liebig's organic chemistry. 
185 
present are compared, not by actual weight, but by the rela- 
tive or proportional weight and saturating power, it results 
that the amount of acids necessary to saturate the bases 
would be the same in all. When one metallic oxide is de- 
ficient, its place is supplied by another; not in the same ac- 
tual weight, but in the precise amount indicated by its che- 
mical equivalent. The quantity of acid present, and which 
is generally organic, would seem to regulate the supply of 
the inorganic base; but the extent to which this substitution 
of one base for another may take place, has not been suffi- 
ciently ascertained. It is only known that, in some cases, 
lime or magnesia may, to a certain extent, replace potassa; 
and that some of these may be replaced by an organic base: 
while, on the other hand, the organic acid may occasionally be 
replaced by an inorganic acid. Certain bases are, however, 
known to be indispensable, as potassa to vines; and in every 
instance where any essential organ contains an invariable 
saline constituent, either that or its elements must be sup- 
plied. These views are supported by example and argument 
confirmatory of the position. 
We must pass over the chapters on the Art of Culture 
and Rotation of Crops with very few remarks. All the soil 
on the earth's surface was derived, originally, from the dis- 
integration of rocks. In their solid or unbroken state they 
yield very slowly any of their constituents to the action of 
acids, but the slow and continued action of carbonic acid 
and moisture, on those containing alkalies, gradually decom- 
poses them, and dissolves the alkaline carbonate. By these 
agencies, and the action of change of temperature, disinteg- 
ration takes place, and the soil is formed capable of yielding 
its constituents to plants. The soluble matter will gradual- 
ly be abstracted, and the soil becoming exhausted, tempora- 
ry sterility will be produced. As the disintegration goes 
on, the soil regains its fertility. In this lies the secret of the 
success attending the cultivation of a succession of different 
crops on the same soil. A crop which abstracts potassa largely 
17 
