[ '57 ] 



thrive moft in the vicinity of towns, becaufe the carbonic princi- 

 ple is copioufly difperfed by the fmoak of the various combuftibles 

 confumed in inhabited places — why foot is fo powerful a manure — 

 why burning the clods of gralTy land contributes fo much to its 

 fertility, and then only when the fire is fmothered and coal pro- 

 duced, befides many other agricultural phasnomena too tedious to 

 relate ; but I muft not omit that the phofphoric acid is found 

 in coal, and this enters into the compofition of many vege- 

 tables. 



The quantity of coal in vegetables is various according to their 

 various fpecies, age and degrees of perfedion ; wood and cora 

 contain moft, graffes leafl. Wiegleb found dry beech wood to 

 contain about i of its weight of coal*. Weftromb found trifo- 

 lium pratenfe, a fort of clover, to contain about ^ ; hence after 

 water it is the moft copious ingredient in vegetables. 



Of Earths. 



The next moft important ingredient to the nourifhment of 

 plants is earth ; and of the different earths the calcareous feems. 

 the moft neceffary, as it is contained in rain-water ; and, abfo- 

 lutely fpeaking, many plants may grow without imbibing any 

 other. Mr. Tillet found corn would grow in pounded glafs f; 

 Mr. Succow in pounded fluor fpar, or ponderous fpar, or gyp- 

 fum X '■> but Tillet owns it grew very ill ; and Haflenfraz, who 

 repeated this experiment, found it fcarcely grow at all when the 



glafs 



• Uber die alkalis, p. 76. f Mem. par. 1772. 301. 8vo. % ^^ iftChym. An. i784^ 



