The construction and operation of a microfurnace designed to combine a low thermal capacity with accurate temperature measurement is described. The specimen, which is approximately 1.5 mm in diameter, may be raised to a temperature of 1200° C in less than one minute and maintained to within ±2° C of the working temperature for several hours. For general work the specimen is viewed with a ×5 objective, though a ×10 objective, with a numerical aperture of 0.25, may be used for continuous observation up to 1000° C and for shorter periods at higher temperatures. In the instrument described the specimen is exposed to the air but conversion for work in a controlled atmosphere would be relatively simple.
Though primarily designed for the study of crystal growth from the melt, and the rapid delineation of phase equilibria diagrams, the apparatus has been applied to the study of the growth of single crystals, melting-point determinations and the investigation of phase precipitation in opal glasses. Special attention has been given to the photographic recording of experiments and an example of rate of crystal growth measurement using this technique is given.