R. SH. MIKHAIL
2054
(a)
VoL 67
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Fig. 5.--(it) Ient paper could be taken in favor of the role played by the first of these factors, and work is now being conducted to investigate the effect of producing lattice strains in crystalline solids on its surface activity. Acknowledgments.-Thr author thanks Professor Dr. R. I. Razouk, for hinging his attention to this type of work on solids, and Dr. S. Rrnnaurr and Dr. I,. E. Copeland of the Portland Crnirnt Association, U. S. A., for the snpply of calcium hydroxidc crystals and for taking and intcrprrting tht. el~ctroirmicroscope pictures.
DISCUSSIOS
v. 8 . RAMACHANURbN.--Tlle general ronehlsioes arrived a t in this paper are very similar to those reported by I). R. Glasson in 1958. Mikhail, however, ha8 presented an interesting theory explaining the differing surface properties of calrium liydrovide heated in air and under vacuum. The statement that the number of nuclei from the parent phase determines the mode of recrystallization needs more elaboration RS regards greatrr surface ares obtained under vacuum. L. E. COPEIANO(Portland Cement Association) (fur It. SH. MIKHarL).--The evidence as obtained from both fields of sorfiice chemistry and electron miserosropy are a11 in f w o r of the view that each crystallite of the parent miiterid decomposes to yield a bigger number of crystallites of the product. 1:nder vacuum, the number of crystallites produced is much greater thnn those obtsined in the presence of air. Assuming that each crystallite of the product is developed from a single nucleus, which seems to be B plausible assumption, then the number of nuclei developed through the stage of deeomp,sitim determines the mode of recrystallization. The number of nuclei Beems to he sensitive to the prevailing atmosphere under whirli decomposition is effected. I also believe that this point needs more elahoratinn, especially if the evidence is collected from other fields of reseiwli hesides surface chemistry and electron microscopy. the hcst being the direct optical observation on single r r y ~ t d dewrnposition under different atmospheres.
