NATURAL OCCURRENCE OF PHOSPHATES 29 



Perhaps the most complete exposition of the theory of the re- 

 covery of waste phosphates, with especial reference to their de-- 

 posit in Florida, has been given by Eldridge. 17 He calls atten- 

 tion to the universal presence of phosphates in sea water 

 and to the probability that in earlier times, as during the 

 miocene and eocene geological periods, the waters of the 

 ocean contained a great deal more phosphate in solution than at 

 the present time. He cites the observations of Bischof, which 

 show the solubility of different phosphates in waters saturated 

 with carbon dioxid. According to these observations apatite 

 is the most insoluble form of lime phosphate, while artificial 

 basic phosphate is the most soluble. Among the very soluble 

 phosphates, however, are the bones of animals, both fresh and 

 old. Burnt bones, however, are more soluble than bones still 

 containing organic 'matter. Not only are the organic phos- 

 phates extremely soluble in water saturated with carbon dioxid, 

 but also in water which contains common salt or chlorid of am- 

 monium. The presence of large quantities of common salt in 

 sea water would, therefore, tend to increase its power of dissolv- 

 ing lime phosphates of organic origin. It is not at all incredible, 

 therefore, to suppose that at some remote period the waters of 

 the ocean, as indicated by these theories, were much more 

 highly charged with phosphates in solution than at the present 

 time. 



According to Eldridge, the formation of the hard-rock and 

 soft phosphates may be ascribed to three periods: First, that in 

 which the primary rock was formed; second, that of secondary 

 deposition in the cavities of the primary rock; third, that in 

 which the deposits thus formed were broken up and the result- 

 ing fragments and comminuted material were redeposited as 

 they now occur. 



"The first of these stages began probably not later than the 

 close of the older miocene, and within the eocene area it may 

 have begun much earlier. Whether the primary phosphate re- 

 sulted from a superficial and heavy deposit of soluble guanos, 

 covering the limestones, or from the concentration of phosphate 

 17 Preliminary Sketch of Florida Phosphates, Author's Edition : 18. 



