Analyses of Ashes of Plants. 



177 



already been built up with the vegetable organization, and is there- 

 fore essential to the plant, the other portion present in the vege- 

 table matter merely as it were accidentally — that is, the water 

 entering a plant by its roots, necessarily carries into the circulation 

 more or less of the soluble ingredients of the soil and manure, and 

 at the time a plant is removed from the soil, its mineral food is 

 about to be or has been selected from the mixed supplies so intro- 

 duced. We have not at present, and it is very questionable 

 whether we ever shall, the means of discriminating between the 

 necessary and " accidental ash of a plant,* and we can only there- 

 fore judge by comparison of one specimen with another how far 

 the ash which may in any case be examined is to be looked upon 

 as a mixture of the two. 



Now the quantity of this accidental ash ought to be larger in 

 those plants which contain much water; and accordingly we 

 should, as before said, anticipate greater differences in respect to 

 turnips than wheat. Indeed it may be taken as a most decisive 

 proof, if such were wanted, of the intimate connection between 

 the organic and inorganic parts of plants, that notwithstanding 

 the large proportion of water, the difference of ash should be 

 comparatively so slight. 



A ton of turnip bulbs contains no less than 18 cwt., or 2016 

 lbs., of water. Now spring water, which has simply percolated 

 the ordinary porous strata of the earth, contains usually about 

 3 grains of salts of lime, potash, &c., in every pound, and very 

 frequently the proportion is found greatly to exceed this. 2016 

 lbs. of water, at 3 grains in the pound, would contain 6048 

 grains, or nearly 1 lb. of mineral matter : so that in a ton of tur- 

 nips, which gives usually from 16 to 20 lbs. of ash (see p. 182), 

 the water would retain in solution 1 lb. of the difference. But it 

 is not to be supposed that the water passing in by the roots of a 

 plant growing on a fertile and highly-manured soil is charged 

 with salts to the same extent only as that which has passed 

 through the hard and oft-washed beds of our sandstone and lime- 

 stone strata ; and it is easy to conceive that a great quantity of 

 mineral matter may at any time be accidentally present in plants 

 containing so much water as the turnip. 



* It might be possible to effect a separation of any soluble substances 

 merely passing through the plant, by causing it to vegetate for a few hours 

 in pure water after it is removed from the soil ; there would, however, be 

 danger in this plan fi-om the abrasion of the roots. No washing of the 

 plant for such a purpose would be admissible— for so soon as the organism 

 of a vegetable is interfered with (by cutting it up or otherwise), there is 

 no knowing what modifications of the essential mineral matter might 

 occur. 



VOL. viir. 



N 



