360 ANNUAL OF SCIENTIFIC DISCOVERY. 



It will be observed tbat, if we omit the moisture and organic matter, 

 there are 75 parts of bone phosphate of lime in 100 of the dry guano, con- 

 stituting a source of this prime requisite in the constitution of fertile soils 

 highly important. From the nature of the decomposition, this bone phos- 

 phate is soluble to some extent in water, and thus adapted to application 

 when the immediate effects are desired. 



Comparing the composition here given with that of fish bones, we ob- 

 serve an increased amount of phosphate of lime, and are led to the consid- 

 eration of the cause of this anomalous composition. 



Another variety of this guano appears as a solid compact rock, banded 

 in lines by dark-brown colors. Although the irregular forms of the mass- 

 es mark it as an aggregate, its hardness, next to that of feldspar, and 

 greater than that of fluorspar, removes it from the class of ordinary calca- 

 reous aggregates. But the chemical composition is more remarkable. 



One hundred parts afford : 



Moisture from air dried state, ..... 0.80 



Organic matter and water, ....*. 11.00 



Bone phosphate of lime, ...... 110.20 



Sulphate of lime, ....... 7.90 



Sand and dirt, ........ .80 



130.70 



The 50.47 parts of phosphoric acid are, for convenience of comparison, 

 supposed to be united with lime to constitutue bone phosphate of lime. 

 For economical purposes, it is necessary to grind the masses to a fine 

 powder ; it then dissolves slowly in water. 



This compound generally forms a covering of 10 to 24 inches thick, over 

 the guano on those islands not frequented by birds. Some rough masses 

 are found in the mass of the arenaceous guano, but they appear to have 

 been once a surface covering. 



Dr. Hayes explains the singular composition of this aggregate and the 

 guanos more rich in bone phosphate than the bones of birds by referring 

 to the kind of fermentation which organic animal matter undergoes in 

 presence of excess of humidity. Briefly, it is the reverse of that which 

 produces ammonia salts in the Peruvian guano, acids being the result 

 here. The whole series of acids, the products of humus decomposition, 

 carbonic acid, and probably acetic acid, being generated in the mass, have 

 dissolved the carbonate of lime of the deposit, while the resulting salts 

 have been washed away by the rains, leaving the phosphate of lime in 

 excess. Where daily depositions are taking place this effect does not follow, 

 as the first decomposition produces ammonia ; but under other conditions 

 the carbonate of lime of the bony structure is removed, and the phosphate 

 is left in excess. 



The occurrence of rocky masses at the surface is explained by the well- 

 known fact that the solutions of salts formed tend to the surface ; and as 



