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through. Take two bottles like those in Fig. 8, stop up 

 the bottom tubes, and fill with water. Then put a 

 funnel through each cork and fit the cork in tightly, 

 covering with clay if there is any sign of a leak. Put 

 a perforated tin disk into each funnel, cover one well 

 with clay and the other with sand. Open the bottom 



Fig. 8. 

 Sand allows air to pass through it, and so water runs 

 out of the bottle. Clay does not let air pass, and 

 the water is therefore kept in, even though the 

 tube is open. 



tubes. No water runs out from the first bottle because 

 no air can leak in through the clay, but it runs out very 

 (juickly from the second because the sand lets air 

 through. These properties of clay and sand are very 

 important for plants. Sow some seeds in a little jar 



