COOTENTS. XIX 



CHAPTER VIII. 



EARTHY niOSniATES. 



High agricultural value of phosphates — Phosphates of conimorce ; selection 

 of the kind to be used depeudeut on the object in view, and on tlie nature 

 of the soil — The rapidity and the duration of the effect of the neutral 

 and of the soluble phosphate (superphosphate) of lime — The Saxon 

 manuring experiments ..... page 27G 



CHAPTER IX. 



GROUND RAPE-CAKE. 



Nature and composition of; the difFnsibility of its constituents in the soil is 

 comparatively great — Its importance as a manuring agent is small — 

 The Saxon agi'icultural experiments with rape-cake — The inferences from 

 them ......... 2&2 



CHAPTER X. 



WOOD-ASir. 



The amount of the food of plants in it — Box-wood ash gives only the half 

 of its potash readily to water — Convenience in mixing wood-ash with 

 earth before applying it — Lixi\dated ash, its value — Proper mode of 

 applying ashes as a manure ...... 287 



CHAPTER XL 



AMMONIA AND NITRIC ACID. 



Source of the nitrogen of plants — Amount of ammonia and nitric acid in 

 rain and dew : Bineau, Boussingault, Knop — Quantity of ammonia in the 

 air — Quantity of nitrogenous food brought to the soil yearly by rain and 

 dew; more present in the soil than is removed by the crops — Tlio 

 general reason for decrease of productive power in soils — Classification 

 of manures according to the amount of nitrogen; assimilable and spar- 

 ingly assimilable nitrogen ; the nitrogen theory ; only ammonia according 

 to this theoiy is wanting ; resemblance to the humus theory — Manuring 

 experiments with compounds of ammonia by Schattenmann, by Lawos 

 and Gilbert, by the Agi-icultural Union of Munich, and by Kuhhnann — 

 The efficacy of a manure is not in proportion to its amount of nitrogen : 

 experiments — Large amount of nitrogen in soils; the experiments of 

 Schmid and Pierre ; the arable surface soil contains most nitrogen — 

 Form of the ammonia in the soil; Mayer's experiments — Comportment 

 of soil and farm-yard manure with tlio alkalies — The ineffective nitrogen 

 of the soil made eifectiye by the supply of ash-constituents that are 



