On Agricultural Chemistry. 



39 



acid, on the other hand, is sent off the farm in much larger 

 quantities than the alkalies; but under good cultivation it is 

 already in actual practice frequently more than restored by the 

 import of cattle food, or direct manures, such as bones, guano, &c. 

 Baron Liebig, indeed, himself asserts that farm-yard manure is 

 the universal food of plants; and we should never lose sight of 

 the fact, that the very practice of agriculture in this country 

 necessitates the production of this manure, by means of which it 

 is that so large a proportion of the mineral elements of the crops 

 raised upon the land are in due time restored to it ; all our cal- 

 culations, therefore, should be made on a full consideration of 

 what is involved in its use. This is, however, not generally 

 sufficiently borne in mind by chemists unconnected with prac- 

 tical agriculture ; and to this cause may, in great part, be attri- 

 buted the reiterated recommendations to imitate in artificial 

 manures the composition of the ashes of the plants to be grown. 



But further than this, takino; into careful consideration the 

 ... 



tendency of all experience in practical agriculture^ as well as the 

 collective results of a most laborious experimental investigation 

 of the subject, both in the field and in the laboratory, it is our 

 deliberate opinion that the analysis of that portion of a crop 

 which is sent off the farm, whether of its organic substance or of 

 its ashes, is no direct guide whatever as to the nature of the 

 manure required to be provided for its increased growth in the 

 ordinary course of agriculture, from sources extraneous to the home 

 manures of the farm; that is to say, by artificial means. 



In conclusion, then : if the theory of Baron Liebig simply im- 

 plies that the growing plant must have within its reach a suf- 

 ficiency of the mineral constituents of which it is to be built up, 

 we fully and entirely assent to so evident a truism ; but if, on the 

 other hand, he would have it understood that it is of the mineral 

 constituents, as would be collectively found in the ashes of the 

 exported produce, that our soils are deficient relatively to other 

 constituents, and that, in the present condition of agriculture in 

 Great Britain, " we cannot increase the fertility of our fields by 

 a supply of nitrogenized products, or by salts of ammonia alone, 

 but rather that their produce increases or diminishes, in a direct 

 ratio, with the supply of mineral elements capable of assimilation," 

 we do not hesitate to say that every fact with which we are 

 acquainted, in relation to this point, is unfavourable to such a 

 view. We have before stated, however, that if a cheap source of 

 ammonia were at command, the available mineral constituents 

 might in their turn become exhausted by its excessive use. 



But it is at any rate certain that for icheat^ of all our crops, no 

 supply of minerals, phosphates, &c., to the fields of Great Britain 

 generally, will enable it to " obtain a sufficient supply of ammonia 



