292 AMMONIA AND NITKIC ACID. 



ation 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 combi- 

 nations, it was evidently unwarrantable to place those 

 nitrogenous compounds in manures, which were neither 

 ammonia nor nitric acid, in the same class with these 

 two elements of food. 



But in the classified estimate of manures, a high 

 place was given to dried blood, horn shavings, gelatine, 

 and the nitrogenous constituents of rape-cake, all sub- 

 stances which contain neither nitric acid nor ammonia. 

 The favourable effect of these manures was, in the ma- 

 jority 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 nitro- 

 genous compounds of these manures, the albumen of 

 the blood, the rape-cake, or the gelatine, was gradually 

 converted into ammonia, and so became operative ; but 

 it was taken for granted as a matter of course, that the 

 so-called inoperative nitrogenous compounds present in 

 the soil do not possess the power of yielding ammonia, 

 or of being oxydised into nitric acid. 



It was well known, indeed, that if one of two fields 

 contained more lime than the other, the one richer in 

 lime, often did not on that account produce more clover. 

 Yet no one thought of assuming that the lime in the 

 richer field existed in a two-fold condition, operative 

 and inoperative, or that the active portion of the lime 

 had caused the difference in the clover crops. 



It was also well known that if two fields be manured 

 with the same bone-earth, the one often gave a higher 

 crop than the other, and yet no one thought of assum- 

 ing that in the second field the inefficiency of the bone- 

 earth was due to the fact that it had passed into a state 

 of inactivity. 



It was further known, that the excess of no individ- 

 ual nutritive substance exercised any influence upon 



