Present-day microcomputers offer a wealth of computing power at very liBited costs. In fact, it is now well possible, as we showed some years ago, to have a simple least-squares structure refinement progran running on a $ lOOO.-computer.Another, and possibly more important, field in which microcomputers can be applied is teaching. As a rule, crystallographic methods depend heavily on computing, and the associated programs are nearly always black boxes which do not elucidate anything of uhat is g0ing on. To explain these methods to students, simulations can be used. As an example, a direct ~ethod teaching

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The transformations that occur in ices II, III, and V at atmospheric pressure when they are heated from liquid-nitrogen temperature have been examined by simple thermal analysis and by x-ray diffraction. They transform first to cubic ice I (ice Ic). The rate of transformation of ices II and III depends upon the temperature, and that of ice II probably depends upon its thermal history. The temperature dependence of the rate for ice V, and the history dependence of the rate for ices III and V were not examined. Ice Ic has previously been made only in small quantities; it can now be made in as large quantities as required by transformation of the high-pressure ices. The transformation of ice Ic to ordinary hexagonal ice (ice Ih) has also been examined. The rate depends markedly on the thermal history of the sample and this may help to explain the apparently inconsistent rates that have been reported by various workers.

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