456 OP THE DROPPINGS OF BIRDS. 



While, then, we put so much faith in theory as to believe that suo- 

 stances which contain much nitrogen are very likely to prove valua- 

 ble manures, — we must not allow ourselves to be so carried away by 

 the simplicity of the principle as to believe either that their relative 

 effects upon our crops may be always estimated by the proportion of 

 nitrogen they contain, or that a substance may not largely increase 

 the produce of our fields in which no nitrogen is present at all. In- 

 deed, the effects of saline substances alone are sufficient to satisfy us 

 how untrue to nature this latter opinion would be. 



§ 9. Of the droppings of fowls — pigeons^ dung, and guano. 



The droppings of birds form one of the most powerful of known ma- 

 nures. This arises in part from the circumstances that in the econo- 

 my of birds there is no final separation between the liquid and solid 

 excretions. Both escape mixed together from the same aperture. 



1°. Pigeons^ dung is much prized as a manure wherever it can be 

 obtained in any considerable quantity. In Belgium it is esteemed as 

 a top-dressing for the young flax, and the yearly produce of 100 

 pigeons is sold for about 20s. Its immediate effect depends upon the 

 quantity of soluble matter it contains, and this varies much accord- 

 ing to its age and the circumstances under which it has been pre- 

 served. Thus Davy (Davy's Agricultural Chemistry, Lecture VI.,) 

 and Sprengel obtainea respectively of 



Recent. Six months' old. After fermentation. 



(Davy.) (Sprengel) (Davy.) 



Soluble matter in ) ^3 ^g g 



pigeons' dung. . ^ ^ ^ ^ 



The soluble matter consists of uric acid in small quantity, of urate 

 sulphate, and especially of carbonate of ammonia, common salt, anc 

 sulphate of potash ; — the insoluble chiefly of phosphate of lime, with 

 a little phosphate of magnesia, and a variable admixture of sand and 

 other earthy matters ( Sprengel's Lehre vom Diinger, p. 140.) When 

 ex^sed to moisture, the pigeons' dung, especially if recent, undergoes 

 fermentation, loses a portion of its ammoniacal salts, and thus be- 

 comes less valuable. When it is intended to be kept it should be 

 mixed with a dry vegetable soil, or made into a compost with earth 

 and saw dust, with a portion of pulverized or charred peat, or with 

 such a disinfecting charcoal as that which is employed in the manu- 

 facture of the animalized carbon above described. 



2^. Hens^ dung often accumulates, decomposes, and runs to waste 

 in poultry yards, when, with a little care, it might be collected in 

 considerable quantities. 



3°. Goose dung is less rich than that of hens or pigeons, because 

 this bird feeds less upon grain, and derives a considerable portion of 

 its nourishment from the grass which it crops, when allowed to go at 

 liberty over the fields. Its known injurious effects upon the grass 

 upon which it falls arise from its being in too concentrated a state. 

 In moist weather, or where rain soon succeeds, it- does no injury, and 

 even when in dry weather it kills the blades on which it drops, it 

 brings up the succeeding shoots with increased luxuriance. 



4°. Rooks'' dung unites with the leaves of the trees among which 

 they live, in enriching the pasture beneath them. In old rookeries the 

 soil JB observed also to be slowly elevated above the surrounding land. 



