ific Ocean.

2. _Mejillones_, on the coast of Bolivia.

3. Aves, _Tortola_, _Mona_, and other deposits in the West Indies.

4. _Kuria Muria_ islands, in the Arabian Gulf.

For further particulars as to the composition of these different guanos,
the reader is referred to the Appendix, Note V., p. 329.

_Inequality in Composition._

That guano was a substance of by no means uniform composition was a fact
early recognised in the history of the trade. Not only did guano from
different deposits show on analysis different percentages of the
manurial ingredients, but different samples of guano from the same
deposit were often found to differ very considerably from one another.
It soon became the custom, therefore, to sell it on chemical analysis,
each separate cargo being carefully analysed. But this custom did not
wholly obviate the difficulty, as the guano in even one cargo might
differ. In the case of the older and richer guanos, there was certainly
more uniformity in quality, but they were liable to differ in their
percentage of nitrogen.[195] As, however, the deposits became gradually
worked out, their lower layers were found more or less largely admixed
with stony and earthy matter, and their composition was naturally
rendered very variable. This state of matters was unsatisfactory to
buyers and sellers, and led to much friction between the two, as it was
found wellnigh impossible on the part of the seller to guarantee the
composition of his manure. The custom of preparing the material by
reducing it to a fine powder before sending it into the market, and the
custom, subsequently introduced, of treating it with sulphuric acid,
have done away with this difficulty to a large extent.

_"Dissolved" Guano._

The treatment of guano with sulphuric acid was first had recourse to in
the case of cargoes damaged with water. In such guano, as has been
already pointed out, fermentation has been permitted to take place, with
the result of the formation of volatile carbonate of ammonia in greater
or less quantity. By the addition of sulphuric acid the ammonia was
fixed, and the guano was prevented from losing its most valuable
constituent. It was soon found, however, that guano so treated possessed
greater activity as a manure. The result of the sulphuric acid was to
increase very materially the amount of its soluble phosphates, and also
its soluble nitrogen compounds.[196] It had, moreover, the effect of
producing a guano