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XVI. — On Phosphatic Guanos. By Dr. Augustus 
VOELCKEE, F.R.S. 
Guano, it is well known, is the name given to the accumulated 
Isccal matters (chiefly of sea-birds) which have been deposited 
on different parts of the earth's surface in greater or less purity, 
and have sustained more or less change by the subsequent action 
of the atmosphere. The quality and value of different kinds 
commercially depend almost entirely upon the amount of de- 
composition which they have undergone by the action of rain, 
and other atmospheric influences. 
The recent droppings of sea-birds which have fed upon fish, 
a highly nitrogenous food, consist chiefly of uric acid, urea, 
urate of ammonia, and a variety of other nitrogenous organic 
compounds, and variable proportions of the phosphates of lime 
and magnesia, phosphate and sulphate of potash and soda, 
chloride of sodium, and some other saline matters. 
The nitrogenous organic portion constitutes fully two-thirds 
of the dry birds'-dung, and the phosphatic and saline inorganic 
substances form the remaining one-third. 
In dry climates, where little or no rain falls — as in some parts 
of Peru and Bolivia, on the western coast of South America — 
the droppings of the sea-birds suffer little from the action of the 
atmosphere, so that the greater part of the nitrogenous matters, 
and the whole of the saline and phosphatic constituents of the 
birds'-dung, remain in such guano-deposits. 
The most recent deposit of birds'-dung brought under my 
notice was obtained from a rocky promontory on the Bolivian 
coast, called Angamos. Occasionally a small cargo of Angamos 
guano finds its way into England, and meets with a ready sale, 
as it is, when pure, an extremely valuable manure. Angamos 
guano is collected by hand, with considerable danger and diffi- 
culty, from the bare surfaces of the precipitous cliffs frequented 
by the sea-birds. Being produced only in very limited quan- 
tities, it is not of much practical importance to the farmer. Its 
composition, however, presents several points of interest, to which 
I would invite the attention of the reader. (See Table, p. 441.) 
Both samples were very dry ; they had a light-yellow colour, and 
a fishy, but by no means pungent, smell. The one contained as 
much as 21*15 per cent, and the other 19"3 per cent, of nitrogen, 
or considerably more than the best Chincha Island guano which 
ever passed through my hands. In the finest samples of the 
old and now exhausted Chincha Island guano I found in round 
numbers 16 per cent, of nitrogen, which is equal to about 19J 
l)er cent, of ammonia ; and on an average the bulk of the deposit 
