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* mineral-hunger" of the plant, and represents the mineral sub- 
stance which does not perform any special function. "This excess 
indifferent substance, such as silica. The observation is of 
considerable interest to the farmer, for it shows that it is not 
economical to manure crops with pure substances, 
II. SOILS AND MANURES. 
Having ascertained in general what substances are necessary as 
UN ox agricultural chemist has next to apply this e 
informatio id manuring of soils which are more or les 
deficient i i er ingredients. It has been found, unfortunately, 
that the chethical analysis of a soil is of little use as a guide 
unless accompanied by what may be termed a “ mechanical 
analysis," by which is meant chiefly a determination of the 
mde of finely-divided constituents present in the soil. It is 
he finely-divided earth which presents a Dokl large 
ss for the exercise of the solvent action of the water and its 
dissolved carbonic acid. There is one case, however, in which 
: : ; h 
ind traces of some necessary element are present in a soil. 
E on rii other hand, large quantities of an elementare present, 
it does not follow that there is a sufficiency in the soil even when 
the latte er = in a e state of division, for the substance 
in question may be present in an insoluble or refractory form. 
This is cominoniy the eats with nitrogen, which exists in the soil 
chiefly in the form of a mixture of indefinite nitrogenous sub- 
stances known as humus, or mould. These substances sometimes 
easily give up their nitrogen to plants, but in other case : 
refractory. The uncertainty as to their action is indeed so great 
that certain peaty soils are known which consist almost entirely 
of cr but contain, nevertheless, an insufficiency of available 
nitrogen 
Poito acid affords another illustration. The soluble 
phosphoric acid of the manure is absorbed by the soil as dicaleld 
peres which is comparatively easily soluble in the soil-water. 
With time, however, it may change in the soil to the insoluble 
tric eem phosphate, or even to iron or aluminium phosphates, 
which are still less soluble. 
n the case of caleium, chemical analysis has been found to be 
of considerable service in determining what manuring is required, 
since calcium is chiefly valuable in the form of carbonate or 
humate, and these are easily estimated in the soil. l 
Since then the direct method of prep sie dens is an insufficient 
guide to manuring, it is fortunate that chemists have been able to 
evelop successfully an indirect method. This is the cultivation 
method, by which hiris are allowed to grow in the soil under 
examination, after taking care to provide a sufficiency of all 
plant-food stuffs except the one, e.g., phosphoric acid, whose 
presence in available form is being tested. The plants are then 
