450 
On Phosphatic Guanos. 
Two of these three samples contained a good deal of organic 
matter, capable of producing on final decomposition over 1 per 
cent, of ammonia. They were also rich in phosphate of lime, 
and altogether indicated very valuable phosphatic guano deposits. 
The sample marked No. 2 was remarkably rich in phosphoric 
acid, but it contained less nitrogen than the two other samples. 
It appears to me probable that j\o. 2 was a crust guano, upon 
which the powdery portion w-as deposited. On many guano 
islands the powdery phosphatic deposits rest upon, or are mixed 
up with, hard unpromising-looking crusts, or stone-like masses, 
which often assume considerable dimensions, and possess the 
physical characters of hard rocks. In most places these crusts 
are more valuable than the powdery portion of the deposit, for 
in many localities the pow dery surface-layers are contaminated 
with fine drift-sand, sometimes to an extent to render the guano 
not worth exporting. The crusts are not only free from sand, 
or contain but little of it, but they often consist principally of 
bibasic phosphate of lime, and not of the ordinary tribasic 
phosphate Avhich forms the bulk of the powdery phosphatic 
deposit. In other words, these crusts not only contain a high 
percentage of phosphoric acid, but they contain this acid united 
with less lime than in ordinary tribasic or bone-phosphate of 
lime, which constitutes the bulk of bone-ash and of most 
phosphatic guanos and minerals. 
The analysis of sample No. 2 shoAvs that it is a crust guano, 
to a very large extent consisting of bibasic phosphate of lime. 
This circumstance renders this and other crust guanos of a 
similar chemical constitution extremely valuable for the pro- 
duction of high grade superphosphates. 
In dissolving ordinary phosphatic materials, which often 
contain a good deal of carbonate of lime, a certain amount of 
sulphuric acid is wasted in neutralising it ; and in order to 
produce soluble or monobasic phosphate of lime from the 
tribasic compound, two equivalents of lime are removed by 
the acid and changed into two equivalents of sulphate of lime ; 
whereas in dissolving crust guanos, which generally do not 
contain any carbonate of lime, and which consist, to a large 
extent, of bibasic phosphate of lime, only one equivalent of 
lime has to be removed and to be combined with sulphuric 
acid when such crust guanos are transformed into soluble or 
monobasic phosphate of lime. In the former case, for every 
equivalent of soluble phosphate two equivalents of sulphate of 
lime (gypsum) are necessarily produced ; whereas, in the latter, 
only one equivalent of sulphate of lime is formed simultaneously 
with one equivalent of soluble phosphate, and a much higher per- 
centage of soluble phosphate can be incorporated into a manure 
