CONTENTS. 17 



CHAPTER IX. 



GROUND RAPE-CAKE. 



Nature and composition of ; the, diffusibility of its constituents in the soil is com- 

 paratively great Its importance as a manuring agent is small The Saxon 

 agricultural experiments with rape-cake The inferences from them, . 267 



CHAPTER X. 



WOOD-ASH. 



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 Lixiviated ash, its value Proper mode of applying ashes as a 

 manure, .......... 272 



CHAPTER XI. 



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 The general reason for decrease of 

 productive power in soils Classification of manures according to the amount 

 of nitrogen ; assimilable and sparingly assimilable nitrogen ; the nitrogen 

 theory ; only ammonia according to this theory is wanting ; resemblance to 

 the humus theory Manuring experiments with compounds of ammonia by 

 Schattenmann, by Lawes and Gilbert, by the Agricultural Union of Munich, 

 and by Kuhlmann 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 the alkalies The ineffective nitrogen of the soil made 

 effective by the supply of ash-constituents that are wanting Progress in ag- 

 riculture impossible if dependent on a supply of ammoniacal compounds ; re- 

 sults of Lawes' experiment with salts of ammonia The artificial supply of 

 ammoniacal manures contrasted with the crops produced and the increase of 

 population Increase of nitrogenous food by natural means ; formation of 

 nitrite of ammonia by oxidation in the air according to Schonbein Supply of 

 food in excess necessary to produce corn-crops ; reasons How the necessary 

 excess of nitrogenous food for corn maybe obtained from natural sources The 

 supply of nitrogen in farm-yard manure in the Saxon experiments correspond- 

 ed to the crop of clover-hay Loss of nitrogen in lime soils by oxidation ; 

 utility of a supply of nitrogen to such soils Effect of nitrogenous food on the 

 aspect of young plants ; on potatoes Empirical and rational systems of agri- 

 culture, . 274 



