A High Temperature Gauge Glass for the Visual Observation of Critical Phenomena

A capillary tube variable volume cell is described, which has operatedsatisfactorily over a range of 100'F and 3,500 psi to 550'F and 1,500 psi. Thecell contents are entirely visible over the length of the capillary with theexception of a space at the top amounting to three per cent of the totalvolume. Observations on the critical behavior of simple systems have beengreatly facilitated by the apparatus, it being possible to establish thecritical conditions for a particular mixture in the course of a day'srun. Introduction Many types of apparatus have been designed for obtaining data on the phaserelationships of hydrocarbon systems. Such apparatus can in general besubdivided into two classifications;indirect measurement of phase volume, anddirect visual observation of phase volume, each of which hasoutstanding advantages and disadvantages. Indirect measurement of phase volume requires the use of rather elaborateapparatus including internal probes in which are located the device fordetermining the locus of the interface between phases. Such equipment is by itsvery nature costly, and is complex from the standpoint of operating technique.Probing techniques can be used, however, over wide ranges of temperature andpressure with a high degree of reproducibility. Apparatus for visual observation of phase behavior obviously has theadvantage of enabling the experimenter to see exactly what takes place, butbecause the material to be tested is contained in a cell constructed of bothmetal and glass, is limited severely as to the temperature range of operation.Furthermore, the maximum pressure usually is limited by the choice of materialused for sealing the glass to the metal, and by the strength of the glassitself. In the interest of increased efficiency of observation, as much of thecell as possible should be visible to the eye. Glass capillary tubes have beenused successfully but have always given difficulty at the metal-to-glass seal.An apparatus has been devised to overcome the problems of sealing andresistance to temperature effects that have heretofore been the limiting factorwith glass apparatus in the observation of phase volumes at elevatedtemperature and pressure. T.N. 85