550 



Miscellaneous. 



is to prove that the ashes obtained from a plant, if all its salts have 

 been taken up as humates, are only sufficient to account for one- 

 thirtieth part of the carbonic acid vs^hich is produced. Here we first 

 meet with the erroneous assumption that potash and soda do not 

 differ from lime in their capacity of saturation. I should have 

 expected Dr. Liebig to know that the difference is very great. Fur- 

 ther, he has entirely omitted ammonia, which forms the salt richest 

 in humus, and which, in his own opinion, is introduced into the 

 plant by the roots, on account of its great affinity to the humic acid 

 of the soil, probably as a humate, being afterwards decomposed by 

 the plant for the purpose of forming matters containing nitrogen. 

 Lastly, the author has not taken notice of secretion from the roots, 

 of which he is elsewhere a strenuous advocate. According to this 

 theory, it would be probable that a great quantity of bases, after 

 having given the plant this humus, are secreted, and consequently 

 cannot be found in the ashes. But these bases can again be direct- 

 ly saturated with humic acid, can thus re-enter the plant, arid 

 will then undergo again decomposition and secretion, and so on. 

 This calculation, then, is entirely void of all the fundamental data 

 required to prove, even remotely, the improbability of the theory 

 of humus. The second calculation has for its object the quantity of 

 humic acid which may be introduced into a plant by the water 

 which is contained in the soil. Liebig begins by assuming that 

 (according to Schiibler) an acre of land receives, during a period of 

 four months' vegetation, 700,000 lbs. of rain water, which reaches 

 plants while saturated with that salt which is the most soluble and 

 contains the greatest quantity of humic acid, i. e. with lime ; but by 

 this, not one- sixth of the carbonic acid which is produced can be ac- 

 counted for. This calculation is equally worthless with the last, be- 

 cause lime constitutes neither the most soluble salt, nor that which 

 contains the greatest portion of humic acid. Ammonia, indeed, 

 is such a salt ; and this, according to Liebig himself, is always found 

 in sufficient quantity. The following calculation, which I oppose to 

 those of Dr. Liebig, will show how insignificant such estimates are : — 

 An acre contains 40,000 square feet. If the crust of soil operative 

 in vegetation is taken to extend to the depth of a foot, and the speci- 

 fic gravity of the earth at 2.0, the acre contains 4,000,000 cubic 

 feet. Suppose that it contains one per cent, of humus, the humus 



