Philosophy of Manures. 409 



humic acid contains most carbon, but must, therefore, consume 

 more organic matter in its formation ; and carbonic acid being 

 so much more largely soluble in water (rather more than its own 

 bulk), would seem to point it out as the medium of conveying 

 carbon to plants. Humic acid abounds in moss water, which is 

 rather prejudicial to growth than otherwise; but it contains 

 tannin, which is thought to act on the membrane of the spon- 

 giole of the roots by its astringent nature. I have seen 

 plants exposed to the bottom heat of bark often spoiled ; they 

 get hard and stunted, the leaves of a reddish brown colour. 

 The reviewer notices Dr. Liebig's admission, that carbonic acid 

 forms the food of the young plant by the roots, and considers it 

 contradictory of his former statement, that manure yielded no 

 carbon to plants by the soil. As to the statement of Dr. Liebig, 

 of soil becoming progressively richer in carbon every year, not- 

 withstanding the quantities of carbon extracted from it, endea- 

 vouring thus to show its being chiefly derived from the atmo- 

 sphere, the reviewer here enters into a calculation of the 

 quantity of carbon deposited in the soil by thirty tons of farm- 

 yard manure (which he estimates at 15,281 j lb.), the quantity 

 per acre for a crop of turnips. He next calculates the quantity 

 removed in four succeeding crops of turnips, barley, hay, and 

 oats, which he estimates at 9,54<3f lb. More than a half of this 

 quantity, or 5,7371 lb., has, therefore, been deposited in excess, 

 when the field was dunged for turnips. Dr. Liebig has stated 

 that no more carbon is produced from manured than unmanured 

 land ; and has stated the quantity from woodland as 2, 166 J lb. 

 of carbon annually per acre. The reviewer, however, shows 

 that an ordinary crop of turnips (30 tons) will yield 2,889f lb., 

 while an extra crop (45 tons) would yield 4,334f lb. of carbon. 

 It is further incorrect, he says, to consider forest land as un- 

 manured, when so much is furnished to it by birds and the 

 leaves. The dung annually of 100 sparrows he calculates at 

 36 lb., of a manure five times as strong as farm-yard manure ; 

 and the leaves of an acre at 772j lb. of carbon. These all give 

 reasons for the increase of carbon, independent of the atmo- 

 sphere. The fact, also, of firs consuming less nitrogen than the 

 cultivated plants, he says, accounts for the accumulation of car- 

 bon in woodlands. As all the carbon, he thinks, is given to the 

 plant in combination with ammonia, he considers ammonia as 

 the most important solvent for carbon; and, therefore, manures 

 containing nitrogen as the most beneficial. If, however, carbonic 

 acid itself is so largely soluble, I do not perceive the need of 

 ammonia as a solvent. 



On the subject of nitrogen, the reviewer cordially agrees with 

 Dr. Liebig, in all his statements, as to the importance of this 

 substance. He has verified the experiments, and found the 



