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GEORGEJ. LEVINSICAS AND WILLIAM F. NEUMAN
thermodynamic relations was not exact in this instance. The exact relation between kl and k, may be obtained by calculating the limiting interaction
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coeficient from each of them and equating the resulting expressions. This reduces to McKay's relation as ml. and m2. both become very small.
THE SOLUBILITY OF BONE MINERAL. I. SOLUBILITY STUDIES OF SYNTHETIC HYDROXYLAPATITE1 BY GEORGE J. LEVINSKAS~ AND W . F . NEUMAN School of Medicine and Dentistry, University of Rochester, Rochester, N . Y . Received August 6 , 1064
By means of high speed centrifugation, which achieves an efficient separation of the basic calcium phosphates from aqueous solutions, the problem of the solubility of the bone mineral has been reinvestigated using a relatively pure sample of crystalline hydroxylapatite. The steady state was approached sat,isfactorily from undersaturation and supersaturation. A number of variables: time, solidjsolution ratio, pH, Ca/P ratio, etc., were studied. The solubility (in watcr containing traces of chloroform) of hydroxylapatite at 1 g./l., 24", p = 0.165 (NaCl), pH M for Ca and 7.0 averaged 1.23 and 0.711 X P, respectively. This crystalline solid exhibited incongruent solubility, Le., the solutions gave a higher Ca/P ratio than that present in the solid phase in most instances.
Numerous conflicting studies of the solubility of bone mineral have been reported.a-z2 Not one of these studies has offered conclusive evidence that the system under study was a t equilibrium or even reversible. By means of high speed centrifugation, which achieves an efficient separation of the basic calcium phosphates from aqueous solutions, the problem has been reinvestigated. Evidence is presented that the system, under the conditions of the present study, is reproducible and reversible. If not a t final equilibrium, the system a t least attains the same end-point whether approached from supersaturation or undersaturation. Experimental Materials.-Because bone mineral itself is variable in composition and requires drastic treatment for its isolation, a relatively pure sample of commercial hydroxylapatite, (1) Abstracted from the Ph.D. Thesis of George J. Levinskas, June, 1953, University of Rochester. (2) Atomic Energy Commission Predoctoral Fellow, 1949-1952. (3) N . Bjerrum, Paper read a t the Nordic Scientist Meeting in Helsingfors, August 11, 1936. Translated from the report of the meeting, 344. (4) C. Blarez, Compt. rend., 103, 264 (1886). (5) A. A. Browman, Doctoral Thesis, Univ. of Chicago. 1953. (6) F. K . Cameron and L. A. Hurst, J . A m . Chem. Soc., 2 6 , 885 (1904). (7) H. Danneel and K. W. Frohlioh, Z . anorg. aElgem. Chom., 186, 14 (19hO). (8) Y. Eriosson, Acta Ondont. Scandinauica, 8, Supplement 3 (1949). (9) I. Greenwald, J. Eio!. Chem., 143, 703 (1942). (10) E. Hayek, F. Mtlllner and I
