[ i6i ] 



tain that it enters copioufly into vegetables. Both his experi- 

 ments, and efpecially thofe of Mr. Macie, eftablifh this point 

 beyond contradiaion*. Argillaceous earth may alfo be fo finely 

 difFufed as to pafs through the beft filters, fo alfo may calx, as 

 appears from the quantity Margraaf found in the pureft rain 

 water. This earth is even foluble by means of an excefs of 

 fixed air in about 1500 times its weight of water. It may alfo 

 be and moft frequently is converted into gypfum by the vitriolic 

 acid which moft clays contain, as Mr. Morveau has ftiewnt, and 

 then it is foluble in 500 times its weight of water. 



Vegetables not only require food, but alfo that this food be 

 duly adminiftered to them ; a furfcit is as fatal to them as abfo- 

 lute privation. Dodor Hales obferved that a young pear-tree, 

 whofe roots were fet in water, abforbed a fmaller quantity of it 

 every day, the fap veffels being faturated and clogged by it ; and 

 Mr. Miller found that too much water rotted the young fibres of 

 the roots as faft as they pufhed outf- Saturated folutions of 

 dung appeared to Mr. Du Hamel equally hurtful §. Now the 

 prefervation and due adminiftration of this liquid food is effeded 

 by due proportions of the fimple earths and their loofe or con- 

 denfed ftate. Their fituation in other refpcds being the fame, 

 thofe that abound in the argillaceous principle are the moft reten- 

 tive of water : thofe that abound in the coarfe filiceous, leaft— 

 the calcareous being intermediate between both ; various fpecies 



Vol. V. X ^ «f 



• Phil. Tranf. 1791. t "^ Eneycloped. Chymlc. 123. 



f ift Hales, 17. § Mem. Par. 1748. 



