, was considered a fair
sample, but now the proportion rendered soluble is greatly increased;
and where bone ash alone is employed, as much as thirty and even forty
per cent of soluble phosphates is occasionally found. This, of course,
is an exceptional case, and great attention and care in the selection of
materials are necessary to obtain so large a proportion. The analyses
already given will shew the farmer what he has to expect in good
superphosphates, but it is very necessary that he should take care to
obtain from the manufacturer a manure equal to the guarantee; and he
ought to bear in mind that, owing to the difficulty of getting materials
of constant composition, variations often take place to a considerable
extent in manures which are supposed to be made in exactly the same
manner.

_Phospho-Peruvian Guano._--Under this name a kind of superphosphate,
which is understood to be made by dissolving a native "rock guano," has
recently attracted considerable attention, and is used to a large
extent. Its composition is--

Water 9.54
Organic matter 21.38
Biphosphate of lime, equivalent to 25.22 soluble
phosphates 16.81
Insoluble phosphates 10.88
Sulphate of lime 37.21
Alkaline salts, containing 1.32 of phosphoric acid,
and equivalent to 2.86 soluble phosphates 2.22
Sand 1.81
------
100.00
Ammonia, 3.50

It is chiefly distinguished by the large proportion of valuable
ingredients it contains, and the care taken to secure uniformity of
composition.

A variety of substances are sold under the name of nitrophosphate,
potato manure, cereal manure, etc. etc., which are all superphosphates,
differing only in the proportion of their ingredients, and in the
addition of small quantities of alkaline salts, sulphate of magnesia,
and other substances, but they present little difference from ordinary
superphosphates in their effects.

The use of superphosphate has greatly extended of late years, and its
consumption has increased in a greatly more rapid ratio than that of
guano or any other manure. Ten or tw