t valuable and complete
carried out on basic slag, we shall give a somewhat detailed account of
them.

_Darmstadt Experiments._

Professor Wagner's experiments were carried out on such different kinds
of crops as flax, rape, wheat, rye, barley, peas, and white mustard, and
the object of the experiments was to ascertain the comparative activity
as fertilisers of superphosphate, basic slag of different degrees of
fineness, Peruvian guano, damped bone-meal, and very finely ground
coprolites. In order to obtain a correct estimate of the relative value
of these different forms of phosphatic manures, it was necessary to
render the nitrogen in the bone-meal and the nitrogen and potash
contained by the Peruvian guano inactive--_i.e._, to limit the test
strictly to phosphoric acid. This was done by adding to the super, basic
slag, and coprolites, quantities of nitrogen and potash equal to those
contained by the other manures. There was further added to all the
experiments (the unmanured ones, of course, as well) an excess of
nitrogen and potash. In this way the increase in returns could only be
due to the phosphoric acid.

The general results obtained from these experiments may be summed up as
follows: Taking the activity of "super" to be represented by 100, then
the relative activity of--

Basic slag of No. 1[236] fineness is 61
Basic slag, No. 2[237] 58
Peruvian guano 30
Basic slag, No. 3[238] 13
Bone-meal 10
Coprolites 9

From these results the value of the commercial article has been
attempted to be ascertained. As it contains 80 per cent or thereby of
fine meal and 20 per cent of coarse, its activity may be stated to be
50, or half as active as super. Thus 2 cwt. of basic slag is equal to 1
cwt. of super. This only refers to the first year's effect. Professor
Wagner has made further experiments as to the after-effects of the
different manures, with the result that he has found that the
after-effects of the basic slag are even _better_ than those of the
"super." This stands to reason, for if twice as much phosphoric acid be
added in the form of basic slag as is added in the form of "super," and
the effect of the first year is similar--that is, the same quantity of
phosphoric acid is assimilated by the plant from the soil in both
cases--there is naturally more phosphoric acid le