442 
On Pliosphatic Guanos. 
bj placing a little of the wetted guano upon reddened litmus- 
paper, when its original blue colour will at once be restored. 
Bv this simple experiment it will be seen how rapidly the 
urea and compounds of uric acid of birds'-dung are transformed 
into carbonate of ammonia in the presence of water. Most 
guanos which have a strongly pungent ammoniacal smell, and 
are dark coloured, are poorer in nitrogen and richer in phosphates 
than lighter-coloured and less pungent-smelling samples of the 
same kind. The former, as a rule, contain more ready-formed 
carbonate of ammonia and less uric acid than the latter, which, 
however, are more valuable, inasmuch as the total percentage 
of nitrogen, which mainly regulates the value of such guano, is 
higher than in dark-coloured and pungently smelling samples. 
The first effect of water upon birds'-dung is to transform its 
urea and uric acid partly into volatile carbonate of ammonia, 
which gradually escapes, and partly into non-volatile soluble 
salts of ammonia, whilst at the same time a portion of the 
insoluble phosphates are rendered soluble. If, in this par- 
tially decomposed condition, the guano is exposed to occasionjil 
heavy rains, the most valuable soluble ammoniacal constituents 
and the soluble phosphates will be removed to a greater or less 
extent, according to the amount of rain which will have acted 
upon it. The partial removal of th<e nitrogenous constituents 
is the cause of the inferior quality of the guano-deposits which 
are found in the Falkland Islands, on the Patagonian coast, and 
in various other places in South Africa, Bolivia, and Chili, such as 
the Ichaboe, Saldanha Bay, Bolivian, Upper Peruvian, Chilian, 
and Californian guanos. If the solvent action of water continues 
to operate for a long time upon guano-deposits, the nitrogenous 
constituents of the original birds'-dung are almost entirely re- 
moved, together with the soluble saline mineral matters, so that 
finally phosphatic guanos are produced, which consist principally 
of phosphate of lime. Most of the phosphatic guanos are yellow 
or light brown, or chocolate- or reddish-coloured, fine powdery 
manures, which still contain more or less organic matter poor 
in nitrogen. In this way the phosphatic guanos which are 
found on a number of islands in the Caribbean Sea and in the 
South Pacific Ocean have been produced. Some of' the South 
African and South American guanos also belong to the class of 
phosphatic guanos. All true guano-deposits, according to their 
composition, may conveniently be divided into three classes : — 
1st. Nitrogenous guanos, consisting chiefly of the fa-cal 
matters of sea-birds, which have suffered little by the action of 
rain, and which retain the greater part of the nitrogenous con- 
stituents originally present in the birds -dung, and all the saline 
and phosphatic compounds. 
