132 The Principles of Part III. 



manures, in a found or putrid ftate, as our 

 experiments have fhewn. But whence the 

 fait, the moft adive, and, therefore, moft 

 neceffary principle of all ? We have not 

 as yet difcovered any in rich foil, nor in the 

 manures moft ufed, r j/#. lime, marl, mells, 

 chalk, &c. This is an important queftion ; 

 opens up the action of almoft all manures, 

 and of rich foils ; mows wherein the effect 

 of the air confifts j and, therefore, deferves 

 a particular difcuffion. 



THE preceding experiments have mown, 

 that all fertile foils, and all manures, ex- 

 cept thofe already converted into a mucila- 

 ginous nature, confift of particles, .which, 

 in part, or all together, attract acids. 

 Dung, the afhes of vegetables, burnt earth, 

 contain fuch particles j lime, marl, animal 

 (hells, chalk, &c. are wholly of this nature. 

 Thefe then muft attract and retain all 

 acids, when they come within the fphere 

 of their attra&ion. If the air, to which 

 the foil is continually expofed, contains any 



acids, 



