ON THE CULTIVATION OF THE EARTH. 69 



*' also of magnesia in various proportions, a very 

 ** considerable quantity of" water, and some fixed 

 " air. The most fertile also contain a small 

 " portion of oil, roots of decayed vegetables, a 

 " coaly substance arising from putrefaction, 

 *' some traces of marine acid, and gypsum. On 

 " the other hand, if vegetables be analyzed, 

 ** they will be found to contain a large portion of 

 " water and charcoal, also of fat and essential 

 " oils, resins, gums, and vegetable acids ; all 

 " which are reducible to water, pure air, inflam- 

 •' mable air, and charcoal ; a small portion of 

 '* fixed alkali is also found ; some neutral salts, 

 *' most commonly Epsom, tartar vitriolate, com* 

 •' mon salts, and salts of sylvius. 



Thus far, we may consider all things reducible 

 to primitive principles, or simple substances, and 

 the opinions of these great men are accordant : 

 our next object must be, to consider how those 

 principles or elementary substances are again 

 to be brought together, put into action, and 

 combined ; and particularly for the different pur- 

 poses of husbandry. Agreeably to the rules of 

 chemistry, to demonstrate the correctness of an 

 analysis of any body, it is required, that the 

 same body be again produced by a recombination 

 of the parts discovered, and this is called a syn- 

 thesis ; but although it is clearly obvious to the 



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