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Fig. 2. Photograph of a crystal of an alcohol dehydrogenase under oil. Courtesy of
Y. Korkhin. Scale: 1.5cm = 0.5 mm.
methods in which the conditions gradually change until equilibrium is
reached. The stability of the batch is an important benefit for conduct-
ing diagnostic studies on the process of crystal growth since the history
of the sample can be followed reliably. However, this benefit may
become a handicap in the case of screening for crystallization conditions
since it is conceivable that the gradual change of conditions (en route
to equilibrium), which occurs by the other methods, may be the crucial
factor for the formation of crystals (Chayen, 1996, 1997a, 1997b; D'Arcy
et al ., 1996).
A major element in making the microbatch experiment a batch, as
opposed to a diffusion system, is the sealing of the samples by the paraf-
fin oil. Paraffin oil has proved to be a good sealant, allowing only a neg-
ligible amount of water evaporation through it during the average time
required for a crystallization experiment.
Experience has shown that although oil and water are thought to be
immiscible, water can evaporate at different rates from different oils. Paraffin
oil allows for little or no diffusion of water through it, while a drop incu-
bated under silicone fluid (a polymer of repeating dimethylsiloxane units)
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