CHEMISTRY OF SOIL. 33 



chemical equivalents is important to the farmer, even 

 if he pursues it no farther than to understand, and re- 

 member the combining proportions of a few sub- 

 stances, known to him only by name ; such are the 

 common acids, oil of vitriol, aquafortis, spirits of 

 salt, or sulphuric, nitric, and muriatic acids ; the 

 usual alkalies, ammonia, potash, soda, lime ; acids 

 and bases, which combine only in their equivalents. 

 It is sometimes remarked, in agricultural experiments, 

 with different salts, that equal quantities, if correct 

 comparative trials are to be made, should be used. 

 The doctrine of equivalents, teaches not an equal, but 

 an equivalent portion — that is, 28 of lime are equal 

 to 48 of pure potash. It may assist the memory 

 here, and furnish a good " rule of thumb," to recol- 

 lect, that the three alkalies, ammonia, soda, potash, 

 are to each other, as 17 : 32 : 48, or as 1:2: 3, 

 nearly. When the subject of manures is considered, 

 the doctrine of equivalents will be found important, 

 in determining their relative value. Though the 

 numbers here used, are those of some chemists, of 

 high authority, they are not all universally admitted. 

 They have the convenience of being small whole 

 numbers. They are readily retained in the memory, 

 and simplify the subject, by freeing the calculation 

 from multiplication and division of equivalent num- 



