BY SALINE MANURES. 317 



vegetable matter must also be added, to ensure its good ef- 

 fects. 



The utility cf lime in agriculture, when properly applied, 

 is well established by experience. The quantity required is 

 small, one per cent., and even twelve bushels to the acre, are 

 valuable additions. " A quantity of lime," says Mr. Puvis, 

 " which does not exceed the thousandth part of the tilled 

 surface layer of the soil, a like proportion of drawn ashes, or 

 a two-hundreth part, or even less of marl, are sufficient to 

 modify the nature, change the products, and increase by one 

 half, the crops of a soil destitute of the calcareous principle." 

 Sir John Herschel found that minute portions of calcareous 

 matter, " in some instances less than the millionth part of the 

 whole compound, are sufficient to communicate sensible me- 

 chanical motions, and definite properties to the bodies with 

 which they are mixed." As such effects seem to be electrical 

 in their character, we may conclude that there is a fifth office 

 of lime, to act as a 5#/;?m/«?«#, by developing electrical cur- 

 rents. Upon the whole, we should prefer potash to lime, but 

 the latter is unquestionably beneficial in its action, and may 

 be applied in small quantities, as a cask to an acre, without 

 any fear of injury, and with the certainty of ultimate benefit. 



Carbonate potash. Potash is a carbonate, that is, it con- 

 sists of carbonic acid combined with potassa. The action of 

 the potash has already been considered, p. 306. It is some- 

 times applied to the soil from 100 to 150 lbs. to the acre. 

 But the form in which it is usually applied is that of 



Ashes. The value of ashes depends upon the kind of wood 

 from which they are derived. Those fi-om hard wood are 

 more valuable than those from soft. 



One hundred parts of hard wood, such as dry oak, beach, 

 birch, etc. yield 2.87 parts of ashes. One hundred parts of 

 dry pine yields only 00.83 of ashes, while 100 parts of wheat 

 straw affords 0.44 per cent. The ashes consists of two parts, 

 soluble and insoluble portions. 

 27 



