in our laboratories. The water which falls to the earth is also
quite another kind of water from that which the chemist uses; it
not alone assumes power by its fall, it is also freshly impregnated
with the constituents of the atmosphere: carbonic acid, oxygen
and ammonia, substances which very much aid, either directly or
indirectly, in dissolving the nourishing ingredients of soils. The
water of which the chemist can dispose has lost already most of
these substances, and, when boiled, even loses them entirely. Be-
sides, we know that the better the adaptation of a soil for the pur-
pose of cultivation, so much the longer will it retain its nourishing
ingredients, and proportionably resist their loss by the action of
water. A really good soil may therefore, mutatis mutandis, yield
less quantities of nourishing substances to water, than one of an in-
ferior quality.

Water acts principally as an acid and, most especially when im-
pregnated with carbonic acid and oxygen, as is the case with rain-
water. The best way to imitate nature when extracting from soils
their nutrient ingredients, seems therefore to remedy the deficien-
cies of pure water by the addition of an acid, and this is the method
which we have adopted.                                                             

Determination of Phosphoric Acid.

Of the different methods of the determination of Phosphoric
Acid, that by which Phosphoric Acid is detected by molybdate of
ammonia, is distinguished, as the most advantageous for application
to soils, furnishing indisputably the most exact results of all, and
requiring besides little skill, and the least time.

As to the preparation of the molybdate of ammonia, it is most
commonly made from the natural Sulphuret of molybdenum. This
is to be pulverized, or on account of its toughness ground to pow-
der and then, whilst being exposed to the air, heated and constant-
ly stirred; Sulphurous acid will then escape, and molybdic acid be
left behind. To prevent the melting, or the escaping of the latter,
the heat must be moderate, most especially towards the end of the
process. The residue is digested for some time with ammonia,
which dissolves the molybdic acid, whilst undecomposed sulphuret
of molybdenum, quartz and other substances remain. The filtrate
evaporated, and if necessary, once more filtrated, then boiled and
mixed, whilst yet hot, with strong ammonia, will, by cooling, leave
crystals of molybdate of ammonia.

A concentrated solution of these crystals in water furnishes the
above mentioned re-agent.

The effect of molybdate of ammonia on phosphoric acid and its
salts, in a solution which has been acidulated by nitric acid, mani-
fests itself, first, in the forming of a white precipitate of molybdic
acid, which is re-dissolved, however, in the excess of the nitric

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