r.
One of its most characteristic properties, and the one which seems to
have impressed the public most, was its pungent odour. Undue importance
was attached to this property, in the belief that it was caused by the
ammonia it contained. It may be doubted, however, whether the
characteristic smell of guano is due so much to its ammonia as to
certain fatty acids.

_Composition._

In composition it is of a most complex nature. It contains its nitrogen
in a great variety of forms, the chief of these being urate, oxalate,
ulmate, humate, sulphate, phosphate, carbonate, and muriate of ammonia;
and also in a rare form of organic nitrogen peculiar to guano, called
guanine. According to Boussingault, some guanos contain small quantities
of nitrates. Its phosphoric acid is present both in the soluble
state--viz., as phosphates of the alkalies (ammonia and potash)--and in
the insoluble state as phosphate of lime; and lastly, its potash is
present as sulphate and phosphate. The proportion in which these
different forms of nitrogen and phosphoric acid are present varies
considerably in different samples. The richer a sample, as a rule, the
more nitrogen in the form of uric acid it contains. The most of the
nitrogen is present as uric acid and ammonia. Damp guanos contain more
of their nitrogen as ammonia than dry ones, this being due to the
fermentation which goes on in the former. On an average, about a third
of its total nitrogen is soluble in water. Of its phosphates, on the
other hand, only about a fourth are soluble in water.

The following analyses of a sample of Chincha island guano by
Karmrodt[191] will illustrate this. (Sample dried at 212 deg. Fahr.):--

1. _Constituents easily soluble in Water._

Urate of ammonium 12.74
Oxalate of ammonium 13.60
Nitrogenous and sulphurous organic substances 3.61
Ammonium-magnesium phosphate 4.00
Ammonium phosphate .90
Ammonium sulphate 1.82
Ammonium chloride 1.55
Potassium sulphate 3.30
Sodium chloride 2.44
-----
43.96
-----

2. _Difficultly soluble in Water, soluble