]4 CALCAREOUS MANURES— THEORY. 



lumps, by slowly imbibing the water, are distended enough to fill the space 

 occupied before. 



Calcareous earth, or carbonate of lime.;* is lime combined with carbonic 

 acid, and may be converted into pure or cjuick-lime by heat ; and quick-lime, 

 by exposure to the air, soon returns to its former state of calcareous earth. 

 It forms marble, limestone, chalk, and shells, with very small admixtures of 

 other substances. Thus the term calcareous earth will not be used here to 

 include either lime in its pure state, or any of the numerous combinations 

 which lime forms with the various acids, except that one combination (car- 

 bonate of lime) which is beyond comparison the most abundant throughout 

 the world, and most important as an ingredient of soils. Pure lime attracts 

 all acids so powerfully, that it is never presented by nature except in com- 

 bination with some one of them, and generally with the carbonic acid. 

 When this compound is thrown into any stronger acid, as the muriatic, 

 nitric, or even common vinegar, the lime, being more powerfully attracted, 

 unites with and is dissolved by the stronger acid, and lets go the carbonic, 

 which escapes with effervescence in the form of air. In this manner, the 

 carbonate of lime, or calcareous earth, may not only be easily distinguished 

 from silicious and aluminous earth, but also from all other combinations 

 of lime. 



The foregoing definition of calcareous earth, which confines that term to 

 the carbonate of lime, is certainly liable to objections, but less so than any 

 other designation. It may at first seem absurd to consider as one of the 

 three principal earths which compose soils, one only of the many combina- 

 tions of lime, rather than either pure lime alone, or lime in all its combina- 

 tions. One or the other of these significations is adopted by the highest 

 authorities, when the calcareous ingredients of soils are described; and in 

 either sense, the use of this term is more conformable with scientific ar- 

 rangement, than mine. Yet much inconvenience is caused by thus apply- 

 ing the term calcareous earth. If applied to lime, it is to a substance which 

 is never found existing naturally, and which will always be considered by 

 most persons as the artificial 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 phos- 

 phate 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 impor- 

 tant ingredients. A subsequent part of this essay will show why the oxa- 

 late of lime is also supposed to be highly valuable as a manure, and far 

 more abundant. Many other salts of lime are known to chemists; but 

 their several qualities, as affecting soils, are entirely unknown — and their 



* Carbonate of lime is the chemical name for the substance formed by the combination 

 of carbonic acid with lime. The names of all the thousands of different substances 

 {neutral sails) which are formed by the combination of each of the many acids with 

 each of the various earths, alkalies, and metals, are formed by one uniform rule, which 

 is as simple, and easy to be understood and remembered, as it is useful. To avoid re- 

 peated explanations in the course of this essay, the rule will now be stated by which 

 these compounds are named. The termination of the name of the acid is changed to the 

 syllable ale, and then prefixed to the particular earth, alkali, or metal with which the 

 acid is united. With this explanation, any reader can at once understand what is meant 

 by each of some thousands of terms, none of which might have been heard of before, 

 and which (without this manner of being named^ would be too numerous to be fixed in 

 the most retentive memory. Thus, it will be readily understood that the carbonate of 

 magnesia is a compound of the carbonic acid and magnesia— the sulphate of lime, a com- 

 pound of sulphuric acid and lime — the sulphate of iron, a compound of sulphuric acid 

 and iron — and in like manner for all other terms so formed. 



