192 LECTURES ON 



field culture.) that gypsum has the influence of a body that attracts 

 moisture. 



The facts brought to light by the researches of Way, Eichhorn, 

 and Voelcker, already described, indicate another general mode by 

 which fertilizers, especially soluble saline bodies, may operate indi- 

 rectly. The investigations referred to, show that the bases (and 

 acids?) may replace each other in insoluble or slightly soluble combi- 

 nations, i. e., soluble lime may displace insoluble potash, making this 

 soluble and becoming insoluble itself. Soda may, in the same manner, 

 displace lime or potash, or ammonia, the rule being that the body 

 in excess goes into combination and expels those before combined. 

 We observe here a tendency to bring all the bases into what we may 

 designate as an equilibrium of solution. This principle appears adapted 

 more than any other yet discovered to generalize the phenomena of 

 indirect action, and enables us to forsee and explain them. Proofs 

 are not wanting of the actual operation of this principle in the soil. 



Wolff (Naturgesetzlichen Grundlagendes Ackerbaues, 3d ed., p. 148,) 

 found in fact that the ashes of the straw of buckwheat grown with 

 a large supply of common salt, compared with the ashes of the same 

 part of that plant grown on the same soil minus this addition, con- 

 tained less chlorid of sodium but much more chloric! of potassium, 

 there having occurred an exchange of bases in the soil. 



Closely connected in many points with these phenomena of dis- 

 placement, yet in many respects different and peculiar, are the sol- 

 vent effects of saline bodies, alkalies, and carbonic acid in dilute 

 watery solution, to which allusion has been so frequently made in the 

 foregoing pages. We refer to this subject once more in this place 

 in order to give the results of some actual trials as to the disintegrat- 

 ing effect of these substances on soils and rocks. Dietrich, to whom 

 we owe these investigations, found that from a diluvial loamy soil con- 

 taining humus, the amount of matters rendered soluble by a dilute 

 solution of carbonate of ammonia (containing one per cent, of the salt) 

 was twice as great as that set free by water saturated with carbonic 

 acid, and of the alkalies, potash and soda, four times as much were 

 dissolved by the former as by the latter liquid. Solution of sulphate 

 of ammonia dissolved six times as much as carbonated Avater. 



The action of carbonated water and carbonate of ammonia extended 

 chiefly to the alkalies. Sulphate of ammonia, while equally effective 

 in their solution, likewise dissolved a large amount of lime and mag- 

 nesia as sulphates. Caustic lime (one per cent.) in most cases pro- 

 duced a remarkable increase of volume in the earths submitted to its 

 action; the loam just mentioned became nearly three times as bulky 

 as it was at first, a decomposition of the silicates having taken place. 

 Carbonate of lime, in solution in carbonated water, had the most 

 vigorous action in eliminating the alkalies. Even gypsum, (sulphate 

 of lime,) in moist contact with powdered basaltic rock, sets free a 

 considerable amount of alkalies in a few days. Ammonia salts exert 

 a strong action on insoluble silicates, the ammonia and silica being 

 partially set free, the other acids and bases remaining in soluble com- 

 binations. 



