44 FAMILIAR LETTERS ON CHEMISTRY. 



3. The produce of nitrogen in clover and peas, which agriculturists will acknow- 

 ledge require no nitrogenized manure, is far greater than that of a potato or turnip 

 field, which is abundantly supplied with such manures. 



Lastly : and this is the most curious deduction to be derived from the above facts. 

 If we plant potatoes, wheat, turnips, peas, and clover (plants containing potash, 

 lime, and silex), upon the same land, three times manured, we gain in sixteen 

 years, for a given quantity of carbon, the same proportion of nitrogen which we 

 receive from a meadow which has received no nitrogenized manure. 



On a morgen of meadow land, we obtain in plants, containing silex, lime, and 

 potash, 984 carbon, 32.2 nitrogen. On a morgen of cultivated land, in an average 

 of sixteen years, in plants containing the same mineral elements, silex, lime, and 

 potash, 857 carbon, 26.8 nitrogen. 



If we add the carbon and nitrogen of the leaves of the beetroot, and the stalks 

 and leaves of the potatoes, which have not been taken into account, it still remains 

 evident that the cultivated fields, notwithstanding the supply of carbonaceous and 

 nitrogenized manures, produced no more carbon and nitrogen than an equal surface 

 of meadow land supplied only with mineral elements. 



What, then, is the rationale of the effect of manure of the solid and fluid excre- 

 ments of animals ? 



This question can now be satisfactorily answered : that effect is the restoration 

 of the elementary constituents of the soil which have been gradually drawn from 

 it in the shape of grain and cattle. If the land I am speaking of had not been 

 manured during those sixteen years, not more than one half, or perhaps than one 

 third part of the carbon and nitrogen would have been produced. We owe it to 

 the animal excrements, that it equalled in production the meadow-land, and this, 

 because they restored the mineral ingredients of the soil removed by the crops. 

 All that the supply of manure accomplished, was to prevent the land from becoming 

 poorer in these, than the meadow which produces two thousand five hundred pounds 

 of hay. We withdraw from the meadow in this hay as large an amount of mineral 

 substances as we do in one harvest of grain, and we know that the fertility of the 

 meadow is just as dependent upon the restoration of these ingredients to its soil, 

 as the cultivated land is upon manures. Two meadows of equal surface, containing 

 unequal quantities of inorganic elements of nourishment other conditions being 

 equal are very unequally fertile ; that which possesses most, furnishes most hay. 

 If we do not restore to a meadow the withdrawn elements, its fertility decrease's. 

 But its fertility remains unimpaired, with a due supply of animal excrements, fluid 

 and solid, and it not only remains the same, but may be increased by a supply of 

 mineral substances alone, such as remain after the combustion of ligneous plants 

 and other vegetables ; namely, ashes. Ashes represent the whole nourishment 

 which vegetables receive from the soil. By furnishing them in sufficient quantities 

 to our meadows, we give to the plants growing on them the power of condensing 

 and absorbing carbon and nitrogen by their surface. May not the effect of the 

 solid and fluid excrements, which are the ashes of plants and grains, which have 

 undergone combustion in the bodies of animals and of man, be dependent upon the 

 eame cause ? Should not the fertility, resulting from their application, be altogether 

 independent of the ammonia they contain ? Would not their effect be precisely the 

 same in promoting the fertility of cultivated plants, if we had evaporated the urine, 

 and dried and burned the solid excrements ? Surely the ceralia and leguminous 

 plants which we cultivate must derive their carbon and nitrogen from the same 

 source whence the graminea and leguminous plants of the meadows obtain them ! 

 No doubt can be entertained of their capability to do so. 



In Virginia, upon the lowest calculation, twenty-two pounds weight of nitrogen 

 were taken on the average, yearly, from every morgen of the wheat-fields. This 

 would amount, in one hundred years, to two thousand two hundred pounds weight. 

 If this were derived from the soil, every morgen of it must have contained the 

 equivalent of one hundred and ten thousand pounds weight of animal excrements 

 (assuming the latter, when dried, at the temperature of boiling water, to contain 

 two per cent.). 



In Hungary, as I remarked in a former letter, tobacco and wheat have been 



frown upon the same field for centuries, without any supply of nitrogenized manure. 

 s it possible that the nitrogen essential to, and entering into, the composition of 

 these crops, could have been drawn from the soil ? 



Every year renews the foliage and fruits of our forests of beech, oaks, and chest- 

 nuts; the leaves, the acorns, the chestnuts, are rich in nitrogen; so are cocoa-nuts, 

 bread-fruit, and other tropical productions. This nitrogen is not supplied by man. 

 Can it, indeed, be derived from any other source than the atmosphere? 



In whatever form the nitrogen supplied to plants may be contained in the atmo- 



