36 OF THE ASSIMILATION OF CARBON. 



and manganese have the same capacity of saturation 

 as lime with respect to humic acid, and then we may 

 take as the basis of our calculation the analysis of 

 M. Berthier, who found that 1000 lbs. of dry fir-wood 

 yielded 4 lbs. of ashes, and that in every 100 lbs. of 

 these ashes, after the chloride of potassium and sul- 

 phate of potash were extracted, 53 lbs. consisted of 

 the basic metallic oxides, potash, soda, lime, magne- 

 sia, iron, and manganese. 



One Hessian acre* of woodland yields annually, 

 according to Dr. Heyer, on an average, 2920 lbs. of 

 dry fir-wood, which contain 6.17 lbs. of metallic 

 oxides. 



Now, according to the estimates of Malaguti and 

 Sprengel, 1 lb. of lime combines chemically with 12 

 lbs. of humic acid; 6.17 lbs. of the metallic oxides 

 would accordingly introduce into the trees 74.04 of 

 humic acid, which, admitting humic acid to contain 

 58 per cent, of carbon, would correspond to 100 lbs. 

 of dry wood. But we have seen that 2920 lbs. of 

 fir-wood are really produced. 



Again, if the quantity of humic acid which might 

 be introduced into wheat in the form of humates is 

 calculated from the known proportion of metallic 

 oxides existing in wheat straw, (the sulphates and 

 chlorides also contained in the ashes of the straw 

 not being included,) it will be found that the wheat 

 growing on 1 Hessian acre would receive in that 

 way 63 lbs. of humic acid, corresponding to 93.6 lbs. 

 of woody fibre. But the extent of land just men- 

 tioned produces, independently of the roots and 

 grain, 1961 lbs. of straw, the composition of which 

 is the same as that of woody fibre. 



It has been taken for granted in these calculations 

 that the basic metallic oxides which have served to 

 introduce humic acid into the plants do not return 

 to the soil, since it is certain that they remain fixed 



* One Hessian acre is equal to 40,000 square feet, Hessian; or 26,910 

 square feet, English measure. — P. 



