Phosphatic Materials used for Ar/ricuUiiral Purposes. 365 
artificial manures. They are generally distinguished from tlu; 
Peruvian by the almost entire absence of ammonia and soluble 
phosphates, by the small (quantity of organic matter, and by the 
large proportion of insoluble phosphates which they contain. On 
the latter the commercial value of these guanos chiefly depends. 
They usually contain a considerable quantity of gypsum, and 
occasionally carbonate of lime besides. If a guano is to be used 
as a manure Avithout any further preparation, the presence of car- 
bonate of lime, though it does not add to, does not detract from 
its value ; but if the guano is to be employed as the basis for 
super jihosphate, or for drying artificial manures containing soluble 
phosphate, the less cai'bonate of lime it contains the better. 
If guano containing carbonate of lime is mixed with sulphuric 
acid, all the carbonate must be saturated with acid before any 
soluble phosphate can be formed ; and again, if such a guano be 
added as a drying material to a manure containing soluble phos- 
phate, the carbonate of lime of the guano, taking up the acid 
which keeps the phosphate in a soluble state, renders the latter 
insoluble. In either case more acid is required for the produc- 
tion of a given amount of soluble phosphate than is wanted if 
phosphatic materials free from carbonate of lime are employed. 
Saldanha Bay guano. South African, Pedro Keys, Swan 
Island, Baker Island, Birds' Island guanos are some of the in- 
ferior phosphatic guanos which may be used either by them- 
selves, or better after having been treated with some sulphuric 
acid. As the composition of nearly every cargo of these guanos 
varies greatly, the analysis of particular samples is of no general 
interest. I therefore pass them over as well as the analyses of 
some other kinds of phosphatic guanos which occasionally find 
their way into the market. 
9. Bone-Ash. 
Bone-ash of good quality unquestionably is one of the most 
valuable materials for making superphosphate of lime. Indeed, 
it is far too good to be used for agricultural purposes in any 
other form. Most of the bone-ash of commerce comes from 
South America, and possesses, like other commercial articles, a 
variable composition, arising chiefly from the mechanical im- 
purities, such as sand and earth, with which it is always more or 
less contaminated. 
The following commercial analyses of different samples of 
South American bone-ash will give an idea of the extent of this 
variation : — 
2 c 2 
