564 CYCLES OF ORGANIC AND IXORGAXIC SUBSTANCES 



Probably some iron species exist in sea water other than those 

 we have considered. One might think of the organic matter present, 

 which certainly does not represent an ultimate equilibrium state 

 but still may form rather stable complexes in water. Concentrations 

 of organic carbon have been given ranging from 0.14 to 2.72 mg 

 C/liter, thus from lO"^-' to IQ-^-^M. It is conceivable that this 

 carbon is partly in the form of some strong and relatively stable 

 complex former. Howe\er, until something definite is known about 

 these organic substances, one should look out for other possible 

 forms of iron. One possibility is indicated in recent work by 

 Lengweiler (1959), who studied the solubility of FeOOH at various 

 pH and found a pH-independent term of about 10^' Jf. which may 

 correspond to uncharged Fe(0H)3 or a polymer of it. This may be 

 the species we ha\'e in sea water. \\'e ma\' note that Lewis and 

 Goldberg (1954) reported a practically constant concentration of 

 "soluble iron" as distinguished from "particulate iron" of 10~'-'-AI. 



It is desirable to have the solubilities of a series of hydroxides 

 and oxides in water studied by some method, such as radioactive 

 tracers, that would allow one to measure concentrations a few 

 powers of ten lower than those usually studied. It seems very 

 likely that one would then find e\idence for uncharged species, 

 like the previously known Si(0H)4 and Hg(0H)2. It is also possible 

 that such species would be the prevalent form of several elements 

 in the ocean. 



Whereas fluoride, chloride, or sulfate complexing of iron(III) 

 do not seem able to compete with hydroxo complexing, too little 

 is known about phosphate complexing to exclude it. 



Titonium 



Next addition to our equilibrium mixture is 0.06 mole of TiOj. 

 At equilibrium, some Ti may have entered the silicate phases by 

 substitution, and the rest remained as TiOo (s), probably rutile. 

 There seems to be no laboratory evidence of any soluble species 

 that one could expect to find at the conditions of sea water; the 

 analyses of up to 10~'''-'Jlf in sea water mav refer to uncharged 

 Ti(0H)4. 



