Abstract
The writer reported some time ago on the natural cleavage of KCl single crystal that had been derived by rapidly cooling the melt in the crucible. The edge length of the crystal pieces d depended on that occasion on the cooling velocity v as d∝1/v2. On the other hand the commercial steel had grain structure. In this paper it is demonstrated that, in spite of the fact that both the materials differ remarkably from each other in several physical features, e. g. brittle or ductile, their apporoximate grain size can be formulated in a single expression representing the temperature gradient and the cooling velocity of the specimens in operation. In consequence of their numerical estimation their practically fit value have been obtained. Furthermore the standard cooling velocity has been theoretically studied and established by reference to which the cooling operation may be defined either as rapid or as slow.
