AGRICULTURE WITH CHEMISTRY. 107 



however, been analysed with more care, and when newly 

 made, they probably would have been found to contain 

 a hepar of lime, a salt which is soluble in water ; whilst 

 gypsum, to which it reverts on exposure to air, is inso- 

 luble. To this hepar may the fertilizing power of these 

 ashes most probably be ascribed. 



As mineral springs are frequently found to arise in 

 peat mosses, it necessarily follows, that the ashes of dif- 

 ferent peat will contain very different saline and other 

 matters. When a too large proportion of vitriol of iron, 

 or green vitriol, is contained in peat, its ashes must of 

 course be inimical to vegetation; but the injurious 

 effefts of this salt are to be corrected by the addition of 

 lime, magnesia, alkaline salts, or clung. Of these sub- 

 stances, the preference is to be given to magnesia and 

 alkaline salts; for, whilst they decompose the metal- 

 lic salt, they form Epsom salt, Glauber salt, or vitrio- 

 lated tartar, all of which are conducive to vegetation. 

 The effe6l of dung on such ashes requires to be explain- 

 ed in a different manner. The iron, in this case, is by the 

 application of the dung changed into a metallic state; 

 whilst the vitriolic acid combines with the .volatile alkali 



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