orm into which soluble phosphate in superphosphate is
converted when "reversion" takes place. Hitherto it has not been
customary in this country--although the custom is prevalent both on the
Continent and in America--to distinguish in the analysis of a
superphosphate the "reverted" phosphate from the undissolved phosphate;
since the superior value of the former as a manure is not recognised in
the manure-trade.[249]

_Importance of Mechanical Condition of Phosphate._

A further point to which it is desirable to draw attention is the
_mechanical_ condition of the different insoluble phosphates, which has
an important influence on their value. A very wide difference, for
example, exists between the value of phosphate of lime in such a manure
as Malden guano and in the crystalline mineral apatite; although,
chemically considered, the form in which the phosphoric acid is present
is the same in both substances.

_Potash._

Potash ought only to occur in a soluble form in manures. It is generally
stated as so much potash, and in a footnote the equivalent amount of
muriate or sulphate of potash is given, the former being the more
concentrated form of potash.

For purposes of reference a table will be found in the Appendix[250]
giving some useful factors for converting different forms of nitrogen,
phosphoric acid, and potash into one another.

_Other Items in the Chemical Analysis of Manures._

The other items in the analysis of a manure are of comparatively
secondary importance compared with those already named. Among them may
be mentioned the _moisture_, the _insoluble matter_, and the _organic
matter_. The amount of moisture and the amount of sand are two items of
importance, since, if these are excessive, they afford presumption that
the manure has been adulterated.

_Fertilisers and Feeding Stuffs Act._

An Act was passed, and came into operation in January 1894, for the
purpose of compelling every vendor of manure manufactured in this
country or imported from abroad to give to the purchaser "an invoice
stating the name of the article, and whether it is an artificially
compounded article or not, and what is at least the percentage of the
nitrogen, soluble and insoluble phosphates, and potash, if any,
contained in the article, and this invoice shall have the same effect
as a warranty by the seller of the statements contained therein."

_Different Methods of Valuing Manures._

The monetary value of a m