On Agricultural CJiemistry. 



37 



the idea of the produce of the latter, that is corn, being maintained 

 irrespectively of that of the former — that is to say, by imported 

 manures alone, and to the exclusion of the consumption of food 

 upon the farm by stock. And here we might suggest as a consi- 

 deration well worth the attention of practical men, as a test of the 

 Mineral Theory/' how it would be possible that the increased 

 growth of wheat should be so limited and that its cost should 

 be so great as in experience it is found to be, if the only manure 

 required were the mineral constituents found in its ashes ? And fur- 

 ther, we would ask how, on the idea, on the other hand, that the 

 nitrogen supplied in our manures determines the produce of wheat, 

 they could account for the relative prices of wheat and ammonia, 

 unless on the supposition that the expenditure and loss of the latter 

 during the growth of the plant, is a fact which fundamentally 

 affects the production and cost of grain in practical agriculture ?* 



But to return to our illustration. The animals kept upon the 

 farm for labour too, must either consume part of the produce of 

 the farm itself, in which case the sales of corn must be reduced, 

 and consequently the exhaustion of the alkalies also, or they must 

 be provided for by purchased fgod ; in which case, while most or 

 all of the minerals of such food will be retained upon the farm, 

 much of its Nitrogen, and more still of its Carbon, will be lost by 

 the vital processes. 



It will be understood that the precise circumstances assumed 

 in the illustration which we have given, will only be met with in 

 certain cases, but w^hatever deviation from it may be found in ordi- 

 nary practice in Great Britain, we believe that the line of argu- 

 ment here adopted is very generally applicable, and that it will 

 also generally lead to a similar result. 



It is true that owing to proximity to large towns, or other local 

 circumstances, in many cases hay and straw, and even root-crops, 

 may be sent off the farm ; but in such cases local circumstances 

 are generally found fully to compensate for this otherwise exhaust- 

 ing process, by the return of stable manure, night-soil, and other 

 natural town manures. Indeed, that the alkalies are not relatively 

 to nitrogen exhausted by the sale of straw in the neighbourhood of 

 London, for example, is evident from the extensive use and marked 

 effects even of soot and other non-mineral manures on the land 

 from which this straw is taken. But if it were not so, such 

 instances need not come into our calculations when speaking of 

 agriculture generally. 



But further, Baron Liebig has said that a knowledge of our 



* One hundredweight of Peruvian guano will supply as much phosphoric acid as 

 would be contained in about 18 bushels of wheat and its equivalent of straw — say 

 ISOO lbs. ! And of nitrogen this quantity of guano will contain about as mucli as 

 11 bushels of wheat and 1 100 lbs. of straw ! 



