In terms of the true equilibrium constant fCa1 and the activity coefficients, K, can be equated to K'ai7aquo/"yH+Yhydroxo> where the subscripts "aquo" and "hydroxo" refer to the tetraaquo and triaquo-hydroxo complexes, respectively. Assuming that the 7aqu0/ 7hy*>xo ratio remains relatively constant, one would expect a decreaseIn K, on increasing the ionic strength from 1.0 to 5.0 M, since yH+ increases rapidly in this high ionic strength range. (30) It has been noted (ref 26) that K) for the c/s(py)2 complex is probably about 10~1, while for fec(NH3)3 a value of about 10"5 is indicated (ref 31), with values of about 10~e and 10"7 applicable to the c/s(NH3)4 and (NH3)5 species, respectively (ref 27). (31) (a)