XVI 11 COXTENTS. 



CHAPTER Y.—cantmucd. 



conclusions drawn from them as to the condition of the fields — Produce 

 of these fields from farm-yard manm-e ; the increase of produce cannot be 

 calculated from the amount of manure used — Restoration of the power of 

 production of exhausted fields by the increase of the necessaiy elements of 

 food present in the soil in minimum amount; advantageous use of farm-yard 

 manm-e in this respect; explanation of the result — Action of manure as 

 compared with quantity used: experiments — Rational system of cultivation 

 — Depth to which the food of plants penetrates is dependent on the power 

 of absorption of the soil; the Saxon fields considered in this respect ; the 

 power of absorption considered in manuring — Change produced in the 

 composition of the soil by the system of farm-yard manuring ; the dif- 

 ferent stages of this system, the final result — Examples of these stages in 

 the Saxon experimental fields — Cause of the growth of weeds; reme- 

 dies — The history of husbandry, what is taught by it — Present condi- 

 tion of European husbandry — Present production of the land compared 

 with the earlier ; conclusions — Continuation of production regulated by 

 a natural law — Law of restoration ; defective practice of it — Agi-icul- 

 ture in the time of Charlemagne — Agriculture in the Palatinate — Com 

 fields in the valleys of the Nile and Ganges ; nature provides in them for 

 the restoration of food of plants — Practical agricultin-e and the law of 

 restoration — The statistical returns of average crops aiford an explana- 

 tion of the condition of com fields .... page 188 



CHAPTER YI. 



GUANO. 



Composition compared with that of seeds ; small amoimt of potash in it ; 

 its action — Guano and bone-earth, similarity of their active ingredients 

 — Guano acts quicker than bone-earth, or a mixture of the latter and 

 ammoniacal salts ; reason of this — Oxalic acid in Peruvian guano ; the 

 phosphoric acid rendered soluble by its means — Peruvian guano, its effect 

 on the cultivation of corn — Moist guano loses ammonia — Moistening 

 guano with water acidulated with sulphuric acid ; effect — Inactivity of 

 guano in diy and very wet weather — Rapidity of its action as a manure, 

 on what dependent — Comparison of the effect of farm-yard manm-e 

 and guano ; effect produced by mixing the two — Gnano on a field rich 

 in ammonia — Increased produce by guano, what it presupposes — 

 Exhaustion of the soil by continuous use of guano — Mixture of guano 

 with gypsum and with sulphuric acid — The Saxon agricultural expei-i- 

 ments ; their results ....... 250 



CHAPTER YII. 



POUDRETTE HUMAN EXCREMENTS. 



Poudrette, nature of ; small amount of the food of plants in it — Human 

 excrement, its value — Construction of the privies in the barracks at 

 Rastadt — Calculation of the amoimt of com produced by the excrement 

 collected ; importance to the neighbourhood — Its effect not impaired by 

 deodorising with sulphate of iron — The excrement of the inhabitants of 

 towns as manure — Its importance ..... 271 



