On Lime, 



effect. From this I conclude that lime must act as a 

 stimulant, and that the quantity applied to the land 

 ought to bear an exact proportion to the carbonic, or 

 vegetable matters contained in the soil. It is well 

 known that stimulants used in small quantities are in 

 some cases very useful in the animal economy, but in 

 great quantities they will destroy animal life. 



I would not by any means presume to call in ques- 

 tion the results of Mr. Tennant's or Dr. Black's expe- 

 riments ; on the contrary, I am rather inclined to be- 

 lieve, that all stone lime contains a greater or lesser 

 proportion of magnesia ; but that the lime which con- 

 tains the greatest proportion of that earth, is totally un- 

 fit to be used upon land as a maimre, I think, deserves 

 a second consideration. 



Dr. Darwin observes that the substance called chalk- 

 stone is almost wholly magnesia ; now I know from 

 experience that chalk-stone land is tlie most kindly to 

 all sorts of grain of any soil I am acquainted with, and 

 will bear a longer succession of severe cropping before 

 it is exhausted. But perhaps it is the process of calci- 

 nation which gives to the magnesia that caustic quality 

 which renders it so hurtful to vegetation, as Mr. Ten- 

 nant found by his experiments, that thirty or forty 

 grains of lime did not retard the growth of seeds, more 

 than thiee or four of calcined magnesia. From which 

 Dr. Darwin concludes, that, as both injure vegetation 

 in large quantities, they may both assist vegetation in 

 small ones. 



Consistent with the Doctor's remark I would just ob- 

 serve, that there are many substances which make rich 

 manures, when used in small quantities ; for instance 



