CALCAREOUS EARTH. 



j it is to a substance which is never found existing naturally, 

 and which will always be considered by most persons as the artifi- 

 cial product of the process of calcination, and as having no more 

 part in the composition of natural soils than the manures obtained 

 from oil-cake or pounded bones. It is equally improper to include 

 under the same general term all the combinations of lime with the 

 fifty or sixty various acids, Two of these compounds, the sulphate 

 and the phosphate of lime, are known as valuable manures ; but 

 they exist naturally in soils in such minute quantities, as not to 

 deserve to be considered as important physical ingredients. Many 

 other salts of lime are known to chemists ; but their several quali- 

 ties, as affecting soils, are entirely unknown and their quantities 

 are too small, and their presence too rare, to require consideration. 

 If all the numerous different combinations of lime, having perhaps 

 as many various and unknown properties, had not been excluded 

 by my definition of calcareous earth, continual exceptions would 

 have been necessary to avoid stating what was not meant. The 

 carbonate of lime, to which I have confined that term, though only 

 one of many existing combinations, yet in quantity and in import- 

 ance, as an ingredient of soils, as well as a part oT the known por- 

 tion of the globe, very far surpasses all the others. 



But even if calcareous earth, as thus defined and limited, is ad- 

 mitted to be the substance which it is proper to consider as one of 

 the important earths of agriculture, still there are objections to its 

 name which I would gladly avoid. However strictly defined, many 

 readers will attach to terms such meanings as they had previously 

 understood : and the word calcareous has been so loosely and so 

 differently applied in common language, and in agriculture, that 

 much confusion may attend its use. Anything " partaking of the 

 nature of lime" is "calcareous," according to Walker's Dictionary; 

 Lord Kanies limits the term to pure lime ;* Davyf and Sinclair^ 

 include under it pure lime and all its combinations; and Kirwan,|| 

 Iiozier,^f and Young, whose example I have followed, confine the 

 name calcareous earth to the carbonate of lime. Nor can any other 

 term be substituted without producing other difficulties. Carbon- 

 ate of lime would be precise; but there are insuperable objections 

 to the frequent use of chemical names in a work addressed to ordi- 

 nary readers, and this one would be especially awkward and incon- 

 venient for such use. Chalk/or shells, or mild lime (or what had 

 been quick-lime, but which, from exposure to the air, had again 



* Gentleman Farmer, page 264 (2d Edin. ed.) 



f Agr. Chem., page 223 (Phil. ed. of 1821.) 



J Code of Agriculture, page 134 (Hartford cd. 1818.) 



|| Kirwan on Manures, chap. 1." 



^[ " Terres" Cours Complet d' Agriculture Pratique. 



Young's Essay on Manures, chap. 3. 



