308 A3DI0XIA AND JN'ITEIC ACID. 



nitrogen as was equivalent to six, four, three, or two per 

 cent, of the whole quantity of nitrogen in the soil, the 

 reason was that there were present in the field six, four, 

 three, or two per cent, of active nitrogen, while the 

 remaining 94, 96, 97, or 98 per cent, were inoperative 

 nitrogen. 



The cause of the efiect (the amount of active nitrogen 

 in the soil) was consequently inferred from the effect (the 

 amount of nitrogen in the" crops). If more of the whole 

 quantity of nitrogen was in an active form, then higher 

 crops Avould foUow ; if the crops were lower, the reason 

 Avas that there was a deficiency of active nitrogen. If in 

 guano or farm-yard manm'e additional active nitrogen was 

 supphed, the crops would be increased. 



By taking a new standard for estimatmg the productive 

 power of the soil, the former one for the valuation of 

 manure was virtually abandoned. For when efficiency 

 was allowed only to nitric acid and ammonia in the soil, 

 and denied to all other nitrogenous combinations, it was 

 evidently unwarrantable to place those nitrogenous com- 

 pounds m manures, which were neither ammonia nor 

 nitric acid, in the same class with these two elements of 

 food. 



But in the classified estimate of mamu'es, a high place 

 was given to dried blood, horn shavings, gelatine, and the 

 nitrogenous constituents of rape-cake, all substances 

 which contain neither nitric acid nor ammonia. The 

 favourable effect of these manm^es was, in the majority of 

 cases, undoubted, but still not determinable by analysis. 

 Of two fields, the one manured with rape-cake, the other 

 not, the former yields a larger corn or turnip crop than 

 the latter, but it is not possible to show that there was 

 more ammonia in- the one case than in the other. True, 

 it was assumed that the mtrogenous compounds of these 



