pond-, river- or tap- 

 w^ater (giving the same amounts to each). We may 

 also grow the plants directly in water. For this pur- 

 pose slips (about eight inches long) of the Wandering 

 Jew or Inch Plant (Tradescantia) may be recom- 

 mended. The slips are placed in fruit -jars contain- 

 ing about two quarts of water, and placed where they 

 will receive about the same amount of light as is 

 needed by ordinary house -plants. We may carry the 



