254 



On the A jpU cation of Manures. 



order that their reinainlng constituents may become assimilated; 

 for it is evident, that however small the amount of any one of the 

 component parts of a compound may be, still its presence is just 

 as essential as that of the rest. 



This ingredient is nitrogen, which exists in the seeds of most 

 plants, and seems essential to all those vegetable principles that 

 afford the staple from w^hich animal life obtains its support. 



The dependence of the nutritive qualities of various articles of 

 food upon the proportion of nitrogen is well shown in a recent 

 Memoir of Monsieur Eoussingault,* who gives, on the authority 

 of the celebrated agriculturist Von Thaer, a scale of the relative 

 degree of nutriment afforded by various plants to cattle, and then 

 places by the side of it a statement of the proportion of azote 

 present in them, from which it appears that the nutritious quality 

 of each bears a pretty constant ratio to the quantity of nitrogen 

 they contain. 



This may be seen by the following table : — 





Equiv. 





Ordinary hay. . 



. 100 its azote being 0-0118 



Red clover 



. 90 . . . 



. 0-0176 



Beans 



83 . . . 



. 0-0I4I 



Wheat- straw 



. 400 . . . 



. 0-0020 



Potatoes . 



. 200 . . . 



. 0-0037 







. 0-0026 



Maize 



. 59 . . . 



. 0-0164 



Barley 



54 . . . 



. 0-0176 



Wheat . . . 



. 27 . . . 



. 0-0213 



When we reflect, indeed, that animal matter, which so abounds 

 in nitrogen, is nevertheless derived, either directly or indirectly, 

 from vegetable, it follows, as a necessary consequence, that ex- 

 istence can only be maintained by the aid of those principles in 

 plants which contain a certain proportion of the element al- 

 luded to. 



And this has been shown by the experiments of Magendie upon 

 dogs which were fed on sugar, starch, gum, and other substances 

 destitute of nitrogen, and in a very short time pined away and died. 



Now, in inquiring as to the source from which plants derive 

 their nitrogen, it might at first sight strike us, that the atmosphere 

 itself, which contains as much as 80. per cent, of this gas, would 

 supply it. To this supposition, however, there appear to be grave 

 objections, from the indisposition which nitrogen evinces to enter 

 into combination with any elementary substances, excepting 

 oxygen and hydrogen. | With the latter, indeed, it is only when 



* Aniiales de Chimie, vol. Ixiii. 



I It unites indeed with carbon, chlorine, &c., but only through the inter- 

 vention of other substances. ^ 



