1252. The substances used as manure act in various ways. 'Some of the substances added to the soil,' Professor Solly observes, 'act principally in a mechanical way, improving its texture; others are chiefly valuable as sources of carbonic acid and ammonia; whilst many are useful as supplying saline and earthy matters in which the soil may be deficient. It would be easy to divide all manures into these three classes; but it is more convenient to divide them simply into the organic and the inorganic, because many manures act in all these three ways at once, improving the texture of the soil, and supplying carbonic acid, ammonia, and saline matters.'-(Solly's Rural Chemistry, 2nd ed., p. 170.)
