PRACTICAL AGRICULTURE. *^ 



be substituted. One hundred tons of fresh horse-dung, 

 if dried, would leave only from 25 to 30 tons of sohd 

 matter, the rest being only water; and if (his dried mat- 

 ter (itself only one-fourth of the original weight) were 

 burnt, so as to decompose its vegetable ingredients, we 

 should obtain, perhaps, 10 per cent, of really useful 

 saline and earthy matters, (one-fortieth of the original 

 weight,) according to the richness or poverty of the food 

 the liorse had taken. 



Now, this minute proportion of saline and earthy mat- 

 ters, and its relative quantity, in the various kinds of 

 excrement, forms, evidently, the chief topic of interest 

 to which our attention should be directed; inasmuch as 

 what is left upon such examination and analysis, is 

 exactly what has made up the component inorganic 

 parts of the hay, straw, grass, or oats, on which the ani- 

 mal has been fed ; or, in other words, exactly what has 

 been removed from the soil, and requires to be replaced, 

 if the next crop is to equal the last. If our object is 

 increased fertility, more must be added than has beea 

 taken away. Hay, straw, and oats, formed (for illustra- 

 tion's sake) the food of a horse. Their principal con- 

 stituents are the phosphates of lime and magnesia, car- 

 bonate of lime, and silicate of potash ; the first three of 

 these preponderated in the corn, the latter in the hay — 

 and these, removed from the soil with the crop, are pre- 

 cisely the saline matters which would be found in the 

 excrement of the animal for whose support that crop 

 was intended. 



In order, then, to atone for the absence of that excre- 

 ment which derives its value from the soil which has 

 produced it, and for which it is peculiarly fitted, as con- 

 taining what that soil has lost, the ashes of wood or bones 

 may often be judiciously substituted — and for this rea- 

 son : wood-ashes contain silicate of potash, exactly in 

 the same proportion as that salt is found to exist in the 

 straw of the last crop ; and as to bones, the greatest part 

 of their bulk consists of the phosphates of lime and mag- 

 nesia. Ashes obtained from various trees are of un- 

 equal value : those from oak-wood are the least— those 



