hosphate of iron and alumina. Where the ash is
white, but excessive in quantity, adulteration with common salt,
sulphate of magnesia, gypsum, or chalk, may be suspected. The last-named
substance is easily detected by treating it with any of the common
acids, when brisk effervescence, due to the liberation of the carbonic
acid, will ensue.[198] A further point of importance with regard to the
ash is its solubility in water and in acids. A large insoluble residue
may be taken as indicating adulteration with sand. Adulteration with
water is also easily detected by heating a sample to the boiling
temperature and determining the loss it sustains. Of course the amount
of water varies in different samples. The appearance of the guano will
serve fairly well to detect whether it is abnormally moist. It may be
added, in conclusion, that Peruvian guano is extremely light; and while
this by itself is not a sufficient test of genuineness, it may serve to
confirm other tests.

III.--SO-CALLED GUANOS.

Before concluding this chapter, reference may be made to certain manures
which are commonly known under the name of guanos--such as "fish-guano,"
"flesh-guano," "meat-meal-guano," and "bat-guano,"--as well as to
manures which may more conveniently be described here--viz., "fowl and
pigeon dung."

_Fish-Guano._

The application of fish, not suited for other purposes, to the fields
as a manure is a practice which has obtained in certain parts of the
country for a number of years. In many districts on the sea-coast, where
fishing is the chief industry, the only way in the past of disposing of
a superabundant catch of herrings, for example, has been to utilise them
as a manure. From such a practice has sprung up what is now an important
and ever-increasing trade--viz., the manufacture of fish-guano.

This manufacture was first started, and is still most largely practised,
in Norway. The guano obtained varies very considerably in quality
according to the nature of the process employed, and as to whether the
guano is made from whole fish or merely from fish-offal. The latter
source is the common one. The manufacture is carried on at the
fish-curing stations, and the quality of the guano made from this source
is somewhat different from that made from whole fish, as a large
proportion of the fish-offal is made up of bones and heads. Large
quantities of Norwegian fish-guano are exported to various parts of
Europe.

The best quality o