Agricultural Chemistry — Turnips. 



535 



elusions otherwise arrived at, but as opening out points of interest, 

 both in science and in practice, not hitherto brought to view. 



The atmosphere and the virgin soil being originally the exclu- 

 sive sources, the former of the " organic'^ and the latter of the 

 " inorganic'' or mineraV constituents of plants, it has been sup- 

 posed that the amount of produce which a given space of ground 

 would yield must depend upon its richness in those substances 

 proper to itself, namely, the mineral constituents ; and that these 

 being supplied in full quantity, according to the indications of the 

 analyses of the ashes of the crops it is wished to grow, the atmos- 

 phere would always prove an ample available resource for the 

 more peculiarly vegetable matters. It will be readily understood 

 that on such a view as this, economy in agriculture would be 

 attained by a very different course of practice from that required 

 were it to be shown that cultivation should effect an artificial 

 accumulation in the soil of those constituents primarily derived 

 from the atmosphere^ rather than of such as more especially 

 belong to its own constitution. 



The theory referred to has led to the analysis of the ashes of a 

 great many agricultural crops, and upon the data thus obtained 

 (rather than upon a consideration of the requirements actually 

 induced by an artificially enhanced vegetation, or of the real 

 source and destination of the constituents under a course of prac- 

 tical agriculture), recommendations to the agriculturist have been 

 founded, the validity of which it was desirable should be tested 

 by actual experiment, as well as by the presumed dictates of ex- 

 perience. The field results which we have detailed, both upon 

 the subjects of wheat and of turnips, are unfavourable to these 

 opinions and recommendations, and analysis will be found to bear 

 testimony in the same direction. 



A knowledge of the composition of our crops, as affected by 

 climate and cultivation, is however of great importance, not only 

 as showing what are the sources which must be relied upon for 

 the various constituents, but as assisting a judgment of the feeding- 

 value of the produce, and of the economy of the means to the 

 adoption of which the variations in composition may be traced. 

 It is more especially with a view to these points of interest that 

 our results have been sought, and that their bearings will be now 

 considered. 



In the course of an analytical examination of an agricultural 

 specimen, the first steps are to determine the per centages re- 

 spectively of dry vegetable substance and of mineral matters. For 

 this purpose a known weight of the produce is exposed for a 

 length of time to such a temperature as will only expel all the 

 water it contains ; a portion is then burnt to an ash, which is 

 presumed to retain all the mineral,"' but none of the " vegetable,'' 



2 N 2 



