8 On the Theory of .Manures. 



monia, but also the phosphuretted and sulphuretted hydrogens, 

 of the composts. Dr. Madden, as we noticed in our former 

 essay, considers ammonia as the greatest solvent of humus, 

 and the way in which the principal part of the carbon and ni- 

 trogen of the plant is furnished. It is true that this is also 

 doubted by such eminent men as Liebig, Johnson, and Schlie- 

 den, the great liability of the humates to decomposition seem- 

 ing to be one of the principal objections ; but if formed by the 

 every-day action of the manures in the soil, and carried to the 

 roots of plants, their liability to decomposition, if once ab- 

 sorbed, may be a benefit in place of the reverse, and may 

 account for one of the principal objections of Liebig, that 

 humates, or humic acid, are not found to descend to any great 

 depth in the soil. 



Nitrogen being so indispensable an article \ being necessary, 

 according to Dumas, in forming the fibrin of which all the 

 vessels of plants are composed ; being deposited in the form of 

 diastase, gluten, and albumen, wherever food is stored up for the 

 future use of the plant ; and, by its action in the form of ammo- 

 nia, which is largely formed in all young shoots w^herever life 

 is most active, probably assisting in the chemical changes neces- 

 sary to prepare the food for the vital organs ; it is of great con- 

 sequence to know Avhether the food we administer contains this 

 valuable substance in proper quantity. Being exceedingly vola- 

 tile in the caustic state of ammonia, it is of great importance to 

 prevent evaporation as much as possible ; and, if deposited in 

 composts containing humus or vegetable remains in a state of 

 decay, it is reckoned by some sufficient to prevent escape, and 

 will be united to another essential element of vegetation, thus 

 simplifying and rendering more intelligible the feeding of 

 plants. Such as do not believe in the power of composts to 

 absorb and retain ammonia, and such as dwell in large towns 

 where composts are not so easily to be had, use a variety of 

 substances to fix the ammonia by uniting it to some more pow- 

 erful acid, of which the best and most economical appears to 

 be sulphuric acid or vitriol. 



As to the comparative quantities of nitrogen in crops and 

 manures. Dr. Madden, in his Prize Essay on Physiology and 

 Chemistry applied to Agriculture, published in the Highland 

 Society's Transactions for March last, reckons that in a four- 

 course rotation of 30 tons of turnips, 42 bushels of wheat with 

 2000 lb. of straw, 200 stones of hay, and 48 bushels of oats 

 Avith 2500 lb. of straw, which the four years wou^ld furnish 

 from an acre of ground, there would be produced and carried 

 off", in all, about 8183 1b. of carbon, 248^ lb. of azote, and 

 1190 lb. of saline matter. The manure, at the rate of 30 

 tons of farm-yard manure, deposited in the soil as a preparationt 



