232 /. D. Hague on the Guano Islands of the Pacific Ocean. 



The first named deposit, lying on the sulphate of lime bed, 

 has a peculiar character. It is covered by, or consists of, a hard 

 crust that is from one-fourth of an inch to an inch and a half in 

 thickness, beneath which lies a stratum of guano varying ia 

 depth from one inch to a foot. In many places where the guano 

 was originally shallow the whole is taken up and formed into 

 the hard crust which then lies immediately on the sulphate. 

 This crust, when pure, is snow-white, with an appearance some- 

 what resembling porcelain, but is usually colored more or less 

 by organic matter. Generally it is very'hard, and strongly co- 

 hesive, though sometimes friable, and it lies unevenly on the 

 surface in rough fragments that are warped and curved by the 

 heat of the sun. It consists chiefly of phosphoric acid and lime, 

 but, owing to the variable amount of sulphate of lime with which 

 it is mechanically mixed, there is a lack of uniformity in differ- 

 ent samples. Hence the percentage of phosphoric acid varies 

 from over 50 per cent to less than 30 per cent. 



The phosphoric acid and lime, moreover, are not combined in 

 constant proportions, some existing as bone phosphate, the 

 greater part, doubtless, in most specimens, as the neutral phos- 

 phate, and, possibly, a part as the superphosphate. 



The following is an analysis of a piece of pure crust. '^^^ 



o-iio luiiuwjug js an analysis ot a pie 

 nple, in question, was a snow-whit 

 scarcely any organic matter. 



fragment, containing 





This presents a somewhat remarkable character. It appears 

 to be a nearly pure di-phosphate of lime. After allowing to the 

 sulphuric acid the requisite amount of lime, there remains 

 enough of the latter to form ninety per cent of the salt 2CaO, 

 HO, PO, leaving an excess of about three per cent of pb^" 

 phone acid, which would suggest the possibility that a part of toe 

 phosphoric acid and lime may be combined as CaO, 2H0, P^s- 



So small an amount of sulphuric acid is also noticeable m a 

 specimen of Jarvis guano which usually contains a large per- 

 centage of that acid, but in this case it is owing to the purity o^ 

 the crust and the absence of mechanically mixed sulphate of Hnje- 

 . Samples of Jarvis guano have been examined by many cbem- 

 ista, but their results are not always uniform, because, as I have 

 already explained, their samples were mixtures of this crust and 

 the underlying guano or gypsum. A number of analyses, mad® 

 i°'"ufu T''^'^^ purposes by Prof. Johnson of iNTew Haven, I ^f 

 published in a guano pamphlet, issued by Mr. Webb as a trade 

 circular. Prof. Liebig'^haB^also pubUshefa yeVcomplete ^T 



