On the different Soris of Lime u/edtn Agriculture. 441 



affords no nourifhinent to vegetables. Pieces of each fort of flone were then burnt to 

 lime ; and after they had been expofed fome weeks to the air, that their caufticity might 

 be dimininied, fome feeds were fown in them. In the kind of Hme which was found 

 moft beneficial to land, almoft all the feeds came up and continued to grow as long as 

 tliey were fupplied with water, and the roots of the plants had many fibres which had 

 •penetrated to the bottom of the cup in which they grew. Upon examining the compo- 

 fition of this fort of lime, it proved to confift entirely of calcareous earth. By its ex- 

 pofnre to the air for about three months it was found to have abforbed four fifths of the 

 fixed air required to faturate it. In the other kind a few only of the feeds grew, and 

 the plants produced froia them had hardly any ftalks or roots, being formed almoft en- 

 tirely of the two feed leaves which lay quite loofe upon the furface. This fort of lime 

 being fpread upon a garden foil, to the thicknefs of about atentliof an inch, prevented 

 nearly all the feeds which had been fown from growing up, whilft no injury was occa- 

 fioned by common lime ufed in the fame manner. Upon examining thecompofition of 

 this fubflance, which was fo deftruflive to the plants, it was difcoveredto contain three 

 pattsoF pure calcareous earth, and two of magnefia. The quantity cf fixed air which 

 it had abforbed by being expofed for about the fame time as the pure lime jufl; mention- 

 ed, was only 42 hundredths of that combined with it before it was burnt. 



As it feemed probable that the magnefia contained in this lime was the caufe of its pe- 

 culiar properties, the following experiments were made to determine the cfFeSs of that 

 fubftancc'upon the growth of vegetables. Some feeds, chiefly of colewort, which were 

 preferred from their growing quickly, wete fown in uncalcincd magnefia ; but though 

 they fprouted, the leaves never rofe above the furface, and the plants ^vere entirely with- 

 out roots, nor did they appear to grow better in magnefia which had .been wafbed in 

 water containing fixed all-. Calcined magnefia was, however, much more deflruftive, as 

 the feeds would not come up in it. To compare its efFefts on vegetables with thofe of 

 Hme, each of thefe earths were mixed in different proportions with fand in fmall cups, 

 in which feeds were then fown. The lifne was obtained from marble ; and before il 

 was put into the fand, was Tnadc to fall to powder by being moiflened with water. In a 

 mixture of fo'ur ounces of fand with three or four grains of calcined magnefia, it was a 

 long time before the feeds came up, and the pbnts had hardly ajiy roots or flalks ; and 

 tcTi grains or more of magnefia, there was no appearance of vegetation. Thirty or forty 

 o-rains of lime did not retard the growth of the feeds more than three or four of magnefia, 

 and the injurious effefts were not fo falling. The lime, by abforbing fixed air, foon loft 

 its dellruftive properties ; fo that after keeping thefe mixtures four or five weeks feeds 

 were found to grow in that with forty grains of lime nearly as well as in the pure fand ; 

 but in that with lour grains of magnefia they produced only the feed leaves, as was de- 

 fcribed before. It was nerellary, otcafionally, to break in pieces the fand which had fo 



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