FAMILIAR LETTERS ON CHEMISTRY. 43 



most alkaline phosphates and earthy salts, will produce more or a greater weight of 

 seeds than another which, in an equal time, has absorbed less of them. We con- 

 sequently observe, in a hot summer, when a further supply of mineral ingredient! 

 from the soil ceases through want of water, that the height and strength of plants, 

 as well as the development of their seeds, are in direct proportion to its absorption 

 of the elementary parts of the soil in the preceding epochs of its growth. 



The fertility of the year depends in general upon the temperature, and the 

 moisture or dryness of the spring, if all the conditions necessary to the assimilation 

 of the atmospheric nourishment be secured to our cultivated plants. The action 

 of humus, then, as we have explain-ed it above, is chiefly of value in gaining time. 

 In agriculture, this must ever be taken into account ; and in this respect humus is 

 of importance in favoring the growth of vegetables, cabbages, &c. 



But the ceralia, and plants grown for their roots, meet on our fields, in the 

 remains of the preceding crop, with a quantity of decaying vegetable substances 

 corresponding to their contents of mineral nutriment from the soil, and consequently 

 with a quantity of carbonic acid adequate to their accelerated development in the 

 spring. A further supply of carbonic acid, therefore, would be quite useless, with- 

 out a corresponding increase of mineral ingredients. 



From a morgen of good meadow land, two thousand five hundred pounds weight 

 of hay, according to the best agriculturists, are obtained on an Average. This 

 amount is furnished without any supply of organic substances, without manure 

 containing carbon or nitrogen. By irrigation, and the application of ashes or 

 gypsum, double that amount will be grown. But assuming two thousand five 

 hundred pounds weight of hay to be the maximum, we may calculate the amount 

 of carbon and nitrogen derived from the atmosphere by the plants of meadows. 



According to elementary analysis, hay, dried at a temperature of one hundred 

 degrees of Reaumur, contains 45.8 per cent, of carbon, and 1.5 per cent, of nitrogen. 

 Fourteen per cent, of water retained by the hay, dried at common temperatures, is 

 driven off at one hundred degrees. Two thousand five hundred pounds weight of 

 hay, therefore, corresponds to two thousand one hundred and fifty pounds, dried at 

 one hundred degrees. This shows us, that nine hundred and eighty-four pounds 

 of carbon, and 32,2 pounds weight of nitrogen, have been obtained in the produce 

 of one morgen of meadow-land. Supposing that this nitrogen has been absorbed 

 by the plants in the form of ammonia, the atmosphere contains 39.1 pounds weight 

 of ammonia to every three thousand six hundred and forty pounds weight of 

 carbonic acid (=984 carbon, or 27 per cent.); or, in other words, to every 

 thousand pounds weight of carbonic acid, 10/jths pounds of ammonia, that is, to 

 about Tirs'ffff^h the weight of the air, or ^^^^th of its volume. 



For every hundred parts of carbonic acid absorbed by the surface of the leaves, 

 the plant receives from the atmosphere somewhat more than one part of ammonia. 



With every thousand pounds of carbon, we obtain 



From a meadow . . . 32 T \ths pounds of nitrogen. 

 From cultivated fields 



In wheat , 21.5 



Oats 



%e , 



Potatoes 

 Beetroot 

 Clover 

 Peas 



22.3 



15.2 



34.1 



39.1 



44 



62 



Boussingault obtained from his farm at Bechelbronn, in Alsace, in five years, in 

 the shape of potatoes, wheat, clover, turnips, and oats, 8383 of carbon, and 250.7 

 nitrogen. In the following five years, as beetroot, wheat, clover, turnips, oats, 

 and rye, 8,192 of carbon, and 284.2 of nitrogen. In a further course of six years, 

 potatoes, wheat, clover, turnips, peas, and rye, 10,949 of carbon, 356,6 of nitrogen ; 

 in sixteen years, 27,424 carbon, 858,5 nitrogen : which gives, for every 1,000 carbon, 

 31.3 nitrogen. 



From these interesting and unquestionable facts, we may deduce some conclusions 

 of the highest importance in their application to agriculture. 



1. We observe that the relative proportions of carbon and nitrogen, stand in a 

 fixed relation to the surface of the leaves. Those plants in which all the nitrogen 

 may be said to be concentrated in the seeds, as the ceralia, contain on the whole 

 less nitrogen than the leguminous plants, peas and clover. 



2. The produce of nitrogen on a meadow which receives no nitrogenized manure, 

 is greater than that of a field of wheat which has been manured. 



