L AGRICULTURE AND RURAL ECONOMY. 333 



ness of land destitute of lime, and that of pure peat, and the 

 necessity of adding calcareous substances, independently of 

 the recognized requirements of lime as an element in the 

 constitution of the plants. 



The renewal of the oxygenated combinations of nitrogen 

 in the calcareous humus is an important fact, which explains 

 the exceptional fertility of lands alternating between frequent 

 rains and dry heat, as in the season of 1872, these alterna- 

 tions being, in fact, equivalent to an addition of manure. This 

 reiterated renewal, and the singular affinity of the humus 

 for the soluble salts, especially those of ammonia, explain the 

 effect of fertilizincc substances in fallow lands. It also eluci- 

 dates the fertilizing influences of tillage, which multiplies 

 the surfaces exposed to the alternations of moisture and dry- 

 ness. The nitrates and nitrites, formed at the expense of the 

 atmosphere by the calcareous humus, are reduced by the 

 humus itself, and the vegetable matter in general, to a con- 

 dition of inferior oxidation, which probably paves the way 

 for the absorption of nitrogen by the roots; and it is highly 

 probable that the nitric acid is replaced, little by little, by 

 the carbonic acid in the air. 9 D, July 25, 1872, 594. 



INFLUENCE OF SALINE SOLUTIONS ON FELDSPAR. 



A series of experiments has been made by Birker and Ul; 

 bricht, upon the influence of saline solutions and other agents 

 on the weathering and decomposition of feldspar, from which 

 it appears that the action of distilled w\ater, with or with- 

 out air, is practically the same. Calcium, carbonate, calcium- 

 nitrate, with and without carbonic acid ; gypsum, with or 

 without carbonic acid ; potassium, carbonate, and bicarbon- 

 ate, and ferrous hydrate, had little more action than water 

 alone. Carbonic acid and calcium carbonate, with carbonic 

 acid, showed an increased action on the alkalies and silica. In 

 the experiments with lime a much larger quantity of alkalies 

 was dissolved, the lime at the same time entering into com- 

 bination with the silica. Sulphate of ammonia had an ener- 

 getic action, more especially on the potash ; only in the ex- 

 periments with this salt, and in that with lime, was potash 

 dissolved in larger quantity than soda. 



In the case of the ammonia sulphate, the base had entered 

 into some combination w^ith the silica, which was not decom- 



