. Elementary chemical microscopy. Microscopy; Microchemistry. DETERMINATION OF MELTING POINTS 221 butyrorefractometer may be employed. By regulating the heating flame and the rate of flow of hot water, very gradual or very rapid rises of temperature may be obtained or the temper- ature may be maintained almost constant. Jacketing the cell with asbestos simplifies the regulation of temperature. Heaters functioning on the principle of the thermo-siphon, Fig. 133, may also be employed for temperatures up to 85 to 900 C; but above 90 de- grees the regulation of the height of the heating flame beco
. Elementary chemical microscopy. Microscopy; Microchemistry. DETERMINATION OF MELTING POINTS 221 butyrorefractometer may be employed. By regulating the heating flame and the rate of flow of hot water, very gradual or very rapid rises of temperature may be obtained or the temper- ature may be maintained almost constant. Jacketing the cell with asbestos simplifies the regulation of temperature. Heaters functioning on the principle of the thermo-siphon, Fig. 133, may also be employed for temperatures up to 85 to 900 C; but above 90 de- grees the regulation of the height of the heating flame becomes rather diffi- cult and the sudden formation of steam usually results in a blow-off through the safety tube, in which the thermometer is only very loosely in- â * serted. Substituting brine or oil for water, the temperatures can be raised to 125-150 degrees if the heating coil be used, but the author has never found hot oil to give satisfactory results in any thermo-siphon system, since the Fig. 133. Heater for Melting viscosity of the oil in the glass cell Polnt APParatus- is too great to permit an even and sufficiently rapid rate of flow unless large conducting pipes be employed, necessitating a cell far too thick for use. The temperatures may be conveniently measured by means of a set of Anschiitz thermometers. Thermometers of this type are sufficiently small, so as not to project too far, and their graduations are such as to permit readings to be taken to degree. A convenient arrangement for reading the thermometer and observing the melting point of the substance under observation is given below. With hot stages of the sort just described it is always a wise precaution to place the cell in a glass tray or shallow crystallizing dish to guard .against damage to the microscope should the hot stage Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illust
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