MANURE. 193 



action, any action which the light of chemistry may not 

 kindle in similar substances. By reference to (228) its 

 chemical constitution approaches geine, and they are here 

 presented side by side. 



234. The glycerine resolves itself into water, free carbon 

 and carburetted hydrogen, or the gas of marshes or stagnant 

 pools ; the geine into carbon and water. In the series of 

 changes which they may undergo, let it be supposed that 

 carburetted hydrogen gas is evolved by glycerine. There is 

 no reason for assuming, as do some, that carbonic acid is the 

 only source of the carbon of plants. The volumes of car- 

 buretted hydrogen produced in the decay of plants, may be 

 intended, as well as carbonic acid, for their nutriment. Sup- 

 pose, of which there is no doubt, that carburetted hydrogen 

 of glycerine contributes to this effect, there remains then 

 free carbon, which, being perfectly insoluble and changeless, 

 acts only by condensing gases in its pores. 



235. Geine, by tillage, air and moisture, evolves also car- 

 bonic acid. As gas, no one will deny that it thus affords 

 carbon to plants ; its carbonic acid is absorbed and its car- 

 bon assimilated, and hence, if either glycerine or geine 

 afford carbon, the circumstances under which they may be 

 applied to the land, are less favorable to the production of 

 carburetted hydrogen, than of carbonic acid. The balance 

 then is in favor of geine. 



236. There are two circumstances wherein geine and gly- 

 cerine differ. The latter is soluble to any extent in water, it 

 is applied to the land in spent lye, already dissolved. The 



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