CHEMISTRY. 243 



sandstone aggregate ; and they show individually as the grains of sand in that 

 rock. In the guano-rock, this individuality is entirely lost, and the eye 

 detects nothing in the close-grained and compact banded mass, which indi- 

 cates its origin. Indeed, it would be difficult to find two bodies mineralogi- 

 cally more diverse than the two specimens before you. It is to this loss of 

 the granular form, and the production of a compact, remarkably close textured 

 rock, that I wish especially to call attention. 



This guano-rock has a composition not very different from that of the 

 arenaceous guano ; both, however, present a very novel result, by analysis. 

 In stating the composition, I purposely omit several constituents which occur 

 in minute quantity only, and keep in view the bone phosphate of lime and 

 organic matter, as the prominent constituents of both. 



100 parts of the Guano Rock consist of, Moisture, O'SO ; Dry Organic 

 Acids, &c., 11 '00; Sulphate of Lime, 7 '90; Bone Phosphate Lime and Mag- 

 nesia^ 110-20 ; Sand, 0'80. 



100 parts of the Arenaceous Guano, from below the guano rock, contain, 

 Combined water, 6*84; Dry Organic matter, T80; Sulphate of Lime, 7 '00; 

 Bone Phosphate Lime and Magnesia, 114'40 ; Sand, O'GO. 



Considering the mineral matter of each, that in 100 of guano rock weighs 

 88^-, in 100 of arenaceous guano 91^; the proportion of bone phosphate 

 of lime and magnesia becomes 110 nearly in each, when an equal weight 

 is taken. The question, from whence does phosphate of lime, of this 

 composition, come? at once arises in the mind of any one who has a 

 recollection of the composition of fish bones, and especially the composition 

 of the ordinary Atlantic guano of the Aves, and other Islands. In 100 parts 

 of calcined ox bone, there are 86 parts of bone phosphate of lime and magne- 

 sia, and 14 parts of carbonate and silicate of lime ; rarely 88'5 parts as given 

 by Heintz. Fremy has recently classed the bones of man, elephant, lion, 

 calf, kid, ostrich, serpents, codfish, and other fish, as identical in composition. 

 I have found the bone phosphates of lime and magnesia, in the burnt bones 

 of the halibut, to equal 86'SO per cent., while the bone and organic matter 

 of the vertebra of this fish, as extracted by acids, afforded 92 per cent, of 

 the mixed phosphates. Taking, therefore, the highest result on any fish 

 bones, we have hi the dry matter only 92 per cent, of bone phosphate of 

 lime and magnesia^ while 100 parts of the dry mineral part of the guano rock 

 afford the phosphoric acid sufficient, when combined with lime, to produce 

 125 parts of the same salt. 



As we can look to no natural source for bones having the composition of 

 guano rock, we inquire into the chemical influences exerted while the excre- 

 ment of birds, mixed with more or less of other annual remains, undergoes 

 decomposition at a temperature never lower than 85 F., moisture and water 

 being present. 



Experiment shows that under these conditions, the putrefaction proceeds 

 with the production of acids. The bones of the halibut give to sea- water lime 

 salts, at the expense of a portion of the bone. Abstracting lime from the 

 bone, leaves in excess the phosphoric acid, and the washing away of the 

 soluble salts of lime formed, by rains, adds them to the constituents of sea- 



