1864.] CHEMISTRY OF MANURES. 213 



accomplished) of "a cheap source of ammonia" ; and, secondly, 

 of the '* excessive" use of such newly-found nitrogenous supplies: 

 in which case, said the theorists, " the available mineral [cinereal] 

 constituents might, in their turn, become exhausted." — (loc. 

 prec.) 



Reverting to the paper of 1861 for one more quotation, — and it 

 shall be the last, — the doctrine that nitrogen is a " specific" for 

 corn, and a " good substitute " for einereals, is, in tolerably explicit 

 terms, abandoned by its authors themselves ; wlio, after referring 

 to the comparative crops they obtained by means of (1) ammoriia 

 salts alone, and (2) mineral [cinereal] constituents only, thus 

 epitomise their experience : — 



" But in neither of these cases was there anything like the 

 amount of mineral constituents obtained in the crop, that there 

 was when the ammonia-salts and mineral manures were used 

 together, or when farm -yard manure was employed." 



To sum this matter up in plain words : the " good substitute " 

 for einereals, put forth in 1851, has had a fair trial, and has failed. 

 Ammonia, judged by the experiments of its advocates (as well as 

 by many other trials), proves not to be, as was alleged, a " specific " 

 manure for corn. The " specific " value of potash and the phos- 

 phates, for leguminous and root crops respectively, stands equally 

 disproved. Corn and meat cannot be continuously exported from 

 soils for 6000, 2000, or 1000 years, without restitution (respec- 

 tively) of the silica, potash, and phosphates, removed in their 

 tissue^ from the soils. These illusory views which their advocates 

 (to do them justice) have already, to a large extent, honorably 

 renounced, must be utterly abandoned. The celebrated "nitrogen 

 theory " is at an end ; and with it falls also the doctrine of 

 ''manurial specifies." 



We now know that the costliest ammoniacal salt, and the cheap- 

 est and commonest of the einereals (say for example silica or lime), 

 judged by the spongiole of a plant's root, are of precisely equal 

 value ; — each priceless, so far as essential to the plant's nutrition; 

 each worthless, as to every molecule beyond. 



We know also that the great law of Restitution applies equally 

 to fixed and volatile, to scarce and to abundant, ingredients of plant- 

 food ; though the fulfilment of that law devolves unequally on man 

 and nature, in every difierent case. 



We know that the prosperity of the crop, which represents 



