AGRICULTURAL CHEMISTRY AND GEOLOGY. 159 



The carbonate of lime here given is an essential part of each particle of the bone re- 

 mains, and does not exist, except occasionally as mixture to the amount of one or two per 

 cents., independently. The humic acid is often in union with, ammonia and magnesia, the 

 whole percentage of ammonia, or rather nitrogen, not exceeding in the ancient deposits 

 more than two per cent. A more solid aggregate of grains afforded — 



Moisture from air-dried state 5"40 



Organic matter, huinates, humus — 



Oleates and stearates 8*40 



Bone phosphate lime 64-SO 



Carbonate of lime 16-20 



Sulphate 2S0 



Phosphate magnesia 1"60 



Sand -46 



99-66 



The grains adhered slightly ; the dry mass was of a pale, nankin color, and exhibited the 

 first step in a change which results in a consolidation of the arenaceous remains into a solid 

 rock. 



It will be observed that, if we admit the moisture and organic matter, there are seventy- 

 five parts of bone phosphate of lime in one hundred of the dry guano, constituting a source 

 of this prime requisite in the constitution of fertile soils highly important. From the nature 

 of the decomposition, this bone phosphate 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 observe an increased 

 amount of phosphate of lime, and are led to the consideration 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 masses mark it as an aggregate, its hard- 

 ness, next to that of feldspar and greater than that of fluorspar, removes it from the class 

 of ordinary calcareous 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 constitute bone phosphate of lime. For economical purposes, it is neces- 

 sary to grind the masses to a fine powder ; it then dissolves slowly in water. 



This compound generally forms a covering of ten to twenty-four 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 de- 

 composition 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 the water evaporates under the 

 sun's rays, the earthy salts dissolved by the acid fluids below are left in the interstices existing 

 in the sand-like deposits of food-remains until they are filled, and every trace of granules ob- 

 literated. The increased amount of sulphate of lime, the uniform acid state of these guanos 



