The Story-Book of the Fields 



is dusted with plaster. The plaster absorbs 

 the ammoniacal vapour, parting with some 

 of its sulphuric acid and forming a compound 

 — sulphate of ammonia — which cannot be re- 

 duced to vapour. The plaster is said to fix 

 the ammonia ; that is, to prevent it from 

 dispersing. 



With regard to the fertilising effect of 

 plaster on lucerne, the following experiment 

 is related. Franklin, one of the greatest men 

 in the United States of America, knowing the 

 powerful effect of plaster, tried to spread its 

 use among his fellow-citizens ; but they, 

 faithful to their old customs, would not listen 

 to him. In order to convince them Franklin 

 sowed plaster in a field of lucerne, beside the 

 most frequented road in Philadelphia, spread- 

 ing it over the plants so as to trace out letters 

 and words. The lucerne grew everywhere, 

 but much taller, greener and thicker in the 

 parts that had been plastered, so that the 

 passers-by could read in the lucerne these 

 words in gigantic letters — " This was plas- 

 tered." The ingenious experiment was quite 

 successful, and plaster was immediately used 

 in agriculture. 



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