164 IMPORTANCE AND VALUE 



latter, however, cannot be regarded as furnishing a 

 criterion, since rags are not to be procured in so 

 large a quantity as to satisfy a general demand ; 

 and the nitrogen they contain is, moreover, held in 

 such firm combination, that, without a previous pro- 

 cess of decay or decomposition, which again costs 

 money and labor, it cannot be rapidly absorbed by 

 plants. 



3. Organic or humus-forming substances : — 1 lb. = 

 about half a farthing. Here those substances are to 

 be understood that undergo combustion by long-con- 

 tinued heating of the manure, irrespectively, how- 

 ever, of the nitrogen they contain, which, on account 

 of its very peculiar importance, is calculated by itself, 

 as just mentioned. It would be still more accurate 

 to ascertain and value separately that most impor- 

 tant ingredient, carbon ; but to do this, in examining 

 manures for practical purposes, would involve too 

 great minuteness of detail and too much loss of 

 time. The error which may be produced from this 

 circumstance is, moreover, extremely insignificant, 

 since, in calculating the price of a hundred-weight, it 

 would amount, at the most, to a few farthings. In 

 estimating the price of these substances, the cost of 

 straw-litter and wood-fibre was taken as our basis. 

 In the form of brown-coal, earth, peat, etc., the or- 

 ganic ingredients would be reduced to a much 

 lower price. In this calculation, the nitrogen must, 

 in strictness, be previously withdrawn ; but this sub- 

 traction may be omitted without causing an inaccu- 

 racy worth mentioning. 



