Agricultural Chemistry. 313 



necessary constituents, the more and the oftener will the farmer 

 make use of them ; and the production of farm-yard manure, by 

 which the misproportions caused by the other manures alluded 

 to in the quality of the soil are in part corrected, must diminish 

 in the same proportion. Many farmers will believe, but only for 

 a time, that they may dispense entirely with it under these cir- 

 cumstances. 



I entertain the hope, that perhaps among a thousand one 

 or two may be found who may be induced, by the simple 

 reflection that it can do his land no harm, to follow my advice ; 

 and I am certain, in that case, that they will acknowledge in a 

 few years the value of this advice. Their heavy crops 'will 

 perhaps not be rendered heavier by the restoration of all the 

 mineral constituents, but they will at all events be rendered jier- 

 manent. We shall never have a rational agriculture until, by 

 such experiments, the law of the fertility of the soil, in reference 

 to time, has been brought home to the minds of agriculturists. 



The final result of my researches on the nutrition of plants 

 was, that organic manure .acted by its constituents, and that it 

 must therefore admit of being replaced by these constituents 

 (p. 177). 



A real progress in agriculture appeared to me to l^e only pos- 

 sible through its emancipation from farm-yard manure, the value 

 of which I recognised, and knew how to estimate perhaps more 

 accurately than any one had done before me. 



I regarded as the problem of our day the use of artificial 

 manure, containing in itself all the efficient constituents of farm- 

 yard manure. 



I expressed my views on the principles of the preparation of 

 artificial manure in two short papers — ' An Address to the Agri- 

 culturists of Great Britain, explaining the Principles and Use of 

 Artificial Manures,^ and ' On Artificial Manures,^ Liverpool, 

 1845. These papers were circulated at that time both in Eng- 

 land and Germany. I there said : — 



" The duration of the fertility of a field depends on the amount of the 

 mineral elements of the food of plants contained in it ; and its productive 

 power, for a given time, is directly proportional to that part of its composition 

 which possesses the capacity of being taken up by the plants." — p. 10. 



Again : 



" It has been sho\v7i that the fertility of the soil depends on certain mineral 

 substances. If tlie restoration of the fertility of exhausted fields, by means 

 of the excreta of man and animals, depends on their ])roportion of these 

 matters — if the eflect of accderutiiuj tlie vegetation depends on their projior- 

 tion of ammonia — it is clear that we can only dispense with tlie latter (excreta 

 of men and animals) when we jirovide all (tlieir) eflicacious elements exactly 

 in those pro[)ortions, and in tliat I'urm, most proper for assimilation by tlie 

 vegetable organism, in wliich they are found in the most fertile soil, or in the 



